| Abstract No.: | A-D1146 |
| Country: | USA |
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| Title: | LANDMARK NAVIGATION AND PATH INTEGRATION IMPAIRMENTS FOLLOWING NEUROTOXIC DAMAGE OF THE INTERPEDUNCULAR NUCLEUS IN RATS |
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| Authors/Affiliations: | 1 Benjamin Clark*; 1 Jeffrey Taube;
1 Dartmouth College, Hanover, USA
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| Content: | Objectives: An understanding of directional heading is a crucial element of accurate spatial navigation. 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. Experiments have shown that the generation of these HD cells relies heavily on vestibular information while the stability of their preferred firing direction depends on motor/proprioceptive information (Taube, 2007). Motor input to the HD circuit may stem from the interpeduncular nucleus (IPN), a mid-brain structure that projects into the HD circuit and recieves major input from the habenular nuclei of the diencephalon. The habenula is heavily innervated by the entopeduncular nucleus, the major output pathway of the basal ganglia. Preliminary research has shown that electrolytic or neurotoxic damage of the IPN disrupts landmark control of HD cells and the updating of their preferred firing direction by self-movement cues. Thus, we investigated the role of the IPN in two forms of spatial navigation: landmark navigation and path integration. Landmark navigation refers to the use of stable external information or allothetic cues for accurate navigation, whereas path integration refers to the use of internal information or idiothetic cues to determine a current location and a return path to a starting location.
Methods: The task used was a standard food-carrying paradigm in which a rat searches for a food pellet in an open-field, and accurately returns to a refuge after finding the food (Frohardt et al., 2006; Whishaw et al., 2001). Landmark navigation was evaluated during trials performed under lighted conditions and path integration was tested under darkened (infrared) conditions so as to eliminate visual allothetic information. Auditory and olfactory cues were removed during both lighted and darkened conditions using white noise and by washing and rotating the table and refuge between trials.
Results: Here we report that IPN lesions increase the number of errors made by rats and reduce heading accuracy under both lighted and darkened (infrared) conditions.
Conclusion: The results suggest that the IPN is critical for accurate landmark navigation and path integration.
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