Computation at the edge of chaos: phase transitions and emergent computation
CNLS '89 Proceedings of the ninth annual international conference of the Center for Nonlinear Studies on Self-organizing, Collective, and Cooperative Phenomena in Natural and Artificial Computing Networks on Emergent computation
Actor-critic models of the basal ganglia: new anatomical and computational perspectives
Neural Networks - Computational models of neuromodulation
2005 Special Issue: Modelling divided visual attention with a winner-take-all network
Neural Networks - 2005 Special issue: IJCNN 2005
What do the basal ganglia do? A modeling perspective
Biological Cybernetics
Modeling basal ganglia for understanding parkinsonian reaching movements
Neural Computation
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We present a neural network model of basal ganglia that departs from the classical Go/NoGo picture of the function of its key pathways-the direct pathway (DP) and the indirect pathway (IP). In classical descriptions of basal ganglia function, the DP is known as the Go pathway since it facilitates movement and the IP is called the NoGo pathway since it inhibits movement. Between these two regimes, in the present model, we posit that there is a third Explore regime, which denotes random exploration of the space of actions. The proposed model is instantiated in a simple action selection task. Striatal dopamine is assumed to switch between DP and IP activation. The IP is modeled as a loop of the subthalamic nucleus (STN) and the globus pallidus externa (GPe), capable of producing chaotic activity. Simulations reveal that, while the system displays Go and NoGo regimes for extreme values of dopamine, at intermediate values of dopamine, it exhibits a new Explore regime denoting a random exploration of the space of action alternatives. The exploratory dynamics originates from the chaotic activity of the STN-GPe loop. When applied to the standard card choice experiment used in the imaging studies of Daw, O'Doherty, Dayan, Seymour, and Dolan (2006), the model favorably describes the exploratory behavior of human subjects.