Electrophysiological Recordings of Brain Activity

What are micro-electrode recordings

thin electrodes inserted into tissue to record neuronal electrical activity

what level of activity do micro-electrodes measure

single-cell (single neuron) activity

why are micro-electrode recordings invasive

electrodes must be inserted into brain tissue

when are micro-electrode recordings used in humans

usually during brain surgery

what is firing rate (spike rate)

frequency of action potentials a neuron generates

main advantage of micro-electrode recordings

most direct and precise measure of brain activity

main limitation of micro-electrode recordings

restricted subjects and brain areas available

what did medial temporal lobe recordings show

some neurons respond selectively to specific people/items

why are some selective cells not purely visual

they respond to names as well as faces

what is EEG

recording of voltage changes from sensors on the scalp

is EEG invasive or non-invasive

non-invasive

what neural activity is EEG most sensitive to

postsynaptic potentials, especially EPSPs

Why is EEG not very sensitive to action potentials

spikes are too brief and spatially small

what is a field potential

electrical potential measured outside neurons

which brain tissue contributes most to EEG

cortical tissue near the scalp

Can EEG detect deeper brain activity

sometimes, but less well

what is temporal resolution

precision in measuring timing of brain activity

EEG has high or low temporal resolution

high temporal resolution

EEG has high or low spatial resolution

low spatial resolution

What is frequency in EEG?

Number of oscillations per second (Hz).

What does 4 Hz mean?

Four oscillations per second.

What can EEG frequency analysis study?

Sleep states, arousal, and pathology.

What does higher-frequency EEG often indicate?

Greater cortical activity.

Greater cortical activity.

Cheaper and more portable

What EEG pattern is common in epilepsy?

Large abnormal synchronized discharges.

What is ictal activity?

EEG activity during a seizure.

What is inter-ictal activity?

Abnormal EEG activity between seizures.

What are event-related potentials (ERPs)?

EEG responses time-locked to specific events/stimuli.

How are ERPs created from EEG data?

Average many time-locked EEG segments.

Why average ERP trials?

reduce noise and real stimulus-related signals

What is an ERP component?

Distinct peak or feature in waveform.

What does P1 mean?

First positive peak.

What does P100 mean?

Positive peak around 100 ms after stimulus.

What are P1 and N1 linked to?

Perceptual analysis and attention.

What is P3 linked to

decision-making about a stimulus

what is the N400 associated with

semantic processing (meaning)

when is N400 larger

when a word is unexpected in context

why is EEG source localisation difficult

electrical signals spread through brain tissue

what is the inverse problem in EEG

hard to infer exact brain source from scalp signals

main strength of EEG/ERP

excellent timing information

In ERP graphs, what does an upward positive peak represent

a positive ERP component (e.g. P1, P3)

In ERP graphs, what does the x-axis usually show

time after stimulus onset

in seizure EEG images, what pattern is often seen

large high-amplitude synchronised spikes/waves

in averaging diagrams, why do repeated trials reveal ERP signals

random noise cancels while consistent responses remain

in scalp topography maps, what do different regions show

distribution of electrical activity across the scalp