Effects of transcranial direct current stimulation on the excitability of the leg motor cortex

Transcranial direct current stimulation (tDCS) of the human motor cortex at an intensity of 1 mA has been shown to be efficacious in increasing (via anodal tDCS) or decreasing (via cathodal tDCS) the excitability of corticospinal projections to muscles of the hand. In this study, we examined whether tDCS at currents of 2 mA could effect similar changes in the excitability of deeper cortical structures that innervate muscles of the lower leg. Similar to the hand area, 10 min of stimulation with the anode over the leg area of the motor cortex increased the excitability of corticospinal tract projections to the tibialis anterior (TA) muscle, as reflected by an increase in the amplitude of the motor evoked potentials (MEPs) evoked by transcranial magnetic stimulation. MEP amplitudes recorded at rest and during a background contraction were increased following anodal tDCS and remained elevated at 60 min compared to baseline values by 59 and 35%, respectively. However, in contrast to the hand, hyperpolarizing cathodal stimulation at equivalent currents had minimal effect on the amplitude of the MEPs recorded at rest or during background contraction of the TA muscle. These results suggest that it is more difficult to suppress the excitability of the leg motor cortex with cathodal tDCS than the hand area of the motor cortex.

[1]  D.B. McCreery,et al.  Charge density and charge per phase as cofactors in neural injury induced by electrical stimulation , 1990, IEEE Transactions on Biomedical Engineering.

[2]  L. Cohen,et al.  Induction of plasticity in the human motor cortex by paired associative stimulation. , 2000, Brain : a journal of neurology.

[3]  S. Sato,et al.  Safety and cognitive effect of frontal DC brain polarization in healthy individuals , 2005, Neurology.

[4]  M. Hallett,et al.  Responses to rapid-rate transcranial magnetic stimulation of the human motor cortex. , 1994, Brain : a journal of neurology.

[5]  Sergio P. Rigonatti,et al.  A sham-controlled, phase II trial of transcranial direct current stimulation for the treatment of central pain in traumatic spinal cord injury , 2006, PAIN.

[6]  T. Sawaguchi,et al.  Behavioral deficits induced by local injection of bicuculline and muscimol into the primate motor and premotor cortex. , 1991, Journal of neurophysiology.

[7]  D B McCreery,et al.  Considerations for safety in the use of extracranial stimulation for motor evoked potentials. , 1987, Neurosurgery.

[8]  M. Nitsche,et al.  Modulating parameters of excitability during and after transcranial direct current stimulation of the human motor cortex , 2005, Clinical Neurophysiology.

[9]  D. Liebetanz,et al.  MRI study of human brain exposed to weak direct current stimulation of the frontal cortex , 2004, Clinical Neurophysiology.

[10]  M. Nitsche,et al.  Pharmacological approach to the mechanisms of transcranial DC-stimulation-induced after-effects of human motor cortex excitability. , 2002, Brain : a journal of neurology.

[11]  M. Nitsche,et al.  Shaping the effects of transcranial direct current stimulation of the human motor cortex. , 2007, Journal of neurophysiology.

[12]  Walter Paulus,et al.  Modulation of cortical excitability by weak direct current stimulation--technical, safety and functional aspects. , 2003, Supplements to Clinical neurophysiology.

[13]  M. Hallett.  Surround inhibition. , 2003, Supplements to Clinical neurophysiology.

[14]  William F. Agnew,et al.  Histological Evaluation of Neural Damage from Electrical Stimulation , 1981 .

[15]  J. Rothwell,et al.  Level of action of cathodal DC polarisation induced inhibition of the human motor cortex , 2003, Clinical Neurophysiology.

[16]  A. Priori.  Brain polarization in humans: a reappraisal of an old tool for prolonged non-invasive modulation of brain excitability , 2003, Clinical Neurophysiology.

[17]  M. Nitsche,et al.  Safety criteria for transcranial direct current stimulation (tDCS) in humans , 2003, Clinical Neurophysiology.

[18]  D. McCreery,et al.  Histological evaluation of neural damage from electrical stimulation: considerations for the selection of parameters for clinical application. , 1981, Neurosurgery.

[19]  M. Gorassini,et al.  Increases in corticospinal tract function by treadmill training after incomplete spinal cord injury. , 2005, Journal of neurophysiology.

[20]  L. Cohen,et al.  Effects of non-invasive cortical stimulation on skilled motor function in chronic stroke. , 2005, Brain : a journal of neurology.

[21]  L. Cohen,et al.  Non-invasive brain stimulation: a new strategy to improve neurorehabilitation after stroke? , 2006, The Lancet Neurology.

[22]  C. Capaday,et al.  Input-output properties and gain changes in the human corticospinal pathway , 1997, Experimental Brain Research.

[23]  J. Rothwell,et al.  Short latency inhibition of human hand motor cortex by somatosensory input from the hand , 2000, The Journal of physiology.

[24]  John Rothwell,et al.  Does brain stimulation after stroke have a future? , 2006, Current opinion in neurology.

[25]  M. Hallett.  Chapter 13 Surround inhibition , 2003 .

[26]  M. Hallett,et al.  Modeling the current distribution during transcranial direct current stimulation , 2006, Clinical Neurophysiology.

[27]  J. Rothwell,et al.  Driving Plasticity in Human Adult Motor Cortex Is Associated with Improved Motor Function after Brain Injury , 2002, Neuron.

[28]  M. Nitsche,et al.  Sustained excitability elevations induced by transcranial DC motor cortex stimulation in humans , 2001, Neurology.

[29]  M. Nitsche,et al.  Facilitation of Implicit Motor Learning by Weak Transcranial Direct Current Stimulation of the Primary Motor Cortex in the Human , 2003, Journal of Cognitive Neuroscience.

[30]  M. Nitsche,et al.  Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation , 2000, The Journal of physiology.