Effects of time and tasks upon auditory and somatosensory evoked potentials in man.

Auditory evoked potentials (AEPs) recorded from the vertex and somatosensory evoked potentials (SEPs) recorded from the somatosensory and motor areas and vertex were examined during visual and auditory discrimination tasks, with and without motor responses, and during motor tasks alone in normal human subjects. These procedures allowed the separation of sensory discrimination from motor activity effects on the evoked potentials. It was observed that EPs were modified systematically by task and by temporal variables, even though vigilance, as evaluated through EEG recording and performance level, was stable throughout the experimental recording session. 1. AEPs were minimally influenced by time, but very sensitive to task. Inversely, the SEP amplitude decreased considerably with time and less with task. There was evidence of time/task interaction. 2. The magnitude of SEP attenuation in time was reduced by intervening rest periods. 3. The sensory modality in which the discrimination task was performed did not influence the effect on EPs. A discrimination task involving a motor response reduced EPs more than a pure discrimination or a pure motor task. The task effect seems to involve a general, mechanism (load imposed upon the subject) not dependent on the particular sensory channel used to deliver task-relevant information.     

Temperature-dependent hysteresis in somatosensory and auditory evoked potentials.

Fourteen adult patients undergoing open heart surgery under induced hypothermia had median nerve, short-latency somatosensory evoked potentials (SSEPs) recorded during cooling (from 36 degrees C to 19 degrees C) and subsequent rewarming. Similar data on another group of patients who had brain-stem auditory evoked potentials (BAEPs) were also analyzed. Hypothermia produced increased latencies of the major SSEP and BAEP components and the latencies returned to normal with subsequent warming. The temperature-latency relationship during the cooling phase was significantly different from that during the warming phase. For SSEP components the temperature-latency relationship was linear during cooling and curvilinear during warming, whereas for BAEP it was curvilinear both during cooling and warming. Furthermore, the regression curves were different during the two phases of temperature manipulation, particularly for temperatures below 30 degrees C both for SSEP and BAEP components. At the onset of warming there was an initial exaggerated warming response on the evoked potential (EP) latencies and amplitude of the EP components. The temperature-latency regression curves were uniformly less steep during the warming phase compared to those during cooling. These findings suggest the existence of hysteresis in the relationship between temperature and EP latencies. The latencies at a given temperature below 30 degrees C depend on whether that temperature is reached during cooling or during warming.     

Proprioceptive modulation of somatosensory evoked potentials during active or passive finger movements in man.

The effects of active and passive finger movements on somatosensory potentials evoked by stimulation of the median nerve at the wrist or of finger I were investigated in 15 healthy volunteers. As compared to the resting condition, both active and passive movements of the stimulated hand fingers induced a marked reduction in the amplitude of the primary cerebral response (N20-P25 complex) as well as of the N17 SEP component, which is supposed to reflect the activity of the thalamo-cortical radiation. The following cerebral SEP components, within 100 ms after the stimulus, were also depressed during motor activity. Neither N11 nor N13 components of the cervical response, reflecting the activation of dorsal columns and dorsal column nuclei respectively, were modified. The SEP changes induced by active or passive movements were absent after ischaemic block of large group I afferent fibers from the hand, thus suggesting the relevance of the feedback generated by such peripheral afferents during movement. The results indicate that the activation of peripheral receptors (probably muscle spindle endings) during both active and passive finger movement would induce a gating effect at both cortical and subcortical (thalamic) level, which might modulate selectively the different sensory inputs to the cortex.     

Influence of magnetic resonance imaging on somatosensory and brain-stem auditory evoked potentials in man

Summary There is still a need to prove that even static magnetic fields up to 1.5 T used in magnetic resonance imaging (MRI) are biologically safe and harmless for humans. Recordings of median and ulnar nerves and brain-stem auditory evoked potentials in 20 patients were completed prior to and after MRI investigation of the central nervous system. Neither the somatosensory nor the auditory evoked potentials exhibited any significant change of latencies, interpeak latencies or amplitudes. Since these electrophysiological parameters are highly dependent on the quality of nerve conduction and integrity of information processing in various nuclei, it may be assumed that MRI causes no lasting changes in either respect.     

