Amygdala input promotes the spread of excitatory neural activity from the perirhinal cortex
to the entorhinal/hippocampal neurocircuit.
Kajiwara, Riichi, Ichiro Takashima, Yuka Mimura, Menno P. Witter, and Toshio Iijima.
† Brain Architecture Analysis Group, Neuroscience Research Institute, National Institute of
Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, 305-8568, Japan; ‡
Graduate School Neurosciences Amsterdam, Research Institute Neurosciences, Department of
Anatomy, Vrije Universiteit Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam,
The Netherlands; and § Systems Neuroscience, Graduate School of Life Sciences, Tohoku
University, Katahira, Aoba, Sendai, 980-8577, Japan
APStracts 10:0117J, 2003.
A number of sensory modalities most likely converge in the rat perirhinal cortex. The perirhinal
cortex also interconnects with the amygdala, which plays an important role in various
motivational and emotional behaviors. The neural pathway from the perirhinal cortex to the
entorhinal cortex is considered one of the main paths into the entorhinal-hippocampal network,
which has a crucial role in memory processes. To investigate the potential associative function of
the perirhinal cortex with respect to sensory and motivational stimuli and the influence of the
association on the perirhinal/entorhinal/hippocampal neurocircuit, we prepared rat brain slices
including the perirhinal cortex, entorhinal cortex, hippocampal formation, and amygdala. We
used an optical imaging technique with a voltage-sensitive dye to analyze (1) the spatial and
functional distribution of inputs from the lateral nucleus of the amygdala to the perirhinal cortex,
(2) the spread of neural activity in the perirhinal cortex after layers II/III stimulation, which
mimics sensory input to the perirhinal cortex, and (3) the effect of associative inputs to the
perirhinal cortex from both the lateral amygdaloid nucleus and layers II/III of the perirhinal
cortex on the perirhinal-entorhinal-hippocampal neurocircuit. Following stimulation in the
superficial layers of the perirhinal cortex, electrical activity only propagated into the entorhinal
cortex when sufficient activation occurred in the deep layers of perirhinal area 35. We observed
that single stimulation of either the perirhinal cortex or amygdala did not result in sufficient
neural activation of the deep layers of areas 35 to provoke activity propagation into the
entorhinal cortex. However, the deep layers of area 35 were depolarized much more strongly
when the two stimuli were applied simultaneously, resulting in spreading activation in the
entorhinal cortex. Our observations suggest that a functional neural basis for the association of
higher-order sensory inputs and emotion-related inputs exists in the perirhinal cortex, and that
transfer of sensory information to the entorhinal-hippocampal circuitry might be affected by the
association of that information with incoming information from the amygdala.
Received 24 May 2002; accepted in final form 18 November 2002
APS Manuscript Number J1033-2.
Article publication pending Am J Physiol
ISSN 1080-4757 Copyright 2003 The American Physiological Society.
Published in APStracts on 30 May 2003