Differences in human evoked potentials related to olfactory or trigeminal chemosensory activation

The aim of the present study was to determine, whether there are differences in the topographical distribution of chemosensory evoked potentials (CSEPs) due to stimulation with different odous substances. The odorants used in the study which mainly excited the olfactory nerve were vanillin and acetaldehyde; those which additionally excited the trigeminal nerve were sulphur dioxide and ammonia. Twelve subjects participated in the study. The subjects separately estimated the intensity of the odorous and of the painful/pricking sensation caused by the stimuli, and described the odorous qualities in their own words. CSEPs were recorded from 7 positions.After stimulation with “olfactory” subsances maximum CSEP amplitudes were recorded at parietol-central sites, and after stimulation with “trigeminal” substances maximum amplitudes were obtained at the vertex. Following stimulation with ammonia and sulphur dioxide amplitudes were largest contralateral to the stimulated nostril. In contrast, little difference in CSEP amplitudes was observed between hemispheres after stimulation with vanillin or acetyldehyde.Thus, the topographical distribution of CSEP amplitudes may provide information with regard to the sensory system (olfactory or trigeminal) activated by the presentation of an odorous stimulus.     

Findings of somatosensory evoked potential to stimulation of the sciatic nerve in two different rat strains.

No comparative study about somatosensory evoked potentials (SEP) on different rat strains has been done yet. It is evident that comparative SEP studies are important since different rat strains have different physiological properties. We aimed to compare early latency SEP values from stimulation of sciatic nerve in Wistar (Wr) and Sprague-Dawley (SDr) rats which are frequently used rat strains in experimental studies. In Wr group, the mean of first far field potential (Ff1) latency was shorter and the mean Ff1 amplitude was lower than that of Sprague-Dawley rat group. Mean cortical potential latency in Wr group was longer than that of SDr group while amplitude was not different. Central conduction time (CCT) in Wistar rat group was found to be longer than that of SDr group. Shorter Ff1 latency in Wr group implies that afferent volley reaches cervical posterior fasciculus from sciatic nerve earlier than SDr group while longer CP latency implies that afferent volley reaches cortex later than SDr group. Similarity between the latencies of lumbar potentials implies that peripheral conduction velocity has no effect on the difference of Ff1 latencies.     

Long sensory tracts (cuneate fascicle) in cervical somatosensory evoked potential after median nerve stimulation

Low amplitude high frequency waves (LHW) were investigated in normal and patient cervical somatosensory evoked potentials after median nerve stimulation (CSEP) in parallel to normal and patient conducted somatosensory evoked potentials (SEP) after tibial nerve stimulation. Normal recordings were obtained in five subjects undergoing dorsal root entry zone (DREZ) coagulation for pain relief. Patient recordings were obtained in 11 subjects suffering from either syringomyelia, spinal cord tumour, or both. All recordings were made intraoperatively from the dorsal spinal cord surface using the subpial recording technique. Normal CSEP showed typical triphasic potential starting with an initial P9, followed by N13 and a final positivity, P1. Numerous LHW were superimposed on slow triphasic potential. To improve the visibility of LHW, slow triphasic potential was removed from the original CSEP. Potentials thus obtained contained only high frequency components of CSEP, i.e. LHW. They were compared with conducted SEP after tibial nerve stimulation. Comparison revealed similarities in high frequency, low amplitude and general wave form, LHW thus showing characteristics of conducted potential. Duration was found to be significantly shorter than normal duration in both patient LHW (Student's t-test, P<0.0005) and patient conducted SEP (Student's t-test, P=0.064). A shorter duration was associated with worsening of configuration in patient LHW and patient conducted SEP. These changes of LHW could not be connected with distortion of N13 seen in patient CSEP. A shorter duration and worsening of configuration in patient LHW were most prominent in cases with a loss of vibration and posture senses, but were also observed in cases where only pain and temperature senses were affected. We therefore concluded that cuneate fascicle is the most likely generator of LHW, although the participation of other cervical long sensory tracts, e.g. spinothalamic tract, cannot be ruled out.     

