MEG Motor Experiments in (Hemi-) Parkinson

Movement-related cerebral potentials in patients with Parkinson`s disease (PD) have been recorded so far by using the EEG (Deecke et al. 1973-77, Barrett et al. 1986, Dick et al. 1989, Harasko van der Meer et al. 1996, Lang & Deecke, 1998). Movement-related magnetic fields have been recorded in normal subjects only (MEG, Bereitschaftsfeld, BF, Deecke et al. 1982, 1983, Weinberg et al. 1983, Cheyne, Kristeva & Deecke 1991]. To our knowledge, in PD patients, MEG recordings have not been systematically studied so far. Therefore, in the present project, we intend to carry out MEG motor experiments both in Hemiparkinsonian patients and in bilateral Parkinsonism. The Bereitschaftspotential paradigm (self-initiated voluntary movement paradigm) seems us to be the best choice to be applied to the prime central motor disorder, PD, and the MEG with its excellent localizatory power seems highly appropriate to clarify, which brain areas are involved that show changes through disease in PD. Hemiparkinsonian patients will perform voluntary movements (index finger flexion/ extension) of both crossed hemisphere hand systems, the most affected and the less affected system in counterbalanced blocks for comparison. Bilateral Parkinsonian patients will be compared with normal controls matched in number, gender and age. It is the aim of the present project to facilitate better understanding of specific differences between patients and controls and of the underlying mechanisms including the cortical functional localizations of the changes through disease at both the primary motor areas and the supplementary motor areas. This is thought to be of advantage for fundamental research in motor physiology as well as for clinical-neurologic diagnostics and therapy including pharmacotherapy, surgical therapies and physiotherapy.

The aim of the present research project was to examine the `Bereitschaftsfield` of patients with Parkinson`s disease by using MEG (magnetoencephalography). The `Bereitschaftsfield` (BF) in the MEG is analogous to the `Bereitschaftspotential` in the EEG (electroencephalography). It shows activation of motor areas of the cerebral cortex in the time course prior to self-initiated movements or actions. Two components of the Bereitschaftsfield can be differentiated, an early one (BF1) and a late one (BF2). For each of these components different brain areas are responsible. BF1 (duration from 1 sec to sec before movement onset) is predominantly generated by the supplementary moror area (SMA), whereas BF2 (from sec to movement onset) stems mainly from the primary motor area (MI). SMA activity is related to the planning, preparation and initiation of our movements and actions. With patients with Parkinson`s disease it is affected. They have great difficulties with the performance of spontanous, not externally triggered movements. Thus, it is of great interest to examine the Bereitschaftsfield before volitionally initiated movements in Parkinson patients is of great interest to illuminate the mechanisms, which play a role with the planning and performance of movements, and to develop possible options for therapy. Right-handed patients in an early state of disease, so called Hemiparkinson patients, who show unilateral pathology, were compared with right-handed healthy controls, and also a group of bilateral progressive Parkinson pathology, all right-handed. The Results show that with healthy controls, when comparing the two sides of movement, in the range of usual SMA activity the present Bereitschaftsfields are basically symmetrical. With Hemiparkinson patients the activation of the SMA of the affected hand is slightly higher. With the group of the bilateral Parkinson patients the usual fronto-mesial activity shifts to frontopolar and frontolateral regions. The findings of the Hemiparkinson group are very interesting: if there is stronger activation at the more handicapped side, this shows, that the more affected hemisystem has to exert more effort in an attempt to compensate the deficit. Additionally the influence of the intensity of "volitionality" in the initiation of a sequential movement was examined with healthy subjects using EEG. Stronger SMA activation could be observed when the sequences of movement were performed with a higher load of conscious initiation. Furthermore, in this condition SMA activation started earlier than with careless (automatic) movement performance. The present project gives essentially new insights in the plasticity of the brain in case of a handicap (Parkinson`s desease) and helps to detect brain processes that are engaged in the conscious, willed performance of movements or actions.