Cortical projections from the rat suprageniculate nucleus demonstrated with the PHA-L method

$25 CORTICAL PROJECTIONS FROMTHE RAT SUPRAGENICULATE NUCLEUSDEMONSTRATED WITH THE PHA-L METHOD. KUROKAWA.1. KAZUNORI YOSHIDA.2, TETSURO YAMAMOT03AND HIROSHI OKA3, DeDartments of olarynQoloqy, 2psycholoqy an__dd3Physioloqy, Fukui Medical School, Matsuoka-cho, Fukui 910I I , Japan. Cortical projections from the suprageniculate nucleus (SG) of the rat thalamus were examined by anterograde axonal transport of Phaseolus vulgaris-leucoagglutinin ( PHA-L ). Following PHA-L injection into SG, anterogradely labeled terminals with PHA-L were distributed not only in the temporal cortical region but also in the frontal cortical region with superficial (layer I) and deep (layer IV) cortical innervation. In the frontal region, innervation for the superficial cortical layer spread more widely than that for the deep cortical layer. The former was distributed largely in the caudal portion of the frontal motor areas, while the l a t t e r was more caudal. The primary motor area was scarcely covered with these innervations. In the temporal region, innervation to the superficial cortical layer spread much more widely than that for the deep cortical layer. The former was distributed in the primary auditory area and surrounding auditory association areas, the l a t t e r more v e n t r a l l y and covering l i t t l e of the primary auditory area. These results suggest that ascending auditory inputs through SG influence, though superficial and deep cortical innervation, the frontal motor areas in addition to the temporal auditory areas in the rat.

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FREQUENCY REPRESENTATION IN THE AUDITORY CORTEX OF GUINEA PIGS. HIDEKAZU TANAKA* AND IKUO TANIGUCHI, Dept. of Auditory Disorders, Medical Research Institute, Tokyo Medical and Dental University,

1-5-45 Yushima, Bunkyo-ku, Tokyo 113, Japan.

Responses of neurons in the auditory cortex to pure tones were examined with microelectrodes in guinea pigs anesthetized by Ketalar.

Two main auditory fields (AI, AII) were found.

AI,

located anteriorly, had tonotopic organization with low frequencies rostrally and high frequencies caudally.

In AII, located posteriorly, the tonotopicity was reversed, with rostral-to-caudal

progression from high to low characteristic frequency. be clearly determined. not clear.

The border of these two areas could not

AII was smaller than AI and in some cases the tonotopicity in AII was

Many neurons in both areas exhibited a typical V-shaped tuning curve, but AI neurons

were more sharply tuned to pure tones than AII neurons.

There was no significant difference in

response latencies between the two areas.

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