The time interval between anaesthetic induction and the ECT stimulus – It’s time to time!

Abstract

Introduction: Voluntary movement has two components e (a) movement initiation and (b) perception of willing the movement (sense of volition). It is believed that movement is subconsciously initiated by the frontal lobes and the sense of volition arises from other areas such as the parietal cortex and insula. Thus, it should be possible to influence each of these components independent of the other. A handful of studies that used single pulse transcranial magnetic stimulation (TMS) failed to demonstrate convincingly that movement generation could be influenced without affecting the sense of volition. Single pulse TMS, however, is not an effective method to modulate cortical excitability. In this study, we aimed at determining whether choice of movement can be modulated by transcranial direct current stimulation (tDCS). We hypothesized that tDCS-induced change in motor cortex excitability could influence movement selection without altering the sense of volition in healthy human subjects. Methods: Six right-handed healthy volunteers participated in this study. They performed a forced choice task by having to make a choice to move either their right or left index finger in response to a visual cue. Direct current (sham or 1.5mA) was applied using wet sponge-covered rubber electrodes that were placed over both motor cortices randomly during each trial. Results: We found that with sham stimulation the subjects showed higher preference to move the dominant hand. Cathodal stimulation to left motor cortex abolished this preference. Anodal stimulation to left motor cortex increased the preference of the ipsilateral (non-dominant) hand. Subjects also had the sense that they were making a free choice. Discussion: Our preliminary results show that tDCS can be successfully used to influence movement selection without changing the sense of volition in healthy human subjects. These results confirm the dissociation of the brain’s movement selection and the sense of volition.