Download Neural Communication and Electrical Potentials in the Brain: ERPs and EEG and more Study notes Philosophy of psychiatry in PDF only on Docsity! 1 Neural Basis & Technical Details What are ERPs? Could that work? Neurons communicate with electrical signals Action Potential • “All-or-none” change in voltage • Begins in the axon hillock • Actively propagated down the axon • Involves voltage-gated channels 2 Synapse • Neural “communication” requires chemical transfer • Synapse Synapse • The action potential moves down the axon until it reaches the terminal (synapse) • Its wave of depolarization opens voltage-activated Ca2+ channels • Influx of Ca2+ causes vesicles to fuse with presynaptic cell membrane • Transmitter diffuses across synaptic cleft and binds to receptors on post-synaptic cell Post-Synaptic Potentials • When transmitter bins to receptor, ion channels open • Ions rush into postsynaptic cell • Excitatory Post-Synaptic Potentials – Ions flow into the cell – Ions depolarize the cell • Inhibitory Post-Synaptic Potentials – Make post-synaptic membrane more negative – Ions flow out of the cell • Both excitatory & inhibitory nerves coming into most synapses Potentials • Action Potentials occur in axons • Synapses form on axon hillock, cell body, and especially on dendrites Summation of Post-Synaptic Potentials • Temporal Summation – If PSPs occur close in time, they summate • Spatial Summation – If PSPs occur in close proximity, they summate • EPSPs and IPSPs summate (and cancel) 5 All together now! Summates Cancels out Which brain areas? • Pyramidal cells in the cortex – Open field arrangement – Synchronously active – Close to the scalp • Hippocampal neurons • Brainstem nuclei • Many nuclei have closed field arrangement • Do you think we could record potentials from these cells ( ) with electrodes on the scalp? Non-brain areas? • Eyes • Muscles • Heart • “Artifactual activity” 6 EEG invented 1928 Hans Berger Early recording set-up Human Subject EEG monitors alertness EEG and ERPs What are ERPs? • ERPs formed by averaging EEG time-locked to the onset of stimuli that require cognitive processing • ERPs represent electrical activity associated with the processing of the stimuli • ERPs can be related to different kinds of cognitive tasks, e.g. attention, memory, & language comprehension 7 Why averaging works… What do ERPs reflect? • Sensory, motor, and/or cognitive events in the brain • Synchronous activity of large populations of neurons engaged in information processing ERP Components Characteristics of ERP components • Polarity – Is it a positive wave or a negative one? • Latency – How long after stimulus presentation does it peak? • Functional Significance – What cognitive (or perceptual) activity is it sensitive to? – What makes it bigger or smaller? Early Components • Waves I-VI represent evoked activity in auditory pathways in the brainstem • Driven by sensory factors – What are the features of the stimulus?
