| Abstract No.: | A-D1145 |
| Country: | USA |
| | |
| Title: | HEAD DIRECTION CELL INSTABILITY IN THE ANTERIOR THALAMUS AFTER LESIONS OF THE INTERPEDUNCULAR NUCLEUS |
| | |
| Authors/Affiliations: | 1 Benjamin Clark*; 1 Asha Sarma; 1 Jeffrey Taube;
1 Dartmouth College, Hanover, USA
|
| | |
| Content: | Objectives: A large body of research has identified a class of neurons in the limbic system that discharge as a function of an animal’s head direction (HD), independent of location and on-going behavior. HD cells are found in particularly high numbers in the anterodorsal thalamus (ADN). Experiments have shown that the generation of HD cells relies heavily on vestibular information while the stability of their preferred firing direction depends on motor/proprioceptive information (Taube, 2007). Although it is generally thought that vestibular information is projected to HD cell containing brain regions via a pathway originating in the medial vestibular nucleus to nucleus prepositus to supragenual nucleus to dorsal tegmental nucleus, it is presently not clear where motor cues might be integrated. One possible candidate is the interpeduncular nucleus (IPN) because of its reciprocal connections with HD cell circuitry, and the finding that it contains neurons sensitive to running speed. The present study tested this hypothesis by recording neurons in the ADN of rats with either neurotoxic or electrolytic lesions of the IPN.
Methods: In Experiment 1, we tested whether ADN HD cells in animals with lesions of the IPN maintain their preferred firing direction when locomoting to a novel environment. Because signals from motor and proprioceptive systems appear to be critical for stabilizing directional tuning when a rat moves into a novel environment, the presence of significant drift in the preferred firing direction (i.e., direction of maximum discharge) would support the notion that the IPN is a key component of a motor input to the HD system. Experiment 2 monitored the control exerted by a salient visual landmark on the preferred firing direction of HD cells in the ADN. Finally, Experiment 3 monitored HD cell activity in a testing environment in which salient visual cues were removed by turning the room lights off.
Results: In Experiment 1 a total of 9 HD cells in IPN lesioned animals were recorded while locomoting into the novel environment. In general, HD cells in lesioned animals failed to maintain their orientation when entering the novel environment. In Experiment 2 a total of 29 HD cells in lesioned rats were monitored before, during, and after the visual landmark rotation. A mild impairment was observed as the preferred firing directions of HD cells sometimes failed to rotate in register with the visual landmark. Finally, in Experiment 3, several of the 25 HD cells recorded in IPN lesioned rats drifted when the room lights were turned off.
Conclusions: Taken together, the results suggest that the IPN is crucial for the general stability of ADN HD cells. The results are consistent with the interpretation that the IPN relays motor information into the HD cell circuit.
|
| | |
| Back |
|
