The Journal of Neuroscience, December 15, 2000, 20(24):9298-9309
Dynamics of Hippocampal Ensemble Activity Realignment: Time
versus Space
A. David
Redish,
Ephron S.
Rosenzweig,
J. D.
Bohanick,
B.
L.
McNaughton, and
C. A.
Barnes
Division of Neural Systems, Memory, and Aging, Arizona Research
Laboratories, University of Arizona, Tucson, Arizona 85724-5115
Whether hippocampal map realignment is coupled more strongly to
position or time was studied in rats trained to shuttle on a linear
track. The rats were required to run from a start box and to pause at a
goal location at a fixed location relative to stable distal cues
(room-aligned coordinate frame). The origin of each lap was varied by
shifting the start box and track as a unit (box-aligned coordinate
frame) along the direction of travel. As observed by Gothard et
al. (1996a), on each lap the hippocampal activity realigned
from a representation that was box-aligned to one that was
room-aligned. We studied the dynamics of this transition using a
measure of how well the moment-by-moment ensemble activity matched the
expected activity given the location of the animal in each coordinate
frame. The coherency ratio, defined as the ratio of the matches for the
two coordinate systems, provides a quantitative measure of the ensemble
activity alignment and was used to compare four possible descriptions
of the realignment process. The elapsed time since leaving the box
provided a better predictor of the occurrence of the transition than
any of the three spatial parameters investigated, suggesting that the
shift between coordinate systems is at least partially governed by a stochastic, time-dependent process.
Key words:
place cell; hippocampus; tetrode; spatial navigation; attractor map; coherency ratio
Copyright © 2000 Society for Neuroscience 0270-6474/00/20249298-12$05.00/0
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