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

Abstract

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.

Noninvasive Neuromodulation in Poststroke Gait Disorders

“…These areas are less easily approached with NIBS techniques, especially when dealing with distal muscles. However, studies on healthy individuals have demonstrated that rTMS, tDCS, and PAS protocols are able to modulate the excitability of the leg motor cortex, 82,99,117 and a behavioral effect of anodal tDCS on lower-limb motor performance, as transient enhancement of maximal leg force, has been observed. 118 Because the pathophysiological reorganization of leg motor areas after stroke is still unclear, based on the model of interhemispheric competition after stroke established for the upper extremity, NIBS techniques have been mainly applied for inhibiting the unlesioned hemisphere or facilitating the lesioned hemisphere.…”

The Effects of Transcranial Direct Current Stimulation on Functional Movement Performance and Balance of the Lower Extremities

“…Among research on agility in accordance with tDCS application, Boggio et al 31) reported that performance time decreased in their study of hand response speed, and Kim Joong-sun et al 32) also reported reduced response times. Jeffery et al 17) observed improved performance and increased response time of the lower extremities in normal subjects. According to the present study results, tDCS application may effectively enhance normal people's agility, and the resulting activation of the motor cortex has a sustained influence on treadmill gait, as asserted by Antal et al 7) .…”

“…Noninvasive tDCS has drawn attention as a potential area of research on neurological reversibility through its application to the premotor area 29,30) . Although research on tDCS application to the upper extremity areas has been active, research on its application to the lower extremity areas has concerned only response time and single muscle activity 17) .…”

“…The intention was to look at the effects of tDCS application on agility, power, and balance of the lower extremities. The current intensity of the tDCS was 2 mA 17) and its application duration was 20 minutes. In order to examine whether tDCS application sustained activation of the lower extremity motor cortex, as reported by Antal et al 7) , the present study applied treadmill gait training for 20 minutes after tDCS.…”

“…Nitsche 14) and Madhavan et al 15) reported that adjustment of tDCS intensity and duration may increase motor function and excitability, and in an MRI study, KIM et al 16) observed the possibility of motor adjustment of the lower extremity area. Jeffrey et al 17) noted that a current intensity of 2mA increased response time and muscle activity of the lower extremities more than a current intensity of 1mA level, and activation of the pre-motor area continued for some time after stimulation 7,[18][19] . Among research on lower extremity motor functions, Ghanim et al 20) reported improved activity of the soleus muscle during sitting and standing motions.…”