Abstract
Low-frequency rTMS (lf-rTMS) to the intra-parietal sulcus (IPS) in the healthy hemisphere of patients with parietal lesion leads to improved visual attention up to 30 minutes post-rTMS. This behavioral improvement may be due to upregulation of functional communication in the attention network, compensating for the inhibited IPS. However, to aid clinical intervention, enduring effects that outlast lf-rTMS are crucial. We hypothesize stimulation effects may persist through multi-method stimulation. We paired 20-min transcranial random noise stimulation (tRNS) with lf-rTMS in healthy subjects (n=5) to examine if priming the cortex with tRNS can prolong subsequent lf-rTMS effects in a bilateral multiple object tracking task. Participants were asked to track two moving discs amidst two moving distractor-discs in each visual field, either side of a fixation point. Prior to stimulation, disc speed was thresholded to the speed at which subject performance was 75% correct. The four within-subjects, neuro-navigated stimulation sessions consisted of: 1) tRNS over bilateral IPS with subsequent lf-rTMS over left IPS, and 2) over right IPS, 3) SHAM-tRNS over bilateral IPS with subsequent lf-rTMS over left IPS, and 4) over right IPS. We normalized tRNS conditions relative to SHAM-tRNS, ensuring effects specific to the tRNS and lf-rTMS combination. Results showed that tRNS extended the effect of rTMS. Specifically, in the visual field ipsilateral to lf-rTMS, there was an initial boost in tracking performance but only after lf-rTMS to the right IPS. This is potentially an effect of priming the cortex with bilateral tRNS, resulting in left IPS excitation. In the contralateral visual field to rTMS, there was an initial decrement in tracking ability, followed by a late improvement at 82 minutes. The late enhancement on contralateral attention may reflect functional compensation of inhibited IPS. Our results demonstrate a prolonged modulation in behavioral response to visual-field specific attention after multi-method stimulation.
Meeting abstract presented at VSS 2018