Object-specific adaptation in the auditory cortex of bats

Identifying behaviorally relevant sounds is a vital function of the auditory system. Echolocating bats must negotiate a wealth of sounds during navigation and foraging. They must detect relatively rare but behaviorally relevant echoes and segregate them from many unimportant background echoes. For this, the bat's auditory system might rely on neural deviance detection-a process influencing the excitability of a neuron depending on the frequency of occurrence of a stimulus. To investigate neural deviance detection in the auditory cortex (AC) of anesthetized bats (Phyllostomus discolor), we designed sequences of repetitive virtual echoes differing in the spectrotemporal envelope, resembling those that bats might perceive in their natural environment. A standard echo was repeatedly played 10 times in these sequences, followed by a deviant echo at the end. Time intervals between echoes within the sequences varied. Our results show that neurons in the AC of the bat P. discolor are sensitive to novel virtual echoes presented at the end of these repetitive sequences: In 49% (62/126) of cortical neurons, extracellularly recorded responses adapted to the standard echo but showed a strong response to the deviant echo presented at the end. This effect depended strongly on the time intervals between echoes, with stronger adaptation at shorter intervals. This type of response might indicate a form of neuronal deviance detection mechanism in the AC that could help the bats to detect echoes of novel and potentially important objects within a stream of homogeneous background echoes.NEW & NOTEWORTHY In this study, we show that neurons in the auditory cortex of the bat Phyllostomus discolor are sensitive to novel acoustic stimuli in the context of repetitive virtual echo sequences differing in spectrotemporal envelope. This represents a form of neuronal deviance detection that might help the bats to detect echoes of rare but relevant objects among the clutter.