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J. D. Wallis, Single neuron activity underlying behavior-guiding
rules [in:] S. A. Bunge, J. D.
Wallis, (eds.), The Neuroscience of Rule-Guided Behavior, Oxford
University Press, pp. 23-
45.
Theses:
1. Using abstract information to guide behavior is an important
and potentially uniquefunction of Prefrontal Cortex (PFC). This
capacity might underlie two of the hallmarks
of PFC, flexibility and ability to deal with novelty.
2. The mechnisms of learning abstract information remain
unclear. Reason: this isusually analyzed (the brain imaging data
are recorded) when the task has already been
learned.
Experimantal setting:
Three monkeys were to apply the rules act X if the two pictures
are the same, otherwise act
Y and act X when the two pictures are different, otherwise act
Y. With the first picture
there was given a cue (a drop of juice or no juice) as to which
of the two rules is to be applied
(juice rule 1; no juice rule 2). The monkeys performed above the
chance (70% correct
responses) applying the rules the first time they encountered a
new picture. In subsequent
behavioral tests the monkeys performed the task easily when new
pictures were used on every
trial (90% success). This means, according to the author, that
the monkeys had to be
solving the task by using the abstract rule.
The monkeys brain avtivity of four regions was recorded: PFC,
inferior temporal cortex
(ITC), Premotor Cortex (PMC) and the striatum (STR). The imaging
showed that PFC was
the only area from which the data was recorded that encoded all
of the task-relevant
information, namely both the picture and the rules. PMC and STR
encoded the rule only,
while ITC encoded the sole picture. It is further assumed that
the activity of PMC (which
encodes the rule more strongly and earlier than PFC) is such
only in the case of familiar rules;
for learning new rules PFC is more critical.
Additional argument in favor of the role of PFC in learning and
applying abstract rules
includes:
(a) PFC damage leads to disexecutive syndrome, i.e. inability to
use high-level, abstract
rules to control behavior;
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(b) some species are able to solve matching-to-sample rule;
these include chimpanzees,
rhesus monkeys, dolphins and sea lions, as well as some birds
(corvids ) in which the
analogon of PFC, mesopallium and nidopallium, is bigger than in
other birds. Even some
insects (bees) are capable of using the sameness rule.
Comments
It must be asked whether the behavior of the monkeys in the
experiment can justly be called
rule-governed. The monkeys spend some significant time learning
in a stimulus-response
way the constraints of the task. They do exhibit some second
level stimulus response, i.e.
thay adapt their behavior in the pictures-action task according
to an additional stimulus
(juice/no juice). The question is whether this amounts to
applying a rule?
