Innate Navigation: Magnetic Sensation and Maze Learning

Abstract

This thesis aims to advance the understanding of the neurobiology of navigation through the investigation of two topics: magnetic sensation and maze navigation. The central question of this work may be framed as follows: how do animals find their way to key resources that are necessary for survival? Three projects are presented to address this.

Chapter II explores a sensory hypothesis that some animals may navigate long distances by directly sensing the earth’s magnetic field. Awake zebra finches were stimulated with magnetic fields that varied sinusoidally in time while electrical recordings were collected via multi-channel electrodes. Preliminary negative results are presented, along with a detailed statistical treatment indicating no significant effect of magnetic stimulation on neural activity.

Chapter III presents a novel approach to studying learning and navigation in animal subjects. Mice are allowed free passage between a normal home cage and a complex maze environment, coming and going as they please. Sated animals, with free access to food and water, spend significant portions of a given multi-hour experiment in the maze and display efficient exploration. Water-restricted animals show three additional phenomena: immediate knowledge of the route home, rapid learning of the location of a single water port among 64 similar locations, and a moment of "sudden insight" in which the rate at which long, direct routes to the water source, beginning from many locations, increases discontinuously.

Chapter IV offers a simple, biologically feasible circuit model that recapitulates and explains some of the rapid learning behaviors we observe in mice. This model suggests a mechanism that might allow mice to flexibly store and recall direct routes to different resources that are activated by different internal drives.

The final chapter outlines some potential directions for future inquiry, including potential maze experiments to conduct with wireless electrophysiology and expansion of the range of species tested for magnetic perception. The Appendix briefly describes some follow-up experiments and intriguing preliminary results. Similarities in the navigation deficit displayed by mice that have been experimentally perturbed in several disparate ways is noted briefly. These perturbations include whisker trimming, olfactory neuron ablation, genetic ablation of cortex and hippocampus, and opiate intoxication.