Origin of motor evoked potentials in the rat.
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Animals↗
Biomedical subjects
R D Linden
Publications and source records attributed to R D Linden.
Motor and somatosensory evoked potentials recorded from the rat.
An accurate neurophysiological technique that is able to monitor both the sensory and motor tracts of the spinal cord is required to assess patients with injury or other lesions of the cord, and for the evaluation of experimental studies of cord injury. We have recorded and characterized the motor and somatosensory evoked potentials (MEPs and SSEPs) from 20 normal rats and from 16 rats with cord lesions. MEPs were elicited by applying constant current anodal stimuli to the sensorimotor cortex (SMC) with the responses recorded from microelectrodes in the spinal cord at T10 (MEP-C) and from a bipolar electrode placed on the contralateral sciatic nerve (MEP-N). SSEPs were elicited by stimulating the sciatic nerve and were recorded from the cord at T10 and the contralateral SMC. The MEP-C consisted of an initial D wave (mean latency 1.21 +/- 0.12 msec and 4 subsequent I waves, 11-14). The D wave was elicited at stimulation frequencies exceeding 100 Hz. The initial positive wave of the MEP-N (mean latency 3.09 +/- 0.19 msec) was followed by several slower components which were attenuated by repetition rates exceeding 8.2 Hz. The grand mean SSEP consisted of 7 peaks. Sectioning of the dorsal columns abolished the SSEP but spared the MEP. Complete cord transection abolished both the MEP and SSEP. These experiments demonstrate that the combined recording of MEPs and SSEPs is an accurate and easily performed method of monitoring the functional integrity of the rat cord, and suggest that this technique would be of value in patients, especially those undergoing operative treatment of spinal lesions.
Animals↗
Electrophysiological monitoring during acoustic neuroma and other posterior fossa surgery.
Techniques used to monitor the function of the seventh and eighth cranial nerves during acoustic neuroma and other posterior fossa surgery are reviewed. The auditory brainstem response (ABR), electrocochleogram (ECochG) and direct recording from the auditory nerve (CNAP) were compared. The best technique is the ECochG, although in many cases, the CNAP should be used as a back-up technique. The CNAP is especially useful for the identification of the auditory nerve. Both can provide real-time feedback on the physiological integrity of the auditory nerve. The ABR may be helpful in monitoring brainstem function. For some procedures, optimal monitoring requires the combined recording of all three techniques. Monopolar constant-voltage intracranial stimulation of the facial nerve is helpful for the identification and preservation of the facial nerve. Audio monitoring of spontaneous electromyographic activity provides real-time feedback on the effect of surgical manipulation of the nerve. Monitoring of ephaptic transmission in the facial nerve during microvascular decompression for hemifacial spasm aids in the identification of the offending vessel.
Action Potentials↗
The effect of direct-current field on recovery from experimental spinal cord injury.
Recent work has indicated that direct-current (DC) fields may promote recovery after acute spinal cord injury. In the present experiments, the therapeutic value of an applied DC field was studied in 40 rats with clip compression injuries of the cord at C7-T1. The rats were randomly allocated to one of four groups including 10 rats each: two groups received a 17-gm cord injury and two groups a 53-gm injury. One group at each injury severity received implantation of a treatment (14 microA) DC stimulator and the other group a control (0 microA) stimulator. Clinical neurological function was assessed weekly by the inclined-plane technique. At 8 weeks after injury, motor and somatosensory evoked potentials (MEP's and SSEP's) were recorded, and the axonal tracer horseradish peroxidase (HRP) was introduced into the cord at T-6. The total number of HRP-labeled cells was counted in every sixth coronal section through the brain stem and motor cortex. All outcome parameters were assessed blindly. In the 17-gm group, there were no significant differences in any outcome measure between control and treated rats. In contrast, in the 53-gm group, the inclined-plane scores, the amplitude of the MEP's, and the number of labeled cells in the red nucleus, raphé nuclei, and vestibular nuclei were greater in treated than in control rats. These data strongly indicate that an applied DC field can produce functional neurological and anatomical improvement in rats with acute spinal cord injuries.
Animals↗
Human auditory steady-state evoked potentials during selective attention.
The human auditory steady-state evoked potentials were examined during several different tasks requiring attention. Both Fourier analysis and signal averaging were used to measure the responses at stimulus rates between 37 and 41/sec. There was no effect of attention on the amplitude and phase of the steady-state evoked potentials when subjects either counted successive increments in stimulus intensity or read a book. In a dichotic listening task, there were clear changes in the late transient evoked potentials with selective attention but no changes in the steady-state responses. Furthermore, the steady-state potentials recorded during reading were not different from those obtained while the subjects were selectively attending to the auditory stimuli in one ear. There is therefore no evidence that the auditory steady-state responses are affected by attention.
Adult↗
Current status and future prospects for the neurosurgical management of acute spinal cord injuries.
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Evoked Potentials↗
Motor evoked potentials recorded from normal and spinal cord-injured rats.
