Abstract
Daily sessions of therapeutic transcranial brain stimulation are thought to prolong or amplify the effect of a single intervention. Here we show in patients with focal hand dystonia that additional, new effects build up progressively over time, making it difficult to predict the effect of long term interventions from shorter treatment sessions. In a sham-controlled study, real or sham continuous theta burst stimulation (cTBS) was given once daily for five consecutive days to dorsolateral premotor cortex (PMd). Five days of real, but not sham, premotor cTBS improved intracortical inhibition in primary motor cortex (M1) to a similar extent on day 1 and day 5. However 5 days of cTBS were required to restore the abnormal PMd-M1 interactions observed on day 1. Similarly, excessive M1 plasticity seen at baseline was also significantly reduced by five days of real premotor cTBS. There was only a marginal benefit on writing. The results show that additional, new effects, at sites distant from the point of stimulation, build up progressively over time, making it difficult to predict the effect of long term interventions from shorter treatment sessions. The results indicate that it may take many days of therapeutic intervention to rebalance activity in a complex network.
Highlights
Transcranial brain stimulation is used increasingly as a potential therapeutic intervention for a variety of conditions
We applied continuous theta burst stimulation (cTBS) to PMd for 5 days and measured effects on physiological markers of dystonia: the network interaction from PMd-M1, and the increased plasticity and reduced inhibition within M1 in writer’s cramp (WC) patients [10,19,20,21]. cTBS is generally believed to suppress the stimulated cortex [22,23], recent reports using protocols slightly different from that used in the current study suggest that the response to Theta burst stimulation (TBS) protocols is variable and the effect of cTBS may not be always inhibitory [24,25,26]
On day 1 and 5, rest motor threshold (RMT), hand writing assessed with writing speed and Gibson Spiral Maze tests and two blocks of short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were recorded before cTBS600
Summary
Transcranial brain stimulation is used increasingly as a potential therapeutic intervention for a variety of conditions. The effects of a single session of stimulation are often assumed as valid predictors of long-term changes that might be expected in a therapeutic protocol [5]. There is some evidence that the effects of long-term treatment may differ in quality from those of a single session. Effects of repetitive transcranial magnetic stimulation (rTMS) in excess of those of placebo can only be observed after several weeks of treatment. A progressively developing response to therapeutic brain stimulation can be observed after implantation of deep brain stimulation (DBS). In dystonia, implantation of DBS may initiate progressive changes in underlying motor physiology that are not apparent when testing acutely [9]
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