Middle-latency somatosensory evoked potentials following median and posterior tibial nerve stimulation in Down's syndrome

Middle-latency somatosensory evoked potentials (SEPs) following median and posterior tibial nerve stimulation were studied in 40 patients with Down's syndrome and in age- and gender-matched healthy controls as well as in middle-aged and aged healthy subjects. In median nerve SEPs, latencies of the initial cortical potentials, N18 and P18, showed no significant difference, but the following potentials N22, P25, N32, P41 and P46 were relatively or significantly shorter in latency in Down's patients than in the controls. Amplitudes of all components in Down's patients were significantly larger than those of age- and gender-matched controls as well as of those of middle-aged healthy subjects, but there was only a small difference in their amplitudes from aged healthy subjects. Results of posterior tibial nerve SEPs were generally consistent with those of median nerve SEPs. Therefore, ‘short latency with large amplitude’ is the main characteristic of middle-latency SEPs in Down's syndrome, possibly related to accelerated physiological aging of the central nervous system.     

Identification and Prediction of Diabetic Sensorimotor Polyneuropathy Using Individual and Simple Combinations of Nerve Conduction Study Parameters

Objective

Evaluation of diabetic sensorimotor polyneuropathy (DSP) is hindered by the need for complex nerve conduction study (NCS) protocols and lack of predictive biomarkers. We aimed to determine the performance of single and simple combinations of NCS parameters for identification and future prediction of DSP.

Materials and Methods

406 participants (61 with type 1 diabetes and 345 with type 2 diabetes) with a broad spectrum of neuropathy, from none to severe, underwent NCS to determine presence or absence of DSP for cross-sectional (concurrent validity) analysis. The 109 participants without baseline DSP were re-evaluated for its future onset (predictive validity). Performance of NCS parameters was compared by area under the receiver operating characteristic curve (AROC).

Results

At baseline there were 246 (60%) Prevalent Cases. After 3.9 years mean follow-up, 25 (23%) of the 109 Prevalent Controls that were followed became Incident DSP Cases. Threshold values for peroneal conduction velocity and sural amplitude potential best identified Prevalent Cases (AROC 0.90 and 0.83, sensitivity 80 and 83%, specificity 89 and 72%, respectively). Baseline tibial F-wave latency, peroneal conduction velocity and the sum of three lower limb nerve conduction velocities (sural, peroneal, and tibial) best predicted 4-year incidence (AROC 0.79, 0.79, and 0.85; sensitivity 79, 70, and 81%; specificity 63, 74 and 77%, respectively).

Discussion

Individual NCS parameters or their simple combinations are valid measures for identification and future prediction of DSP. Further research into the predictive roles of tibial F-wave latencies, peroneal conduction velocity, and sum of conduction velocities as markers of incipient nerve injury is needed to risk-stratify individuals for clinical and research protocols.     

Motor and sensory nerve conduction velocities in Yucatan minipigs

Motor and/or sensory conduction velocities are used to assess peripheral nervous system disorders. Although the miniature pig represents a model of choice for long-term pharmacological experimentation, no study has so far been reported on this model in relation to the measurement of nerve conduction velocities. We developed the present technique and applied it to 34 3-18-month-old Yucatan minipigs. Motor and sensory conduction velocities were measured using the anterior tibial nerve and the internal plantar nerve, a branch of the posterior tibial nerve, respectively. The nerve conduction velocity data of motor (MNCV) and sensory (SNCV) nerves, together with the amplitude of the sensory nerve signal, were logarithmically dependent on the age of the tested animals (r(2)=0.92, 0.81 and 0.76, respectively). The mean values of MNCV and SNCV were 70.9 +/- 1.1 and 67.9 +/- 0.2 m/s, respectively, at the age of 16 months for these miniature pigs. In order to validate this model, we compared it with other known models when the velocities reached a plateau at the end of the study. These values were found to be higher than those in humans or rats, but are comparable to those of the baboon, one of the best large animal models for human pathologies. Because the physiology and metabolism of the minipig resemble those of humans, and due to its long lifetime, this animal represents a good model for studying the development of neuropathology.     

