Abstract
Two learning mechanisms contribute to decision-making: goal-directed actions and the “habit” system, by which action-outcome and stimulus-response associations are formed, respectively. Rodent lesion studies and human neuroimaging have implicated both the medial prefrontal cortex (mPFC) and the orbitofrontal cortex (OFC) in the neural basis of contingency learning, a critical component of goal-directed actions, though some published findings are conflicting. We sought to reconcile the existing literature by comparing the effects of excitotoxic lesions of the perigenual anterior cingulate cortex (pgACC), a region of the mPFC, and OFC on contingency learning in the marmoset monkey using a touchscreen-based paradigm, in which the contingent relationship between one of a pair of actions and its outcome was degraded selectively. Both the pgACC and OFC lesion groups were insensitive to the contingency degradation, whereas the control group demonstrated selectively higher performance of the nondegraded action when compared with the degraded action. These findings suggest the pgACC and OFC are both necessary for normal contingency learning and therefore goal-directed behavior.
Highlights
Optimal decision-making is important in the face of a dynamic and often unpredictable environment
We sought to reconcile the existing literature by comparing the effects of excitotoxic lesions of the perigenual anterior cingulate cortex, a region of the medial prefrontal cortex (mPFC), and orbitofrontal cortex (OFC) on contingency learning in the marmoset monkey using a touchscreen-based paradigm, in which the contingent relationship between one of a pair of actions and its outcome was degraded selectively. Both the pgACC and OFC lesion groups were insensitive to the contingency degradation, whereas the control group demonstrated selectively higher performance of the nondegraded action when compared with the degraded action
An alternative explanation of the Hammond result was that the delivery of noncontingent reward could strengthen competing responses, such as approach to the reward source, and it would be impossible to conclude that the reduction in responding was due to sensitivity to contingency degradation (Colwill and Rescorla 1986; Dickinson and Mulatero 1989; Balleine and Dickinson 1998b)
Summary
Optimal decision-making is important in the face of a dynamic and often unpredictable environment. The subjective value of the outcome and the contingent relationship between the action and the outcome are both important facets of goal-directed actions They can be assessed using outcome revaluation and contingency degradation tests, respectively, thereby determining whether behavior is goaldirected or habitual. Consideration of cytoarchitecture and receptor distribution points to primate perigenual anterior cingulate cortex (pgACC), area 32, as equivalent to PL (Gabbott et al 2003; Vogt et al 2013) These discrepancies highlight the need to perform experimental studies of contingency learning in a nonhuman primate species, in which the structure and functional organization of PFC has a greater similarity to humans compared with that of rodents (Uylings and van Eden 1991). Their sensitivity to contingency degradation was investigated by reducing the contingent relationship between responding to one of the stimuli and its associated reward but not altering the contingent relationship between responding to the other stimulus and its associated reward
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