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Notepad
Reward
processing and decision making in the human striatum P. Mauricio Delgado &
Elizabeth Tricomi, Rutgers University & California Institute of Technology
P. In:- Neuroscience of Decision Making – Eds. Oshin Vartanian & David
Mandel P. Psychology Press – Taylor and Francis Group (2011) P. Making a
decision is viewed as a complicated assessment of potential benefits and
costs. Evaluation of the outcomes of
earlier decisions informs the choice of repeating a particular behaviour or
trying an alternative. Rewarding choices of behaviour come to be repeated. This
involves not only the existence of a rewarding or punishing aspect to the
decision, but also the ability to learn from this. P. Research has shown that
the striatum, which is the input unit of the basal ganglia, has an important
role in decision making. The striatum is divided into the ventral and dorsal
striatum, and the dorsal part is further divided into the caudate nucleus and
the putamen. The striatum receives inputs from the prefrontal, the amygdala,
the hippocampal region and the midbrain. In the opposite direction, information
goes from the striatum via the thalamus to the prefrontal. This arrangement constitutes
a frontal-striatal-thalamic loop. Dopamine is seen as important in modulating
information processing between the striatum and the cortex. P. The striatum is
divided into the ventral and dorsal striatum.
The main structure in the ventral striatum is the nucleus accumbens. The
nucleus accumbens is subdivided into a shell and a core subregion. The shell
region has a large number of opiate receptors suggesting it is involved in the
actual reward process, while the core is more involved with dopamine, which is
thought to relate to incentivising subjects to aim for particular outcomes. P. The
basal ganglia were previously seen as being mainly concerned with the motor
cortex, but modern research has shown important connections to the cognitive
and emotional related areas of the prefrontal. The dorsolateral prefrontal,
involved with executive functions, projects to the striatum. The ventromedial
prefrontal, the orbitofrontal and the anterior cingulate, which are involved
with reward evaluation and decision making also project to the striatum. Projections
from the orbitofrontal and the anterior cingulate converge with those from the
dorsolateral. This is suggested to put the striatum in the position of
integrating cognitive and reward related processing. The dopamine neurons of
both the substantia nigra and the ventral tegmental area also project to the
striatum. The dopamine neurons are seen as being involved in assessing the
reward rather than actually delivering the reward. The dopamine signal is
viewed as coding for the difference between predicted and actual reward or
prediction error. This is seen as helping with learning and goal-directed
behaviour. P. The ventral striatum is thus seen as involved in the predicting
the reward and its timing. Numerous studies show activation of the ventral
striatum when there is anticipation of a reward. Unexpected rewards lead to an
increase in ventral striatum activity, while unexpected lack of reward leads to
a reduction in activity. The system can be more subtle than a simple response
to pleasure or pain. Thus avoidance of punishment may be taken as a reward,
while missed opportunities can be taken as a punishment. The striatum can also
be active in response to social interaction and cooperation. P. The caudate nucleus,
which is a part of the dorsal striatum, processes both positive and negative
outcomes. The caudate processing is seen as context dependent in that it deals
with information related to particular goals. A group of interneurons in the
striatum, known as TANs or tonically active neurons, are also context related
and are modulated by motivational states. The caudate may integrate particular
contexts with reward related dopamine signals. The caudate region may also
respond to 'counterfactuals' being outcomes that were not experienced but might
have been experienced. The caudate is also thought to be important when an
outcome is seen as linked to an action. The focus on action is suggested to deal
with possible consequences of actions, and may be related to the choice of best
possible option where neither option is intrinsically attractive. Activation
here may also be related to goal achievement as such rather than actual rewards,
and this may be help to guide future actions.
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