Auditory belt and parabelt projections to the prefrontal cortex in the rhesus monkey

Recent anatomical and electrophysiological studies have expanded our knowle dge of the auditory cortical system in primates and have described its orga nization as a series of concentric circles with a central or primary audito ry core, surrounded by a lateral and medial belt of secondary auditory cort ex with a tertiary parabelt cortex just lateral to this belt. Because recen t studies have shown that rostral and caudal belt and parabelt cortices hav e distinct patterns of connections and acoustic responsivity, we hypothesiz ed that these divergent auditory regions might have distinct targets in the frontal lobe. We, therefore, placed discrete injections of wheat germ aggl utinin-horseradish peroxidase or fluorescent retrograde tracers into the pr efrontal cortex of macaque monkeys and analyzed the anterograde and retrogr ade labeling in the aforementioned auditory areas. Injections that included rostral and orbital prefrontal areas (10, 46 rostral, 12) labeled the rost ral belt and parabelt most heavily, whereas injections including the caudal principal sulcus (area 46), periarcuate cortex (area 8a), and ventrolatera l prefrontal cortex (area12vl) labeled the caudal belt and parabelt. Projec tions originating in the parabelt cortex were denser than those arising fro m the lateral or medial belt cortices in most cases. In addition, the anter ior third of the superior temporal gyrus and the dorsal bank of the superio r temporal sulcus were also labeled after prefrontal injections, confirming previous studies. The present topographical results suggest that acoustic information diverges into separate streams that target distinct rostral and caudal domains of the prefrontal cortex, which may serve different acousti c functions. (C) 1999 Wiley-Liss, Inc.