Focal activations of human cerebral cortex during auditory discrimination.

Abstract

Local increases in regional cerebral glucose and O2 consumption leads to proportional increases in regional cerebral blood flow (rCBF). rCBF was used as an indicator of regional cerebral metabolism. After intracarotid injection of 133Xe, rCBF was measured in 254 cortical regions of 12 patients with no major neurological deficits. Two measurements were taken, the 1st at rest and the 2nd during auditory discrimination of tone rhythms. Auditory discrimination increased the rCBF bilaterally in the following cortical regions: the auditory areas, the posterior inferior frontal regions (Broca area), the frontal eye fields, the frontal polar regions and the superior frontal regions close to the midline. Differences in activation between the right and the left (dominant) hemisphere were noted: the inferior and midparietal region was activated on the right side but not on the left; the rCBF increase in the right auditory area was more intense than that in the left; the adjacent part of the mid and inferior temporal region was activated on the right, whereas there was no statistically significant activation on the left; the activation of the posterior inferior frontal area spread over a greater cortical area on the right side than on the left; there was a greater area of activation in the superior frontal region on the right side than on the left; and a small activation was found in the right temporal operculum. The major part of the analysis of complex nonverbal auditory signals apparently takes place in focally activated areas in the right temporal and parietal lobe and in the right posterior inferior frontal area. The role of the frontal eye fields may be to turn the attention to and from extrapersonal space. The superior frontal regions were activated when subjects were required to follow a plan of action according to a prior instruction. Of the 12 subjects, 8 had, in addition to the increases discussed, a diffuse increase of rCBF in the association cortex but not in the Rolandic strip. This is assumed to reflect a basic principle of brain work: the areas that potentially could be included in the information processing are selectively facilitated.