Non-Invasive Brain Stimulation and its Supposed Site of Action in the Rehabilitation of Parkinson’s Disease and Stroke

Abstract

Two non-invasive brain stimulations have spread all over the world: repetitive trasncranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS). TMS is based on the current induction with a changing electromagnetic field in the nervous system [1] while tDCS changes the polarity of cell membranes [2]. General Aspects of TMS and tDCSTMS is widely used in research and daily medical practice. It was introduced as a diagnostic tool about thirty years ago to test functioning of motor pathways [3]. The motor evoked potential (MEP) and the measurement of the central motor conduction time (CMCT) has entered into daily practice. The other parameters of the electrophysiological examination assessed by TMS are mainly used in scientific work [4]. TMS aids the diagnosis of multiple sclerosis, furthermore the prognosis of stroke can be indicated by TMS [5]. Different paired pulse stimulations with TMS give a new insight into the function of the brain. In recent years, sophisticated brain plasticity can be detected by the measurement of intracortical excitability [6,7]. We learnt from these studies how different conditions can modify brain plasticity. It can be changed by different diseases, altered by drugs [8] and strongly influenced by non-invasive stimulations [2,9]. The single TMS and one session of repetitive stimulation have a short after-effect. However the effect of repeated stimulation for days exceeds the stimulation period and many times it lasts for months. This effect of rTMS has made it useful for therapy for the last 20 years. The low and high frequency stimulation, continuous theta burst stimulation (cTBS), intermittent theta burst stimulation (iTBS), anodal or cathodal stimulation are used for therapy. The intensity of rTMS was around the motor threshold and the duration of stimulation was 7-10 days. This paper reviews the most frequently studied symptoms of Parkinson's diseases and stroke although rTMS has been tried to treat all disorders of the central nervous system (CNS). Parkinson's Disease (PD)The first protocol was low frequency, low intensity monophasic stimulation for 7 days which improved the Parkinsonian symptoms and its results were maintained for several months after the stimulation [10,11]. The authors performed a "dose (intensity) response" curve with 1 Hz stimulation and they indicated that there is an optimal intensity using 1 Hz [12]. We learned from these studies that the therapeutic effect of rTMS develops after a delay in time of a few weeks. The improvement can be maintained for several months. The later studies confirmed these observations not only in PD but other diseases. Although, the high frequency stimulations over the primary motor cortex [13,14] had the same effect on the Parkinsonian scores but the after-effect lasted for a shorter time. iTBS over the dorsolateral prefrontal area improved the depression without effecting on bradykinesia [15]. The studies concentrated on varying the frequency which was applied but they did not try to find the optimal in...