Neuroscience

 

 

85266_largeThis chapter discusses the role of the anterior cingulate cortex. This brain region can be seen as part of a circuit involving the orbitofrontal, the ventral striatum, the dopamine neurons and finally the dorsolateral prefrontal. From the point of view of subjective consciousness, the orbitofrontal can be seen as injecting a subjective consciousness element into the final selection of extended behaviours by the anterior cingulate, which in turn acts on the executive area of the dorsolateral prefrontal.

The anterior cingulate cortex (ACC) is regarded as an important brain area for cognitive control.  The ACC receives inputs from the limbic areas, the orbitofrontal and the midbrain dopamine neurons, and has dense projections to the motor cortex. It is seen as part of an ‘executive network’  involving other regions of the sensory and frontal cortex. There are four main theories, which to a good degree overlap, concerning the function of the anterior cingulate. Firstly there is a concept of monitoring behaviour, error detection and response to this.  Secondly action selection focusing on the wilful generation of behaviour.  Thirdly, reinforcement learning focused on learning to select particular behaviours. Finally, some theories focus on the ACC’s role in determining the cost of behaviours.

A unified theory for the role of the anterior cingulate has yet to be developed, but the authors try to move towards one in this chapter.  One hypothesis is that the ACC monitors for when more cognitive control of actions is required, although activity in the region can increase even without errors. It is variously suggested that the ACC could predict the likelihood of errors or conflicts between actions, and signal the need for the increased involvement of the dorsolateral prefrontal.

Conflict-related ACC activity in one experimental trial is predictive of more dorsolateral activity in the next trial, which in turn leads to improved performance suggestive of a feedback loop between the anterior cingulate and the dorsal prefrontal. However, this is not the extent of the ACC’s role as shown by neural imaging, which also points to sustained activity related to task preparation and execution. The anterior cingulate is also considered to learn about the consequences of internally generated actions through dopamine projections. P. The anterior cingulate has for a long time been seen as part of the limbic circuit. It is seen as integrating presumably conscious and subjective hedonic value into action plans, and may produce emotional responses to events as they occur. There is evidence that ACC lesions encourage the selection of less costly actions, and that dopamine input to the ACC is necessary for the selection of more costly actions.

The authors offer the hypothesis that the ACC supports the selection and execution of complex behaviours over time, such as the decision to run up a mountain rather than remain home on the sofa. Lesions to the ACC result in more immediate responses rather than the ability to carry out extended and often costly behaviours. Options supported by the ACC may provide excitatory input to the dorsolateral. The orbitofrontal is seen as being involved in this circuit by providing positive or negative evaluations for the options for actions found in the ACC. The ventral striatum of the basal ganglia is seen as supporting individual steps towards the longer term options selected by the ACC.

 

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