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Questions and Answers
What technology is used to enhance the safety of brain surgery?
Tractography involves the use of MRI-based diffusion tensor imaging.
True
What does EMG stand for?
Electromyography
________ is a technique that helps visualize white matter pathways in the brain.
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Match the following terms with their definitions:
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Which of the following is NOT a function associated with the basal ganglia?
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The basal ganglia are located at the base of the forebrain and the top of the midbrain.
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What is the primary role of the direct pathway in the basal ganglia?
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The basal ganglia modulate _______ reflex arcs, typically through inhibition.
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What is the first line of therapy for Parkinson's disease?
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Match the following components of the basal ganglia pathways with their roles:
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Which of the following tasks do the basal ganglia NOT contribute to?
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Deep brain stimulation is used in cases of drug resistance for Parkinson's disease.
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Name one neurophysiological biomarker used in DBS for Parkinson's disease.
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The indirect pathway of the basal ganglia facilitates movement.
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What structure within the basal ganglia is responsible for input from the cortex?
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The primary function of the vestibulocerebellum is the maintenance of ______ and equilibrium.
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Match the following components of the cerebellum with their primary functions:
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The basal ganglia are primarily embedded in complex _______ loops.
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Which nuclei are major outputs from the basal ganglia to the thalamus?
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Which symptom is NOT typically associated with Parkinson's disease?
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Adverse effects of DBS include cognitive dysfunction and hallucinations.
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What is one strategy to avoid adverse effects during DBS treatment?
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Parkinson's disease can cause ______ instability as a cardinal sign.
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Which of the following best describes PAC in the context of DBS?
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What type of receptors in the striatum yield to inhibition?
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Cortical stimulation results in a biphasic response in the basal ganglia output nuclei.
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What disease is characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta?
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The ______ of dopaminergic neurons leads to hyperactivity of SNret in Parkinson's disease.
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Match the following aspects of motor control with their roles:
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What happens after an increase in activity from cortical stimulation in the basal ganglia?
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D1 receptors in the striatum yield to inhibition.
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What is the response observed in the third phase of cortical stimulation in the basal ganglia?
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The substantial loss of ______ neurons in Parkinson's disease affects movement initiation.
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What effect does the loss of dopaminergic neurons have on thalamocortical projections?
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What is a common cardinal sign of Parkinson's disease?
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Deep brain stimulation (DBS) can be used to treat all types of movement disorders.
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What is the primary purpose of using extracellular microelectrodes in DBS?
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One of the primary adverse effects of DBS is __________.
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Match the following types of DBS optimization with their descriptions:
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Which of the following symptoms is related to bradykinesia?
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Phase amplitude coupling (PAC) refers to the synchronization effects in local field potentials.
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Name one neuropsychiatric symptom that can occur in Parkinson's disease.
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The __________ is responsible for planning and programming movements in the cerebellum.
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Which of the following therapies is considered first-line treatment for Parkinson's disease?
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Which of the following is NOT a function associated with the basal ganglia?
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The direct pathway in the basal ganglia primarily inhibits thalamocortical projections.
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What is the primary role of the indirect pathway in the basal ganglia?
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The basal ganglia are embedded in complex _______ loops.
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Match the following components of the basal ganglia with their functions:
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What is the role of the basal ganglia in procedural learning?
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The output nuclei of the basal ganglia include the striatum and the subthalamic nucleus.
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Which nuclei are primarily responsible for input from the cortex into the basal ganglia?
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The basal ganglia play a role in regulating ______ movements.
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Which characteristic best describes the basal ganglia's involvement in cognition?
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What effect do D1 receptors in the striatum have on movement?
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The hyperactivity of SNret in Parkinson's disease contributes to the inhibition of thalamocortical projections required for the initiation of movements.
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Name a type of response observed due to cortical stimulation in the basal ganglia output nuclei.
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The _____ of dopaminergic neurons affects movement initiation in Parkinson's disease.
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Match the following pathways with their functions in the striatum:
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What is one of the primary motoric tasks associated with the basal ganglia?
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Cortical stimulation in the basal ganglia results in only a decrease of activity.
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What typically follows the disinhibition of thalamocortical projections during cortical stimulation?
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In the degenerative process of Parkinson's disease, there is a loss of _______ neurons in the substantia nigra pars compacta.
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What is one consequence of decreased dopaminergic activity in the basal ganglia?
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Which of the following modalities is used for monitoring the hemodynamic status during surgery?
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Noise in the operating room can consist of both technical and biological noise.
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What does SNR stand for in the context of intraoperative monitoring?
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Intraoperative monitoring methods assess the functional _______ of neural pathways.
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Match the following monitoring modalities with their descriptions:
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Which of the following is NOT a type of evoked potential?
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Spontaneous activity in EMG can provide acoustic feedback during surgery.
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What type of stimulation is associated with Motor evoked potentials?
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The _______ is a recommended frequency range to be monitored for technical noise.
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What plays a key role in evaluating the signal quality in the operating room?
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Which method is NOT considered a modality for intraoperative monitoring?
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Signal-to-noise ratio (SNR) is calculated as the ratio of noise to signal in the operating room.
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What does EMG stand for?
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The measure of functional integrity in monitoring is called __________.
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Match the following modalities with their descriptions:
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Which type of evoked potential is associated with the auditory system?
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Biological noise during monitoring is constant and does not vary based on what is being recorded.
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What does SNR stand for in the context of intraoperative monitoring?