Motor and sensory conduction velocities and amplitude of nerve or muscle potentials in the normal rat according to age

The relative changes in sensory and motor nerve conductions and SNAP and CMAP amplitudes were studied on the sural and tibial posterior nerves in anesthetized male rats, between the 1st and the 23rd month. Neural growth was controlled with the measure of the nerve path length on the skin, between stimulating and recording cathodes for the sural nerve and proximal and distal stimulating cathodes for the tibial posterior nerve. The sural SCV and SNAP amplitude are consistent with a more accurate method than the H-reflex one. Similar changes were observed in both parameters. During the maturation of the peripheral nervous system, between the 1st and the 5th month, parameters rapidly increased. Over 14 months old, parameters decrease: the diminution of SNAP and CMAP amplitudes is characteristic of aging. The results were analyzed through quadratic and linear regression and were similar to those in young and elderly human patients. Parabola curves fitted the best way to represent the evolution of parameters. Moreover, the linear regression permitted to divide the rat life in 3 parts and to distinguish a period between the 6th and 13th months during which studied parameters are considered as constant. SCV, MCV, SNAP and CMAP amplitudes from the 1st to the 5th, from 6th to 13th and over the 14th month, could be used as reference.     

Reconstruction of the Abdominal Vagus Nerve Using Sural Nerve Grafts in Canine Models

Background

Recently, vagus nerve preservation or reconstruction of vagus has received increasing attention. The present study aimed to investigate the feasibility of reconstructing the severed vagal trunk using an autologous sural nerve graft.

Methods

Ten adult Beagle dogs were randomly assigned to two groups of five, the nerve grafting group (TG) and the vagal resection group (VG). The gastric secretion and emptying functions in both groups were assessed using Hollander insulin and acetaminophen tests before surgery and three months after surgery. All dogs underwent laparotomy under general anesthesia. In TG group, latency and conduction velocity of the action potential in a vagal trunk were measured, and then nerves of 4 cm long were cut from the abdominal anterior and posterior vagal trunks. Two segments of autologous sural nerve were collected for performing end-to-end anastomoses with the cut ends of vagal trunk (8–0 nylon suture, 3 sutures for each anastomosis). Dogs in VG group only underwent partial resections of the anterior and posterior vagal trunks. Laparotomy was performed in dogs of TG group, and latency and conduction velocity of the action potential in their vagal trunks were measured. The grafted nerve segment was removed, and stained with anti-neurofilament protein and toluidine blue.

Results

Latency of the action potential in the vagal trunk was longer after surgery than before surgery in TG group, while the conduction velocity was lower after surgery. The gastric secretion and emptying functions were weaker after surgery in dogs of both groups, but in TG group they were significantly better than in VG group. Anti-neurofilament protein staining and toluidine blue staining showed there were nerve fibers crossing the anastomosis of the vagus and sural nerves in dogs of TG group.

Conclusion

Reconstruction of the vagus nerve using the sural nerve is technically feasible.     

Median and tibial nerve somatosensory evoked potentials: middle-latency components from the vicinity of the secondary somatosensory cortex in humans

The topography of the middle-latency N110 after radial nerve stimulation suggested a generator in SII. To support this hypothesis, we have tried to identify a homologous component in the tibial nerve SEP (somatosensory evoked potential). Evoked potentials following tibial nerve stimulation (motor+sensory threshold) were recorded with 29 electrodes (bandpass 0.5–500 Hz, sampling rate 1000 Hz). For comparison, the median nerve was stimulated at the wrist. Components were identified as peaks in the global field power (GFP). Map series were generated around GFP peaks and amplitudes were measured from electrodes near map maxima. With median nerve stimulation, we recorded a negativity with a maximum in temporal electrode positions and 106±12 ms peak latency (mean±SD), comparable to the N110 following radial nerve stimulation. After tibial nerve stimulation the latency of a component with the same topography was 131±11 ms (N130). Both N110 and N130 were present ipsi- as well as contralaterally. Amplitudes were significantly higher on the contralateral than the ipsilateral scalp for both median (3.1±2.4 μV vs. 1.7±1.6 μV) and tibial nerve (1.9±1.2 μV vs. 0.6+1 μV). The topography of the N130 can be explained by a generator in the vicinity of SII. The latency difference between median and tibial nerve stimulation is related to the longer conduction distance (cf. N20 and P40). The smaller ipsilateral N130 is consistent with the bilateral body representation in SII.     

Hoffmann's reflex evoked on the soleus muscle and motor neural conduction velocity of the tibial nerve]

H reflex on the soleus muscle and motor tibial nerve conduction velocity are used to study peripheral nervous system maturation in 68 healthy children, from birth to 4 years of age. Proximal an distal conduction velocities develop in a parallel and approximately exponential way but proximal conduction velocities remain always faster. The latencies slightly decrease during the first 18 months of life and then increase very slowly.     

