DISTRIBUTION OF RESPONSE TYPES ACROSS ENTIRE HEMISPHERES OF THE MOUSTACHED BATS AUDITORY-CORTEX

The responses of neurons in the mustached bat's auditory cortex are sp ecialized to extract particular information from biosonar signals. For this study, we mapped response properties across entire hemispheres i n several animals. These experiments enabled us to construct a standar d map that aided in determining the connections among the areas, as de scribed subsequently. The mapping also yielded quantitative data regar ding the relative sizes of areas and the proportion of cortex devoted to different response types. We identified six response types that wer e distributed in 11 areas. Eight areas, comprising two-thirds of the a uditory cortex, contained neurons sensitive to particular components i n biosonar signals. Most were facilitated by combinations of frequency modulated and constant frequency biosonar signal components (FMs and CFs, respectively). There were three major types of combination-sensit ive neurons: FM-FM, CF/CF, and FM-CF. Each type of combination sensiti vity occurred in multiple areas. The largest proportion were FM-FM neu rons (approximately 30% of all neurons in auditory cortex), followed b y FM1-CF2 (approximately 23%) and CF/CF (approximately 11%). In the ot her three areas comprising approximately one-third of the auditory cor tex, most neurons responded well to frequencies not contained in bioso nar signals. (C) 1998 Wiley-Liss, Inc.