LACK OF HYSTERESIS OF PLACE FIELDS DURING RADIAL MAZE ROTATIONS

A.P. Maurer * ; S.L. Cowen; S.N. Burke; J. Meltzer; J.A. Dees; B.L. McNaughton; C.A. Barnes

NSMA , Univ Arizona, Tucson, AZ, USA

Activity of hippocampal principal cells is highly correlated with a rat’s position in space (O'Keefe and Dostrovsky, 1971), and several studies have suggested that some form of attractor dynamics underlie this activity. In particular, Rettenmaier et al. (SfN 1999) reported hysteresis during the rotation of a radial 3 arm maze away from its previously learned orientation.  Fields were present over a greater angular range when rotating away from this orientation than as the maze rotated back toward it. We attempted to replicate this finding using high density neural ensemble recording in CA1. Rats were pre-trained, for at least eight days, to traverse a 3-arm radial maze (120º symmetry) for food reward in an environment rich in distal visual cues. On each of these days, the rats ran 47 trials with the maze in the standard configuration relative to the distal environmental cues. A trial consisted of a single visit to each arm, followed by replacement in the nest for approximately 1 min. After pre-training, rats ran 5 trials in the standard configuration followed by 36 rotation trials in which the maze was rotated clockwise by 10º increments. Rotation trials were then followed by an additional 6 trials in the standard configuration. A random rotation session was conducted 3-5 days after the serial rotation session. During these intervening days, the task was run in the standard configuration without rotation. The population state vectors correlations of place cell activity for the adjacent 10º maze rotations away from and back to the standard orientation were symmetric.  We were unable to find any evidence in these studies for an abrupt transition in the neural ensemble activity or hysteresis, which might reflect attractor dynamics.

Support Contributed By: AG012609 & NS020331

Key words: place cells, networks, learning