DEOXYGLUCOSE UPTAKE IN THE FERRET AUDITORY-CORTEX

Histological methods and 2-deoxyglucose autoradiography were used in a n attempt at finding distinguishing characteristics that would permit the clear definition of different auditory areas on the ectosylvian gy rus. This region was studied in both coronal and flattened tangential sections. In tangential sections a crescent-shaped region of high deox yglucose uptake was identified. The centre of this crescent was in the position of the primary auditory area on the middle ectosylvian gyrus . The ventro-anterior arm of the crescent was on the surface of the an terior ectosylvian gyrus and the ventro-posterior arm on the posterior ectosylvian gyrus. All three parts of the crescent appear to have an auditory function, because ablating the inferior colliculus or inserti ng a contralateral earplug reduced their deoxyglucose uptake. This was shown by using two separately distinguishable forms of 2-deoxyglucose , incorporating the F-18 and C-14 isotopes. In addition, another area of high deoxyglucose activity was identified in the ventral wall of th e suprasylvian sulcus, which seems to correspond to the anterior audit ory field. These four areas with high deoxyglucose uptake also have hi gh levels of succinate dehydrogenase activity and moderately high dens ities of myelinated fibres. Succinate dehydrogenase histochemistry pro vides a simple method for identifying auditory cortical areas and shou ld be of use in future physiological studies. These results provide ev idence that the ferret has four separate auditory areas with relativel y high metabolic and functional activity.