Biomedical subjects
D N Rushton
Publications and source records attributed to D N Rushton.
Gating of somatosensory evoked potentials during different kinds of movement in man.
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.
Electrical splinting of the knee in paraplegia.
Two men with T7 and T12 complete traumatic lesions have received implants to stimulate the femoral nerves and (in the T7 case) the inferior and superior gluteal nerves. By using these continuously at 13 pulses/sec they can stand and walk, as other paraplegics do with calipers. Regular stimulation at 11 or 13 pulses/sec greatly increases the force exerted by the quadriceps femoris muscles and their resistance to fatigue, and this improvement is not lost during 2 months without stimulation.
Gating of somatosensory evoked potentials by active and passive movements in man [proceedings].
Explore the source record for details and available documents.
A method for plotting the optimum positions of an array of cortical electrical phosphenes.
The cortical visual prosthesis provides one approach to the substitution of vision in blind people. Usable visual information is provided in the form of phosphenes, and in order to make use of the prosthesis the positions of the phosphenes in visual space must first be determined. Such phosphene maps have to be constructed from observations of the angle and distance between various pairs of phosphenes. Because of the variation in repeated observations of the same phosphene pair, some method is needed to provide the 'best' fitting map to the observations. By formulating the problem as one involving the minimization of a function of many variables, an algorithm is constructed which determines a two-dimensional co-ordinate for each phosphene by minimizing one of two criteria indicating the fit of the map to the observations. The minimization algorithm employed is, essentially, a 'steepest descent' procedure, and initial co-ordinate values are provided by a triangulation method.
The stability of the electrical stimulation map of the motor cortex of the anesthetized baboon.
We have made repeated maps of the movements obtained by threshold electrical stimulation, with surface cathodal trains of pulses, of the motor cortex of 4 baboons, using chronically implanted arrays of electrodes. The electrode arrays were judged to remain in a constant relationship with the cortex because they did not move relative to the skull, and the arm/leg border obtained remained stable. There was evidence of a stability of response over a period of weeks. In 3 of the 4 animals, there was stability of the responding digit(s) regardless of the movement made by the digit(s), and of the digital movements performed (regardless of the digits involved). The stability of the map from minute was almost complete. Those variations that occur do so mainly by confusion within the motor homunculus, rather than by its movement as a whole across the cortex. Reasons for the imperfect long-term stability of the map are discussed in terms of variations in the physiological 'set' of the presumed polysynaptic pathways that are stimulated.
The pressure exerted by the external sphincter of the urethra when its motor nerve fibres are stimulated electrically.
Explore the source record for details and available documents.
Fatigue in the human external anal sphincter and external urethral sphincter under electrical stimulation of their motor nerve fibres.
Explore the source record for details and available documents.
The extent of the region of occipital cortex that when stimulated gives phosphenes fixed in the visual field.
Explore the source record for details and available documents.
Reaction times for simple shape discriminations requiring one or both visual cortices.
Explore the source record for details and available documents.
Technical note. Estimated electrode operating conditions of the first London Mk V implanted stimulator.
The electrodes of an implanted stimulator must be operated in such a way that the task of converting an electron current in metal to an ion current in tissue is achieved without release of noxious chemical species into the tissue, and without significant corrosion of the electrode metal. Both these effects depend on the charge density at which the electrodes are operated. In bringing a newly designed multichannel stimulator into service, the charge densities can only be known when the operating stimulus strengths have been determined. Even then, unless the stimulator is arranged to telemeter out what it is doing, any charge-density figures obtained have the character of estimates, rather than measurements. The first London Mk. V stimulator is used to enable a paraplegic woman to stand up. This note provides estimates of the average charge density and corrosion rate for the Pt--Ir electrodes used. These fall within limits which we believe to be generally accepted as safe.