Thalamic evoked potentials to somatosensory stimulation in man.

Thalamic somatosensory evoked potentials (ThSEPs) were recorded by averaging technique from various thalamic structures during 59 stereotactic operations. From 372 records, response patterns and latency characteristics were analysed in relation to the intrathalamic localization. The findings can be summarized as follows. In N. ventro-caudalis (VC) and ventro caudalis parvocellularis (Vcpc) ThSEPs showed the most definite (and exclusively contralateral) responses characterized by a single positive (P1) deflection. The latency was shortest in VC (mean value, 17.5 msec) and in Vcpc (15.6 msec). Responses from N. centrum medianum (CM), parafascicularis (Pf) and limitans (Lim) were composed of early P1-N1 and of later P2-N2 components. The P1 latency was relatively consistent, with a mean value of 28.2 msec. Pulvinar responses showed a pattern similar to CM, with a mean P1 latency at 30.5 msec. Responses of N. dorsalis medialis (DM) were small, variable and longest, with a mean P1 latency of 54.2 msec. To ipsilateral stimulation, CM, Pul, DM and N. ventro-lateralis (VL) showed comparable wave forms. The possible role of the CM-Pf-Lim complex and of Pulvinar in the "extra-lemniscal" sensory system was considered. The usefulness of ThSEP recording to identify electrode locations in the thalamus is thus confirmed.     

The scalp topography of human somatosensory and auditory evoked potentials.

The waveform and topography of components of the scalp recorded somatosensory evoked poal (AEP) to click stimulation of the right ear, were determined for scalp electrode locations of the 10-20 system and for locations at the eye, mastoids, and posterior neck. Twenty-one SEP and twenty-two AEP components were analyzed. Differentiation of neurogenic and myogenic components was attempted on the basis of localization and variability. Some components of extracranial origin, apparently originating in frontal musculature, were small in most experienced subjects and large in most experimentally naive subjects. These and other presumptive myogenic potentials can distort adjacent neurogenic components. These data should aid in predicting SEP and AEP characteristics and in assessing myogenic distortion of neurogenic components.     

Magnetic stimulation motor evoked potential in multiple sclerosis. Comparison with visual evoked potentials, brain stem auditory evoked potentials and somatosensory evoked potentials]

This study consists of 45 patients with clinically definite MS, laboratory supported definite MS and clinically probable MS. We compared MEP results with other multimodal evoked potentials (VEP, BAEP and SEP). The abnormal rate of MEP was 87.6%, which was the highest. Abnormal MEP showed prolonged central motor conduction time (CMCT), consistent with pathological change of the demyelination. There was a evident correlation between the abnormal MEP and VEP, which is consistent with the most common MS (Devic Syndrome) in our country.     

Brain stem auditory, visual and somatosensory evoked potentials in leukodystrophies

Brain stem auditory (BAERs), visual (VEPs) and somatosensory evoked responses (SEPs) were recorded in 12 patients with Pelizaeus-Merzbacher leukodystrophy (PMD), three with adrenoleukodystrophy (ALD) and three with metachromatic leukodystrophy (MLD). All the 3 evoked responses were abnormal in all patients except normal VEPs and SEPs in a patient with early ALD. In most patients wave I with and without wave II were the only components of the BAERs that remained, subsequent components (waves III-VII) were absent. VEPs were severely altered; either no identifiable response to flash or pattern reversal stimuli could be recorded or the major components were significantly delayed in latency. Short latency SEPs following median nerve stimulation usually showed a normally recorded Erb's potential (N10), but an absence or marked attenuation of cervical (N14) and early scalp components (N19 and P22) or the occurrence of the scalp components with a significant delay. Multimodality evoked responses provide more information regarding the functional integrity of several afferent systems in patients with white matter disorders.     

