Rougier, N. P. | Search bioRxiv

bioRxiv2017

Modeling the Role of Striatum in Stochastic Multi Context Tasks

Decision making tasks in changing environments with probabilistic reward schemes present various challenges to the agents performing the task. These agents must use the experience gained in the past trials to characterize the environment which guides their actions. We present two models to predict an agents behavior in these tasks - a theoretical model which defines a Bayes optimal solution to the problem under realistic task conditions. The second is a computational model of the basal ganglia which presents a neural mechanism to solve the same. Both the models are shown to reproduce results in behavioral experiments and are compared to each other. This comparison allows us to characterize the theoretical model as a bound on the neural model and the neural model as a biologically plausible implementation of the theoretical model. Furthermore, we predict the performance of the agents in various stochastic regimes which could be tested in future studies.

neuroscience↗

bioRxiv2017

Dual Competition between the Basal Ganglia and the Cortex: from Action-Outcome to Stimulus-Response

Action-outcome (A-O) and stimulus-response (S-R) processes that 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 emerge, cooperate and interact inside the brain in order to issue a unique behavioral answer. Here we propose a model of the interaction between the cortex, the basal ganglia and the thalamus based on a dual competition. 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 hyperdirect 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 (short range excitation, long range inhibition), another competition takes place inside the cortex allowing this latter to make a cognitive and a motor decision. 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 using a two-armed bandit task and a reversible bilateral inactivation of the internal part of the globus pallidus.

neuroscience↗