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Cranial nerve stimulation can be part of __________ modulation during surgery.
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Which of the following is NOT a source of technical noise in the OR?
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Which part of the brain is primarily responsible for executing movements?
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The corticospinal tract is exclusively responsible for slow and controlled movements.
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What type of reflexes are typically modulated by the extrapyramidal system?
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The ________ is involved in the preparation and design of movements.
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Match the following motor pathway components with their functionalities:
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Which of the following statements best describes upper motor neuron lesions?
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Lower motor neuron lesions are characterized by atrophy and flaccid muscle tone.
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What is the primary pathway involved in descending modulation of pain sensitivity?
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The ________ is responsible for processing complex information related to movements.
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Match the following pathways with their characteristics:
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What is the primary electrophysiological assessment technique used for the peripheral nerve?
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The protopathic pathway assesses sharp pain and temperature sensations.
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What is assessed in the primary cortex of the somatosensory pathway?
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The pathway responsible for proprioception and fine touch is known as the __________ pathway.
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Match the following assessments with the corresponding pathway:
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Which level of the nervous system is involved in the somatosensory assessment of the ascending tract?
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H-reflex is primarily used to assess muscle activity.
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Name one type of assessment used for evaluating the protopathic pathway.
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The __________ pathway is associated with the perception of fine touch and proprioception.
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Which component is NOT primarily associated with the secondary/association cortex?
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What is the highest intensity of current that a coil can generate during stimulation?
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The magnetic field generated by the coil penetrates the skin and skull with significant loss.
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What does the primary motor cortex represent?
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The _______ system is characterized as having monosynaptic connections to alpha motoneurons in primates.
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Match each component of the motor system with its function:
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How do electrically evoked motor evoked potentials compare to magnetic motor evoked potentials?
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The association cortex is primarily involved in motion execution only.
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What is the role of the basal ganglia in motor control?
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What is the primary effect of preinnervation of the muscles?
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The brain’s inverse flow direction of induced current aligns with the _______ of the coil during stimulation.
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The early component of the Bereitschaftspotenzial occurs approximately 400 ms prior to a motor task execution.
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Match the following motor cortex areas with their functions:
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What are the surface electrodes used for in motor evoked potentials?
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The central motor conduction time is calculated as T1 minus ________.
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Match the following components with their respective characteristics of motor evoked potentials:
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Which of the following best describes the role of the contingent negative variation (CNV)?
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The amplitude of the Bereitschaftspotenzial is independent of the motor task being executed.
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Name the two components of the Bereitschaftspotenzial.
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During motor evoked potential recording, the responding muscle depends on the coil position and the direction of ________.
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What is the typical signal-to-noise ratio (SNR) for Compound Muscle Action Potentials (CMAP)?
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All biological noise is deemed unmeaningful in evoked potential recordings.
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What kind of noise is associated with electrical devices during evoked potential recordings?
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The formula for signal-to-noise ratio (SNR) is SNR = Psignal/P_______.
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Match the following evoked potentials with their typical SNR:
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Which of the following represents a potential SNR range for Sensory Potentials?
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Electrocerebral silence is characterized by a high SNR.
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Which frequency band in EEG is classified as Gamma?
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Alpha EEG is characterized by irregular rhythms that can differ by more than 1 Hz.
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What EEG frequency band is typically associated with sleep stages?
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The brain shows a permanent electric activity within distinct frequency bands, including Delta, Theta, Alpha, Beta, and __________.
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Match the following EEG frequency bands with their characteristics:
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What factors can influence the normal findings in an EEG?
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In bipolar montages, the source of a signal is localized better than in reference montages.
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What is a normal characteristic of alpha EEG?
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The degree of __________ can also affect normal EEG findings.
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Which of the following is NOT considered a factor influencing EEG normal findings?
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What type of EEG finding is characterized by sharp waves and spikes?
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Normal EEG findings are characterized by abnormal electrical patterns in the brain.
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Name one type of activity monitored during an ictal EEG period.
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The EEG primarily records activity generated by __________ potentials in the uppermost layer of the cortex.
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Match the following EEG frequency bands with their corresponding activities:
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Which of the following correctly describes epilepsy-related EEG findings?
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Spike waves on an EEG are considered a normal finding.
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What role do specific thalamic nuclei play in generating EEG signals?
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Layer I of the cortex has a dense population of synapses on peripheral dendrites of the __________ cells.
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Match the following EEG activities with their definitions:
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Which EEG activity is primarily restored after eye closing?
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Electrocerebral silence is a normal finding in EEG.
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What type of abnormal EEG finding could indicate elevated intracranial pressure?
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EEG is dominated by _____ and/or Delta activity when there are pathologically slowed findings.
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Match the following EEG findings with their associated characteristics:
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Which of the following is commonly observed during drowsiness or sleep?
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Focal abnormalities in EEG can indicate the presence of tumors.
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Name one condition that can lead to burst-suppression EEG.
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During periods of _____, you might observe beta activity exclusively in the EEG.
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Which of the following is the primary purpose of electroencephalography (EEG)?
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Which EEG finding may indicate a drug-induced state?
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The first human EEG was recorded in 1945 by Hans Berger.
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What are the four anatomically defined points used in the International 10-20 system?
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A normal EEG typically shows a range of frequency bands including delta, theta, alpha, and ______.
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Match the EEG frequency bands with their associated states:
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What does an abnormal EEG finding most commonly indicate?
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Clean, well-placed EEG electrodes should show interference from external sources.
