Objective: We propose a model of the interaction between the cortex, the basal ganglia and the thalamus based on a dual competition during instrumental conditioning.

Background: Action-outcome (A-O) and stimulus-response (S-R) processes are two forms of instrumental conditioning that are important components of decision making and action selection. The former adapts its response according to the outcome while the latter is insensitive to the outcome. An unsolved question is how these two processes interact in order to issue a unique behavioural answer.

Methods: Our theoretical approach is based on large scale rate model of the cortex-basal ganglia-thalamus loop (Guthrie et al. 2013). We hypothesize that the striatum, the subthalamic nucleus, the internal pallidum (GPi), the thalamus, and the cortex are involved in closed feedback loops through the hyper-direct and direct pathways. These loops support a competition process that results in the ability for the basal ganglia to make a cognitive decision followed by a motor decision. Considering lateral cortical interactions, another competition takes place inside the cortex allowing this latter to make a cognitive and a motor decision.

Results: We show how this dual competition endows the model with two regimes. One is oriented towards action-outcome and is driven by reinforcement learning, the other is oriented towards stimulus-response and is driven by Hebbian learning. The final decision is made according to a combination of these two mechanisms with a gradual transfer from the former to the latter. We confirmed these theoretical results on primates (Macaca Mulata) using a novel paradigm predicted by the model (Piron etal, 2016).

Conclusions: This model provides a possible solution to an old conundrum concerning Parkinson’s Disease. In the classical view of the BG as a selection device, the effect of the inactivation of the STN or the GPi as a therapeutic approach to parkinsonism is paradoxical. But if we consider that such surgical treatment is practised in a Parkinsonian patient old enough to have an over-trained cortex in the skills he use on a day-to-day basis, one can understand that its cortex doesn’t need subcortical feedback any more. Indeed, some experimental and clinical data have been gathered showing that in those patients despite a general motor improvement, learning of new skills is disrupted.

References: Guthrie M, Leblois A, Garenne A, Boraud T (2013) Interaction between cognitive and motor cortico-basal ganglia loops during decision making: A computational study. J Neurophysiol 109. Piron C, Kase D, Topalidou M, Goillandeau M, Orignac H, N’Guyen T-H, Rougier N, Boraud T (2016) The globus pallidus pars interna in goal-oriented and routine behaviors: Resolving a long-standing paradox. Mov Disord 31.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/dual-competition-between-the-basal-ganglia-and-the-cortex-1-from-action-outcome-to-stimulus-response/