ERP Brain Mapping
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Event-related brain potentials (ERPs) are a non-invasive method of measuring brain activity during
cognitive processing. The transient electric potential shifts (so-called ERP components) are time-locked to
the stimulus onset (e.g., the presentation of a word, a sound, or an image). Each component reflects brain
activation associated with one or more mental operations.
With the proper equipment and training, ERPs can be reliably measured using electroencephalography
(EEG), a procedure that measures electrical activity of the brain through the skull and scalp. As the EEG
reflects thousands of simultaneously ongoing brain processes, the brain response to a single stimulus or
event of interest is not usually visible in the EEG recording of a single trial; to see the brain response to the
stimulus, the neuroscience clinician must conduct many trials (100 or more) and average the results
together, causing random brain activity to be averaged out and the relevant ERP to remain.
While evoked potentials reflect the processing of the physical stimulus, event-related potentials are caused
by the "higher" processes, that might involve memory, expectation, attention, or changes in the mental state,
among others. Recently, ERPs are found to be more sensitive than mental status testing and mild
cognitive impairment that converts to Alzheimer's disease.
cognitive processing. The transient electric potential shifts (so-called ERP components) are time-locked to
the stimulus onset (e.g., the presentation of a word, a sound, or an image). Each component reflects brain
activation associated with one or more mental operations.
With the proper equipment and training, ERPs can be reliably measured using electroencephalography
(EEG), a procedure that measures electrical activity of the brain through the skull and scalp. As the EEG
reflects thousands of simultaneously ongoing brain processes, the brain response to a single stimulus or
event of interest is not usually visible in the EEG recording of a single trial; to see the brain response to the
stimulus, the neuroscience clinician must conduct many trials (100 or more) and average the results
together, causing random brain activity to be averaged out and the relevant ERP to remain.
While evoked potentials reflect the processing of the physical stimulus, event-related potentials are caused
by the "higher" processes, that might involve memory, expectation, attention, or changes in the mental state,
among others. Recently, ERPs are found to be more sensitive than mental status testing and mild
cognitive impairment that converts to Alzheimer's disease.
NOTE: (above) deviations from normality in many components associated with both hyper (occipital-parietal) and hypo
activation (prefrontal) of cortical areas.
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Experimental psychologists and neuroscientists have discovered many different stimuli that elicit reliable
ERPs from participants. The timing of these responses is thought to provide a measure of the timing of the
brain's communication or time of information processing. For example, in the checkerboard paradigm
described above, in healthy participants the first response of the visual cortex is around 50-70 msec. This
would seem to indicate that this is the amount of time it takes for the transduced visual stimulus to reach
the cortex after light first enters the eye. Alternatively, the P300 response occurs at around 300ms
regardless of the stimulus presented: visual, tactile, auditory, olfactory, gustatory, etc. Because of this
general invariance in regard to stimulus type, this ERP is understood to reflect a higher cognitive response
to unexpected and/or cognitively salient stimuli.
Due to the consistency of the P300 response to novel stimuli, a brain-computer interface can be
constructed which relies on it. By arranging many signals in a grid, randomly flashing the rows of the grid
as in the previous paradigm, and observing the P300 responses of a subject staring at the grid, the subject
may communicate which stimulus he is looking at, and thus slowly "type" words.
References
Papaliagkas, V., Kimiskidis, V., Tsolaki, M., Anogianakis, G. (2008). Usefulness of event-related potentials in the assessement
of mild cognitive impairment. BMC Neuroscience, 9:107
Luck, SJ (2005). An Introduction to the Event-Related Potential Technique. Cambridge, Mass.: The MIT Press
Handy, TC (2004). Event-Related Potentials : A Methods Handbook. Cambridge, Mass.: The MIT Press
Fabiani, M, Gratton, G, and Federmeier, KD (2007). Event-Related Brain Potentials : Methods, Theory, and Applications. In:
Handbook of Psychophysiology. Eds. Cacioppo, Tassinary, and Berntson. 3rd. ed. Cambridge: Cambridge University Press,
pp. 85-119
Polich, J and Corey-Bloom, J (2005). Alzheimer's Disease and P300: Review and evaluation of Task and Modality. Current
Alzheimer Research, 2, 515-525
activation (prefrontal) of cortical areas.
-------------------------------------------------------------------------
Experimental psychologists and neuroscientists have discovered many different stimuli that elicit reliable
ERPs from participants. The timing of these responses is thought to provide a measure of the timing of the
brain's communication or time of information processing. For example, in the checkerboard paradigm
described above, in healthy participants the first response of the visual cortex is around 50-70 msec. This
would seem to indicate that this is the amount of time it takes for the transduced visual stimulus to reach
the cortex after light first enters the eye. Alternatively, the P300 response occurs at around 300ms
regardless of the stimulus presented: visual, tactile, auditory, olfactory, gustatory, etc. Because of this
general invariance in regard to stimulus type, this ERP is understood to reflect a higher cognitive response
to unexpected and/or cognitively salient stimuli.
Due to the consistency of the P300 response to novel stimuli, a brain-computer interface can be
constructed which relies on it. By arranging many signals in a grid, randomly flashing the rows of the grid
as in the previous paradigm, and observing the P300 responses of a subject staring at the grid, the subject
may communicate which stimulus he is looking at, and thus slowly "type" words.
References
Papaliagkas, V., Kimiskidis, V., Tsolaki, M., Anogianakis, G. (2008). Usefulness of event-related potentials in the assessement
of mild cognitive impairment. BMC Neuroscience, 9:107
Luck, SJ (2005). An Introduction to the Event-Related Potential Technique. Cambridge, Mass.: The MIT Press
Handy, TC (2004). Event-Related Potentials : A Methods Handbook. Cambridge, Mass.: The MIT Press
Fabiani, M, Gratton, G, and Federmeier, KD (2007). Event-Related Brain Potentials : Methods, Theory, and Applications. In:
Handbook of Psychophysiology. Eds. Cacioppo, Tassinary, and Berntson. 3rd. ed. Cambridge: Cambridge University Press,
pp. 85-119
Polich, J and Corey-Bloom, J (2005). Alzheimer's Disease and P300: Review and evaluation of Task and Modality. Current
Alzheimer Research, 2, 515-525
