Electroencephalography and clinical neurophysiology
-
Electroencephalogr Clin Neurophysiol · May 1990
Case ReportsSpinal intramedullary recording of human somatosensory evoked potentials.
We here report the first description of the intramedullary spatial distribution of evoked dorsal horn potentials in a human spinal cord. Somatosensory evoked potentials (SEPs) to median nerve stimulation were recorded within the cervical spinal cord of a patient with syringomyelia. Spinal intramedullary recording demonstrated a negative slow wave of the same polarity as the dorsal spinal surface response and a complex wave interpreted as the summation of its negativity and phase-reversed positivity. These two wave forms may depend on the locations at which the recording electrodes are attached to the dorsal horn.
-
Electroencephalogr Clin Neurophysiol · Jul 1989
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. ⋯ 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.
-
Electroencephalogr Clin Neurophysiol · May 1989
Epidurally recorded cervical spinal activity evoked by electrical and mechanical stimulation in pain patients.
Spinal SEPs to electrical and mechanical stimulation of the upper limb of the non-painful side in 7 pain patients were recorded from the cervical epidural space. In response to electrical stimulation of the median nerve, the longitudinal distribution of the spinal postsynaptic negativity (N13) along the cord had a distinct level of maximal amplitude at the C5 vertebral body. When recorded at increasing distances cranial or caudal to this level, the latency of N13 was successively prolonged, in agreement with a spread-out near-field generator in the dorsal horn. ⋯ There seemed to be a non-linear relationship between the amplitude of the response and the depth of skin indentation. The presented data contribute a more detailed picture of epidurally recorded spinal SEPs than previous studies. They will serve as a reference for further analysis of SEPs evoked by stimulation of the affected side in pain patients, to explore whether the painful state is associated with altered SEPs before or after therapeutic intervention.
-
Electroencephalogr Clin Neurophysiol · May 1989
Conduction properties of epidurally recorded spinal cord potentials following lower limb stimulation in man.
Spinal somatosensory evoked potentials were recorded in 35 neurologically normal patients undergoing surgery for scoliosis. During posterior procedures the recording electrodes were placed in the dorsal epidural space and during anterior operations in the intervertebral discs. Stimulation was of the tibial nerve in the popliteal fossa and the posterior tibial and sural nerves at the ankle. ⋯ Similar, although smaller, afferent potentials were recorded from the anterior side of the vertebral column. Component 1 is likely to be due to the stimulation of group 1 muscle afferents which terminate in the dorsal horn and activate second order neurones, many of whose axons go to form the ipsilateral dorsal spinocerebellar tract. Components 2 and 3 are believed to be largely cutaneous in origin and to be conducted mainly in the dorsal columns.
-
Electroencephalogr Clin Neurophysiol · May 1989
Comparative StudyAnesthesia effects: auditory brain-stem response.
Auditory brain-stem responses (ABRs) were measured in the awake state and with ketamine and xylazine anesthesia in adult gerbils. Surface recorded vertex-positive components of the ABR were analyzed with respect to the awake and anesthetized states as a function of stimulus frequency. ABR thresholds were not altered with ketamine/xylazine. ⋯ These data confirm previously reported ABR sensitivity to non-barbiturate anesthesia. Direct comparisons of ABR interpeak intervals or amplitude ratios from awake versus anesthetized animals must account for the effects of barbiturate and non-barbiturate agents. However, the stability of response threshold and the small magnitude of latency and amplitude changes with a ketamine and xylazine regimen demonstrate that accurate electrophysiological measures of hearing sensitivity and auditory brain-stem activity can be obtained in anesthetized animals, provided that temperature and other parameters are maintained within normal physiological limits.