Hippocampal neuronal position selectivity remains fixed to room cues only in rats alternating between place navigation and beacon approach tasks

To study the relationship between brain representations and behaviour, we r ecorded hippocampal neuronal activity in rats repeatedly alternating betwee n two different tasks on a circular platform with four reward boxes along t he edge. In the beacon approach task, rewards were provided only at the pai r of diametrically opposite boxes that was illuminated. In the place naviga tion task, rewards were available only at the boxes positioned near the nor th-east and south-west corners of the room. Performance levels were high an d rats rapidly reoriented to changes in lamp cues in the beacon approach ta sk. Neuropsychological studies show that rats with hippocampal lesions read ily employ beacon approach strategies, while place navigation is severely i mpaired. Previous studies suggested that the neurons might change their beh avioural correlates as the rat performed the respective tasks. However, of 34 hippocampal 'place cells' recorded, all showed position selectivity fixe d with respect to room cues, even in the beacon approach task where coding the position of the rat in the room was of no use for locating rewards. Whe ther or not hippocampal signals are actually employed for ongoing behaviour would then be decided by structures downstream from the hippocampus. If th is is the case, then the 'counterproductive' room referred place-related di scharges in the beacon approach task would be a background representation. This would provide support for proposals of multiple memory systems underly ing different types of information processing and contrasts with the popula r notion that local neuronal activity levels are selectively increased to t he degree that the brain region is required for the ongoing function.