A neuromorphic VLSI model of grid cells in the echolocating bat

Neurophysiological experiments in the hippocampal formation of echolocating bats have found grid cells (thought to be used for odometry) as in other mammals, but without continuous theta frequency oscillations (~8 Hz) prominent in other mammals. We describe a `theta-free´ model of grid cell property creation for echolocating bats that is amenable to VLSI implementation of hippocampal models of spatial navigation. We demonstrate a hybrid implementation of a 2-D model (microcontroller and neuromorphic VLSI) using recorded input from a sonar system.