The Operation of Memory Systems in the Brain - Computational Neuroscience: A Comprehensive Approach - page 489

pocampal function (including the memory of recent events or episodes in humans)
is to note that this spatial processing involves a snapshot type of memory, in which
one whole scene with its often unique set of parts or elements must be remembered.
This memory may then be a special case of episodic memory, which involves an
arbitrary association of a set of spatial and/or non-spatial events that describe a past
episode. For example, the deficit in paired associate learning in humans (see [100])
may be especially evident when this involves arbitrary associations between words,
for example, window — lake.
It appears that the deficits in 'recognition' memory (tested for example for visual
stimuli seen recently in a delayed match to sample task) produced by damage to
this brain region are related to damage to the perirhinal cortex [121, 122], which
receives from high order association cortex and has connections to the hippocampus
(see Figure 16.1) [106, 107]. The functions of the perirhinal cortex in memory are
discussed by [82].

16.2.2 Neurophysiology of the hippocampus and connected areas

In the rat, many hippocampal pyramidal cells fire when the rat is in a particular place,
as defined for example by the visual spatial cues in an environment such as a room
[39, 53, 54]. There is information from the responses of many such cells about the
place where the rat is in the environment. When a rat enters a new environment B
connected to a known environment A, there is a period in the order of 10 minutes in
which as the new environment is learned, some of the cells that formerly had place
fields in A develop instead place fields in B. It is as if the hippocampus sets up a
new spatial representation which can map both A and B, keeping the proportion of
cells active at any one time approximately constant [117]. Some rat hippocampal
neurons are found to be more task-related, responding for example to olfactory stim-
uli to which particular behavioural responses must be made [19], and some of these
neurons may in different experiments show place-related responses.
It was recently discovered that in the primate hippocampus, many spatial cells
have responses not related to the place where the monkey is, but instead related to
the place where the monkey is looking [78, 79, 85]. These are called 'spatial view
cells', an example of which is shown in Figure 16.2 . These cells encode information
in allocentric (world-based, as contrasted with egocentric, body-related) coordinates
[29, 93]. They can in some cases respond to remembered spatial views in that they
respond when the view details are obscured, and use idiothetic (self-motion) cues
including eye position and head direction to trigger this memory recall operation
[71]. Another idiothetic input that drives some primate hippocampal neurons is linear
and axial whole body motion [58], and in addition, the primate presubiculum has
been shown to contain head direction cells [72].
Part of the interest of spatial view cells is that they could provide the spatial repre-
sentation required to enable primates to perform object-place memory, for example
remembering where they saw a person or object, which is an example of an episodic
memory, and indeed similar neurons in the hippocampus respond in object-place
memory tasks [84]. Associating together such a spatial representation with a repre-