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Define what EEG montages refer to.
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EEG stands for _______.
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Which electrode positions in the International 10-20 system are designated with the letter 'P'?
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What does EEG stand for?
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The first human EEG was recorded in 1924 by Hans Berger during a neurosurgical operation.
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What is the primary purpose of electroencephalography?
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The _______ of the head are used as reference points for electrode placement in the International 10-20 system.
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Match the electrode position nomenclature with their meanings:
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Which of the following describes what EEG records?
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Electrode connections in EEG have no effect on the recordings obtained.
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What is the International 10-20 system used for?
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In EEG montages, the _______ montage records locations along the same axis.
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What are the four anatomical points used in the International 10-20 system?
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Which EEG frequency band is classified as Gamma?
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Bipolar montages are generally less sensitive than reference montages in EEG recording.
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Name one factor that influences the normal EEG readings.
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The EEG frequency band that ranges from 8 to 12 Hz is known as the ______ band.
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Match the following EEG frequency bands to their ranges:
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In which stage of sleep does rapid eye movement (REM) occur?
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Side differences in amplitude exceeding 50% are considered normal in alpha EEG findings.
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What is a primary advantage of using bipolar montages in EEG?
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EEG readings can be influenced heavily by ______ stimuli.
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Which of the following is NOT a factor affecting normal EEG?
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What type of EEG activity is identified as interictal epileptic activity?
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Layer I of the cortex has the least population of synapses compared to other layers.
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What function does the ascending reticular activating system (ARAS) primarily serve?
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Electroencephalography (EEG) recordings are mainly generated by _______ potentials in the uppermost layer of the cortex.
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Match the following terms with their descriptions:
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What determines the potential differences at the scalp in EEG recordings?
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The orientation of a dipole remains the same regardless of its location in the brain.
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What is the relationship of specific thalamic nuclei to EEG generators?
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The _______ is responsible for the biggest dipole with surface negativity perpendicular to the surface after activation of the unspecific thalamocortical projections.
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Which layer of the cortex is primarily involved in generating EEG signals?
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What is the primary characteristic of alpha EEG activity?
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Beta EEG activity is commonly seen during drowsiness or while sleeping.
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What type of abnormalities can indicate elevated intracranial pressure in EEG findings?
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Electrocerebral silence may be used to shorten waiting time in the diagnosis of __________.
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Match the abnormal EEG findings with their implications:
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What is a common artifact that can affect EEG results?
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Theta or delta activity can increase during certain sleep stages without indicating pathology.
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State one potential cause of focal abnormalities in EEG findings.
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A blockade in alpha EEG activity occurs predominantly during __________.
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What can be indicated by circumscribed slowing in EEG readings?
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Study Notes
Navigated TMS
- Uses a neuronavigation system to precisely target specific brain regions for TMS stimulation
- Nexstim is a leading company in navigated TMS
Tractography
- Uses MRI-based diffusion tensor imaging (DTI) to map white matter pathways in the brain
- Allows visualization of nerve fiber tracts, providing insights into brain connectivity
- DTI measures the movement of water molecules in the brain, revealing the orientation of nerve fibers
Neuronavigation
- Involves using a navigation system to visualize and target anatomical structures in the brain
- Often used in conjunction with TMS and DTI for more precise interventions.
- Allows for virtual planning and guidance during procedures
Cardinal signs of Parkinson's disease
- Akinesia/Bradykinesia
- Start/Stop disturbance
- Impaired facial expression
- Micrography
- Parkinsonian gait
- Tremor
- Rigidity
- Postural instability
Other symptoms:
- Neuropsychiatric
- Vegetative
Parkinson's Disease - Therapy
- First line: drugs (L-Dopa, Dopamine agonists)
- In case of drug resistance: Deep Brain Stimulation (DBS)
DBS: Targeting the optimal location
- DBS electrodes record activity from surrounding neurons, which can be used to optimize DBS location
- Raw data is filtered to get neuronal firing and local field potential
- High-pass filtering results in neuronal firing
- Low-pass filtering results in local field potential
Parkinson's disease – DBS optimization with local field potentials
- E0 is chosen as the optimal electrode location based on local field potential
- Modern DBS systems record local field potential from multiple channels
- LFP can be used for closed-loop stimulation (aDBS)
Parkinson's disease: DBS effect on local field potentials
- Phase amplitude coupling (PAC) can be used to analyze the relationship between neural activity in different frequency bands
Parkinson's disease: DBS segmented stimulation
- DBS can be modulated based on the phase of neural oscillations using segmented stimulation.
