Subdivisions of auditory cortex and processing streams in primates

The auditory system of monkeys includes a large number of interconnected su bcortical nuclei and cortical areas. At subcortical levels, the structural components of the auditory system of monkeys resemble those of nonprimates, but the organization at cortical levels is different. In monkeys, the vent ral nucleus of the medial geniculate complex projects in parallel to a core of three primary-like auditory areas, Al, R, and RT, constituting the firs t stage of cortical processing. These areas interconnect and project to the homotopic and other locations in the opposite cerebral hemisphere and to a surrounding array of eight proposed belt areas as a second stage of cortic al processing. The belt areas in turn project in overlapping patterns to a lateral parabelt region with at least rostral and caudal subdivisions as a third stage of cortical processing. The divisions of the parabelt distribut e to adjoining auditory and multimodal regions of the temporal lobe and to four functionally distinct regions of the frontal lobe. Histochemically, ch impanzees and humans have an auditory core that closely resembles that of m onkeys. The challenge for future researchers is to understand how this comp lex system in monkeys analyzes and utilizes auditory information.