Permanent alterations of spinal cord reflexes following nerve lesion in newborn rats

Sciatic nerve lesion in newborn rats is known to cause degeneration of a large number of axotomized motoneurones and spinal ganglion cells. Some of the surviving motoneurones exhibit abnormal firing properties and the projection pattern of central terminals of sensory neurones is altered. We report here on long-term changes in spinal cord reflexes in adult rats following neonatal nerve crush. In acutely spinalized and anaesthetized adult rats 4-6 months old in which the sciatic nerve had been crushed on one side at birth, the tibial nerve, common peroneal nerve or sural nerve were stimulated on the reinnervated and control side and reflex responses were recorded from the L5 ventral spinal roots. Ventral root responses (VRRs) to tibial and peroneal nerve stimulation on the side of the nerve lesion were significantly smaller in amplitude representing only about 15% of the mean amplitude of VRRs on the control side. The calculated central delay of the first, presumably monosynaptic component of the VRR potential was 1.6 ms on the control side while the earliest VRR wave on the side of the nerve lesion appeared after a mean central latency of 4.0 ms that seems too long to be of monosynaptic origin. These results suggest that neonatal sciatic nerve injury markedly alters the physiological properties and synaptic connectivity in spinal cord neurones and causes a marked depression of spinal cord responses to peripheral nerve stimulation.     

Attenuation of phrenic motor discharge by phrenic nerve afferents

Short latency phrenic motor responses to phrenic nerve stimulation were studied in anesthetized, paralyzed cats. Electrical stimulation (0.2 ms, 0.01-10 mA, 2 Hz) of the right C5 phrenic rootlet during inspiration consistently elicited a transient reduction in the phrenic motor discharge. This attenuation occurred bilaterally with an onset latency of 8-12 ms and a duration of 8-30 ms. Section of the ipsilateral C4-C6 dorsal roots abolished the response to stimulation, thereby confirming the involvement of phrenic nerve afferent activity. Stimulation of the left C5 phrenic rootlet or the right thoracic phrenic nerve usually elicited similar inhibitory responses. The difference in onset latency of responses to cervical vs. thoracic phrenic nerve stimulation indicates activation of group III afferents with a peripheral conduction velocity of approximately 10 m/s. A much shorter latency response (5 ms) was evoked ipsilaterally by thoracic phrenic nerve stimulation. Section of either the C5 or C6 dorsal root altered the ipsilateral response so that it resembled the longer latency contralateral response. The low-stimulus threshold and short latency for the ipsilateral response to thoracic phrenic nerve stimulation suggest that it involves larger diameter fibers. Decerebration, decerebellation, and transection of the dorsal columns at C2 do not abolish the inhibitory phrenic-to-phrenic reflex.     

The peripheral nerves of non-diabetic rats after streptozotocin administration using automatic microscopic image analysis

Electrophysiologic studies of posterior tibial nerves by averaging method and morphometric investigations of sural nerves by automatic image analysis were performed in 7 non-diabetic rats 42 d after the administration of 55 mg streptozotocin/kg b.w. and in 10 untreated controls. Morphometry of stained semithin sections was carried out with system A 6471-AMBA/R (Robotron, Dresden, G.D.R.). There was no decrease of motor nerve conduction velocity in streptozotocin injected animals. The investigated morphometric parameters showed no significant alterations in the streptozotocin group. The studies show that in streptozotocin diabetic rats electrophysiological and morphological alterations of the peripheral nerve are caused by hyperglycemia but not by direct neurotoxic effects of streptozotocin.     

In vivo measurement of conduction velocities in afferent and efferent nerve fibre groups in mice