Parkinson's disease: DBS – Adverse Effects
- Infections
- Hemorrhage
- Speech arrest
- Apathy
- Hallucinations
- Hypersexuality
- Cognitive dysfunction
- Depression
- Euphoria
Parkinson's disease: Avoiding DBS side effects
- Single shot antibiotics
- Electrophysiologically optimized placement of DBS electrodes
- Closed loop stimulation
- Electrode optimization (directional stimulation)
Cerebellum
- Vestibulocerebellum
- Maintenance of posture and equilibrium
- Maintenance of muscle tone
- Spinocerebellum
- Error correction, adjust posture
- Smoothness and coordination of movements
- Cerebrocerebellum
- Planning and programming of movements
- Coordination of complex movements
- Sequence and precision of movements
- Timing of movements
Extrapyramidal system
- All nuclei and tracts except the pyramidal system
- Polysynaptic corticospinal projections
- Cerebellum
- Basal ganglia
- Modulates spinal reflex arcs (usually inhibition)
Basal ganglia
- A group of subcortical nuclei at the base of the forebrain and the top of the midbrain
- Associated with a variety of functions:
- Control of voluntary movements
- Procedural Learning
- Habit learning
- Conditional learning
- Eye movements
- Cognition
- Emotion
Basal Ganglia Circuit
- Input: Striatum
- Output: Globus pallidus interna (GPi) and substantia nigra pars reticularis (SNret)
- Direct Pathway
- Striatum -> SNret/GPi -> Thalamus (disinhibition = facilitation of thalamocortical projections)
- Indirect Pathway
- Striatum -> globus pallidus externa (GPe) -> subthalamic nucleus (STN) -> SNret/GPi -> Thalamus (inhibition of thalamocortical projections)
Substantia nigra pars compacta
- Dopaminergic projections to the striatum
- D1 receptors in the striatum are excitatory
- D2 receptors in the striatum are inhibitory
Cortical stimulation
- A triphasic response in basal ganglia output nuclei (SNret/GPi)
- Increased activity after a delay (inhibition of thalamocortical projections)
- Decreased activity (disinhibition, possibly associated with movement release)
- Increased activity (inhibition of thalamocortical projections, stopping movement release)
Motoric tasks
- Initiation and termination of movements
- Stabilization of movements
- Stabilizing muscles at rest
Parkinson's disease
- Loss of dopaminergic neurons in the substantia nigra pars compacta
- Cortical activation results in hyperactivity of SNret and inhibition of thalamocortical projections needed
Basal Ganglia Diseases
- Cardinal signs: akinesia/bradykinesia, tremor, rigidity, postural instability
- Other symptoms: neuropsychiatric, vegetative
-
Parkinson's disease therapy:
- First-line: drugs (L-Dopa, Dopaminagonists)
- Drug resistance: Deep brain stimulation (DBS)
Deep Brain Stimulation
- Targets the subthalamic nucleus (STN)
- DBS is implemented using implanted electrodes
- Neurophysiological biomarkers can be recorded via extracellular microelectrodes or the DBS electrodes
-
Local field potentials (LFP):
- Recorded by low-pass filtering raw data
- Provide information on pre- and postsynaptic potentials (input)
- Can be analyzed in the frequency domain and labeled according to EEG frequency bands
-
Neuronal firing:
- Recorded by high-pass filtering raw data
- Represent action potentials of local neurons (output)
-
DBS electrodes:
- Record from a larger population of neurons in the surrounding area compared to microelectrodes
DBS Optimization
- Optimal DBS location: identified by analyzing neuron firing
- Local field potentials (LFP): used to optimize DBS and identify optimal electrodes
-
Closed-loop stimulation (aDBS):
- Adaptation of DBS that uses LFP recordings to adjust stimulation parameters
-
Phase Amplitude Coupling (PAC):
- A phenomenon where the amplitude of oscillations in one frequency band is modulated by the phase of oscillations in another frequency band
-
Segmented stimulation:
- DBS delivered in discrete, time-limited segments
- Aims to optimize stimulation patterns based on specific motor tasks or neural activity
Adverse Effects of DBS
- Infection: can occur following surgery
- Hemorrhage: can occur during electrode implantation
- Speech arrest: can be caused by stimulation of areas near the speech centers
- Apathy, hallucinations, hypersexuality, cognitive dysfunction, depression, and euphoria: can be side effects of stimulation
Strategies to Minimize Adverse Effects
- Single-shot antibiotics: help prevent infection
- Electrophysiologically optimized placement of DBS electrodes: minimizes stimulation of areas associated with adverse effects
-
Closed-loop stimulation (aDBS):
- Adapts stimulation based on real-time neural activity
- May help mitigate side effects
-
Electrode optimization (directional stimulation):
- Targets specific neural circuits
- Can reduce stimulation of unintended areas
Cerebellum
-
Vestibulocerebellum:
- Maintains posture and equilibrium
- Regulates muscle tone
-
Spinocerebellum:
- Error correction
- Postural adjustment
- Smoothness and coordination of movements
-
Cerebrocerebellum:
- Planning and programming of movements
- Coordination of complex movements
- Sequence and precision of movements
- Timing of movements
Motor Pathways
-
Extrapyramidal system:
- Historically, all nuclei and tracts except the pyramidal system
- Polysynaptic corticospinal projections:
- Cerebellum
- Basal ganglia
-
Modulates spinal reflex arcs
- Primarily through inhibition
Basal Ganglia
-
Group of subcortical nuclei:
- Located at the base of the forebrain and top of the midbrain
- Associated with a variety of functions
-
Functions:
- Control of voluntary movements
- Procedural learning
- Habit learning
- Conditional learning
- Eye movements
- Cognition
- Emotion
-
Embedded in complex motor loops:
-
Tasks:
- Initiation and termination of movements
- Stabilization of movements
- Stabilizing muscles at rest
-
Tasks:
Basal Ganglia Pathways
-
Input from the cortex to basal ganglia:
- Striatum (caudate nucleus & putamen)
-
Output to thalamus:
- Globus pallidus interna (GPi)
- Substantia nigra pars reticulata (SNret)
-
Direct pathway:
- Striatum -> SNret/GPi -> Thalamus
- “- x - = +“: Inhibition of SNret/GPi disinhibits thalamocortical projections, facilitating movement
-
Indirect pathway:
- Striatum -> Globus pallidus externa (GPe) -> Subthalamic nucleus (STN) -> SNret/GPi -> Thalamus
- Results in inhibition of thalamocortical projections: inhibits movement
-
Substantia nigra pars compacta (SNc):
-
Dopaminergic projections to the striatum: act as complex modulators
- D1 receptors in the striatum: excitation
- D2 receptors in the striatum: inhibition
- Both pathways result in facilitation of thalamocortical impulse transmission
- Loss of SNc neurons: is a hallmark of Parkinson's disease
-
Dopaminergic projections to the striatum: act as complex modulators
Cortical Stimulation of Basal Ganglia
-
Yields to a triphasic response in the basal ganglia output nuclei (SNret/GPi):
- Phase 1 (Increased activity): inhibition of thalamocortical projections, stopping movement
- Phase 2 (Decreased activity): disinhibition of thalamocortical projections, facilitating movement
- Phase 3 (Increased activity): inhibition of thalamocortical projections, stopping movement
Cortical Stimulation in Parkinson's Disease
-
Loss of dopaminergic neurons in substantia nigra pars compacta (SNc):
- Results in hyperactivity of SNret and inhibition of thalamocortical projections
- This inhibition prevents initiation of movement, leading to akinesia and bradykinesia, which are cardinal signs of Parkinson's disease.