Brainstem auditory and somatosensory evoked potentials in neuro-Beh?et's syndrome

Brainstem auditory evoked potentials (BAEPs) and somatosensory evoked potentials after median nerve stimulation (MN-SEPs) and after posterior tibial nerve stimulation (PTN-SEPs) were studied in 17 patients with neuro-Beh?et's syndrome (NB). Eleven patients (64.7%) showed an absence of wave I, III or V or a prolongation of the interpeak latency I-III, or III-V in BAEPs. Six patients (37.4%) showed a prolongation in the latency of cortical P37 of PTN-SEPs and/or the interpeak latency EP-N13 or N13-N18 of MN-SEPs. The BAEP and SEP abnormalities indicated a conduction failure of the acoustic lateral lemniscus pathway and the medial lemniscus pathway in the brainstem of the patients with NB. Abnormal EPs can provide sensitive information which shows the presence of subclinical lesions in the central nervous system.     

听觉诱发电位及体感诱发电位在颅脑外伤致昏迷患者的应用

严重颅脑损伤昏迷患者脑功能的监测是判断预后和指导治疗的重要手段。听觉诱发电位(BAEP)及体感诱发电位(SSEP)因其方便、无创并能连续实时监测昏迷患者相关神经传导通路电生理的变化,间接反映脑干上行激活系统、大脑皮层结构与功能的完整性,越来越成为临床对严重颅脑损伤昏迷患者预测预后和指导治疗的重要手段。本文就近年来相关研究进行综述,旨在指导临床实践。     

Pain-Related somatosensory evoked potentials.

The authors reviewed basic and clinical reports of pain-related somatosensory evoked potentials (SSEP) after high-intensity electrical stimulation [pain SSEP(E)] and painful laser stimulation [pain SSEP(L)]. The conduction velocity of peripheral nerves for both pain SSEP(E) and pain SSEP(L) is approximately 10 to 15 m/second, in a range of Adelta fibers. The generator sources are considered to be the secondary somatosensory cortex and insula, and the limbic system, including the cingulate cortex, amygdala, or hippocampus of the bilateral hemispheres. The latencies and amplitudes are clearly affected by vigilance, attention-distraction, and various kinds of stimulation applied simultaneously with pain. Abnormalities of pain SSEP(L) reflect an impairment of pain-temperature sensation, probably relating to dysfunction of A5 fibers of the peripheral nerve and spinothalamic tract. In contrast, conventional SSEP after nonpainful electrical stimulation reflects an impairment of tactile, vibratory, and deep sensation, probably relating to dysfunction of Aalpha or Abeta fibers of the peripheral nerve and dorsal column. Therefore, combining the study of pain SSEP(L) and conventional SSEP is useful to detect physiologic abnormalities, and sometimes subclinical abnormalities, of patients with peripheral and central nervous system lesions.     

Portal-systemic encephalopathy: alterations in somatosensory and brainstem auditory evoked potentials

Median somatosensory and brainstem auditory evoked potentials (SEP and BAEP) were studied in 40 patients with liver cirrhosis consequent to chronic viral hepatitis. The patients were divided into 4 groups: group 1 with liver cirrhosis only, group 2 with hepatic failure (HF), group 3 with grade 1 or 2 hepatic encephalopathy (HE), and group 4 with grade 3 or 4 HE. The control group consisted of 10 age-matched normal subjects. The major changes occurred in the median cortical SEP late components (peaks after N20 and P25). From group 1 to group 4, there were progressive prolongation and sequential disappearance of the late components. Those changes in the cortical SEPs were reversible. The subcortical somatosensory and brainstem auditory conductions (SEP N13-N20 and BAEP I-V interpeak latencies) were slightly prolonged in all groups of patients. The present data indicate that SEP may be useful in detecting subclinical HE and in monitoring the clinical course of HE. The present data further indicate that chronic portal-systemic shunting in liver cirrhosis may result in a minimal impairment of cerebral function and sensory conduction in the CNS.     

