Analog VLSI Models of Range-Tuned Neurons in the Bat Echolocation System

Matthew Cheely,Timothy Horiuchi

doi:10.1155/s1110865703302045

Matthew Cheely, Timothy Horiuchi

Open Access

https://doi.org/10.1155/s1110865703302045

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Abstract

The neural computations that support bat echolocation are of great interest to both neuroscientists and engineers, due to the complex and extremely time-constrained nature of the problem and its potential for application to engineered systems. In various areas of the bat's brain, there exist neural circuits that are sensitive to the specific difference in time between the outgoing sonar vocalization and the returning echo, or time-of-flight. While some of the details of the neural mechanisms are known to be species-specific, a basic model of re-afference triggered, post-inhibitory rebound timing is reasonably well supported by the available data. We have designed low-power neuromorphic VLSI circuits to mimic this mechanism and have demonstrated range-dependent outputs for use in a real time sonar system. These circuits are being used to implement range-dependent vocalization rates and amplitudes.

Highlights

Information about target range has many uses for bats during both prey capture and navigation tasks
Neurons have been found in bats that show a “facilitated” response to paired sounds presented at particular delays
Delay-tuned cells are found at many levels in the bat auditory system

Summary

INTRODUCTION

Information about target range has many uses for bats during both prey capture and navigation tasks. Delaytuned neurons in the big brown bat (Eptesicus fuscus) respond preferentially to an initial loud sound and a delayed softer sound, with no clear frequency relationship [16] Both of these mechanisms are thought to relate to discrimination between outgoing calls and returning echoes. An instability in the membrane dynamics of the delay-tuned neuron leads to a brief depolarizing jump above resting potential following the release of inhibition This type of rebounding behavior has been documented or Figure 2: Schematic of the PIR network model for delay-tuned cells. Studies of VNLLc (a subregion of VNLL known for short and remarkably precise latencies with broad frequency tuning) have shown that it contains glycinergic cells that project broadly and densely to the IC [21]

VLSI CIRCUIT IMPLEMENTATION

THE NARROWBAND ECHOLOCATION SYSTEM

CHIP PERFORMANCE

Findings

DISCUSSION