Transcutaneous electrical nerve stimulation effects on neglect: A visual-evoked potential study

Abstract

We studied the effects of transcutaneous electrical nerve stimulation (TENS) in six right brain-damaged patients with left unilateral spatial neglect, using both standard clinical tests (reading, line and letter cancellation and line bisection) and electrophysiological measures (steady-state visual evoked potentials, SSVEP). TENS was applied on left neck muscles for 15′ and measures were recorded before, immediately after, and 60′ after stimulation. Behavioral results showed that the stimulation temporarily improved the deficit in all patients, reducing the asymmetry of performances in the two sides of space by reducing the omissions on the left side; the error in line bisection was reduced by about 50%. Electrophysiological data showed that, before TENS, SSVEP latency to stimuli displayed in the left visual half-field [LVF, (160 ms)] was remarkably longer than to stimuli shown in the right visual half-field [RVF, (120 ms)]. Immediately after TENS the latency to LVF stimuli was 130 ms; one hour after the stimulation the effect of TENS faded, with latency returning to the pre-treatment value. TENS similarly affected also the latency SSVEP of a group of twelve healthy subjects, and their line bisection; however in this group, the effects were smaller. Present study, first, replicates evidence concerning the positive behavioral effects of TENS on the manifestations of left spatial neglect in right-brain-damaged patients, and, second, shows parallel electrophysiological effects on the SSVEP latency. These behavioral and novel electrophysiological results are discussed in terms of specific directional effects of left somatosensory stimulation on the egocentric coordinates, which in patients with neglect are distorted towards the side of the brain lesion. Showing that VEP latency might be modulated by proprioceptive stimulation, we provide electrophysiological evidence to the effect that TENS may improve manifestations of neglect, and may contribute to its rehabilitation. © 2013 Pitzalis, Spinelli, Vallar and Di_russo.