Binaurality and azimuth tuning of neurons in the auditory cortex of the big brown bat

By using a combined closed and free-fleld stimulation system, binaurality and azimuth tuning of the neurons in the auditory cortex of the big brown bat, Eptesicus fuscus, were studied. A variety of azimuth-tuning functions were demonstrated for the binaural neurons. The large majority of EE (contralateral and ipsilateral excitatory) neurons exhibited azimuth selectivity with the best azimuths (BA) at contralateral 30degrees-40degrees, some at ipsilateral 20degrees-40degrees and preferred azimuth ranges (PAR, response amplitude >75% of maximum) between 8degrees and 40degrees. Sound source azimuths strongly modulate spike counts with a mean modulation depth of 83.8% for EE neurons. El (contralateral excitatory and ipsilateral inhibitory) neurons have simple azimuth tuning with BA located at contralateral 20degrees-40degrees and a broad PAR ranged from 30degrees to 55degrees. The present results suggest that azimuth-tuning characteristics of binaural neurons in the auditory cortex of the bat are of significance for acoustic behaviour.