| Abstract No.: | A-D1147 |
| Country: | USA |
| | |
| Title: | THE INFLUENCE OF SUPRAGENUAL NUCLEUS LESIONS ON HEAD DIRECTION CELL ACTIVITY |
| | |
| Authors/Affiliations: | 1 Joel Brown*, 1 Benjamin Clark, 1 Jeffrey Taube;
1 Dartmouth College, Hanover, NH, USA |
| | |
| Content: | Objectives: Neural activity in several brain areas varies as a function of the animal’s head direction (HD) in the horizontal plane and the cells encoding this signal are known as HD cells. Lesions of the vestibular periphery abolish the HD cell signal (Stackman and Taube, 1997), but the organization of brainstem pathways relaying vestibular information to the HD circuit is poorly understood. Recent anatomical work has identified the supragenual nucleus (SG) as a putative relay (Brown et al., 2005; Biazoli et al., 2006). This project was designed to elucidate the contribution of the SG to the HD signal. Three rats received unilateral neurotoxic lesions of the SG and were implanted with recording electrodes in the ipsilateral anterior dorsal thalamic nucleus.
Methods: Following recovery from surgery the rats were screened daily for HD cells as they foraged for scattered food pellets in a high-walled cylinder containing a prominent visual cue card. HD cells were identified and recorded over five 8 min sessions. The rats were removed from the cylinder between each session and either the visual cue was rotated 90° or the lights were turned off. The cells were then monitored in an apparatus consisting of a cylindrical and a rectangular shaped chamber connected by a passageway requiring the rats to navigate two right-angle turns to move between the chambers. Each chamber contained a prominent visual cue card that was offset by 90° relative to the other cue card.
Results: The cells recorded during visual cue rotation sessions (n = 3) rotated ~90° in register with the cue card and returned to baseline in the following standard sessions. When the lights were turned off, the cells' preferred firing directions drifted slowly throughout the session. When tested in the differently shaped environments, the preferred firing direction of two HD cells shifted ~90° when the rats entered the rectangle and remained aligned with the cue card, and then returned to its original orientation when the rats returned to the cylinder. HD cell activity in a third rat shifted 45° in the rectangle, or halfway between the two cue cards, and returned to its original orientation when the rat returned to the cylinder. The preferred firing direction of HD cells in control rats do not normally shift substantially as they locomote between the chambers.
Conclusion: Taken together, these results suggest that SG lesions disrupt the flow of vestibular information to the HD circuit such that the rats become more dependent on visual cues.
|
| | |
| Back |
|
