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### Methods to Perturb Neural Function [ ] the use of drugs, whether it be coffee, chocolate, beer, or something stronger. Newer methods include transcranial TAKE-HOME MESSAGES - Research involving patients with neurological disorders is used to examine structure--function relationships. S...

### Methods to Perturb Neural Function [ ] the use of drugs, whether it be coffee, chocolate, beer, or something stronger. Newer methods include transcranial TAKE-HOME MESSAGES - Research involving patients with neurological disorders is used to examine structure--function relationships. Single and double dissociations can provide evidence that damage to a particular brain region may result in a selective deficit of a certain cognitive operation. - Surgical procedures have been used to treat neurologi- cal disorders such as epilepsy or Parkinson's disease. Studies conducted in patients before and after surgery have provided unique opportunities to study brain- behavior relationships. ##### Pharmacology a. b Fixation 100 50 0  ##### Transcranial Magnetic Stimulation 1.0 0.8 0.6 0.4 0.2 b. Pulse before stimulus (ms) Pulse after stimulus (ms) ##### Transcranial Direct Current Stimulation ##### Genetic Manipulations ### Structural Analysis of the Brain instance, when you look at an X-ray, the first thing you no- tice is that bones appear starkly white and the surrounding TAKE-HOME MESSAGES - Brain function can be perturbed by drugs, magnetic or electrical stimulation, and through genetic manipulations. - A major drawback of drug studies, in which the drug is injected into the bloodstream, is the lack of specificity. - Transcranial magnetic stimulation (TMS) uses magnetic pulses to transiently alter local brain physiology. - Gene knockout technology allows scientists to explore the consequences of the lack of expression of a specific gene in order to determine its role in behavior. ##### Computed Tomography 0.5 to 1.0 cm in all directions. ##### Magnetic Resonance Imaging ##### Diffusion Tensor Imaging TAKE-HOME MESSAGES - Computed tomography (CT or CAT) uses X-rays to image the 3-D structure of the brain. - Magnetic resonance imaging (MRI) exploits the magnetic properties of the organic tissue of the brain to image its structure. The spatial resolution of MRI is superior to CT. - Diffusion tensor imaging (DTI), performed with magnetic resonance scanners, is used to measure white matter pathways in the brain and thus can offer information about anatomical connectivity between regions. ### Methods for the Study of Neural Function ##### Single-Cell Recording in Animals Electrode **a** --4 --3 ##### Single-Cell Recordings in Humans ##### Electroencephalography - After a stimulus, the earliest components are connected with sensory processing and occur within - Waves that occur 100 ms after the stimulus presentation are no longer solely derived from sensory processing, but are modulated by attention. The N100 and P100 waves are associated with selective attention. - The N200 wave is known as the mismatch negativity component. It is found when a stimulus is physically deviant from the preceding stimuli, such as when a G tone is heard after a series of C tones. - The P300 wave is seen when an attended stimulus is presented, especially if the stimulus is relatively rare. - The N400 component is observed when a stimulus is unexpected. It differs from the N200 in that the surprise event here might be a violation of semantics ##### Event-Related Potential 700 ms Time (ms) ##### Magnetoencephalography ##### Electrocortogram TAKE-HOME MESSAGES - Single-cell recording allows neurophysiologists to record from individual neurons in the animal brain in order to understand how increases and decreases in the activity of neurons correlate with stimulation of one of the senses or behavior. - With multiunit recording, the activity of hundreds of cells can be recorded at the same time. - Electroencephalography (EEG) measures the electrical activity of the brain. The EEG signal includes endog- enous changes in electrical activity as well as changes triggered by specific events (e.g., stimuli or movements). - An event-related potential (ERP) is a change in electrical activity that is time-locked to specific events, such as the presentation of a stimulus or the onset of a response. When the events are repeated many times, the relatively small changes in neural activity triggered by these events can be observed by averaging of the EEG signals. In this manner, the background fluctuations in the EEG signal are removed, revealing the event-related signal with great temporal resolution. - Electrocortogram (ECoG) is similar to an EEG, except that the electrodes are placed directly on the surface of the brain. - Magnetoencephalography (MEG) measures the magnetic signals generated by the brain. The electrical activity of neurons also produces small magnetic fields, which can be measured by sensitive magnetic detectors placed along the scalp. MEG can be used in an event-related manner similar to ERPs, with similar temporal resolution. The spatial resolu- tion can be superior because magnetic signals are minimally distorted by organic tissue such as the brain or skull. ### The Marriage of Function and Structure: Neuroimaging ##### Positron Emission Tomography  a. Baseline condition: Blood flow when the participant fixated on a central cross. Activity in this baseline condition was subtracted from that in the other conditions in which the participant views a checkerboard surrounding the fixation cross to help participants from moving their eyes. The stimulus is presented at varying positions, ranging from near the center of vision to the periphery **(b--d)**. A retino- topic map can be identified in which central vision is represented more inferiorly than peripheral vision. Areas that were more active when the participant was viewing the checkerboard stimulus will have higher counts, reflecting increased blood flow. This subtractive procedure ignores variations in absolute blood flow between the brain's areas. The difference image identifies areas that show changes in meta- bolic activity as a function of the experimental manipulation. ##### Functional Magnetic Resonance Imaging 2 1 0 --1 --5 0 5 10 15 20 Time after stimulus onset (s) 3. Mov. Stat. Mov. Stat. 4. Mov. Stat. Mov. Stat. a. Block design b. Event-related Right motor ##### Limitations of PET and fMRI - Pittsburgh Compound B (PiB) is a tracer that binds to beta-amyloid and is used as an in vivo assay of the presence of this biomarker for Alzheimer's disease. - Functional magnetic resonance imaging (fMRI) uses MRI to measure changes in the oxygen content of the blood (hemodynamic response). These changes are assumed to be correlated with local changes in neuronal activity. ### Brain Graphs nodes that act as connectors, providing links to more dis- tant clusters. Beyond simply showing the edges, a brain TAKE-HOME MESSAGES - Positron emission tomography (PET) measures meta- bolic activity in the brain by monitoring the distribution of a radioactive tracer. The PET scanner measures the Brain graphs are a valuable way to compare results £om experiments using different methods (Bullmore S ##### Representations in Computer Models ##### Models Lead to Testable Predictions  TAKE-HOME MESSAGE - Computer models are used to simulate neural networks in order to ask questions about cognitive processes and generate predictions that can be tested in future research. ### Converging Methods 0.0 Uncertainty-exploration parameter ECoG PET TMS Millisecond \ TAKE-HOME MESSAGE - Powerful insights into the structural and functional underpinnings of cognitive behavior can be gained from experiments that combine methods such as genetic, behavioral, and neuroimaging techniques.