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Neurochemical regulation of auditory information ... - Helda - Helsinki.fi

(Pekkonen 2000), and of Parkinson’s (Pekkonen et al. 1995) and Alzheimer’s diseases

(Pekkonen et al. 1994). MMN recording could provide a non-invasive tool for exploring

the neurophysiological functional deficits related to chronic alcoholism (Ahveninen et

al. 2000a; Marco-Pallares et al. 2007) and drug abuse (Kivisaari et al. 2007). As MMN

represents the earliest cognitive component registered from the human brain (Draganova

et al. 2007), abnormalities in MMN generation could represent core cognitive dysfunction

in the human brain, thus leading to dysfunction in further higher cognitive processing as

a whole.

P300 potential

The P300 first described by Sutton et al. (1965) is a positive potential occurring at an

approximate latency of 300 ms and is evoked by the presentation of a novel target stimulus

embedded among irrelevant stimuli, while the subject is actively reacting (pressing a

button or mentally counting) to the target stimuli (Polich 2004). Classical P300 response

usually embodies two subcomponents. The first one, which is elicited automatically by

an infrequent stimulus novelty, has fronto-central scalp maximum and is called P3a,

whereas the second one, which requires positive response to the infrequent stimulus of

an “odd-ball” task, has a parietal scalp maximum, and is called P3b (Squires et al. 1975).

A specially designed “distraction” paradigm uses novel (distractive) stimuli to elicit P3a

response (Escera et al. 2001; Schroger and Wolff 1998b), which is considered to reflect

the orienting of attention towards the distracting stimuli. P300 is usually interpreted as

an electrophysiological correlate of active attentional processes and working memory

(Karakas and Basar 2006). The latency of P300 could correspond to the speed of cognitive

processing or to that of stimulus classification (Magliero et al. 1984). It is notable that P300

latency is negatively correlated with mental function in normal subjects, such that shorter

latencies are related to superior cognitive performance (Polich et al. 1985). A number

of studies showed an increase in P300 latency with age (Korostenskaja et al. 2003a;

Korostenskaja et al. 2000; Pfefferbaum et al. 1984a). This dependence was linear and in

some studies associated with ability to concentrate on particular stimuli (O’Donnell et al.

1992). As far as P300 amplitude is concerned, it is proposed that it mainly corresponds to

the allocation of attention and activation of the immediate memory (Polich and Kok 1995).

This view of P300 amplitude is supported by studies demonstrating that greater P300

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