In healthy subjects, tDCS acutely improves motor performance and motor learning. The magnitude and duration of the tDCS after-effect appear to depend on stimulation duration and current intensity for example, in one study, 13 min of stimulation induced a 90-min after-effect. A number of studies have reported that tDCS can affect brain plasticity and function. Noninvasive transcranial direct current stimulation (tDCS) is a safe method for the selective modulation of local cerebral cortex excitability, and has recently received attention for its potential clinical utility. Thus, there is a need for the development of interventions that can produce prolonged increases in corticospinal tract excitability in stroke patients. Unfortunately, changes in the excitability of the corticospinal tract are typically short-lived or occur only during movement execution. Therefore, a number of clinical studies have been conducted to assess different approaches for achieving this goal in stroke patients. In patients with stroke, increases in corticospinal tract excitability and activation in motor association areas in the involved cerebral hemisphere can improve the rehabilitation of sensory-motor function. MI thus results in the activation of movement execution-related neural networks in healthy subjects. Motor imagery (MI) describes the conscious and active psychological representation of movement. Conversely, voluntary motor imagery has also been documented to increase the excitability of the corticospinal tract and activity in motor association areas. Furthermore, the activation of cerebral networks related to movement execution has been reported during the passive experience of KI. Using transcranial magnetic stimulation, we found that corticospinal tract excitability increases concurrently with changes in the subjective feeling of kinesthetic perception. We previously reported that kinesthetic illusion (KI) induced by visual stimuli (e.g., a video) can produce vivid kinesthetic perceptions in healthy subjects and patients with stroke at rest. The observed effects may be related to sustained potentiation of resultant cerebral activity during combined KI, MI, and tDCSa.
Our results suggest that tDCSa + KIMI has a greater therapeutic potential than tDCS alone for inducing higher excitability of the corticospinal tract. In the second experiment, significant effects were not achieved following sham + KIMI. The effect of tDCSa + KIMI on corticomotor excitability was greater and longer-lasting than that achieved in all other conditions. In the first experiment, corticomotor excitability was sustained for at least 30 min following tDCSa + KIMI ( p < 0.01). Corticospinal excitability was examined using transcranial magnetic stimulation of the area associated with the left first dorsal interosseous.
Direct currents were applied to the right primary motor cortex.
In the second experiment, we added a sham tDCS intervention with kinesthetic illusion and motor imagery (sham + KIMI) as a control for the tDCSa + KIMI condition. Four interventions were investigated in the first experiment: (1) anodal tDCS alone (tDCSa), (2) anodal tDCS with visually evoked kinesthetic illusion (tDCSa + KI), (3) anodal tDCS with motor imagery (tDCSa + MI), and (4) anodal tDCS with kinesthetic illusion and motor imagery (tDCSa + KIMI). MethodsĪ total of 21 healthy male volunteers participated in this study. This study aimed to establish whether the combination of tDCS with KI and sensory-motor imagery (MI) induces larger and longer-lasting effects on the excitability of corticomotor pathways in healthy Japanese subjects. Transcranial direct current stimulation (tDCS) is emerging as an alternative potential therapeutic modality for a variety of neurological and psychiatric conditions, such that identifying factors that enhance the magnitude and duration of tDCS effects is currently a topic of great scientific interest. During KI, corticospinal tract excitability increases and results in the activation of cerebral networks. A kinesthetic illusion induced by a visual stimulus (KI) can produce vivid kinesthetic perception.
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