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Event Related Potentials

 

The Event Related Potentials are exported from repeated encephalograms, which are time connected with a (repeated) sensual, intellectual, or kinetic stimulus. Fluctuations of encephalograms, that are irrelevant to the stimulus and the time that it occurred, are removed – on average – from the signal; what remains is the ERP. Therefore, these electric signals are indicators of cerebral activity which is closely connected to the stimulus, for certain time intervals. This is the main advantage of ERPs over EEGs: in the first one's signal the “random” (or better irrelevant with the stimulus) continuous brain activity is not included; it is supposed to depict only the activity which is related to the stimulus under review.

Even if research in the encephalograms has provided interesting results the research in ERPs has provided much more elements that cross-correlate neuropsychological and neurophysiological facts. This means that ERPs can be used in the diagnosis of psychiatric diseases as they demonstrate irregular operation when extracted from patients (naturally, when satisfactory material of control is available). Finally, it can be used for the comprehension of cognitive processes in the healthy brain (Garcia - Larrea et al, 1998; Friederici et al, 1999; Guillem et al 1999; Fabiani et al, 2000).

Because of their high time analysis (they depict brain activity in the second following the stimulus), ERPs provide unique and important time information with regard to the cerebral operation. Intellectual operations, which are related to perception, selective attention, linguistic operation and memory, are impressed in certain time intervals of each ERP. Most other techniques are not capable of depicting the concatenation of the above operations, since they require the recording of cerebral operation for enough seconds. On the contrary ERPs provide a picture of “evoked” cerebral activity, in such small time intervals as the thousandth of the second and for this reason they are ideal for the study of healthy or not intellectual processes, in relation to time.

 

The following table includes relationships between ERP time intervals and corresponding psychiatric notions:

 

ERP characteristics
Name Time (msec) Notion
P50 20-80 Pre-attentive index
N100 76-160 "Mobility" of attention
P200 140-250 Focusing of attention
N200 180-300 Performance of neural circuits under orientation reaction effect
P300 240-500 Neural activity related to apportionment of attention for mobilization of action routines.
N400 280-500 Neural activity related to the "syntax" of each response from the Central Neural System
P600 500-800 Timing indicator of certain response aspects (importance & syntax)

 

Below are useful pictures regarding ERPs. These are samples of my research, in most cases.

Hover over for info and left click to select. More pictures can be found in the ANN section.

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Lead placement

According to 10%-20% rule (Jasper 1958)