Fig. 1: Striatal tTIS during reinforcement learning of motor skills in the MRI machine.
From: Non-invasive stimulation of the human striatum disrupts reinforcement learning of motor skills
a, Motor learning task. The participants were required to squeeze a hand-grip force sensor (depicted in the upper right corner of the figure) to track a moving target (the larger circle with a cross in the centre) with a cursor (the smaller black circle)54,55. Pre- and post-training assessments were performed with full visual feedback of the cursor and no reinforcement. In ReinfON and ReinfOFF trials, the participants practised the task with or without reinforcement feedback, respectively. In ReinfON trials, the colour of the target varied in real time as a function of the participants’ tracking performance. b, Experimental procedure. The participants performed the task in the MRI machine with concomitant tTIS. Blocks of training were composed of 36 trials (4 pre-training, 24 training and 8 post-training trials) interspersed with short resting periods (represented as plus signs in the figure). The six training types resulted from the combination of three tTISTYPES and two ReinfTYPES. c, Concept of tTIS. On the left, two pairs of electrodes are shown on a head model, and currents I1 and I2 are applied with frequencies f1 and f1 + Δf. On the right, the interference of the two electric fields within the brain is represented for two different locations with high and low envelope modulation. E1(t) and E2(t) represent the modulation of the fields’ magnitude over time. tTIS was delivered with a Δf of 20 or 80 Hz or as a sham (a ramp-up and immediate ramp-down of high-frequency currents with a flat envelope). d, Electric field modelling with the striatal montage. The colours show the temporal interference exposure (electric field modulation magnitude). e, Temporal interference exposure in the striatum and in the overlying cortex. The violin plots show the tTIS exposure distribution over the voxels in the striatum and cortex underneath the stimulation electrodes. The magnitude of the field in the cortex was extracted from the BNA64 regions underneath the stimulation electrodes (F3–F4 and TP7–TP8). The black bar represents the mean. Voxels with outlying tTIS exposure (±5 s.d. around the mean) were removed from the plot (21 values from a total of 46,479 considered voxels).
