Journal of Neuroscience, Vol 16, 2809-2819, Copyright © 1996 by Society for Neuroscience
Hippocampal and neocortical cell assemblies encode memory processes for different types of stimuli in the rat
Y Sakurai
Department of Psychology, Toyama Medical and Pharmaceutical University, Japan.
The objective of this study was to determine whether each of several
different memory processes is encoded exclusively by specific single
neurons (single-neuron coding) or by overlapped groups of neurons
(population coding by cell assembly). Single neuronal activity was recorded
from the rat hippocampal formation (CA1, CA3, dentate gyrus) and temporal
cortex during the performance of simple auditory, simple visual, and
configural auditory-visual discrimination tasks. All the tasks employed the
identical apparatus and time parameters and differed only in the type of
stimuli to be processed for correct performance. Single neurons showing
significantly differential activity among the discriminative stimuli in
each task were judged to be task-related and involved in the memory process
of the task. Of the total number of neurons recorded from the hippocampal
formation and temporal cortex, 21- 26% of the neurons showed task-related
activity in only one task, in two tasks, or in all three tasks. This result
indicates some overlapping among the neurons involved in each of teh
different memory processes. A cross-correlation analysis tested activity
correlations among the neurons recorded simultaneously. Most pairs of the
hippocampal neurons related to the same tasks (same memory processes)
showed correlations during performance of the related tasks. This result
showing coactivation of the same types of task-related neurons, together
with the result showing the overlapping of task-related neurons, supports
the concept of population coding by cell assemblies specifically in the
hippocampal formation during memory processing.
Previous Article | Next Article