Intraoperative Monitoring Methods
- Clinical, electrophysiological, hemodynamic, and metabolic methods to check functional integrity.
- Electrophysiological modalities include electroneurography, electromyography (EMG), electroencephalography (EEG), and evoked potentials.
Electroneurography
- Measures compound muscle action potential (CMAP) latency and amplitude.
- Cranial nerve stimulation: Stimulates nerves in the brain, brainstem, and peripheral nerves to assess integrity.
- Measures nerve conduction velocity.
Electromyography (EMG)
- Spontaneous activity with acoustic feedback is monitored.
- Mimic, eye, and laryngeal muscle activity can be assessed.
Electroencephalography (EEG)
- Monitors spontaneous brain activity.
- Processed data can be depicted as Compressed Spectral Arrays (CSA) for analysis.
Evoked Potentials
- Somatosensory evoked potentials (SSEP): Stimulates peripheral nerves and records brain responses; phase reversal SEP is a specific type.
- Brainstem auditory evoked potentials (BAEP): Stimulates auditory pathway and records brainstem responses.
- Electrocochleography: Records cochlear responses.
- Middle latency SEP and/or auditory evoked potentials (AEP): Records cortical responses.
- Visual evoked potentials (VEP): Records visual pathway responses.
Motor Evoked Potentials (MEP)
- Magnetic Transcranial Magnetic Stimulation (TMS): Uses magnetic fields to stimulate the motor cortex.
- Electric TMS: Uses electrical stimulation to stimulate the motor cortex.
- Cortical stimulation: Directly stimulates the motor cortex.
- White matter stimulation: Stimulates the descending motor pathways.
- D-waves: Record presynaptic activity in the corticospinal tract.
Signal-to-Noise Ratio (SNR) in the Operating Room (OR)
- SNR = Psignal/Pnoise
-
Noise sources:
-
Technical Noise:
- Line frequency (50/60Hz)
- 100 Hz noise from electronic devices
- Amplifier, electrode, and operating room equipment (e.g., high-frequency coagulators)
-
Biological Noise:
- Depends on the signal being recorded.
- Meaningful versus Unmeaningful signals need to be differentiated.
-
Technical Noise:
Intraoperative Monitoring Methods
- Functional integrity is checked using clinical, electrophysiological, hemodynamic, and metabolic methods.
### Intraoperative Monitoring Modalities
-
Electroneurography
- Measures compound muscle action potential (CMAP) latency and amplitude.
- Cranial nerve, brainstem, and peripheral nerve stimulation can be used.
- Nerve conduction velocity can also be measured.
-
Electromyography (EMG)
- Used to assess spontaneous muscle activity.
- Acoustic feedback is provided for mimic, eye, and laryngeal muscles.
-
Electroencephalogram (EEG)
- Records spontaneous brain activity.
- Processed to create power spectra, which can be depicted as compressed spectral arrays (CSA).
-
Evoked Potentials
-
Somatosensory Evoked Potentials (SSEP)
- Phase reversal SEP can be measured.
- Brainstem Auditory Evoked Potentials (BAEP)
- Electrocochleography
- Middle Latency SEP (MLSEP) and Auditory Evoked Potentials (AEP)
- Visual Evoked Potentials (VEP)
-
Somatosensory Evoked Potentials (SSEP)
-
Motor Evoked Potentials
- Magnetic Transcranial Magnetic Stimulation (TMS)
- Electric TMS
- Cortical Stimulation
- White Matter Stimulation
- D-Waves
### Signal-to-Noise Ratio in the Operating Room
- Signal-to-Noise Ratio (SNR) = Psignal/Pnoise
-
Noise Sources:
-
Technical Noise
- Line frequency (50/60Hz)
- 100Hz noise from electronic devices
- Amplifier
- Electrode
- High frequency coagulators in the operating room
-
Biological Noise
- The type of recording will influence the biological noise.
- Meaningful versus Unmeaningful signals.
-
Technical Noise
Somatosensory Pathway
- The somatosensory pathway is responsible for transmitting sensory information from the body to the brain.
- It involves several key structures, including the spinal cord, medulla oblongata, and thalamus.
