Rehabilitation following brain damage: some neurophysiological mechanisms. The effects of repetitive stimulation in recovery from damage to the central nervous system

Reflex reciprocal facilitation of antagonist muscles in spinal cord injury

STUDY DESIGN

Electromyographic study in complete and incomplete spinal cord injury (SCI).

OBJECTIVE

To examine the changes in the pattern of reciprocal inhibition between agonist and antagonist muscles in SCI.

SETTINGS

Sensory Motor Performance Program, Rehabilitation Institute of Chicago, IL, USA.

METHODS

Tendon taps were delivered manually with an instrumented hammer to the tendons of the tibialis anterior and soleus muscle in positions of full-ankle dorsiflexion and plantarflexion in eight subjects with complete SCI and eight subjects with incomplete SCI. Electromyographic activity (EMG) was recorded from ankle dorsiflexor and plantarflexor muscles. Tapping force was also recorded by a force sensor mounted to the tendon hammer, indicating the stimulus onset. Measures of reflex EMG magnitude and reflex latency were obtained for both agonist and antagonist muscles. The ratio of antagonist to agonist EMG was computed based on normalized EMG.

RESULTS

Substantial reflex responses occurred in both the stretched muscle and in its antagonist. The reflex in antagonist, which we term 'reciprocal facilitation (RF)', was most evident in subjects with incomplete SCI. The magnitude of RF was consistently greater than reflex responses in agonist muscles under all test conditions. The latency of the RF was comparable to that of monosynaptic reflex response.

CONCLUSIONS

Following SCI, reciprocal organization of segmental reflexes at the ankle is often partially or completely suppressed, allowing reflex activation in antagonist muscles to be manifested. Possible mechanisms underlying these changes in neural organization are discussed.

SPONSORSHIP

This study was supported by Spinal Cord Research Foundation, the Paralyzed Veterans of America.

Attenuation by spinal cord stimulation of a nociceptive reflex generated by colorectal distention in a rat model

The mechanisms underlying the cause and treatment of visceral pain of gastrointestinal origin are poorly understood. Previous clinical studies have shown that spinal cord stimulation (SCS) attenuates neuropathic and ischemic pain, and animal experiments have provided knowledge about probable physiological mechanisms. The goal of the present study was to investigate whether SCS influences colonic sensitivity in a conscious rat. A visceromotor behavioral response (VMR), induced by colorectal distention, was used to quantify the level of colonic sensitivity. Under anesthesia, an electrode (cathode) was placed on the dorsal surface of the spinal cord at L1. One week after implantation of the SCS electrode, the effects of stimulation delivered with different intensities (50 Hz, 0.2 ms for 30 min) on colonic sensitivity were determined. Nociceptive levels of colorectal distention (60 mm Hg for 10 min) induced an enhanced VMR quantified as an increased number of abdominal muscle contractions compared to controls in which the balloon catheter was inserted into the colorectal region but not distended. Colonic sensitization with acetic acid increased the VMR to innocuous levels of colorectal distention (30 mm Hg for 10 min). We found that SCS induced a significant depression of the VMR produced by colorectal distention in both normal rats and those with sensitized colons. The suppressive effect of SCS on colonic sensitivity suggests that SCS may have therapeutic potential for the treatment of visceral pain of gastrointestinal origin associated with abdominal cramping and painful abdominal spasms.

Effect of electrical stimulation on spasticity in hemiparetic patients

Cyclical electrical stimulation has been applied to 10 hemiparetic patients with clinical signs of knee joint spasticity. The programme included 30 minutes of stimulation to the hamstrings followed by another 30 minutes of stimulation to the hamstrings and quadriceps. None of the patients experienced increased spasticity. The reduction in spasticity ranged from none to substantial with some other beneficial side-effects. No conclusions could be drawn as to whether hamstring stimulation is preferred to combined stimulation or to quadriceps stimulation alone. It is suggested that small portable stimulators be introduced for chronic use in spastic patients after an optimum stimulation regimen is individually established for each patient.