Somatosensory evoked potentials after removal of somatosensory cortex in man

Somatosensory evoked potentials (SEPs) to median nerve, ulnar nerve, thumb, middle finger, and posterior tibial nerve stimulation were recorded in a patient with a discrete resection of part of the postcentral somatosensory cortex as a treatment for focal epilepsy. Comparison of the different stimulation sites confirmed electrophysiologically the restricted locus of the lesion. The results strongly suggest that the early negative component (N20) and subsequent components recorded postcentrally are of cortical origin and depend upon postcentral gyrus cytoarchitectonic areas 3, 2, and 1. Moreover, these postcentral SEPs are distinct from precentrally recorded activity.     

Early somatosensory evoked potentials.

The early somatosensory evoked potential secondary to median nerve stimulation in the human had an onset latency of 9--12 msec when recorded from scalp electrodes at vertex-to-mastoid, vertex-to-inion or at the base of the skull. Similar latencies were observed from responses recorded over the cervical dorsal columns during neurologic surgery. A latency difference of 1.5 msec was observed between the early response and the responses recorded from the junction of medial lemniscus and nucleus ventralis posterior lateralis of the thalamus during human stereotaxic surgery. Cervical cord transections and transection at the midpontine levels of the monkey showed that the evoked potential was due to generators between these levels. Depth recording of the monkey indicate that the early evoked potential originates in the region of dorsal column nuclei, while the later components are secondary to generators in cerebral cortex.     

Scalp topography of mechanically and electrically evoked somatosensory potentials in man

Scalp topography of somatosensory evoked potentials following mechanical (SEPs(M)) and electrical (SEPs(E)) stimulation of the left middle finger was investigated with linked ear reference in 21 normal young adults. A small plastic ball (touch) or needle (pain) was used for the mechanical stimulation. With mechanical stimulation, at least 3 positive and 3 negative potentials (P19(M), N24(M), P29(M), N36(M), P49(M) and N61(M] were found in the post-rolandic area contralateral to the stimulation. The wave form in SEPs(M) was similar to those in SEPs(E), but the peak latency of each component in SEPs(M) was 1-4 msec longer than that in SEPs(E). Earlier components such as P19(M), N24(M) and P29(M) were not as clearly recognized as corresponding components in SEPs(E). However, the wave form recorded on the hemisphere ipsilateral to the stimulation or in the frontal area contralateral to the stimulation showed a greater difference from subject to subject. P19(M), N24(M) and P29(M) correlated positively both with arm length and height of the subject. There was no significant difference of the wave form between the linked ear reference and the bipolar (C4-Fz) derivation. Wave form of SEPs(M) by needle stimulation did not significantly differ from that by plastic ball stimulation.     

Temporal variability of somatosensory, visual, and auditory evoked potentials in schizophrenia.

Previous findings in chronic schizophrenics showed greater than normal somatosensory evoked potential (SEP) waveshape stability before 100-ms after stimulus and reduced stability after 100 ms. To confirm and extend these findings, EPs to left and right median nerve stimuli, visual pattern flashes (VEPs), and auditory clicks (AEPs) were recorded from 14 locations in 86 patients and 33 controls. Three sets of analyses compared different patient groups with age- and sex-matched controls. The results confirmed previous SEP findings in chronic schizophrenics; no other subject group displayed the combination of high early and low late SEP stability. The SEP results did not generalize to VEPs and AEPs. Lead location was important for group differences. In overt schizophrenics, late epoch stability was low in all EPs. The results suggest certain limitations to the hypothesis of an impaired subcortical filtering mechanism in chronic schizophrenics.     

Effect of endothelin on somatosensory evoked potentials in rats.

The effects of endothelin 1 (ET-1; 300 pmol/rat intracarotid) on somatosensory evoked potential were investigated in rats. ET-1 led to an amplitude reduction, peak latency prolongations and waveform disturbances. There was a large interindividual variability. The late cortical components were more affected than the earlier potentials at a thalamic or cortical level. ET-1-induced SEP changes developed quickly after the drug injection and persisted for at least 30 min. It is assumed that the observed effects probably reflect the occurrence of a progressively developing ischemia subsequent to ET-1 administration. Moreover, the pattern of ET-1-induced changes suggests a greater sensitivity of the synaptic transmission to the ischemic influence than the axonal conduction.     

