Otoconia-deficient mice show selective spatial deficits

Abstract

The vestibular system contributes to the performance of various spatial memory tasks, but few studies have attempted to disambiguate the roles of the semicircular canals and otolith organs in this performance. This study tested the otolithic contribution to spatial working and reference memory by evaluating the performance of otoconia-deficient tilted mice on a radial arm maze and a Barnes maze. One radial arm maze task provided both intramaze and extramaze cues, whereas the other task provided only extramaze cues. The Barnes maze task provided only extramaze cues. On the radial arm maze, tilted mice performed similar to control mice when intramaze cues were available, but committed more working and reference memory errors than control mice when only extramaze cues were available. On the Barnes maze task, control and tilted mice showed similar latency, distance, and errors during acquisition training. On the subsequent probe trial, both groups spent the greatest percentage of time in the goal quadrant, indicating they were able to use extramaze cues to guide their search. Overall, these results suggest signals originating in the otolith organs contribute to spatial memory, but are not necessary for all aspects of spatial performance.

Keywords: otolith organs; radial arm maze; spatial memory; spatial orientation; vestibular.

Figure 1

Cued navigation performance was similar for control and tilted mice. A, The percentage of correct arm choices increased across trial blocks at similar rates between groups. B, Latency to complete the task decreased across trial blocks at similar rates between groups. Mean ± SEM.

Figure 2

Tilted mice were impaired at place learning on the radial arm maze. A, Percentage of correct arm choices increased more rapidly across trial blocks for control mice than for tilted mice. B–D, Reference Memory (RM), Working Memory – Correct (WM-C), and Working Memory – Incorrect (WM-I) errors decreased across trial blocks for control mice but not for tilted mice. E, Latency to complete the task decreased across trial blocks for both groups. F, Time per arm did not differ between control and tilted mice. Mean ± SEM.

Figure 3

Control and tilted mice performed similarly on the Barnes maze. A,B, Both groups of mice used a serial search strategy most often during the first two days of training, but did not significantly favor a particular strategy during the last two days. C–E, Control and tilted mice showed similar latency, errors, and distance during acquisition training. F, Both groups spent the greatest percentage of time in the goal quadrant during the probe trial on Day 5. Mean ± SEM.