Neurophysiological effects of dorsal column stimulation in man and monkey

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✓ In 18 patients with cancer and intractable pain, capacitatively coupled pulses of 0.25 msec duration were delivered transcutaneously at 100 Hz to sets of five in-line electrodes implanted subdurally over the dorsal columns. Averaged somatosensory-evoked potentials were recorded from scalp electrodes before, during, and after application of current. All but one patient experienced relief of pain during stimulation, persisting for as long as several hours afterward. Eleven patients developed hyperactive deep reflexes, pathological reflexes, and decreased perception of joint rotation, pain, and touch below the level of current application. Somatosensory-evoked potential amplitudes were markedly reduced. All neurological findings returned to control values within 1 hour after each of repeated applications of current. Histological examination of spinal cord sections from four cancer patients showed no changes secondary to long-term current application.

Similar currents were applied to the spinal cord of 15 monkeys with chronically implanted bipolar recording or stimulating electrodes over the lower, middle, and upper thoracic cord, in nucleus ventralis posterior lateralis (VPL), and over the sensory motor cortex (SMC). With application of current, the responses in VPL and SMC to peripheral stimulation were abolished. Evoked potential responses were abolished between bipolar stimulating electrodes and bipolar recording electrodes separated by the five in-line electrodes used to supply the 100 Hz current. However, when both stimulating and recording electrodes were either above or below the five in-line electrode set, evoked responses were unaffected. The findings indicate that applied currents blocked neuronal transmission by producing local changes in the cord. The prolonged alteration of cerebral evoked potentials and relief of pain, however, could also be related to involvement of supraspinal neurons.

Article Information

Address reprint requests to: Sanford J. Larson, M.D., Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, Wisconsin 53226.

© AANS, except where prohibited by US copyright law.

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    Subcutaneous receiver and the five electrode set. Insert at arrow shows side view of electrode array. The electrode set is sutured to the dura with two horizontal mattress sutures placed through the base of the keel on either side of the central cable.

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    Evoked potentials recorded from VPL and SMC of unanesthetized monkey secondary to low-frequency stimulation of bipolar electrode set in the lower thoracic level before, during, and after application of current to five in-line electrodes on the thoracic portion of the spinal cord. Analysis time is 125 msec, stimulus at arrow. Increasing phase of first response has latency of approximately 5 msec. Response obliterated with 700 µA pulse current applied to five electrode set. Recovery approximately 10 minutes after 100 Hz current is off.

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    Recordings of cord-to-cord-evoked potentials before, during, and after current application to five in-line electrodes on the dorsal surface of the cord. The stimulating and recording electrodes are separated by the five in-line current electrodes. Barbiturate anesthesia. Analysis time is 62 msec, stimulus at arrow. Response obliterated with 500 µA peak pulse current applied to five electrode set. Recovery at approximately 10 minutes after 100 Hz current is off.

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    Recordings of the potentials evoked from the cauda equina to the lower thoracic spinal cord. Stimulating and recording bipolar electrodes are both below the five in-line current electrodes. The responses are unaffected by the applied currents. Noise on the lower trace is due to applied currents. Analysis time is 62 msec, stimulus at arrow.

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    Potentials recorded from bipolar electrodes on the dorsal aspect of the spinal cord (upper thoracic) above the five electrode set evoked by stimulation through Electrodes 2 and 4 of the five in-line array before, during, and after application of current at 100 Hz through Electrodes 1, 3 and 5. Barbiturate anesthesia. Analysis time is 31 msec, stimulus at arrow. Response is reduced with 500 µA pulse current applied to Electrodes 1, 3 and 5. Recovery approximately 20 minutes after 100 Hz current is off.

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