Modulation of activity in prefronto-parietal brain systems through the behavioral relevance of low-frequency events: an fMRI study

The aim of this event-related fMRI study was to explore neural correlates involved in the processing of behavioral relevance of low-frequency events. 12 healthy volunteers underwent fMRI while performing a combined task-switching and oddball paradigm in which geometric objects had to be classified according to either color or shape. In the first two sessions of the experiment, beside frequent congruent and incongruent stimuli we introduced rare neutral stimuli that in the first session were behaviorally irrelevant and in the second relevant. In the third session the neutral stimuli became as frequent as congruent and incongruent ones. In session 1, activation in a bilateral network of inferior prefrontal and intraparietal brain regions was associated with oddball occurrence. In session 2, a network of bilateral orbito-frontal and inferior-parietal areas and parts of the midbrain dopamine system were activated in response to the behaviorally relevant infrequent stimuli. By contrast, in session 3 these activations were completely absent. In conclusion, these findings suggest that a network of inferior prefrontal and intraparietal brain areas is involved in the detection and resolution of behavioral conflict induced by irrelevant oddball stimuli, whereas another bilateral orbito-frontal and inferior-parietal brain system may be responsible for the positive evaluation of the behavioral valence of low-frequency events and the rapid adjustment of behavior.