The modulatory role of subthalamic nucleus in cognitive functions - a viewpoint.

The modifications of electrophysiological activities of subthalamic nucleus (STN) by non-motor tasks, i.e. movement observation, emotional stimuli and impulse control, were reported repeatedly. Despite being a small structure, STN is apparently involved in a variety of functions. Based on our own electrophysiological recordings and results of other groups we believe that it acts as an indirect modulator which may be involved in tuning the functional systems. STN may modulate specific cognitive activities via contextual modulation of certain cortical areas. Our findings support the hypothesis of a cortical-STN bypass (via hyperdirect pathway) of "classical" basal ganglia-thalamocortical circuitry, at least during the processing of certain cognitive functions. The modulation of cognitive functions appears to be selective, probably determined by the involvement of cortical neuronal populations interconnected with STN. There could also exist a spatial overlap of areas within STN regulating various functions. That may explain the fact that some non-motor symptoms of Parkinson's disease may improve after deep brain stimulation of STN. These improvements are likely caused by combination of direct stimulation effect on non-motor function and overall beneficial effect of motor improvement on quality of life.