P093 Transcranial cortex stimulation, neuroplasticity and learning: An experimental and computational study

Abstract

Question Noninvasive cortical stimulation techniques such as repetitive transcranial magnetic stimulation (rTMS) are capable of increasing and decreasing cortical excitability and thereby might be clinically relevant for rehabilitation of neurological and neuropsychiatric disorders. However, the induced after-effects are usually too short-lasting to be clinically relevant. In this study we investigated if combining rTMS with operant learning can induce long-lasting after-effects not achievable neither with rTMS alone nor with operant learning alone. Methods Experimental approach: Forty-six subjects were randomly assigned to three experimental groups. Experimental groups 1 & 2 received a psychophysical pretest of tactile discrimination abilities with the left ring finger, a training procedure to improve performance with this finger, and a posttest. In experimental group 1 the training procedure was combined with 15 Hz rTMS over the primary sensory cortex (SI) while in experimental group 2 the training was combined with sham rTMS. In the third experimental group, psychophysical pre- and posttests of tactile discrimination abilities were assessed. However, they received 15 Hz rTMS over SI without training. Computational approach: As a preliminary simulation trial we developed a neural model, which enabled us to discriminate between the encoding and decoding of particular input frequency represented in several scenarios. Results Combining rTMS with operant learning induced long-lasting after-effects not achievable neither with rTMS alone nor with operant learning alone. A conceptual framework for the efficiency of combining cortical stimulation with operant learning can be derived from the Bienenstock–Cooper–Munro theory of bidirectional synaptic plasticity. According to this theory the change of synaptic efficiency during learning processes is dependent on the preactivation level of the involved neural network, suggesting that high-frequency rTMS can transiently decrease the threshold for the induction of LTP-like effects and thereby gate practice-dependent plasticity. Conclusions Our findings provide important implications for the use of rTMS in combination with operant learning as a therapeutic tool for neurorehabilitation.