Frequency arrangement in anterior ectosylvian auditory cortex of dog

¹ Department of Anatomy, University of Oregon Medical School, Portland, Oregon

The anterior ectosylvian (AES) area was studied with local applications of strychnine and stimulation of the ear with known frequencies. The threshold spikes for various frequencies were determined to locate the connections to the area. It was found that low frequencies produced spikes ventrocaudally and higher frequencies produced spikes dorsocephalically. Each patch responded to a wider band of frequencies than observed in other areas. The same general arrangement, although less distinct, was obtained for both AES and MES (middle ectosylvian) areas in the lightly anesthetized dog, using only the evoked potentials as indicators. Considerable variation was found between animals and this variation was thought to be due to development of the nervous system. It was found that a sulcus generally separated the AES and MES areas. Other branch sulci of the ectosylvian sulcus penetrated the MES area, distorting the frequency pattern for sounds. The threshold data for the anesthetized dog in the AES and MES areas agree in absolute values to the minimum audible pressure levels for human hearing.