Reversal of a Virtual Lesion in Human Pharyngeal Motor Cortex by High Frequency Contralesional Brain Stimulation

Background & Aims

Excitatory brain stimulation with repetitive transcranial magnetic stimulation (rTMS) has been proposed as a treatment for dysphagia after stroke. Moreover, 1-Hz rTMS can induce a “virtual lesion” in the human pharyngeal motor cortex that suppresses brain activity and temporarily disrupts swallowing. We thus examined if rTMS could reverse the disrupted brain and swallowing functions following a unilateral virtual lesion in the pharyngeal motor cortex, such that rTMS might be developed as a therapy.

Methods

Healthy subjects (n = 23) were given varying conditions of 5-Hz rTMS over the pharyngeal motor cortex to determine the most effective excitatory parameters. Thereafter, a unilateral virtual lesion was made in the pharyngeal motor cortex using 1-Hz rTMS, followed by contralateral active or sham 5-Hz rTMS. Motor evoked potentials and serial swallowing reaction times were recorded before and for 60 minutes postlesion to assess reversibility of the disruption to the brain and swallowing.

Results

The greatest increase in pharyngeal motor cortex excitability was seen following 250 pulses of 5-Hz rTMS (F(1,11) = 10.3, P = .008), an effect that lasted over 2 hours. In contrast to sham rTMS, active contralateral 5-Hz rTMS completely abolished the cortical suppression induced by the virtual lesion, with effects occurring for up to 50 minutes in both unlesioned (F(1,11) = 6, P = .03) and lesioned (F(1,11) = 67, P < .001) hemispheres. Active rTMS also reversed the changes in swallowing behavior (F(1,8) = 9, P = .018), restoring function to prelesional levels.

Conclusions

Contralesional-targeted neurostimulation modulates brain activity and swallowing motor behavior after experimental disruption and might be usefully applied in stroke-affected patients as a therapy for dysphagia.

Abbreviations used in this paper: EMG, electromyographic, GABA, γ-aminobutyric acid, ICF, intracortical facilitation, ICI, intracortical inhibition, MEP, motor evoked potential, rTMS, repetitive transcranial magnetic stimulation, TMS, transcranial magnetic stimulation