Head Direction Signal Degradation Impairs Spatial Learning
Society for Neuroscience
San Diego, CA
Head direction cells provide a neural representation of perceived directional heading relative to the environment. Lesion studies suggest an important role of this signal in spatial learning and navigation, but brain lesions can damage additional brain structures/signals that may underlie the observed deficits. As a complementary model, we evaluated the spatial performance of otoconia-deficient tilted mice which have intact brains with degraded head direction cell signals. A caveat to this approach is that vestibular dysfunction can alter hippocampal function, and this change may impair spatial abilities. We therefore evaluated the integrity of hippocampal cholinergic afferents to determine whether hippocampal function is altered in tilted mice. Method: Homozygous tilted mice and their heterozygous control littermates performed spatial tasks on two mazes: a 6-arm radial maze and a Barnes maze. Two tasks – an intramaze cue task and an extramaze cue task – were used on the radial arm maze, with the same two arms baited for four trials per day, across ten days. On the Barnes maze, mice performed four acquisition trials per day across four days with a constant goal location, followed by a single 5-min probe trial on the fifth day with no goal available. Optical density was measured in hippocampal sections stained for acetylcholinesterase. Results: Radial arm maze Control and tilted mice showed increased percentages of correct arm choices across days on both tasks. However, tilted mice were impaired on the extramaze cue task but not on the intramaze cue task, relative to control mice. Barnes maze Control and tilted mice showed decreased number of errors, distance, and latency across days. Tilted mice were initially impaired but performed similar to control mice by the last day of acquisition. Both groups spent similar amount of time in the target quadrant during the subsequent probe trial. Optical density analysis Markers of hippocampal cholinergic function were similar across control and tilted mice, suggesting the navigation deficits of tilted mice did not result from structural changes to hippocampus or to the cholinergic septohippocampal projections. Importance: These results support previous suggestions that the head direction signal is an important component of navigation relative to distal cues.
Biological Psychology | Psychology
Seth Kirby, Ryan Harvey, Elizabeth Goebel, Jenny R. Koppen, Douglas G. Wallace, and Ryan M. Yoder (2013).
Head Direction Signal Degradation Impairs Spatial Learning. Presented at Society for Neuroscience, San Diego, CA.
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