Electrophysiology and EEG

how does electrophysiology work

it works by coding by spike rate. an electrode is inserted into a brain area to record action potentials

if neuron is involved in task

excited multiple PSPs or action potentials are present

if neuron is not involved in task

action potentials will occur at a baseline firing rate or low PSPs

if neuron is suppressed by the task

no action potentials

what are spikes

outputs of neurons

what are LFPs

input of neurons or dendritic activity

what does LFPs stand for

local fieldpotential

First step to primary visual cortex

light hits the retina

where does light cross

optic chiasm

where is the first synapse in the visual pathway

LGN (lateral geniculate nucleus)

last synapse to of the primary visual cortex

primary visual cortex

Right field

left side of the brain

Left field

right side of the brain

There is more brain space in the fovea why?

center for highest visual acuity

what can spike rates be used for 

can be used to make maps for different areas of the cortex.

monkey experiment

when you flash a light the money has a fixation point where it fixes the eyes. the area around the stimulus the receptive field. The area with the highest APs indicates where the light is where the light is being shined on.

the spike rates are displayed by what

raster plots and histograms

raster plots

raw data

histogram

the average

why is the action potential peak later

it takes some time for the signal to cross at the LGN to the thalamus after crossing at the optic chiasm

Face selective cell experiment

recording when monkey is looking at a face vs not looking at a face. Recording from face selective cell would be high while the recording from the nonselective cell would be low

what part of the auditory cortex is stimulated

ventral tegmental area

experiment for audition

play tones to see where you get the highest rate.

what does the highest rate at a specific cell signify

this is the frequency that the sound is being processed by.

Tuning curve motor cortex

light comes onto the table and the monkey’s job is to smack it.

action potentials are being recoded from the motor cortex

what graph does the motor cortex experiment signify

Gaussian curve

y axis= firing rate

x axis= degrees

layers of the meninges

dura

subdural space

anorchid

subarachnoid space

pia

how does electrocorticography work

electrodes are placed at the cortex, under the skull so it is invasive. Is used for epileptic zone identification

where can a EcOG be placed

epidural and subdural space. can provide information from the gyrus, sulcus, and epigyrus

EcOG advantages

Much better spatial resolution compared to EEG. Excellent temporal resolution

ECoG disadvantages

invasive

not good at picking up signals deeper in the brain areas

EEG

continuous recording of electrical brain activity

receive signal from dendrites causing polarity change

this can then be used to track signals

LFG

area in which multiple neurons work in concert

equipment of an EEG

EEG cap

EEG amplifier

Data acquisition computer

what does the cap measurre

rapid eye movement

what are the wave functions present in an EEG

Gamma, beta, alpha, theta

what happens when the EEG is time locked to a particular stimulus

ERP

baseline

time period before stimulus

Benefits of EEG

Signals are fast

Noninvasive and safe (record brain activity passively)

Cons of EEG

Poor spatial resoluton

what is an EEG used for

detecting epilepsy

Fast signal

high arousal

Slow signal

low arousal

Gamma

30+ Hz

agitation, motor

Beta

12-30 Hz

thinking

Alpha

8-12 Hz

relaxing

Theta

4-7 Hz, mediation

Delta

1-4 Hz sleep

ERP from EEG

ERP is the average signal to get a line more consistent. 

Used for attention

Above in ERP

negative

Below

positive

<100 mmsec

Sensory processing

P100

selective attention

100 msec

selective attention

N100

selective attention

N200

recognition, and categorization

P300

working memory, cognitive load

300 msec

working memory, cognition load