Changes in Segmental and Motor Cortical Output With Contralateral Muscle Contractions and Altered Sensory Inputs in Humans

Abstract

. Changes in segmental and motor cortical output with contralateral muscle contractions and altered sensory inputs in humans. J Neurophysiol 90: 2451-2459, 2003; 10.1152/jn.01001.2002. Motor or sensory activity in one arm can affect the other arm. We tested the hypothesis that a voluntary contraction can affect the motor pathway to the contralateral homologous muscle and investigated whether alterations in sensory input might mediate such effects. Responses to transcranial magnetic stimulation [motor-evoked potentials (MEPs)], stimulation of the descending tracts [cervicomedullary MEPs (CMEPs)], and peripheral nerve stimulation (H-reflex) were recorded from the relaxed right flexor carpi radialis (FCR), while the left arm underwent unilateral interventions (5 s duration) that included voluntary contraction, muscle contraction evoked through percutaneous stimulation, tendon vibration, and cutaneous and mixed nerve stimulation. During moderate to strong voluntary wrist flexion on the left, MEPs in the right FCR increased, CMEPs were unaffected, and the H-reflex was depressed. These results are consistent with an increase in excitability of the motor cortex, no effect on the motoneuron pool, and presynaptic inhibition of Ia afferents. In contrast, percutaneous muscle stimulation facilitated both MEPs and the H-reflex. However, muscle contraction produced by a combination of voluntary effort and electrical stimulation also reduced the contralateral H-reflex. After voluntary contractions, the H-reflex remained depressed for 35 s, but after stimulationevoked contractions, it rapidly returned to baseline. Under both conditions, MEPs recovered rapidly. After voluntary contractions, CMEPs were also depressed for approximately 10 s despite their lack of change during contractions. Wrist tendon vibration (100 Hz) did not affect, and 20-Hz median nerve stimulation or forearm medial cutaneous nerve stimulation mildly facilitated, the H-reflex without affecting MEPs. Voluntary wrist extension, similarly to wrist flexion, increased MEPs and depressed H-reflexes. However, ankle dorsiflexion facilitated the H-reflex akin to the Jendrassik maneuver. These data suggest that a unilateral voluntary muscle contraction has contralateral effects at both cortical and segmental levels and that the segmental effects are not replicated by stimulated muscle contraction or by input from muscle spindles or non-nociceptive cutaneous afferents.

Unilateral practice of a ballistic movement causes bilateral increases in performance and corticospinal excitability

“…Imaging studies indicate that motor centers in both cerebral hemispheres are active during unilateral muscle contraction (7,9,17,19), and studies involving transcranial magnetic stimulation (TMS) demonstrate that ipsilateral motor cortex excitability is suppressed by weak unilateral contractions (22,23,37) and that it is facilitated by high-force contractions (13,14,38). Strong ipsilateral contractions also depress intracortical inhibition (25).…”

“…Importantly, the scale of these ipsilateral cortical effects is proportional to force production: the greater the force of unilateral contraction, the larger the effect on the opposite hemisphere (9, 14, 25). At a segmental level, movements performed with one limb typically result in depression of the central gain of the Ia afferent reflex pathway (4,6,14). There are also crossed interactions between inhibitory interneurons that receive inputs from primary muscle afferents (8,16, 34).…”

“…Strong ipsilateral contractions also depress intracortical inhibition (25). Importantly, the scale of these ipsilateral cortical effects is proportional to force production: the greater the force of unilateral contraction, the larger the effect on the opposite hemisphere (9,14,25). At a segmental level, movements performed with one limb typically result in depression of the central gain of the Ia afferent reflex pathway (4,6,14).…”

The Effects of Self-induced and Therapist-assisted Lower-limb PNF Pattern Training on the Activation of Contralateral Muscles

“…Munn et al (2005) explained that muscular training on one side of the body can enhance the muscular power of the limbs on the other side because it involves more motor units and the activation increases in the central nervous system 15) . Similarly, Hortobagyi et al (2003) and Kristeva et al (1991) reported that the cross-training effect is controlled at the cortical level; they explained that the cross-training effect occurs as the sensory motor faculty of both sides becomes active 18,19) . The cross-training effect is applied in PNF training to promote muscular power of the weak side and has proven effective.…”

Acute effects of maximal isometric muscle action of the elbow extensors on contralateral dynamic task of the elbow flexors: a pilot study

“…In addition, the cross facilitation phenomenon is related to the propagation of neural signals between the left and right hemispheres in both brain level as in spinal level 25 . Some researchers have demonstrated voluntary contraction of upper limb muscle may enhance the action of the contralateral homologous muscle 26,27 , for example, voluntary contraction of right biceps brachial increase the action of left biceps. However, to the best of our knowledge, this is the first study investigating the effects on non-homologous muscle performance (e.g., biceps and triceps).…”