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Abstract:
A high-level auditory-cortical region was recently identified with functional magnetic resonance imaging (fMRI) in rhesus monkeys. This brain region shows a close functional correspondence to the so called human-voice region. Both human and monkey ìvoice” regions lie anterior and superior on the temporal lobe and appear to be exquisitely sensitive to certain vocal components in species-specific vocalizations that help to identify other conspecific members of the species. To clarify the in-vivo functional connectivity of the rhesus monkey voice region along with its putative auditory cortical network we used microstimulation in combination with high-resolution fMRI. First we functionally localized the voice region with blood-oxygen-level-dependent (BOLD) fMRI, as previously described. Then we microstimulated this region with glass-coated iridium microelectrodes, using biphasic, cathode leading, 250 to 500 ?A pulses of 200 ?s duration. We used the fMRI BOLD response to evaluate the anterograde targets of the microstimulation site. Microstimulation of the voice region, which lies on the rostral superior-temporal plane (rSTP), elicited a BOLD response from hierarchically earlier auditory areas (feed-back), and the surrounding superior temporal plane (STP), gyrus (STG) and sulcus (STS) of the ipsilateral hemisphere. We next microstimulated an upper-bank STS region that was the target of the voice region. The STS microstimulation seemed to show more robust medial and orbital prefrontal cortex activity in comparison to microstimulation of the voice region on the STP. We are currently comparing these results to those obtained from microstimulating the earlier stages of the auditory cortical pathway and aim to compare our functional connectivity results to anatomical tractography from the analysis of retrograde and anterograde tracers placed in some of the microstimulated regions.