Electrophysiological Assessment of Somatosensory Pathway
- Peripheral Nerve: Sensory electroneurography, H-reflex, and short-latency SEP can be used to assess the peripheral nerve portion of the somatosensory pathway.
- Ascending Tract: Short-latency SEP is used to assess the ascending tract.
- Primary Cortex: Short-latency SEP is used to assess the primary cortex.
- Secondary/Association Cortex: Middle-latency SEP and event-related potentials are used to assess the secondary/association cortex.
Protopathic Pathway
- The protopathic pathway is responsible for transmitting pain, temperature, and crude touch sensations.
- Specific stimulation techniques such as laser and thermic stimuli are not suitable for assessing the protopathic pathway due to their non-selective nature.
Afferent Pathway Information Processing
- Descending Modulation: Mainly inhibitory, it controls sensitivity of peripheral receptors, impacting the afferent pathway.
- Alertness: Amplification, convergence/divergence, LCCS/ARAS-activation via the unspecific thalamus, and cortico-thalamo-cortical loops all contribute to alertness, influencing the afferent pathway.
- Processing: Spatial and temporal resolution occur in primary and secondary cortex, integration of different inputs happens in tertiary cortex, and comparisons with memory contents further refine information processing in the afferent pathway.
- Response: The afferent pathway prepares complex motor programs including flight, attack, grip, and speech based on processed sensory information.
- Modulation: Habituation (excluding pain) and lateral inhibition at various levels further modify the sensory input. Descending input control also modulates the afferent pathway.
Motor Systems
-
Motor Cortex: Consists of association cortex, supplementary motor area, premotor cortex, and primary motor cortex.
- Association Cortex: Responsible for complex information processing to prepare for complex movements, including speech.
- Supplementary Motor Area: Involved in preparing and designing movements.
- Premotor Cortex: Also involved in preparing and designing movements.
- Primary Motor Cortex: Executes movements, represented by the Homunculus.
Motor Pathways
- Corticospinal (Pyramidal) Tract: One of several motor systems, it's responsible for fast execution of movement programs, represented by the Homunculus, and involves monosynaptic connections to α-motoneurons in primates.
- Extrapyramidal System: Includes all nuclei and tracts except the pyramidal system, utilizes polysynaptic cortico-spinal projections, involves cerebellum and basal ganglia, and modulates spinal reflex arcs, primarily through inhibition.
Motor Pathway Lesions
- Upper Motor Neuron Lesion: Results in paresis of movements, minor atrophy, initial flaccidity (spinal shock), spasticity after weeks, increased reflexes, and pathological reflexes.
- Lower Motor Neuron Lesion: Causes paresis of muscles, atrophy, flaccid muscle tone, and loss of reflexes.
Electrophysiological Assessment of Motor Systems
- Bereitschaftspotenzial: A neurophysiological event that precedes voluntary movement.
- Transcranial MEPs: Electric or magnetic stimulation of the motor cortex to elicit muscle contractions.
- Spinal Magnetic Stimulation: Magnetic stimulation of the spinal cord to assess the integrity of motor pathways.
- Motor Nerve Conduction: Measures the speed of nerve impulses along motor nerves.
- F-Waves: Evoked muscle responses resulting from stimulation of a peripheral nerve and propagation of the impulse back to the spinal cord.
- H-Reflex: A reflex elicited by electrical stimulation of a peripheral nerve, assessing spinal cord function.
- EMG: Measures the electrical activity of muscles to assess their function.
Technical notes
- A coil generates a magnetic field perpendicular to its plane
- Magnetic field penetrates skin and skull with minimal loss
- Induced circular current in the brain has the same plane as the coil but opposite flow direction
- Current intensity is highest under the innermost loops of the coil
Motor Systems
- Primary Motor Cortex (M1) is responsible for movement, not individual muscles, and represented by a homunculus
- Premotor Cortex and Supplementary Motor Area plan and prepare movements
- Association Cortex processes complex information to prepare complex movements, for example, speech
Motor Pathways
- Corticospinal (pyramidal) tract is a fast acting motor system responsible for movement execution
- Homunculus represents movements, not individual muscles, and has a monosynaptic connection to α-motoneurons in primates
- Extrapyramidal system is a polysynaptic cortico-spinal projection system including basal ganglia and cerebellum
Motor Evoked Potential (MEP)
- Stimulation of the motor cortex can be achieved through magnetic or electrical methods
- Electrical stimulation is painful and stimulates different cellular elements
- Electrically evoked MEPs have a shorter latency compared to magnetic MEPs in the same subject
Recording MEPs
- Surface electrodes record MEPs
- The responding muscle depends on the coil position and current direction
MEP Enhancement
- Preinnervation of muscles facilitates synaptic transmission, increases response, and shortens latency
MEP Spinal stimulation
- Distal part of the nerve root or spinal nerve is typically stimulated
- Central motor conduction time is calculated by subtracting the latency recorded at the spinal cord (T2) from the latency recorded at the brain (T1)
Clinical Applications of MEPs
- MEPs can be used to identify nerve compression based on changes in latency
Fig-8 Coil
- Tailored magnetic field for more circumscribed cortical stimulation
- Suitable for navigated stimulation
Bereitschaftspotenzial (Readiness Potential)
- Negative potential generated before a motor task, consists of early and late components
- Early component is generated by the supplementary motor area and premotor cortex (~ 1500 - 400 ms prior)
- Late component is generated by the primary motor cortex (~ 400 - 0 ms prior)
- Amplitude depends on the task (up to 20 µV)
MEP and Bereitschaftspotenzial
- Bereitschaftspotenzial reflects activity of the secondary motor cortex (SMA) and further association cortex
- It is triggered internally (by movement) and recorded before the trigger
Difference to Contingent Negative Variation (CNV)
- CNV is a negative slow surface potential generated between a warning stimulus and an imperative ("go") stimulus.
