ABSTRACT
OBJECTIVES: To evaluate whether the task-specific neural coupling mechanism during the performance of cooperative hand movements is preserved in tetraplegic subjects. METHODS: Recordings of ipsilateral and contralateral electromyographic reflex responses in activated forearm muscles and bilateral somatosensory potentials (SSEP) to unilateral ulnar nerve stimulations during rest, cooperative and non-cooperative hand movements. RESULTS: Contralateral reflex responses were present in almost all patients during cooperative hand movements but small in amplitude when hand function was severely impaired. Ipsilateral SSEP potentials were enhanced during both cooperative and, in contrast to healthy subjects, also non-cooperative bimanual movements. CONCLUSIONS: Both results indicate a strong involvement of ipsilateral non-damaged cervical tracts and hemispheres in the control of bimanual hand movements in tetraplegic subjects. SIGNIFICANCE: This study on the neural control of bimanual movements in patients suffering a cervical injury allows designing therapeutic approaches for the improvement of hand function that are based on physiological insights.
Subject(s)
Evoked Potentials, Somatosensory , Hand/physiopathology , Movement , Quadriplegia/physiopathology , Spinal Cord Injuries/physiopathology , Adult , Aged , Female , Functional Laterality , Humans , Male , Middle Aged , ReflexABSTRACT
Cooperative hand movements (e.g. opening a bottle) are controlled by a task-specific neural coupling, reflected in EMG reflex responses contralateral to the stimulation site. In this study the contralateral reflex responses in forearm extensor muscles to ipsilateral ulnar nerve stimulation was analyzed at various resistance and velocities of cooperative hand movements. The size of contralateral reflex responses was closely related to the level of forearm muscle activation required to accomplish the various cooperative hand movement tasks. This indicates an automatic gain control of neural coupling that allows a rapid matching of corrective forces exerted at both sides of an object with the goal 'two hands one action'.
Subject(s)
Hand/physiology , Movement/physiology , Ulnar Nerve/physiology , Adult , Electric Stimulation/methods , Female , Forearm/physiology , Functional Laterality/physiology , Humans , Male , Muscle, Skeletal/physiology , Reflex/physiologyABSTRACT
OBJECTIVE: Spinal neuronal function is impaired after a severe spinal cord injury (SCI) and can be assessed by the analysis of spinal reflex (SR) behavior. We applied transcutaneous spinal direct current stimulation (tsDCS) and locomotor activity, to determine whether the excitability of spinal neuronal circuitries underlying locomotion can be modulated after motor complete SCI. METHOD: SRs were evoked by non-noxious electrical stimulation of the tibial nerve. SR behavior was assessed before, immediately after, and 20 min after four different interventions (anodal, cathodal, sham tsDCS, or locomotion) in subjects with motor complete SCI and healthy subjects. RESULTS: SR amplitudes in SCI subjects were increased after anodal tsDCS by 84% (p < 0.05). Cathodal, sham tsDCS and locomotion had no influence on SR amplitudes. In addition, reflex threshold was lower after anodal tsDCS and locomotion in SCI subjects (p < 0.05). CONCLUSION: Anodal tsDCS is able to modulate spinal neuronal circuitries after SCI. SIGNIFICANCE: This novel, noninvasive approach might be used as a tool to excite spinal neuronal circuitries. If applied repetitively within a training approach, anodal tsDCS might prevent adverse alterations in spinal reflex function in severely affected SCI subjects, i.e., a manifestation of a spinal neuronal dysfunction taking part below the level of a spinal lesion.
