EFFECTS OF LOCALIZED CORTICAL DESTRUCTION ON AUDITORY DISCRIMINATIVE CONDITIONING IN CAT

Abstract

Cats were trained to discriminate small increments in the frequency of auditory stimuli. The background noise level of the exptl. room was approx. 50 db. S. P. L. Each trial of the 20 in a session began with presentation of a varying number of 1000 cycle tones at 65 db. S. P. L., each 2 sec. in duration and spaced 1 sec. apart. The series was followed by an 1100 cycle tone reinforced with shock and buzzer. The animals learned to avoid shock by running in a rotating cage. Generalization training began after a criterion of 90% responses was reached, and critical tests were given at increments of 20, 40, 60, 80 and 100 cycles. Cats were retrained by the same procedure after production of a variety of symmetrical cortical ablations, the most extensive of which removed all neocortex posterior to somatic area I. Attempts were made to produce discrete destruction of known auditory fields in combination and in isolation. Extirpations of auditory area I; somatic area II; somatic area II and the posterior ectosylvian gyrus; auditory area I, somatic area II and the posterior ectosylvian gyrus; auditory area II, somatic area II and the posterior ectosylvian gyrus; and auditory areas I and II, the posterior ectosylvian gyrus, the cerebellar tuber vermis, suprasylvian gyrus and temporal region are without effect upon frequency discrimination. A lesion that combined destruction of somatic area II, the posterior ectosylvian gyrus, and the middle region of auditory areas I and II failed to produce a decrement, but any lesion that included complete removal of all these areas resulted in a lasting impairment. Animals that could not discriminate frequency could acquire a simple conditioned response and discriminate small changes in intensity.