Signal-to-noise Ratio (SNR)
- SNR is calculated as the power of the signal divided by the power of the noise.
- Noise can be technical or biological.
- Technical noise sources include line frequency (50/60Hz), 100Hz noise from electronic devices, amplifier, electrode, and high-frequency coagulators in the operating room.
- Biological noise depends on the type of signal being recorded.
- It is important to distinguish between meaningful and meaningless signals.
Typical SNRs
-
Electroencephalogram (EEG)
- Normal subjects typically have an SNR of 10:1 - 50:1.
- SNR can be < 1:10 with Electromyographic (EMG) artifacts.
- Electrocerebral silence has an SNR of 3:1.
-
Electromyography (EMG)
- Spontaneous activity has an SNR of 5:1 - 10:1.
- Motor unit potentials (MUPs) have an SNR of > 100:1.
- Interference patterns have an SNR of > 100:1.
-
Evoked Potentials
- Sensory evoked potentials (SEP) and visual evoked potentials (VEP) have an SNR of 1:2 – 1:20.
-
ElectroNeurography (ENG)
- Compound muscle action potential (CMAP) has an SNR of > 100:1.
- Sensory nerve action potentials have an SNR of 1:2 – 10:1.
EEG - Normal Findings
- Alpha - EEG is modulated in the form of a spindle and is blocked by eye opening but restored after eye closing.
- Alpha - EEG is also known as the "My rhythm" and is strongest in the central region of the brain.
- Beta EEG activity is present in all channels with alpha activity occasionally seen for a short time after eye closing.
- Beta EEG activity can also be present in subjects who are drowsy or sleeping, strained or under the influence of pharmaceuticals.
EEG - Abnormal Findings
- Pathologically slowed EEG is dominated by Theta and/or Delta activity.
- It may also indicate elevated intracranial pressure, pathologically impaired consciousness.
- Theta or Delta activity increase during some sleep stages.
- Alpha-coma is another potential finding indicating a slowed EEG.
- Burst suppression is an abnormal EEG pattern.
- Electrocerebral silence is a major finding.
- Amplification of the recording, filter settings, and the presence of ECG artifacts all impact the validity of electrocerebral silence.
- Electrocerebral silence may shorten waiting time in brain death diagnosis.
EEG - Abnormal Findings: Focal Abnormalities
- Focal abnormalities may be characterized by circumscribed slowing or epileptic activity in the EEG.
- This type of abnormality can be present in a variety of conditions such as tumors, small bleedings, infarction, etc.
EEG - Montages
- Each montage has advantages and disadvantages.
- Reference montages are more sensitive, especially if the distance between the active electrode and the reference is larger than in bipolar montages.
- The source of a concrete signal is better localized in bipolar montages.
- Localization in bipolar montages becomes difficult if the source is more widespread and affects the reference electrode.
EEG - Frequency Bands
- The brain exhibits continuous electrical activity.
- EEG recordings display rhythmic activity within distinct frequency bands:
- Gamma > 31 Hz
- Beta 13 – 30 Hz
- Alpha 8 – 12 Hz
- Theta 4 – 7 Hz
- Delta < 4 Hz
- Note: The limits of the alpha- and beta bands may vary in the literature
EEG - Normal Findings: Factors
- The normal EEG is affected by a variety of factors:
- Individual factors
- Normal variants
- The region from which it is derived
- External stimuli
- The degree of attention: awake or sleeping (5 stages - 4 without rapid eye movement and 1 with REM)
- Age
EEG - Normal Findings: Alpha - EEG
- Alpha - EEG is very regular with a variation of no more than 1 Hz.
- The frequency is individual-specific.
- Activity is strongest over the occipital and temporal lobes.
- Side differences in amplitude of less than 50% are normal.
EEG - Abnormal Findings: Epileptic Activity
- Epileptic activity can present in two ways:
- Interictal: Spikes/sharp waves and Spike waves
- Ictal: Seizures
EEG - Generators: Cortical Afferents
- Sensory input.
- Specific thalamic nuclei: Second relay station.
- Primary cortex.
- Association cortex.
- Unspecific thalamic nuclei: Widespread cortical projections.
- Relation to the ascending reticular activating system (ARAS): Cortical inhibition.
EEG - Generators: Relation to Cell Potentials
- Layer I of the cortex has a dense population of synapses on peripheral dendrites of the cortical pyramid cells.
- Excitatory postsynaptic potentials (EPSPs) induce a greater current than inhibitory postsynaptic potentials (IPSPs) or action potentials (APs).
- EPSPs induce a bigger dipole with surface negativity perpendicular to the surface.
- Smaller dipoles are present in adjacent regions following activation of the unspecific thalamo-cortical projections.
- Potential differences at the scalp are determined by the geometric relation of the dipoles and the recording electrodes.
EEG - Generators: The Cortex
- Dipole orientation differs between the tip of a gyrus and the slopes of a sulcus.
- Dipole orientation also differs between the slopes of the sulcus.
EEG - Generators: The EEG
- The EEG is generated by subsynaptic potentials in the uppermost layer (layer I) of the cortex.
- Afferents in this layer are part of the ARAS which regulates consciousness and attention.
