Repetitive peripheral magnetic stimulation alleviates tactile extinction

Abstract

Despite its frequency in right brain damaged patients crucial mechanisms of tactile extinction are still obscure and treatments are unavailable. Recent PET observations suggest a hypometabolism in the primary and secondary somatosensory cortex of the lesioned hemisphere in patients with tactile extinction. Functional and morphological investigations have shown that the sensorimotor cortex has a remarkable capability of reorganization when the sensory inflow is changed. Repetitive peripheral magnetic stimulation (RPMS) applied in patients suffering from central paresis alleviates sensorimotor as well as cognitive deficits by the induction of proprioceptive inflow, thereby activating plasticity in the CNS. Based on the observation of reduced metabolic activity in patients suffering from tactile extinction we applied RPMS to explore the effects of peripheral sensory stimulation on tactile extinction. Fourteen right-hemisphere lesioned patients with tactile extinction were randomly allocated to an experimental and a control group. The experimental group received one single RPMS treatment of the left forearm as well as a condition of attentional cueing known to improve visual extinction. The control group, with comparable tactile extinction scores, neither received RPMS nor verbal cueing, but was tested twice to evaluate possible learning or test repetition effects. In the experimental group RPMS led to a significant reduction of left-sided extinctions in the recognition of different tactual surfaces, but had no effect on ipsilesional errors. In contrast, attentional cueing had no significant effect on left-sided extinction errors but unexpectedly increased right-hand extinction errors slightly but significantly. The control group showed stable extinction scores of the left- and right-hand stimulus across two measurements, thus ruling out learning or test repetition effects. These results show that sensory inflow is an important modulatory factor in tactile extinction. Furthermore, multiple RPMS may prove a promising way for the rehabilitation of patients with this disorder.