Developmental and aging changes in somatosensory, auditory and visual evoked potentials

To assess developmental and aging changes in human sensory systems, components of short-latency somatosensory, brain-stem auditory and pattern-reversal visual evoked potentials, thought to originate in specific structures of these systems, were recorded in 286 normal subjects ranging in age from 4 to 95 years. Analysis was primarily restricted to peak and interpeak latencies; visual evoked potential amplitudes were also analyzed. Major results and conclusions are: (1) 'Developmental' changes (that is, decreases in latency attributable to decreased conduction time in younger subjects) were not seen in the median nerve, in brain-stem auditory pathways, or in some portions of visual cortex. Small developmental changes were seen in the somatosensory afferent pathway from the cervical spinal cord to thalamus, and large changes were seen in somatosensory and visual cortex. Cortical developmental changes appeared not to be complete until 17 years of age or later. (2) 'Aging' changes (that is, increases in latency attributable to increased conduction time in older subjects) were observed in the median nerve, cervical spinal cord, brain-stem auditory pathways, and somatosensory and visual cortex. (3) Visual evoked potential amplitudes tended to decrease with age, particularly during development; amplitude and latency effects were dissimilar for most components. (4) Males tended to show larger aging effects than females. (5) The results suggest that age-related changes in human sensory systems are not uniform, but rather are different in specific portions of these systems, different at particular epochs of the life span, and stronger in males than in females.     

Effect of diazepam on somatosensory evoked potentials

Somatosensory evoked potentials (SEP) were recorded in 15 patients with extrapyramidal disturbances after intravenous administration of 10 mg of diazepam (Relanium, Polfa). Cortical SEP were recorded before and after operations and thalamic SEP were recorded during stereotaxic interventions on thalamic nuclei VL and Vim. The results demonstrated that diazepam had a significant positive influence on the recording of SEP, eliminating muscular artifacts caused by increased muscular tonus and extrapyramidal tremor. Diazepam had no evident effect on the SEP and caused no changes of the short-latency specific cortical SEP. This effect was, however, evident on the later components of the SEP and it seemed to affect mainly the N63 wave whose amplitude was always reduced or absent. In the postoperative investigations the cortical SEP in the hemisphere operated on (contralateral to the site of stimulation) were reduced in the phase of short-latency components. In the ipsilateral hemisphere the cortical SEP remained similar to the normal ones, and after diazepam their amplitude was markedly reduced. Intraoperatively recorded thalamic SEP showed after diazepam a considerable decrease of the amplitude of all components, sometimes the curve was completely flat, including the specific phase of the potential. On the other hand, diazepam failed to extinguish cortical SEP which showed even a greater amplitude of short-latency and long-latency components than in the records obtained without this drug, with the exception of disappearing N63 component.     

Short-latency somatosensory and brainstem auditory evoked potentials in patients with Parkinson's disease

Short-latency somatosensory evoked potentials (SSEPs) and brainstem auditory evoked potentials (BAEPs) were recorded in 44 patients with Parkinson's disease (mean age 67.3 years) and 23 normal subjects (mean age 69.3 years). Patients with Parkinson's disease and normal subjects did not show any significant difference with regard to the interpeak latencies between N13 and N20 central conduction time (CCTs). Likewise, there were no significant differences in CCTs between patients with and without dementia. The interpeak latencies between waves I and V (I-V IPLs) in patients with Parkinson's disease were significantly longer than those of the normal subjects (p less than 0.05). In particular, patients with dementia revealed significant prolongation of I-V IPLs compared to patients without dementia and normal subjects (p less than 0.01, p less than 0.001) although no significant differences were observed between patients without dementia and normal subjects. These results show that auditory brainstem pathways are involved in Parkinson's disease patients with dementia.