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NESC 2470 (13)
Lecture 6

Lecture 6, Nov 28th, 2011.docx

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Dalhousie University
NESC 2470

Lecture 6, Nov 28th, 2011 November-28-11 5:51 AM Electroencephalogram  Enables us to glimpse the generalized activity of the cerebral cortex  First described by Hans Berger in 1929  Used primarily to diagnose certain neurological conditions o Seizures in epilepsy o Sleep studies  Measures voltage change in the brain during synaptic excitation of pyramidal cell dendrites  Amplitude of signal depends on how synchronous activity of underlying neurons is  Can't tell us if a person is thinking, tells us IF they are thinking Magnetoencephalography  Measures the magnetic field produced by the activation of neurons  Much better at locating sources of neural activity in brain, especially when the signals are deep below the surface of the brain  Measure direct flow of neurons (EEG too)  Can measure very rapid changes (EEG too)  Directly measure the activity of neurons Definition of EEG rhythms  Beta rhythms o Anything greater than 14Hz o Signal an activated cortex  Alpha rhythms o 8-13 Hz o Associated with quiet, waking states  Theta rhythms o 4-7Hz o Occur during some sleep states  Delta rhythms o Less than 4Hz o Are the hallmark of deep sleep Generation of synchronous rhythms  They may all take their cures from a central clock, or pacemaker o Like taking direction from the conductor of a orchestra  They may share or distribute the timing function among themselves by mutually exciting or inhibiting one another o More like a jam session Thalamus  Can act as very powerful pacemaker  Neurons have a particular set of voltage-gated ion channels that allow generation of rhythmic, self-sustaining discharge patterns even when external input to cell is lacking  Connection between excitatory and inhibitory neurons force individual neurons to conform to rhythm o These rhythms passed on to cortex by thalamocortical axons Generalized seizure  Involves the entire cerebral cortex of both hemispheres  Neurons within the affected areas fire with a synchrony that never occurs during normal behaviour (for both types of seizure) Partial seizure  Involves only a circumscribed area of the cortex Epilepsy  Affects 1% of U.S. population  More of a symptom than a disease  Cause can be tumors, trauma, metabolic dysfunction, infection, and vascular disease  Can be caused due to genetic predisposition o Mutated sodium channels that stay open longer o Impaired synaptic inhibition mediated by GABA Sleep  Is a readily reversible state of reduced responsiveness to, and interaction with, the environment  Rapid eye movement (REM) sleep o Your EEG looks more like you're awake o Dreams occur in this sleep stage o Oxygen consumption in brain higher than when awake o 25% of when you're asleep  Non-REM sleep o Don't normally have complex dreams o Slow wave sleep o Increase in parasympathetic activity of the ANS o Speed of digestion increases o Period for the body to rest o 75% of when you're asleep o Four Stages:
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