1. UROP Undergraduate Research Opportunities Programme This project was supported through the University of Reading UROP (Undergraduate Research Opportunities Programme). UROP is managed by the Careers, Placement and Experience Centre. Role of S1 in tactile discrimination, Effect of TMS over the primary sensory cortex Blandine French- Cathy Kao- Nick Holmes (The Hand Lab) Introduction Studies on the sense of touch and its neurological component have helped understanding the different brain areas involved in tactile stimulation. Using a measure of tactile acuity, the “ Grating Orientation Task ” (1), these studies are the first part of a project investigating the effect of visual and postural information on tactile spatial acuity. In a first place, the participant's tactile ' threshold ' was determined. Different variables were then analyzed to determine the most reliable paradigm as it has been shown that some variables can affect individual's performances (2-3). The participants then performed a similar GOT task while their brain was stimulated by Transcranial Magnetic Stimulation (TMS). TMS aims to interfere with participants' tactile perception, and demonstrate a causal relationship between brain and behaviour. Figure 1: Diagram illustrating the GOT and the difference in grading width (4) Methods 20 adult participants touched a series of grated “domes” with their fingertips, and decided whether the gratings run 'along' or 'across' their finger. In our first experiment, the GOT task was applied manually in 4 blocks of 45 trials. Each condition experimented on the left or right hand with a single interval paradigm or a 2 interval paradigm, randomly. Different gratings widths allowed us to identify each participant’s 'thresholds’ according to their accuracy. Results The grating performance showed that there was a significant effect of the different paradigms (1-IFC M= 1.78, 2-IFC M=1.50 mm, p=0.006). and a significant gender effect (Female m= 1.38, Male M=1.93 p=0.015). There was no effect of handedness (LH M= 1.58, RH: M= 1.70 mm, p=0.14) Summary & Conclusion The gender and the paradigm of the task were found to significantly affect grating discrimination while handedness didn’t. This allows us to set up experiments differently in accordance to the effect wanted. The stimulation of S1 didn’t affect the tactile perception. This result can be due to confounding variables, or methodology problems. An experiment using TMS directly on the peripheral nerves of the hand would investigate further the cause of our results. References 1. Van Boven, R.W. & Johnson, K.O. (1994). The limit of tactile spatial resolution in humans. Neurology, 44, 2361-2366. 2. Goldreich, D. & Kanics, I.M. (2003).Tactile acuity is enhanced in blindness. The Journal of Neuroscience, 23 (8), 2439-3445 3. Peters, R. M. & Goldreich, D. (2013). Tactile Spatial acuity in childhood. PLOS 4. Zhang, M., Mariola, E., Stilla, R., Stoesz, M., Mao, H., Hu, X. & Sathian, K.2005). Figure 2. : The hand rested face down with the index positioned over a tunnel through which the stimulus rose (4) Figure 4: Performing GOT task with TMS In a second stage, 4 pulses of TMS were applied over the brain of 5 participants while they performed the tactile discrimination task. Two different brain areas ( primary sensory cortex (S1) and intraparietal sulcus (pIPS)) were stimulated alternatively through 4 blocks of 40 trials each, using only a single interval paradigm on the left hand. Figure 3: BrainSight showing exact location on brain The stimulation of S1 and pIPS didn't significantly alter the grating perception (Baseline: M= 1.94, Control: M= 1.94, S1: M= 1.86, p=0.9). Different patterns were found between the participants. Figure 5: Paradigm difference Figure 6: Gender difference Figure 7: Handedness difference Figure 9: Mean threshold for the 3 conditions Figure 8: Average threshold for each participant