Abstract:
In this work we investigated the role of the basal ganglia in gesture recognition through a multimodal approach. To put light into the specific role of the basalganglia, videoclips of different types of movement (isolated hand movements, non-emotional body referred movements and expressive gestures) were presented to Parkinson Patients and compared to an age matched control group, while the BOLD activity was measured in the magnetical resonance tomograph. To be able to conclude about how specific the differences in between the groups would be for the Parkinsons disease, i.e. for the changes within the basal ganglia that come along with the disease, we correlated the fMRI results and the number of mistakes in gesture recognition with a PET-measurement of the dopamine transporter availability (DTA) in the Putamen with [11C]d-threo-methylphenidate as well as with the clinical parameters (UPDRS, Hoehn and Yahr scale).
The striate is connected through several parallel loops with the temporal, limbic and prefrontal areas, which are enroled in gesture and face recognition in healthy subjects. The patients showed an averaged 26% reduced dopamine transport availability compared to the age corrected healthy controls. This reduction correlated not only to the clinical symptoms of the patients but also to the number of mistakes in gesture recognition. These changes correlated with reduced activity within the putamen compared to healthy controls during the presentation of all three kinds of movements, which induced changes of activity in different areas of the brain through the basal ganglia loops.
During all paradigms reduced activity was shown in patients in motor and somatosensoric areas in terms of an impairment of internal movement programs, as well as in temporal areas of face recognition and perception of social stimuli.
Through the greater social relevance, as well as through the inclusion of face and trunk in body referred movements and expressive gestures, the differences in temporal areas of social perception and identy (temporal pole and STS) become more apparent. Specific for the observation of expressive gestures, reduced activity is shown in the left VLPFC (BA 47) and the right STS.
Moreover, the less DTA was present in the left putamen, the lower was the activation in the left VLPFC. In contrast, increased number of mistakes in emotional gesture recognition correlated with increased activation in the bilateral insula – a possible compensation for decreased recognition. We conclude that reduction of DTA in the putamen results in a reduction of ventrolateral prefrontal access involved in the recognition of emotional gestures. Additionaly the Amygdala showed reduced activity during the expressive gesture presentation. This could be one further clue for the involvement of the putamen into emotional processes.
In contrast the insula showed more activity the greater the number of mistakes of the patients in gesture recognition was – maybe a process of compensation. We conclude therefore that the reduction of the DTA in the Putamen leads to a reduction of the ventrolateral prefrontal acces, which is involved in the processing of expressive gestures.