Publication Summary and Abstract
Gurney, K., Redgrave, P. & Prescott, T.J. (1998), Analysis and simulation of a model of intrinsic processing in the basal ganglia, Technical Report AIVRU131, The University of Sheffield.
We have recently suggested (Redgrave et al. 1997, 1998) that the basal ganglia (BG) play a crucial role in solving the action selection problem in vertebrates. We now present a quantitative model of intrinsic BG processing which shows how this might occur. We assume that several command systems with different levels of salience are requesting their actions to be enabled by the BG. Under dopaminergic control the striatum extracts the salience, and selects a subset of actions for subsequent processing by running a series of winner-take-all competitions mediated by short-range recurrent connections. Each such winning command defines a channel of information flow through individual BG nuclei with the exception of the subthalamic nucleus (STN) which integrates information across channels. The model has been subject to an analysis of its equilibrium states and full dynamic computer simulation. There are three main results: (i) Diffuse excitation from STN and focused inhibition from striatum combine to provide input to a feedforward, off-centre on-surround network whose output layer is the globus pallidus internal segment (GPi) and substantia nigra pars reticulata (SNr). This network operates in conjunction with local striatal competitions so that the striatum-STN-GPi/SNr complex forms the primary selection pathway within the BG. (ii) The globus pallidus external segement (GPe) forms the output of a seperate control pathway (whos input is also provided by STN and striatum) which supplies control signals to the switching network. For example, GPe dynamically limits excitation of STN when the latter is driven by a variable number of competing actions. (iii) Differential modulation of each pathway by increased dopamine D1/D2 receptor activation works synergistically to induce less exclusive action selection. We conclude that the functionality of the BG anatomy may be more accurately described in terms of selection and control pathways rather than the more usual direct and indirect pathways and that more promiscuous action selection is fostered by the increased presence of dopamine.
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