COGNITIVE BRAIN POTENTIALS AND REGIONAL CEREBRAL BLOOD-FLOW EQUIVALENTS DURING 2-SOUND AND 3-SOUND AUDITORY ODDBALL TASKS

Ten healthy volunteers were examined with single photon emission tomog raphy and Tc-99m-exametazime. They were studied on 2 occasions, during a 2- and a 3-sound auditory discrimination (oddball) task. Twenty hea lthy volunteers were used as controls, studied once at rest. During th e 2-tone task there was a bilateral posterior (occipito-) temporal and medial frontal activation, a left pericentral increase, and posterior cingulate suppression. During the 3-sound task activation was again f ound in posterior (occipito-) temporal, medial frontal cortex, left pe ricentral, with a small non-significant reduction in posterior cingula te uptake. Compared with the 2-tone task, there was a trend towards hi gher activity in left medial frontal, right posterior temporal and pos terior cingulate cortex in the 3-sound task. P3b amplitudes were negat ively correlated with posterior cingulate tracer uptake during both ta sks. Positive correlations with P3b amplitudes were found in various f rontal and temporal regions. These results are consistent with more in vasive localisation studies of P3b. Posterior cingulate cortex appears to be inhibited during the oddball tasks, the more so, the more restr icted the range of stimuli, and the greater the task-related recruitme nt of neurones (P3b amplitude). As expected from its more frontal dist ribution, P3a amplitude was positively correlated with anterior cingul ate tracer uptake, and negatively correlated with temporal cortical ac tivity.