Keywords: Electroencephalography (EEG), N2, Neuroimaging, P3, Selective attention The widespread adoption of electroencephalography (EEG) for the non-invasive assessment of cortical activity has inaugurated a distinct era in the elucidation of brain function.
Due to its high temporal resolution, EEG imaging of relative scalp electrical positivities and negativities may expose subtle cognitive activity.
The mismatch negativity (MMN), or auditory N2a, is elicited in a task-independent manner by auditory oddball detection paradigms and is believed to reflect disparity between the deviating stimulus and a sensory-memory representation of the standard stimulus .
Thus, MMN data provide a means by which to analyze the characterization of auditory stimulus features in sensory memory .
While the MMN elicited from the presentation of the infrequent stimulus was not affected by intensity and ISI variation, both stimulus conditions significantly altered the MMN component evoked in the intensity-divergence condition, providing evidence for central differences in frequency-evoked and intensity-evoked MMN .
The effects of aging on analytical cognitive operations have become a prominent focus of research. 3 to 8 second) inter-stimulus intervals (ISIs), MMN peak-areas decrease in the older population, suggesting a shortening of the sensory auditory memory trace with increasing age . Numbers of preceding nontargets differentially affect responses to targets in normal volunteers and patients with schizophrenia: A study of event related potentials.
Picton et al., in an excellent review, note that since the MMN is generated regardless of attention to stimuli, it likely represents an automatic novelty-sensing process .
Two constituents of the ERP, the N200 and P300, appear to be closely associated with the cognitive processes of perception and selective attention (Figure 1).
The existence of such an ERP is supported by other experimental observations , with the prestriate region is the likely source, as localized by color discrimination tasks . P300 in serial tasks: An essential post-decision closure mechanism.
Combined brain-lesion studies and functional mapping have established the primary role of the auditory temporal cortex in MMN generation, supporting the independent storage and examination processes of auditory stimuli in the auditory cortical region .
In these experiments, the N200 is typically evoked before the motor response, suggesting its link to the cognitive processes of stimulus identification and distinction .
Several distinct N200 potentials have been characterized : one set reflecting involuntary processing, another evoked through active processing. Age-Related variations in P300 elicited by active, passive and single-tone paradigms in children.