In the short-tailed fruit bat (Carollia perspicillata), the auditory cortex was localized autoradiographically and studied electrophysiologically in detail by using metal microelectrodes and 10-ms tone stimuli. Because, in the weakly-anaesthetized preparation, neuronal responses to pure-tones were even found throughout the non-primary auditory cortex, characteristic frequencies and minimum thresholds of neuron clusters (multiunits) could be mapped consistently and used to define auditory cortical fields conventionally (i.e. as in studies of auditory cortex of non-echolocating mammals). Thus, within the electrophysiologically demarcated auditory cortex, six auditory fields were defined by criteria, as for example a gradient of characteristic frequencies (primary auditory cortex, AI; anterior auditory field, AAF; secondary auditory cortex, AII), reversal of the gradient across the field border (AI, AAF), uniform representation of a restricted band of frequencies (i.e. > 60 kHz; high-frequency fields I and II, HFI and HFII), and transition from low to high minimum thresholds or vice versa [dorsoposterior field (DP), AII, HFI, HFII]. As supportive evidence for the distinction of these auditory cortical fields, differences in neuronal response properties were also used. In comparison with other mammals (e.g. cat and mouse), both the relative position of the auditory fields (mainly AI, AAF, DP and AII) and the representational principles for sound parameters within these forebrain areas seem to reflect a 'fundamental plan' (discussion below) of mammalian auditory cortical organization. Two coherent dorsally displaced high-frequency representations (HFI, HFII) covering approximately 40% of the total auditory cortical surface seem particularly suited for the processing of the dominant biosonar second and third harmonic of this species, and hence can be regarded as an adaptation for echolocation.

Based on neuroanatomical findings it was hypothesized that an area in the bat frontal cortex is part of a sensorimotor feedback loop and probably important to goal-directed behaviors guided by auditory information. The present report describes the basic stimulus preferences and response properties of neurons from this area in the short-tailed fruit bat Carollia perspicillata. Responses to acoustic stimuli mimicking biosonar pulse-echo (i.e. FM-FM) combinations were found to be facilitated throughout but only rarely exhibited tuning to pulse-echo delay. As opposed to the often sharply delay-tuned FM-FM neurons in the species' auditory cortex, frontal cortical FM-FM neurons seem to be suited for indicating the presence of an insonified object irrespective of its distance and hence are likely to function as novelty detectors and to trigger changes in the bats' orientation behavior.