1. Somatosensory evoked potentials from electrical stimulation of the digital nerves of the right thumb have been recorded during the performance of various motor tasks in eight normal subjects. 2. The N20-P30 primary cortical response is only moderately affected by task context, while the P45-N55 secondary response is markedly 'gated' by movement of the stimulated digit. The late N140 vertex is variable. 3. In most subjects, active and passive movements are about equally effective in suppressing the secondary complex; but in one, passive movement has come to be rather less effective than active. 4. Secondary response suppression occurs in proportion to the velocity of the movement of the thumb, up to a velocity of 20 deg/s. 5. Secondary response suppression is unrelated to load in the range 0 to 0.16 Nm. 6. When the stimulus is timed to occur at various points in movement, secondary complex suppression occurs at all stages; but there is little or no suppression when stimulation is timed at 200 ms before the start of or 500 ms after the end of a movement. 7. Secondary response suppression is maximal when the same digit is both moving and shocked. When the right index or little finger are moved instead, the right thumb being stimulated, suppression is less; when the left thumb moves, no suppression is seen. 8. Secondary response suppression is reduced but not lost if the skin and interphalangeal joint of the thumb are anaesthetized distal to the stimulating electrodes. 9. Secondary response suppression is unimpaired when the radial nerve is anaesthetized, paralysing the finger extensors. 10. In an attempt to identify the course taken by the afferent volley between the primary and secondary responses, and to identify the gating site, we recorded the responses in six patients with Parkinson's disease who had undergone thalamotomy. Their secondary responses were present, and gated in the normal way. 11. We are unable to confirm whether the secondary response represents the re-arrival at cortical level of a volley that has traversed the cerebrocerebellar loop. 12. We confirm that the secondary complex is located a little anterior to the primary cerebral response. 13. We conclude that a gating action is exerted in the brain on somatosensory afferent activity, after it first reaches the cortex, and that this gating action associated with movement is controlled by other afferent signals from the stimulated limb, and particularly from the stimulated digit.
Abstract. Nine men and 2 women with spinal injuries have received radiolinked implants to stimulate the S2 , S 3 and S 4 anterior roots. By activating these they can empty their bladders at will with greatly reduced residual volumes , and the majority of them can achieve continence. Follow-ups are from two months to 4 years.
SummaryThe first 50 patients to receive a sacral anterior root stimulator for bladder control were reviewed by questionnaire in mid-1989. At that time, the follow-up period varied from 5 to 11 years, and 48 of the group were alive; 2 had died from unrelated causes. Forty-one used their implants regularly for micturition and of these, 37 were always or usually continent. Twenty-nine reported no symptomatic urinary infections in the previous year, and only 4 had 3 infections or more. Twenty-seven used their implant to assist defaeca tion, and 13 of 32 male users reported full implant-driven erections.Side effects are minor, except for stimulus evoked pain sensation, which prevents use of the implant in 3 of the 7 non-users. Two of the other non-users were awaiting repair of their implant faults.
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