A need exists for an accurate neurophysiological technique that monitors the motor tracts of the cord in patients with spinal cord injury or other cord lesions and for the evaluation of experimental models of cord injury. We have recorded and characterized the motor evoked potentials (MEPs) from 10 normal rats and from 10 rats with the following cord lesions at C-8: 4 animals with complete cord transection and 6 with clip compression injury: 2 at 56.0 g, 2 at 20.0 g, and 2 at 1.5 g. MEPs were elicited by applying constant current anodal stimuli to the sensorimotor cortex with the responses recorded from microelectrodes in the spinal cord at T-10. The MEP consisted of an initial D wave (mean latency, 1.22 +/- 0.09 ms) and 4 subsequent I waves, I1 to I4. The D wave was elicited at stimulation frequencies exceeding 100 Hz, consistent with the hypothesis that it results from direct pyramidal cell excitation. The 56.0-g clip compression injuries and the cord transections abolished the MEP distal to the lesion, whereas the 20.0- and 1.5-g injuries resulted in a latency shift and amplitude decrement of the MEP peaks. These experiments suggest that the recording of MEPs will be an extremely useful and accurate method of monitoring the functional integrity of the cord, of value in patients with cord injury.
Animals↗
Recording technically satisfactory somatosensory evoked potentials during spinal cord operation.
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Evoked Potentials, Somatosensory↗
Pathological gambling and major affective disorder: preliminary findings.
Twenty-five pathological gamblers were examined for additional DSM-III diagnoses and family history of psychiatric illness. Eighteen subjects (72%) had experienced at least one episode of major depression, and 13 (52%) had recurrent major affective episodes. A high prevalence (20%) of panic disorder and/or agoraphobia was also found.
Adult↗
Endocrine cells in the gastrointestinal tracts of 3 teleostean species.
Endocrine cells of the gastrointestinal tracts of 3 teleostean species (Lepomis gibbosus, Morone americana and Notemigonus crysoleucas) were studied using several staining techniques: Masson-Hamperl argentaffin reaction, Singh's argyrophil reaction, Schmorl's ferricyanide test and MacConnail's lead hematoxylin; only the argyrophil method showed a positive reaction. In L. gibbosus and M. americana, endocrine cells of proximal (corporic) stomach were seen singly among the surface epithelial cells while those of distal (pyloric) stomach were more numerous and located in irregular patches. A small number of positive cells were found in the gastric glands of corporic stomach. A few argyrophil cells were seen among the surface intestinal epithelial cells of N. crysoleucas but none were seen in the intestines of L. gibbosus and M. americana.
Animals↗
The relationships among the severity of spinal cord injury, motor and somatosensory evoked potentials and spinal cord blood flow.
To characterize the changes in axonal function in the motor and somatosensory tracts of the cord after spinal cord injury (SCI) and to correlate these changes with spinal cord blood flow (SCBF), the relationships among the severity of SCI, motor and somatosensory evoked potentials (MEPs and SSEPs) and SCBF were examined. Fifteen rats received a 1.5 g (n = 5), 20 g (n = 5) or 56 g (n = 5) clip compression injury of the cord at C8. SCBF at the injury site was measured by the hydrogen clearance technique 35 min before and 30 min after SCI. Concomitantly MEPs from the cord at T10 (MEP-C) and from the sciatic nerve (MEP-N) and SSEPs were recorded. A linear relationship (r = -0.89, P less than 0.002) was found between the severity of SCI and the reduction in SCBF at the injury site. Linear discriminant analysis revealed that both the MEP (P less than 0.0001) and SSEP (P less than 0.003) were significantly related to the severity of SCI. Furthermore, the amplitude of the MEP (r = 0.65, P less than 0.0001) and SSEP (r = 0.58, P less than 0.001) was significantly correlated with the posttraumatic SCBF. Multiple regression revealed that both the severity of cord injury and the degree of posttraumatic ischemia were significantly related to axonal dysfunction after SCI. While the MEP was more sensitive to injury than the SSEP, the SSEP more accurately distinguished between mild and moderate severities of cord injury. Axonal conduction in the motor and somatosensory tracts of the cord was significantly correlated with the reduction in posttraumatic SCBF and, therefore, these data provide quantitative evidence linking posttraumatic ischemia to axonal dysfunction following acute cord injury. Furthermore, this study validates the hypothesis that the combined recording of MEPs and SSEPs is an accurate technique to assess the physiological integrity of the cord after injury.
Animals↗
Human auditory steady state evoked potentials during sleep.
The human auditory steady state evoked potentials were recorded during all-night sleep in 10 subjects. The effects of stimulus rate and intensity on these potentials were measured using on-line Fourier analysis. The amplitude of the response was greatest at stimulus rates of 30 to 50/sec. Although the response amplitude was lower during sleep, the rate at which the amplitude was greatest did not change between sleep and wakefulness. As the intensity was increased above threshold, the amplitude of the response increased linearly. The responses recorded during wakefulness showed a larger amplitude change with increasing intensity than during sleep. The estimated thresholds for the responses, however, did not differ significantly between wakefulness and sleep.
Adult↗