T1GlobalBrainActivity2023 - Tagged.pdf

The presentation is for personal use only and must not be copied or used outside of BSMS Global Brain Activity Dr Natasha Sigala [email protected] Module 202 Neuroscience & Behaviour Outline Activity of large populations of neurons Electroencephalography (EEG): recording brain waves Brain rhy...

The presentation is for personal use only and must not be copied or used outside of BSMS Global Brain Activity Dr Natasha Sigala [email protected] Module 202 Neuroscience & Behaviour Outline Activity of large populations of neurons Electroencephalography (EEG): recording brain waves Brain rhythms and the sleep cycle Methods of imaging the living brain: CT, MRI, fMRI, PET 2 Learning outcomes By the end of this lecture you should be able to: Explain what EEG is, what it measures, and where it is used Describe what the different frequency bands / EEG rhythms indicate Explain the role of the thalamus in the generation of synchronous brain rhythms Describe different stages of sleep Explain the differences of structural and functional imaging techniques, and give examples of each. Compare and contrast CT and MRI, PET and BOLD fMRI; know the physiological signals that each technique measures Understand how different methods of studying the nervous system complement each other in terms of spatial and temporal resolution. 3 Brain Rhythms Rhythmic environment: temperature, day and night, tides… Brain rhythms: sleeping and waking, breathing cycles, steps of walking, stages of night sleep 4 The Electroencephalogram (EEG) •Physiology of sleep •Epilepsy 5 Generation of small fields in pyramidal cells 6 The Electroencephalogram (EEG) Basic requirements for signal detection: 1) A whole population of neurons must be active in synchrony to generate a large enough electrical field at the level of the scalp. 2) This population of neurons must be aligned in a parallel orientation so that they summate rather than cancel out. 7 Synchronous activity (from Purves et al.) The amplitude of the EEG signal partly depends on how synchronous the activity of the underlying neurons is. Number of active cells, total amount of excitation, timing of activity. 8 EEG / brain rhythms correlate with pathology & behavioural states (from Bear, Connors & Paradiso) 9 Generation of synchronous rhythms Afferent pathways (from Bear, Connors & Paradiso) 10 Generation of synchronous rhythms (from Kandel, Schwartz & Jessell) A one neuron oscillator Thalamic cells have a set of voltage-gated ion channels that allow each cell to generate rhythmic, self-sustaining discharge patterns, even in the absence of external inputs. The rhythmic activity of each thalamic pacemaker neuron then becomes synchronised with many other thalamic cells via a hand-clapping kind of collective interaction. 11 Functions of Brain Rhythms? Sensory input – thalamus – cortex Activity coordination (binding) of different cortical regions (synchrony, oscillations) Meaningless by-product of feedback circuits and connections EEG rhythms: Window of the functional states of the brain Sleep Behavioural criteria: •Reduced motor activity •Decreased response to stimulation •Stereotypic postures •Relatively easy reversibility 13 14 Three functional states of sleep Non-REM (from Purves et al.) Awake Non-REM REM (from Bear, Connors & Paradiso) 15 Summary scheme of sleep-wake states (from Purves et al.) 16 During REM sleep the main neurotransmitter modulation is provided by: A Histamine B Serotonin / 5-HT C Acetylcholine D Glutamate E Norepinephrine/Noradrenaline Functions of Sleep and Dreaming? Conservation of metabolic energy Cognition Thermoregulation Neural maturation and mental health 18 Imaging techniques A. 1. 2. B. 1. 2. Structural imaging: Measures of the spatial configuration of types of tissue in the brain (static maps) Computerised tomography, CT Magnetic resonance imaging, MRI Functional imaging: Measures the moment-to-moment variable characteristics of the brain that may be associated with changes in cognitive processing (dynamic maps) Positron emission tomography, PET Functional magnetic resonance imaging, fMRI Structural Imaging CT scan of brain tumour MRI scan of lesions caused by multiple sclerosis Structural imaging CT scans MRI •2003 BasedNobel on theprize amount to SirofPeter X-rayMansfield absorption and in Paul different Lauterbur. types of tissue. •Completely Bone absorbs safe, theso most people (thecan skull beappears scannedwhite), many cerebrospinal times. fluid absorbs the least (the ventricles appear black) andathe brain matter is intermediate •Provides much better spatial resolution. (grey). ••Used in clinical settings, e.g. to diagnose tumours or identify haemorrhaging or other gross brain anomalies. Provides better discrimination between white and grey matter. •Can be adapted for detecting the changes in blood oxygenation associated with neural activity (fMRI). Sequence of events in the acquisition of an MRI scan Magnetic fields of protons initially random Add external magnetic field and some protons align Earth magnetic field: ~ microTesla Brief radio wave pulse orients them to 90 degrees (spin or precess) and produces a measurable MR signal. The protons return back (relax) and a new brain slice is scanned. 22 Basic physiology underpinning functional imaging •The brain makes up 2% of the body weight, but consumes 20% of the body’s oxygen uptake; it can’t store oxygen and only stores little glucose. •Oxygen and energy needs are constantly met by the local blood supply. When the metabolic activity of neurons increases, then the blood supply to that region increases as well. •PET measures change of blood flow to a region. •fMRI is sensitive to the concentration of oxygen in the blood. •Because of constant activity, we always compare an experimental condition with a baseline condition (before and during performance). •Indirect measures of neuronal activity. 23 PET Naïve Practised PET scanner 24 Novel fMRI MRI scanner Functional imaging PET (BOLD) fMRI •Based on blood volume •Based on blood oxygen concentration •Involves radioactivity (signal depends on radioactive tracer) •Participants scanned once or few times •No radioactivity (signal depends on deoxyhaemoglobin levels) •Participants scanned many times •Temporal resolution: 30” •Temporal resolution: 1-4” •Effective spatial resolution: 10mm •Spatial resolution: 1mm •Sensitive to the whole brain •Some brain regions (e.g. near sinuses) are hard to image •Can use pharmacological tracers BOLD signal: blood oxygen-level –dependent contrast, is the signal measured in fMRI that relates to the concentration of oxy- and deoxyhaemoglobin in the blood. HRF: Haemodynamic response function, describes the changes of the BOLD signal over time. The microscope and telescope opened vast domains of unexpected scientific discovery. Now that new imaging methods can visualize the brain systems… a similar opportunity may be available for human cognition… Michael Posner, Seeing the Mind, 1993 28 Imaging techniques summary Structural imaging reveals the static physical characteristics of the brain (useful in diagnosing disease), whereas functional imaging reveals dynamic changes in brain physiology (might correlate with cognitive function). Neural activity consumes oxygen from the blood. This triggers an increase in blood flow to that region (PET) and a change in the amount of deoxyhaemoglobin in that region (fMRI). Functional imaging always measures relative changes in activity (e.g. activity while performing a task vs. baseline or a control task). Spatial and temporal resolution pharmacology lesion optical Optogenetics 30 Reading materials Bear, Connors & Paradiso, Neuroscience: Exploring the Brain 2nd,3rd or 4th ed, Chapter 19 Pinel, Biopsychology, 7th ed, Chapter 5 Purves et al, 4th or 5th ed, Neuroscience , Chapter 28 Kandel, Schwartz & Jessell, 4th ed, Principles of neural science Chapters 46-48 31