Electroencephalography
- Electroencephalography (EEG) records the electrical activity of the brain using multiple electrodes placed on the scalp.
- The electroencephalogram is the recorded electrical activity of the brain.
- A living brain always exhibits continuous electrical activity.
- The first human EEG was recorded in 1924 by Hans Berger in Jena during a neurosurgical operation.
Electrode Placement
- The International 10-20-system is used to place electrodes.
- Four anatomical points on the head serve as references for distance measurement:
- Nasion
- Inion
- Left ear
- Right ear.
Electrode Placement: Nomenclature
- The naming of electrodes is based on the following structure:
-
Region where the electrode is placed:
- Fp – frontoparietal
- F – frontal
- C – central
- P – parietal
- O – occipital
- T – temporal
- A – auricular (ears)
-
Side:
- Z – midline
- Odd – left
- Even - right
-
Region where the electrode is placed:
EEG - What do we record?
- The electrical activity of the brain under the electrodes.
EEG - What do we Record?: Potential Differences
- We are measuring potential differences between pairs of electrodes.
EEG - What do we record?: Montages
- The way we connect electrodes to amplifiers impacts the EEG recording.
- There are two main types of montages:
-
Bipolar:
- Longitudinal
- Transversal
-
Reference:
- Ipsilateral ear
- Cz
- ….
-
Bipolar:
Electroencephalography
- Electroencephalography (EEG) is the technique to record electrical activity of the brain using electrodes placed on the scalp
- EEG is used to detect brain activity, diagnose and monitor brain disorders, and guide brain surgery
- The first human EEG was recorded in 1924 by Hans Berger in Jena during a neurosurgical operation
- The electroencephalogram (EEG) is the recorded electrical activity of the brain
- A living brain exhibits continuous electrical activity
Electrode Placement
- Electrodes are placed according to the International 10-20 system, which is based on distances between four anatomical points: nasion, inion, left ear, and right ear. Electrode positions are named based on the region and side:
- Fp - frontoparietal
- F - frontal
- C - central
- P - parietal
- O - occipital
- T - temporal
- A - auricular (ears)
- Z - midline
- Odd - left
- Even - right
EEG Recordings
- EEG captures potential differences between pairs of electrodes
- The way electrodes are connected to amplifiers (channels) determines what is recorded
- Common EEG montages include:
- Bipolar: Longitudinal and transversal
- Reference: Ipsilateral ear, Cz, average reference, Laplacian
EEG Signal Analysis
- Bipolar Montages: Show phase reversal, helpful in localizing the source of a signal
- Reference Montages: More sensitive, especially for signals with large distances between the active electrode and the reference
-
Frequency Bands: EEG signal is analyzed based on frequency bands, each with a distinct range:
- Gamma: > 31 Hz
- Beta: 13 - 30 Hz
- Alpha: 8 - 12 Hz
- Theta: 4 - 7 Hz
- Delta: < 4 Hz
Normal EEG Findings
- Normal EEG varies based on:
- Individual factors
- Normal variants
- Region of the brain
- External stimuli
- Degree of attention (awake, asleep)
- Age
-
Alpha EEG:
- Regular, with a frequency range of less than 1 Hz
- Individual specific frequency
- Accentuated over the occipital and temporal lobes
- Side differences in amplitude of less than 50% are normal
- Often modulated in form of a spindle
- Blocked by eye opening
- Restored after eye closing
- My - Rhythm: Occurs in the central region
-
Beta EEG:
- Only beta activity in all channels
- Alpha activity may be seen briefly after eye closing
- Influenced by individual factors, drowsiness, sleep, strain, medication
Abnormal EEG Findings
-
Pathologically Slowed EEG:
- Dominated by Theta and/or Delta activity
- Indicates elevated intracranial pressure or impaired consciousness
- Burst - Suppression EEG: Characterized by bursts of high-amplitude activity followed by periods of silence
- Electrocerebral Silence: Absence of any electrical activity, used to diagnose brain death
-
Focal Abnormalities: Circumscribed slowing or epileptic activity, can indicate:
- Tumors
- Small bleedings
- Infarction
-
Epileptic Activity:
- Interictal: Spikes/sharp waves, spike waves
- Ictal: Episodes of high-amplitude activity, corresponding to seizures
EEG Generators
-
Cortical Afferents:
- Sensory input
- Specific thalamic nuclei (second relay station)
- Primary cortex
- Association cortex
- Unspecific thalamic nuclei (widespread cortical projections)
- Ascending reticular activating system (ARAS) (regulates consciousness and attention)
- Cortical inhibition
Relation to Cell Potentials
- Layer I of the cortex has a dense population of synapses on peripheral dendrites of cortical pyramid cells
- EPSPs induce a greater current than IPSPs or APs, creating the biggest dipole with surface negativity perpendicular to the surface
- Activated unspecific thalamocortical projections induce smaller dipoles to adjacent regions
- Potential differences at the scalp are determined by the geometric relationship between dipoles and recording electrodes
EEG and Cortical Anatomy
- Dipole orientation differs between gyri and sulci, influencing EEG recordings
- EEG is mainly generated by subsynaptic potentials in layer I of the cortex, where afferents of the ARAS are located
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Description
This quiz explores advanced techniques in neurology such as navigated TMS, tractography, and neuronavigation. Learn about how these methods use sophisticated imaging and targeting to enhance brain treatment and understanding. Test your knowledge on the impact of these technologies on brain connectivity and stimulation.