The Journal of Neuroscience, March 15, 1999, 19(6):2381-2393
Spatial- and Task-Dependent Neuronal Responses during Real
and Virtual Translocation in the Monkey Hippocampal Formation
Nobuhisa
Matsumura1, 2,
Hisao
Nishijo2,
Ryoi
Tamura2,
Satoshi
Eifuku2,
Shunro
Endo1, and
Taketoshi
Ono2
Departments of 1 Neurosurgery and
2 Physiology, Faculty of Medicine, Toyama Medical and
Pharmaceutical University, Sugitani 2630, Toyama 930-0194, Japan
Neuropsychological data in humans demonstrated a pivotal role of
the medial temporal lobe, including the hippocampal formation (HF) and
the parahippocampal gyrus (PH), in allocentric (environment-centered) spatial learning and memory. In the present study, the functional significance of the monkey HF and PH neurons in allocentric spatial processing was analyzed during performance of the spatial tasks. In the
tasks, the monkey either freely moved to one of four reward areas in
the experimental field by driving a cab that the monkey rode (real
translocation task) or freely moved a pointer to one of four reward
areas on the monitor (virtual translocation task) by manipulating a
joystick. Of 389 neurons recorded from the monkey HF and PH, 166 had
place fields that displayed increased activity in a specific area in
the experimental field and/or on the monitor (location-differential
neurons). More HF and PH neurons responded in the real translocation
task. These neurons had low mean spontaneous firing rates (0.96 spikes/sec), similar to those of rodent HF place cells. The remaining
nonresponsive neurons had significantly higher mean firing rates (8.39 spikes/sec), similar to interneurons or 
cells in the rodent
HF. Furthermore, most location-differential neurons showed different
responses in different tasks. These results suggest that the HF and PH
are crucial in allocentric information processing and, moreover, that
the HF can encode different reference frames that are context or
task-dependent. This may be the neural basis of episodic memory.
Key words:
hippocampal formation; parahippocampal gyrus; monkey; real translocation; virtual translocation; place cells; place fields; cognitive map; reference frame; episodic memory
Copyright © 1999 Society for Neuroscience 0270-6474/99/1962381-13$05.00/0
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