BILATERAL TEMPOROFRONTAL PROJECTIONS IN SQUIRREL MONKEY - ORIGIN DISTRIBUTION AND PATHWAYS

In the chloralose-anesthetized squirrel monkey, electrical stimulation of the lateral aspect of the superior temporal gyrus (STG) near the lateral sulcus elicited prominent positive-negative responses bilaterally in a wide area of dorsal frontal lobe centered around the arcuate sulcus (i.e., in areas 6 and 8). Stimulation at the same voltage of other parts of lateral STG was less effective. Stimulation of primary auditory cortex at the same voltage elicited no frontal response. Stimulation of white matter in STG and anteriorly along the lower part of the extreme and internal capsules (CEx-CE) and dorsal uncinate fasciculus (Un) elicited similar responses; stimulation of other subcortical structures did not. Lesions of this subcortical area (CEx-CE, Un) abolished the frontal responses to STG stimulation bilaterally; lesions elsewhere did not. The contralateral responses were abolished by cutting the genu of the corpus callosum but not by transection of its posterior part, nor by section of the anterior commissure. They persisted after removal of frontal cortex on the stimulated side. It thus appears that the system studied consists of a bundle of small fibers (since conduction velocities were less than 5 m/sec), originating in auditory association cortex (probably area 22) but not in primary auditory cortex, and passing forward in the CE-CEx-Un region en route to the vicinity of the arcuate dimple ipsilaterally, as well as crossing to the same area contralaterally via the genu of the corpus callosum. © 1969.