Three-dimensional space representation by echolocation in bats

Abstract

Echolocating bats are equipped with a biological sonar system that permits spatial navigation and target tracking in complete darkness. By actively controlling the directional aim, timing, frequency content, and duration of echolocation signals to “illuminate” the environment, the bat directly influences the acoustic input available to its sonar imaging system. Detailed analyses of the bat’s sonar behavior suggest that the animal’s actions play into a rich 3-D representation of the environment, which then guides motor commands for subsequent call production, head aim, and flight control in an adaptive feedback system. Studies of the bat’s sonar behavior have motivated neurophysiological studies of the midbrain superior colliculus (SC), a structure implicated in sensorimotor integration and spatial orientation. Using multichannel silicon probe recordings from the freely echolocating big brown bat, we characterized response profiles of single neurons, as the animal tracked moving targets from a stationary position on a platform and in free flight. Our data show premotor activity prior to sonar vocalizations and responses to echoes from objects. Echo responses depended on both the azimuth and delay of sonar returns. These findings demonstrate both auditory and premotor specializations in the bat SC, which contribute to the animal’s 3-D representation of space.