The Electroencephalogram (EEG)

An imaging technique that reads scalp electrical activity

EEG

EEG measures mostly...

the currents that flow during synaptic excitations of the dendrites of many pyramidal neurons in the cerebral cortex

Only large populations of active neurons can generate...

electrical activity recordable on the head surface

The highest influence to the EEG comes from the...

elecrtical activity of the cerebral cortex due to its surface position

Fourier Transform

Takes a time-based pattern, measures every possible cycle, and returns the overall "cycle recipe" (the amplitude, offset, & rotation speed for every cycle that was found).

Beta waves

Dominant during normal state of wakefulness with eyes open

Alpha waves

Induced by closing the eyes and relaxation, abolished with eyes open or being alert (thinking, calculating)

Delta waves

Dominant during stage III and IV NREM sleep

EEG's advantage is..... its disadvantage is...

High temporal resolution, low spatial resolution

Event related potential (ERP)

Significant voltage fluctuations resulting from evoked neural activity. Reflects, with high temporal resolution, the patterns of neuronal activity evoked by a stimulus.

The wake/sleep cycle is generated by synchronous neuronal actvity in the

cortex, thalamus and mesencephalic reticular formation

The reticular formation

modulates the rhythmicity of the thalamocortical loop

Frequency band most dominant in deep, dreamless sleep and coma

Delta

Frequency band that increases during effortful cognitive processing

Theta

Frequency band that decreases during active processing

Alpha

Decreases during active processing, but relatively less than alpha so it seems to increase. Seems to play a role in top-down control between adjacent cortical regions

Beta

Frequency associated with 'feature binding'. Seems to be associated with bottom-up processing between adjacent cortical regions

Gamma

EEG is sensitive to electrical activity on the...

gyri

MEG is sensitive to electrical activity on the

sulci

Fourier transform allows us to get information about (frequency domain)

the timing of oscillations within the cortex that generate the waveforms that make up EEG

The selection of the reference electrode

determines the topography of the recorded signal

The EEG is generated by the

summation of dendritic field potentials of groups of neurons that vary together in time

The Fourier transform

decomposes time domain signals into frequency + phase+ amplitude components.

A method of time domain analysis is ...

event-related potential (ERP)

A method of frequency domain analysis is ...

Fourier Transform

Event-related potentials (ERPs)

Relate scalp electrical activity to cognitive events.

The auditory P300 wave provides evidence for

late selection gating of targets during attention

The visual P1 attention effect is similar to auditory system attention effects in that

there is an enhancement in the early activity elicited by attended stimuli.

MEG

A functional neuroimaging technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain

Auditory N1

A negative-polarity wave occurring about 100 milliseconds after a sound

P20-P50 attention effect

A positive ERP deflection occurring 20-50ms after stimulus presentation. P20-50 is enhanced for selectively attended input compared to ignored input.