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about the object seen [84]. Further evidence for this convergence of spatial and object
information in the hippocampus is that in another memory task for which the hip-
pocampus is needed, learning where to make spatial responses conditional on which
picture is shown, some primate hippocampal neurons respond to a combination of
which picture is shown, and where the response must be made [13, 48].
These primate spatial view cells are thus unlike place cells found in the rat [39, 51,
53, 54, 117]. Primates, with their highly developed visual and eye movement control
systems, can explore and remember information about what is present at places in
the environment without having to visit those places. Such spatial view cells in pri-
mates would thus be useful as part of a memory system, in that they would provide a
representation of a part of space that would not depend on exactly where the monkey
or human was, and that could be associated with items that might be present in those
spatial locations. An example of the utility of such a representation in humans would
be remembering where a particular person had been seen. The primate spatial repre-
sentations would also be useful in remembering trajectories through environments,
of use for example in short-range spatial navigation [58, 79].
The representation of space in the rat hippocampus, which is of the place where
the rat is, may be related to the fact that with a much less developed visual system
than the primate, the rat's representation of space may be defined more by the olfac-
tory and tactile as well as distant visual cues present, and may thus tend to reflect the
place where the rat is. An interesting hypothesis on how this difference could arise
from essentially the same computational process in rats and monkeys is as follows
[17, 79]. The starting assumption is that in both the rat and the primate, the dentate
granule cells and the CA3 and CA1 pyramidal cells respond to combinations of the
inputs received. In the case of the primate, a combination of visual features in the
environment will over a typical viewing angle of perhaps 10-20 degrees result in the
formation of a spatial view cell, the effective trigger for which will thus be a com-
bination of visual features within a relatively small part of space. In contrast, in the
rat, given the very extensive visual field which may extend over 180-270 degrees,
a combination of visual features formed over such a wide visual angle would effec-
tively define a position in space, that is a place. The actual processes by which the
hippocampal formation cells would come to respond to feature combinations could
be similar in rats and monkeys, involving for example competitive learning in the
dentate granule cells, autoassociation learning in CA3 pyramidal cells, and compet-
itive learning in CA1 pyramidal cells [75, 76, 92, 115]. Thus spatial view cells in
primates and place cells in rats might arise by the same computational process but
be different by virtue of the fact that primates are foveate and view a small part of
the visual field at any one time, whereas the rat has a very wide visual field. Al-
though the representation of space in rats therefore may be in some ways analogous
to the representation of space in the primate hippocampus, the difference does have
implications for theories, and modelling, of hippocampal function.
In rats, the presence of place cells has led to theories that the rat hippocampus is
a spatial cognitive map, and can perform spatial computations to implement naviga-
tion through spatial environments [10, 11, 54, 57]. The details of such navigational
theories could not apply in any direct way to what is found in the primate hippocam-
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