Electrophysiological investigations in mice, particularly with altered myelination, require reference data of the nerve conduction velocity (CV). CVs of different fibre groups were determined in the hindlimb of anaesthetized adult mice. Differentiation between afferent and efferent fibres was performed by recording at dorsal roots and stimulating at ventral roots, respectively. Correspondingly, recording or stimulation was performed at peripheral hindlimb nerves. Stimulation was performed with graded strength to differentiate between fibre groups. CVs of the same fibre groups were different in different nerves of the hindlimb. CVs for motor fibres were for the tibial nerve (Tib) 38.5±4.0 m/s (Agamma: 16.7±3.0 m/s), the sural nerve (Sur) 39.3±3.1 m/s (12.0±0.8 m/s) and the common peroneal nerve (Per) 46.7±4.7 m/s (22.2±4.4 m/s). CVs for group I afferents were 47.4±3.1 m/s (Tib), 43.8±3.8 m/s (Sur), 55.2±6.1 m/s (Per) and 42.9±4.3 m/s for the posterior biceps (PB). CVs of higher threshold afferents, presumably muscle and cutaneous, cover a broad range and do not really exhibit nerve specific differences. Ranges are for group II 22-38 m/s, for group III 9-19 m/s, and for group IV 0.8-0.9 m/s. Incontrovertible evidence was found for the presence of motor fibres in the sural nerve. The results are useful as references for further electrophysiological investigations particularly in genetically modified mice with myelination changes.     

Parameters of somatosensory evoked potentials in normal subjects in relation to age and height

Cortical SEPs by stimulation of median nerve at wrist (159 measurements; 144 subjects, 63 M - 81 F; mean age 39.7, range 11-70; mean height 162.5, range 134-190) and cortical SEPs by stimulation of posterior tibial nerve at ankle (100 measurements; 81 subjects, 37 M - 44 F; mean age 34.7, range 11-60; mean height 161.1, range 134-180 cm) have been performed. The latencies of N1 of median SEPs and of N1 and P1 of tibial SEPs significantly increase with the height of subjects. The statistical evaluation of latency values of each subject normalized at a height of 165 cm show a little increase of latency according to the age of the subjects; this increase is quite evident for the latency of P1 of tibial SEP.     

The diabetic polyneuropathy. I. Relation between impaired function in peripheral nerves and clinical findings

789 patients with diabetes mellitus were studied by clinical and electroneurographical investigation. Motor and sensory conduction velocities of the median nerve and motor conduction velocity of the tibial nerve were determined. 86.1% of the patients suffered from juvenile diabetes, and 13.9% from maturity onset diabetes. Average duration of the disease was 9.5 years, average age of the patients was 26.7 years. Clinical signs of polyneuropathy were found in 19.1%. In 40.9% of the patients at least one of 3 conduction velocities was found to be delayed. Patients with clinical signs of polyneuropathy exhibited delayed nerve conduction velocities and delayed distal latencies. Diagnosis of polyneuropathy almost with certainty is possible by determining the three nerve conduction velocities and the three corresponding distal latencies. 22% of patients without clinical signs of polyneuropathy exhibited electroneurographical signs of impaired peripheral nerve function. Heredity, body weight, lipid metabolism, actual metabolic balance, and treatment were found to be without any significant influence on nerve conduction velocity.     

An alternative to the classical nerve graft for the management of the short nerve gap

Reconstruction of a short nerve gap by a nerve graft produces donor-site scarring, loss of donor nerve function, and neuroma formation. This study compared the regeneration achieved after 1 year in 16 monkeys across a 3-cm upper arm ulnar nerve gap with a bioabsorbable polyglycolic acid nerve conduit with the regeneration achieved with a classical interfascicular interpositional sural nerve graft. The results demonstrated electrophysiologic and histologic evidence of neural regeneration across the gaps in all experimental groups. The bioabsorbable nerve conduit groups and the sural nerve graft group had mean fiber diameters, amplitudes, and conduction velocities each significantly less than those of normal control ulnar nerves. There was, however, no significant difference between any of the experimental groups. Electromyography demonstrated recovery of 19 of the 28 (68 percent) intrinsic muscles studied. These results demonstrate that the primate peripheral nerve can regenerate across short nerve gaps when guided by an appropriate nerve conduit, suggesting that a single-stage biodegradable polyglycolic acid conduit may be used as an alternative to a short interfascicular nerve graft.     

Treatment of diabetic polyneuropathy with the antioxidant thioctic acid (alpha-lipoic acid): a two year multicenter randomized double-blind placebo-controlled trial (ALADIN II). Alpha Lipoic Acid in Diabetic Neuropathy.

