Chapter 19 Notes
EEG is the classical way for recording brain rhythms in the cerebral cortex
EEG measures voltages generated by currents that flow during synaptic
excitation of the dendrites of many pyramidal neurons in the cerebral cortex.
The amplitude of an EEG depends on how synchronous the activity of the
An alternative way to record the rhythms of the cerebral cortex is with
It is better than EEG when localizing the sources of neural activity in the
brain, particularly when they are deep in the brain.
EEG and MEG can record rapid fluctuations of neural activity, unlike fmri or
Eeg and meg measure direct neuronal activity, while fmri and mri measure
blood flow or metabolism
EEG can be classified differently according to frequency range:
Beta rythms: fastest, 15-30 Hz, and signal an activated cortex
Alpha rythms: 8-13 Hz, associated with quiet, waking states
Theta rythms: 4-7 Hz and occur during some sleep states
Delta rythms: quiet, slow, <4 Hz, often large in amplitude and signify deep
sleep, like stage 3 and 4 sleep
Gamma rhythms 30 – 90 Hz
Amplitude is higher during resting states such as sleep because of greater
synchrony, while lower in other states such as alertness because of processing
The activity of a large set of neurons will produce synchronized oscillations in one of two
1. They take all their cues from a central block or pacemaker i.e. band leader
2. They may share or distribute the timing function among themselves by
mutually exciting or inhibiting one another i.e jam session
In the mammalian brain, the thalamus is a powerful pacemaker in that it can generate action
potential discharges. How do the thalamic neurons oscillate?
They have a particular set of voltage gated ion channels that allow each cell
to generate self sustaining discharge patterns even when there is no external input
to the cell
Synaptic connections between excitatory and inhibitory thalamic neurons
force each individual neuron to conform to the rythym of the group
These coordinated rythms are then passed on to the cortex by thalamocortical
axons, which excite cortical neurons
Seizures are the most extreme form of synchoronous brain activity.
Generalized seizure: involves the entire cortex of both hemispheres
Partial seizure: involves only a circumscribed area of the cortex
Seizures are accompanied by very large EEG patterns
Epilepsy: repeated seizures
Several mutations of genes that encode fot sodium channel proteins, for
example, have been linked to rare forms of epilepsy. The channels stay open for too long. Another group of mutations impairs synaptic inhibition mediated by
Drugs that block GABA receptors are convulsants (case seizures), while those
that suppress seizures anti-convulsants.
In generalized seizure, because all cortical neurons participate, behavior is are
completely disrupted by tonic (constant) or clonic (ryhtmic) activity, or by both
in sequence, so called tonic-clonic seizure.
Absence seizures occur in childhood and consist of less than 30 sec of
generalized 3 Hz EEG waves accompanied by unconsciousness. The motor signs
of an absence seizure are fluttering eyelids or a twitching mouth.
Partial seizure can be instructive:
If in a sensory area, they can trigger an abnormal sensation, or aura,
such as an odd smell or sparkling lights. Can cause déjà vu, and
hallucinations, impair memory e.t.c
Sleep is a readily reversible state of reduced responsiveness to, and interaction with, the
REM sleep, Rapid Eye Movement, is when your EEG looks more awake than asleep,
your body (except for your eye and respiratory muscles) is immobilized, and you conjure
up the vivid, detailed illusions of dreams. REM sleep is dreaming sleep. Dominated by
Non-REM sleep, also called slow wave sleep, is dominated by large, slow EEG
rhythms. The brain does not generate complex dreams during this stage. Body is capable
of movement during this period. Other body functions decreases, but digestive processes
increase. Dominated by non-sympathetic activity.
Oxygen consumption of the brain is higher in REM sleep than when the brain is awake.
The paralysis that happens during REM sleep is atonia
Look @ table on pg 595