Background Early theories for cervical dystonia, as promoted by Hassler, emphasized the role of midbrain interstitial nucleus of Cajal. Focus then shifted to basal ganglia, and it was further supported with the success of deep brain stimulation. Contemporary theories suggested the role of cerebellum. But even more recent hypotheses renewed interest in midbrain. Although pretectum was visited on several occasions, we still do not know about the physiology of midbrain neurons in cervical dystonia. Methods We analyzed the unique database of pretectal neurons collected in 1970s and 1980s during historic stereotactic surgeries aimed to treat cervical dystonia. This database is valuable because such recordings could otherwise never be obtained from humans. Results We found three types of eye or neck movement sensitivity, eye-only neurons responded to pure vertical eye movements; the neck-only neurons were sensitive to pure neck movements; and the combined eye-neck neurons. There were two neuronal subtypes – burst-tonic and tonic. The eye-neck or eye-only neurons sustained their activity during eccentric gaze holding. In contrast, the response of neck-only and eye-neck neurons exponentially decayed during neck movements. Conclusions Modern quantitative analysis of historic database of midbrain single-units from patients with cervical dystonia might support novel hypotheses for normal and abnormal head movements. This data, collected almost four decades ago, must be carefully viewed, especially because it was acquired using a less sophisticated technology available at that time, the aim was not to address specific hypothesis but to make an accurate lesion providing optimal relief from dystonia.
The contribution of different brain areas to internally guided (IG) and externally triggered (ET) movements has been a topic of debate. It has been hypothesized that IG movements are performed mainly through the basal ganglia-thalamocortical loop while ET movements are through the cerebello-thalamocortical pathway. We hypothesized that basal ganglia activity would be modified in patients with Parkinson's disease during IG movement as compared with normal subjects. We used functional MRI (fMRI) to investigate the differences between IG and ET motor tasks. Twenty healthy participants and 20 Parkinson's disease patients (OFF-state) were asked to perform hand movements in response to sound stimuli (ET) and in advance of the stimuli (IG). We showed that ET movements evoked activation of a few large clusters in the contralateral motor areas: the sensorimotor and premotor cortex, supplementary motor area (SMA), insula, putamen, motor thalamus and ipsilateral cerebellum. IG movements additionally evoked activation of a large number of small clusters distributed in different brain areas including the parietal and frontal lobes. Comparison between the activity of Parkinson's disease patients and healthy volunteers showed few important differences. We observed that along with the activity of the posterior areas, an activation of the anterior areas of putamen was observed during IG movements. We also found hyperactivity of the ventral thalamus for both movements. These results showed that IG movements in PD patients were made with the involvement of both sensorimotor and associative basal ganglia-thalamocortical loops.
Cervical dystonia (CD) is the most common type of focal dystonia causing an abnormal asymmetric head position manifested by neck rotation or tilt (Fahn, Bressman, & Marsden, 1998). The traditional view is that CD is a basal ganglia disorder whereas recent hypotheses have emphasized the role of cerebellum and proprioception. A novel concept unifying these various views assumes the existence of head neural integrator which connects cerebellum, basal ganglia and proprioceptive network in a unifying circuit forming a final common pathway for the control of head position (
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