Short-term trials with the antioxidant thioctic acid (TA) appear to improve neuropathic symptoms in diabetic patients, but the long-term response remains to be established. Therefore, Type 1 and Type 2 diabetic patients with symptomatic polyneuropathy were randomly assigned to three treatment regimens: (1) 2 x 600(mg of TA (TA 1200), (2) 600)mg of TA plus placebo (PLA) (TA 600) or (3) placebo and placebo (PLA). A trometamol salt solution of TA of 1200 or 600 mg or PLA was intravenously administered once daily for five consecutive days before enrolling the patients in the oral treatment phase. The study was prospective, PLA-controlled, randomized, double-blind and conducted for two years. Severity of diabetic neuropathy was assessed by the Neuropathy Disability Score (NDS) and electrophysiological attributes of the sural (sensory nerve conduction velocity (SNCV), sensory nerve action potential (SNAP)) and the tibial (motor nerve conduction velocity (MNCV), motor nerve distal latency (MNDL)) nerve. Statistical analysis was performed after independent reviewers excluded all patients with highly variable data allowing a final analysis of 65 patients (TA 1200: n = 18, TA 600: n = 27; PLA: n = 20). At baseline no significant differences were noted between the groups regarding the demographic variables and peripheral nerve function parameters for these 65 patients. Statistically significant changes after 24 months between TA and PLA were observed (mean +/- SD) for sural SNCV: +3.8 +/- 4.2 m/s in TA 1200, +3.0+/-3.0m/s in TA 600, -0.1+/-4.8m/s in PLA (p < 0.05 for TA 1200 and TA 600 vs. PLA); sural SNAP: +0.6+/-2.5 microV in TA 1200, +0.3+/-1.4 microV in TA 600, -0.7 +/- 1.5 microV in PLA (p = 0.076 for TA 1200 vs. PLA and p < 0.05 for TA 600 vs. PLA), and in tibial MNCV: +/- 1.2 +/- 3.8 m/s in TA 1200, -0.3 +/- 5.2 m/s in TA 600, 1.5 +/- 2.9 m/s in PLA (p < 0.05 for TA 1200 vs. PLA). No significant differences between the groups after 24 months were noted regarding the tibial MNDL and the NDS. We conclude that in a subgroup of patients after exclusion of patients with excessive test variability throughout the trial, TA appeared to have a beneficial effect on several attributes of nerve conduction.     

Diabetic polyneuropathy. 3. Electroneurographic findings in diabetics and their relationships to age and duration of diabetes

Nerve conduction velocities were determined in patients with diabetes mellitus: motor conduction of the median nerve in 778 patients, sensory conduction of the median nerve in 680 patients and motor conduction of the tibial nerve in 745 patients. In 40.9% out of 778 patients at least one of the three nerve conduction velocities were found within pathological ranges. 30.4% of 227 patients below 19 years of age in whom the duration of the disease did not exceed four years exhibited at least one delayed nerve conduction velocity. Clinical signs of polyneuropathy in children and in adolescents below 19 years of age are rare (0.6%). In contrast delayed nerve conduction velocities were found in 29.4%. Metabolic disturbance of peripheral nerve function is assumed to be responsible in these patients, for angiopathy in children and adolescents is very rare too.     

Epidural recordings of electrical events produced in the spinal cord by segmental, ascending and descending volleys

Epidural electrodes implanted for a percutaneous trial of therapeutic spinal cord stimulation were used to record electrical events evoked by the stimulation of peripheral nerves or of the spinal cord itself. The data collected in patients with no neurological deficit were analyzed in order (1) to check the consistency between epidural and surface recordings, (2) to get information on the genesis of such potentials, and (3) to demonstrate the feasibility of complex neurophysiological studies by means of epidural electrodes. Spinal cord potentials evoked by segmental volleys were recorded at cervical levels with the recording electrodes anterior, lateral and posterior to the spinal cord. The refractory period of the evoked potentials has been studied as well. Responses to stimulation of the tibial nerve were obtained at T11-12 vertebral level with posterior epidural electrodes. Segmental cervical potentials were characterized by a P10, N11, N13/P13 followed by a slow positivity/negativity. A response of similar waveform, but with different peak latencies, was recorded at segmental levels following tibial nerve stimulation. Such a response showed an increasing number of spikes while ascending along the spinal cord. Maximum conduction velocities in the cord were between 65 and 85 m/s. Our epidural recordings are similar to those obtained from the skin, but with a greater amplitude and waveform resolution. Furthermore, the use of epidural electrodes made it feasible to perform complex examinations of sensory function (i.e., the study of orthodromic and antidromic conduction along the dorsal cord and of the influence of a single dorsal cord volley on the segmental cervical potential). Finally, the genesis of the potentials recorded is discussed.