Event-Related Potentials (ERPs)

so um event related potentials actually or erps are derived from eeg so you you know you attach electrodes to somebody's you know scalp um and you record eeg but you record the eeg time locked to the presentation of a stimulus event so you present something and then record the eeg that follows you know with the brain activity that follows so let's say you um you know present a sound like ah like that so you you present and then record the eeg time lock to that stimulus onset and then you record it again and timelock that's stimulus onset timelock of that stimulus sounds i'd say you do that like a hundred times these are very exciting experiments by the way um and then you uh you average out all of those eeg recordings and what you get are uh you know anything that wasn't specifically linked to the processing of that particular stimulus event that sound that you presented um you you get you that gets kind of um averaged out basically by averaging out these hundred trials right and what you're left with are a pattern of you know up and down tracings here of signals here you know of you know various speeds and amplitudes happening at specific time points uh or peaking at specific time points uh that are known as event related potentials that are related to the actual presentation of the stimulus um and there are these early latency responses for example and then there are these later uh latency responses these late responses um and you know after 100 milliseconds or so you know typically something that's been presented you know visually or through audition or something is you know is being processed at the level of the cortex um and erps are interesting because um you know they can be uh they can be influenced particularly these these late later latency um you know components um by you know aspects of whether somebody's attending for example you know drugs can have an impact on these for example there's lots of interesting ways you can sort of explore the brain's responses to specific stimulus events um utilizing you know ee uh erp um and you know one of the advantages of eeg and erp is that they're relatively inexpensive technologies there's no giant you know mri facility or something required uh you know so so it's um it's a more accessible you know sort of technology you know another huge advantage of all these electrophysiological techniques of course is that you're um you know measuring actual brain activity one of the great things about an erp for example if you present you'll see these this n1 this p1 you know there's n2 there's a very specific you know erp peaks that are generated um and uh they uh correlate uh with specific you know activity at specific times so so the temporal resolution you know of these electrophysiological techniques is you know excellent it's millisecond to millisecond you're recording electrical activity uh you know a disadvantage of a lot of these electrophysiological techniques of course is that um you you know spatial like uh uh kind of like mapping of where these signals are actually coming from is not so good uh there's something called the inverse problem within you know in uh when you're talking about eg and erp it's like you have a certain pattern of waveforms that you're recording from the surface of the scalp and you could posit many different you know sorts of generators you know uh activity you know within the brain that could lead to a similar you know scalp recording um so that's the inverse problem trying to go back from the scalp report recording to the specific generators of that activity in the brain but just to give an example of erp um like for example if you if you did present 100 you get a very specific pattern of you know activity but if you suddenly went like a really weird noise something unexpected something novel well you generate another peak that would appear about 300 milliseconds after the presentation of the uh or whatever the weird sound is i mean another one um it's called the p300 or the p3 uh and this you know has a there's a frontal aspect of it there's a there's a more posterior aspect of it um but it's uh it's related to you know detection of novelty you know something unusual or unexpected right and that could be you can imagine there are lots of ways you could use erp uh and sort of the study of the uh you know our responses to novel events etc in various experimental paradigms there's also clinical uses of erp for example the um the fact that we have early latency components to a response to um uh you know an auditory stimulus uh is useful um for trying to determine you know where somebody's experiencing for example um hearing loss like if somebody comes in they say i can't hear out of my right ear for example well those early latency components when you're presenting a sound you know into the right ear for example and they say i can't hear anything well you'll see you know these early latency peaks and value ups and downs basically in the recording and the what they call the auditory erp uh again they have to play the sound and like 100 times an average out so you could see these tiny little peaks right they got to be amplified so you could really see them well they each correspond these early latency ones then they're really early you know yeah before like you know 70 milliseconds you know 50 milliseconds some of them are really early like you know 25 milliseconds after the presentation um they each peak actually is related to the processing of the stimulus with the auditory stimulus in a particular you know spot along the way like you know the superior oliver you know cochlear nuclei superior oliver the inferior colliculi um and if the you see like let's see the peak associated with the cochlear nuclei with the superior olive uh but then it flattens out well then you know there's probably something going on at the level of the inferior colliculi so it gives you some clinical information using a relatively inexpensive you know technique to examine actual electrical activity of the brain with very high sort of temporal resolution um the later peaks that you get you know the ones that like the p1 the n1 the p2 the n2 the p3 that i talked about in response to novelty for example these are cortically generated they're more task dependent um and uh you know they're more influenced by you know sort of cognitive or perceptual aspects but these early latency components are invariant and they're fixed they're linked to activities specific subcortical networks and they can be very useful in determining where you know something is going wrong uh in terms of this auditory erp uh in the transit of auditory information you know from the cochlea you know to the brain

Channel: Bill Griesar

Views: 310

Rating: 5 out of 5

Keywords: ERP, electrophysiology, EEG, nwnoggin

Id: O0dxO_Qmv1s

Length: 7min 45sec (465 seconds)

Published: Tue Oct 06 2020