title: Trigeminal nerve stimulation modulates brainstem more than cortical excitability in healthy humans.
abstract: Multiple sites in the central nervous system (CNS) have been hypothesized to explain the beneficial effects of transcutaneous trigeminal nerve stimulation (TNS) on several disorders. This work investigated the acute effects of TNS on the excitability of brainstem and intracortical circuits, as well as on sensorimotor integration processes at cortical level in physiological conditions. Brainstem excitability was evaluated in seventeen healthy subjects measuring the R1 and R2 areas of the blink reflex (BR) and its recovery cycle, with cortical excitability and sensorimotor integration assessed by probing short-interval (SICI) and long-interval (LICI) intracortical inhibition, with short-interval (SICF), intracortical facilitation (ICF), short-latency (SAI) and long-latency (LAI) inhibition measuring motor potentials evoked in the first dorsal interosseous muscle by TMS of the contralateral motor cortex. Neurophysiological parameters were assessed, in seventeen healthy subjects, before and after cyclic 20-min TNS delivered bilaterally to the infraorbital nerve. After TNS, the area of the R2 was significantly reduced (p = 0.018). By contrast, R1 area and R2 recovery cycle were unaffected. Similarly, SICI, ICF, LICI, SICF, SAI and LAI appeared unaltered after TNS. These data suggest that, in normal subjects, TNS mainly acts on brainstem polysynaptic circuits mediating the R2 component of the BR and plays a minor role in modifying the activity of higher-level structures involved in the R2 recovery cycle and in modulation of cortical excitability. A further investigation of a chronic TNS-induced effect may disclose a higher potential for TNS in producing measurable after effects on its CNS targets.
authors.affiliation: Department of Biomedical Sciences, University of Sassari, Viale San Pietro 43/b, 07100, Sassari, Italy. bmercante@uniss.it.
authors.forename: B
authors.initials: B
authors.lastname: Mercante
authors.affiliation: Neurological Clinic, Department of Clinical and Experimental Medicine, University of Sassari, Viale San Pietro 10, 07100, Sassari, Italy. gpilurzi@uniss.it.
authors.forename: G
authors.initials: G
authors.lastname: Pilurzi
authors.affiliation: Department of Biomedical Sciences, University of Sassari, Viale San Pietro 43/b, 07100, Sassari, Italy. fratempo@hotmail.it.
authors.forename: F
authors.initials: F
authors.lastname: Ginatempo
authors.affiliation: Department of Biomedical Sciences, University of Sassari, Viale San Pietro 43/b, 07100, Sassari, Italy. andmanca@uniss.it.
authors.forename: A
authors.initials: A
authors.lastname: Manca
authors.affiliation: Department of Life and Environmental Sciences, University of Cagliari, Cittadella Universitaria Monserrato, 09042, Monserrato, Italy. follesa@unica.it.
authors.forename: P
authors.initials: P
authors.lastname: Follesa
authors.affiliation: Department of Biomedical Sciences, University of Sassari, Viale San Pietro 43/b, 07100, Sassari, Italy. tolue@uniss.it.
authors.forename: E
authors.initials: E
authors.lastname: Tolu
authors.affiliation: Department of Biomedical Sciences, University of Sassari, Viale San Pietro 43/b, 07100, Sassari, Italy. deriuf@uniss.it.
authors.forename: F
authors.initials: F
authors.lastname: Deriu
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001767:Blinking / Q000502:physiology; D001933:Brain Stem / Q000502:physiology*; D002540:Cerebral Cortex / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D050781:Transcranial Magnetic Stimulation; D014276:Trigeminal Nerve / Q000502:physiology*; D055815:Young Adult
keywords: Blink reflex; Brainstem excitability; Cortical excitability; Sensorimotor integration; Transcranial magnetic stimulation; Trigeminal nerve stimulation