The Operation of Memory Systems in the Brain - Computational Neuroscience: A Comprehensive Approach - page 516

system which performs dot products using neuronal ensembles as inputs, which is
precisely what pattern associators in the brain need, because they are implemented
by neurons which perform as their generic computation a dot product of their inputs
with their synaptic weight vectors (see [82] and [92]).
A schematic diagram summarizing some of the conclusions reached [77, 82, 92] is
shown in Figure 16.13. The pathways are shown with more detail in Figure 16.14.
The primate inferior temporal visual cortex provides a representation that is indepen-
dent of reward or punishment, and is about objects. The utility of this is that the out-
put of the inferior temporal visual cortex can be used for many memory and related
functions (including episodic memory, short-term memory, and reward/punishment
memory) independently of whether the visual stimulus is currently rewarding or not.
Thus we can learn about objects, and place them in short-term memory, indepen-
dently of whether they are currently wanted or not. This is a key feature of brain
design. The inferior temporal cortex then projects into two structures, the amyg-
dala and orbitofrontal cortex, that contain representations of primary (unlearned)
reinforcers such as taste and pain. These two brain regions then learn associations
between visual and other previously neutral stimuli, and primary reinforcers [77], us-
ing what is highly likely to be a pattern association network, as illustrated in Figure
16.13. A difference between the primate amygdala and orbitofrontal cortex may be
that the orbitofrontal cortex is set up to perform reversal of these associations very
rapidly, in as little as one trial. Because the amygdala and orbitofrontal cortex rep-
resent primary reinforcers, and learn associations between these and neutral stimuli,
they are key brain regions in emotions which can be understood as states elicited by
reinforcers, that is rewards and punishers), and in motivational states such as feeding
and drinking [77].

16.6 Effects of mood on memory and visual pro-

cessing

The current mood state can affect the cognitive evaluation of events or memories (see
[9], [87]). An example is that when they are in a depressed mood, people tend to re-
call memories that were stored when they were depressed. The recall of depressing
memories when depressed can have the effect of perpetuating the depression, and
this may be a factor with relevance to the etiology and treatment of depression. A
normal function of the effects of mood state on memory recall might be to facilitate
continuity in the interpretation of the reinforcing value of events in the environment,
or in the interpretation of an individual's behaviour by others, or simply to keep be-
haviour motivated to a particular goal. Another possibility is that the effects of mood
on memory do not have adaptive value, but are a consequence of having a general
cortical architecture with backprojections. According to the latter hypothesis, the se-
lection pressure is great for leaving the general architecture operational, rather than