Paired associative transspinal and transcortical stimulation produces plasticity in human cortical and spinal neuronal circuits.
Anatomical, physiological, and functional connectivity exists between the neurons of the primary motor cortex (M1) and spinal cord. Paired associative stimulation (PAS) produces enduring changes in M1, based on the Hebbian principle of associative plasticity. The present study aimed to establish neurophysiological changes in human cortical and spinal neuronal circuits by pairing noninvasive transspinal stimulation with transcortical stimulation via transcranial magnetic stimulation (TMS). We delivered paired transspinal and transcortical stimulation for 40 min at precise interstimulus intervals, with TMS being delivered after (transspinal-transcortical PAS) or before (transcortical-transspinal PAS) transspinal stimulation. Transspinal-transcortical PAS markedly decreased intracortical inhibition, increased intracortical facilitation and M1 excitability with concomitant decreases of motor threshold, and reduced the soleus Hoffmann's reflex (H-reflex) low frequency-mediated homosynaptic depression. Transcortical-transspinal PAS did not affect intracortical circuits, decreased M1 excitability, and reduced the soleus H-reflex-paired stimulation pulses' mediated postactivation depression. Both protocols affected the excitation threshold of group Ia afferents and motor axons. These findings clearly indicate that the pairing of transspinal with transcortical stimulation produces cortical and spinal excitability changes based on the timing interval and functional network interactions between the two associated inputs. This new PAS paradigm may constitute a significant neuromodulation method with physiological impact, because it can be used to alter concomitantly excitability of intracortical circuits, corticospinal neurons, and spinal inhibition in humans.
Department of Physical Therapy, College of Staten Island, New York, New York.
Luke
L
Dixon
Department of Physical Therapy, College of Staten Island, New York, New York.
Mohamed M
MM
Ibrahim
Department of Physical Therapy, College of Staten Island, New York, New York.
Danielle
D
Santora
Graduate Center, City University of New York, New York, New York; and Department of Physical Therapy, College of Staten Island, New York, New York Maria.Knikou@csi.cuny.edu.
Maria
0000-0002-6277-236X
M
Knikou
D000328:Adult; D000704:Analysis of Variance; D001703:Biophysics; D002540:Cerebral Cortex / Q000166:cytology*; D004558:Electric Stimulation / Q000379:methods*; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009415:Nerve Net / Q000502:physiology; D009434:Neural Pathways / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology; D013116:Spinal Cord / Q000166:cytology* / Q000502:physiology; D013979:Tibial Nerve / Q000502:physiology; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
H-reflex; PAS; TMS; motor cortex; spinal cord; transspinal stimulation