The combined effect of subthalamic nuclei deep brain stimulation and L-dopa increases emotion recognition in Parkinson's disease

Deep brain stimulation of the subthalamic nucleus (DBS) is a widely used surgical technique to suppress motor symptoms in Parkinson's disease (PD), and as such improves patients' quality of life. However, DOS may produce emotional disorders such as a reduced ability to recognize emotional facial expressions (EFE). Previous studies have not considered the fact that DBS and L-dopa medication can have differential, common, or complementary consequences on EFE processing. A thorough way of investigating the effect of DBS and L-dopa medication in greater detail is to compare patients' performances after surgery, with the two therapies either being administered ('on') or not administered ('off'). We therefore used a four-condition (L-dopa 'on'/DBS 'on', L-dopa 'on'/DOS 'off', L-dopa 'off'/DBS 'on', and L-dopa 'off'/DBS 'off') EFE recognition paradigm and compared implanted PD patients to healthy controls. The results confirmed those of previous studies, yielding a significant impairment in the detection of some facial expressions relative to controls. Disgust recognition was impaired when patients were 'off' L-dopa and 'on' DBS, and fear recognition impaired when 'off' of both therapies. More interestingly, the combined effect of both DBS and L-dopa administration seems much more beneficial for EVE recognition than the separate administration of each individual therapy. We discuss the implications of these findings in the light of the inverted U curve function that describes the differential effects of dopamine level on the right orbitofrontal cortex (OFC). We propose that, while L-dopa could overdose in dopamine the ventral stream of the OFC, DBS would compensate for this over-activation by decreasing OFC activity, thereby restoring the necessary OFC-amygdala interaction. Another finding is that, when collapsing over all treatment conditions, PD patients recognized more neutral faces than the matched controls, a result that concurs with embodiment theories. (C) 2012 Elsevier Ltd. All rights reserved.