Single cortical neurons serve both echolocation and passive sound localization

The pallid bat uses passive listening at low frequencies to detect and locate terrestrial prey and reserves its high-frequency echolocation for general orientation. While hunting, this bat must attend to both streams of information. These streams are processed through two parallel, functionally specialized pathways that are segregated at the level of the inferior colliculus. This report describes functionally bimodal neurons in auditory cortex that receive converging input from these two pathways. Each brain stem pathway imposes its own suite of response properties on these cortical neurons. Consequently, the neurons are bimodally tuned to low and high frequencies, and respond selectively to both noise transients used in prey detection, and downward frequency modulation (FM) sweeps used in echolocation. A novel finding is that the monaural and binaural response properties of these neurons can change as a function of the sound presented. The majority of neurons appeared binaurally inhibited when presented with noise but monaural or binaurally facilitated when presented with the echolocation pulse. Consequently, their spatial sensitivity will change, depending on whether the bat is engaged in echolocation or passive listening. These results demonstrate that the response properties of single cortical neurons can change with behavioral context and suggest that they are capable of supporting more than one behavior.