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Publication Summary and Abstract

Humphries, M. D., Stewart, R. D. & Gurney, K. (2006), A physiologically plausible model of action selection and oscillatory activity in the basal ganglia, Journal of Neuroscience, 26(50):12921-42. [Code]

The basal ganglia (BG) have long been implicated in both motor function and dysfunction. It has been proposed that the BG form a centralized action selection circuit, resolving conflict between multiple neural systems competing for access to the final common motor pathway. We present a new spiking neuron model of the BG circuitry to test this proposal, incorporating all major features and many physiologically plausible details. We include: effects of dopamine in the subthalamic nucleus (STN) and globus pallidus (GP), transmission delays between neurons, and specific distributions of synaptic inputs over dendrites. All main parameters were derived from experimental studies. We find that the BG circuitry supports motor program selection and switching, which deteriorates under dopamine-depleted and dopamine-excessive conditions in a manner consistent with some pathologies associated with those dopamine states. We also validated the model against data describing oscillatory properties of BG. We find that the same model displayed detailed features of both γ-band (30-80 Hz) and slow (~1 Hz) oscillatory phenomena reported by Brown et al. (2002) and Magill et al. (2001), respectively. Only the parameters required to mimic experimental conditions (e.g. anaesthetic) or manipulations (e.g. lesions) were changed. From the results we derive the novel predictions that the STN-GP feedback loop: (i) is functionally de-coupled by tonic dopamine under normal conditions, and re-coupled by dopamine depletion; (ii) does not show pace-making activity under normal conditions in vivo (but does following combined dopamine-depletion and cortical lesion); (iii) has a resonant frequency in the γ-band.
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