Recording from hippocampal place cells in the free-flying big brown bat

Melville Wohlgemuth and Iven Yu

This movie shows chronic recordings from the Hippocampus of a free-flying bat. LINK

Echolocating bats actively probe the environment by producing sonar signals and represent 3-D space using information carried by echoes from surrounding objects. As bats approach and attend to targets, they increase the rate at which they sample echo information by adjusting their sonar call rate. Increases in sonar call rate directly influence the resolution of space representation by providing frequent updates on the location of objects.

Past research has shown that the tuning of hippocampal place fields in a crawling big brown bat is sharpest within ~75 msec following a sonar vocalization and broadens over time. The time scale over which bat hippocampal place fields show changes in tuning occurs over 500 msec, which corresponds to a portion of the natural range of call intervals used by many lingual echolocators (Ulanovsky, N. and Moss, C.F. 2011. Dynamics of hippocampal spatial representation in echolocating bats, Hippocampus, DOI: 10.1002/hipo.20731; Vol. 21, 2, 150–161).

The sonar call rates of a crawling bat are far lower than those of a free-flying bat. As the free-flying big brown bat forages, its call rate increases from 5-10 calls/sec to over 150 calls/sec as it searches, tracks and intercepts insect prey on the wing. Thus, the intervals for echo processing span 6-200 msec, raising questions about bat hippocampal place field tuning in an animal that dynamically modulates the rate of its calls and its attention to objects in flight.

We are investigating the relationship between sensory sampling and space representation by recording from hippocampal place cells in the free-flying big brown bat, as it dynamically adjusted its sonar call rate in response to objects in the environment. Using synchronized high-speed stereo video, audio and neural telemetry recordings, we compared hippocampal place field tuning as bats adjusted echolocation call rates in response to sonar objects.

Our data show that hippocampal place field tuning depends on the rate at which an echolocating bat samples echoes from objects in its surroundings. Place field tuning is typically 50% tighter when bats rapidly sample spatial information by producing sonar calls at a high rate compared to low. These data have implications for understanding the contribution of spatial attention and sensory sampling to space representation across the animal kingdom.

Copyright@2015 Batlab, Johns Hopkins University
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