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Lab5_EEG_Semmlow

Lab5_EEG_Semmlow - EEG Basics Source What is it EEG is an...

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1 EEG Electroencephalogram Basics - Source What is it? EEG is an oscillatory time varying voltage recorded from scalp electrodes (20-200 μ V). Where does it come from? Summed activity of sub- threshold pre-synaptic activity of 1000+ neurons. Why does it exist? Activity of 1000+ neurons should cancel. Something is synchronizing the signal (thalamus, Cortical-thalamic circuits, feedback loops?) Typical multi-lead EEG signals showing a variety of waveforms including spike activity. PDF Created with deskPDF PDF Writer - Trial :: http://www.docudesk.com
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2 Source of the EEG An electrochemical wave called an action potential travels along the axon of a neuron . When the wave reaches a synapse, it provokes release of a puff of neurotransmitter molecules, which bind to chemical receptor molecules located in the membrane of another neuron, on the opposite side of the synapse. . Source of the EEG Scalp EEG measures summated activity of post-synaptic currents The activity of many types of receptors results in a flow of ions into or out of the dendrite. This results in compensatory currents in the extracellular space. It is these extracellular currents which are responsible for the generation of EEG voltages. The EEG is not sensitive to axonal action potentials. Source of the EEG (continued) Since the EEG is a summation of the synchronous post- synaptic activity of thousands of neurons that have similar spatial orientation: radial to the scalp, it is not possible to determine the activity within a single dendrite or neuron from the scalp EEG. Currents that are tangential to the scalp are not picked up by the EEG. The EEG therefore benefits from the parallel, radial arrangement of apical dendrites in the cortex. Because voltage fields fall off with the fourth power of the radius, activity from deep sources is more difficult to detect than currents near the skull. PDF Created with deskPDF PDF Writer - Trial :: http://www.docudesk.com
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3 EEG Components Scalp EEG activity is comprised of multiple oscillations . These have different characteristic frequencies, spatial distributions and associations with different states of brain functioning (such as awake vs. asleep).
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