TRANSCRANIAL DIRECT CURRENT STIMULATION OF THE TEMPORAL LOBE DOES NOT AFFECT HIGH-INTENSITY WORK CAPACITY

Stimulation of the left insular cortex may affect heart rate variability (HRV) and exercise effort perception. These studies investigated the effects transcranial direct current stimulation (tDCS) and electrode orientation on HRV and repeated maximal knee extensions. In study 1, after sham stimulation, anodal left temporal lobe stimulation, or anodal right temporal lobe stimulation, 10 male and 10 female subjects (age = 21.0 6 +/- 1.5 years) completed 50 maximum isokinetic extensions at 180 degrees.s(-1). There was a significant effect of stimulation condition on HRV for only 1 (SD2; p = 0.037; eta(2) = 0.159) of 5 HRV metrics. There was no significant effect on isokinetic fatigue percent or isokinetic work (all p >= 0.278; all eta(2) <= .065). It has been proposed that placing the cathode electrode on the shoulder may differentially affect tDCS. Therefore, in study 2, the effects of electrode orientation on tDCS-induced changes in HRV was assessed in 10 healthy females and 8 healthy males (21.6 +/- 2.5 years) who completed cephalic, extracephalic, and sham trials. In the cephalic montage, the anode was placed over the left temporal lobe and the cathode was placed over right prefrontal cortex. In the extracephalic montage, the cathode was placed on the shoulder on the same side of the body as the anode. Neither cephalic nor extracephalic montages affected HRV (all p >= 0.152; all eta(2) <= .105). These data suggest that anodal tDCS of the insular cortex has little effect on HRV, and does not improve high-intensity exercise performance in the current population. Therefore, anodal tDCS applied over the left temporal lobe is not recommended for high-intensity performance enhancement.