The assessment of severe head injury by short-latency somatosensory and brain-stem auditory evoked potentials

The relative prognostic value of short-latency somatosensory evoked potentials (SEPs) and brain-stem auditory evoked potentials (BAEPs) was assessed in 35 patients with post-traumatic coma. Analysis of the evoked potentials was restricted to those recorded within the first 4 days following head injury. Abnormal SEPs were defined as an increase in central somatosensory conduction time or an absence of the initial cortical potential following stimulation of either median nerve. Abnormal BAEPs were classified as an increase in the wave I–V interval or the loss of any or all of its 3 most stable components (waves I, III and V) following stimulation of either ear. SEPs reliably both good and bad outcomes. All 17 patients in whom SEPs were graded as normal had a favourable outcome and 15 of 18 patients in whom SEPs were abnormal had an unfavourable outcome. Although abnormal BAEPs were associated with an unfavourable outcome in almost all patients (6 of 7), only 19 of 28 patients with normal BAEPs had a favourable outcome. The finding of normal BAEPs was therefore of little prognostic significance. These results confirm the superiority and greater sensitivity of the SEP in detecting abnormalities of brain function shortly after severe head trauma.     

痛觉诱发电位的研究进展

痛觉诱发电位的研究在过去的几十年内取得了重要进展 ,出现了许多用于被试的诱发明确疼痛感的刺激技术 ,并与诱发电位方法学联合应用 ,已经成为脑映像学研究中重要的组成部分。本文从刺激技术、痛觉诱发电位成分分析和偶极子源分析等方面出发 ,讨论了痛觉诱发电位的研究进展     

Parkinson's disease and aging: Changes of somatosensory evoked potentials in humans

Somatosensory evoked potentials (SSEP) elicited by electrical stimulation of the median nerve were compared in patients with Parkinson's disease and individuals without clinical manifestations of extrapyramidal insufficiency (46 and 55 persons, respectively). The amplitude of the N31 component was found to diminish in Parkinsonian patients while the latency of the P44 component increased significantly. In addition, these parameters depended on the age of the tested subjects; the direction of age-related changes of the N31 and P44 components coincided with those typical of parkinsonism. Our findings seem to suggest that changes in the somatic afferentation caused by Parkinson's disease and aging are of the same type and depend on disturbances in the nigrostriatal dopaminergic system.Neirofiziologiya/Neurophysiology, Vol. 26, No. 3, pp. 141–145, March–April, 1994.     

Reorganization of the pattern of the brain somatosensory evoked potentials after spinal cord injury

Recordings of somatosensory evoked potentials (SEPs) and SEP brain maps of 23 patients with vertebral injury were analyzed. All patients were operated at the Clinic of Military Traumatology and Orthopedics, Military Medical Academy. SEPs (19 sites) were recorded in real time and mapped with "Brain surveyor" neuromapper. Brain lesions were localized before surgery by of MR imaging and CT standard techniques. The results demonstrate that electrical stimulation of peripheral nerves produces a substantially variable SEP pattern. It was shown that SEP formation in more than 60% of recordings suggests a favorable prognosis for rehabilitation, whereas if more than 50% of recording sites are unresponsive, the rehabilitation prognosis is unfavorable. The amplitude of early components (below 60 ms) increases, and that of the late waves reduces.     

Time-frequency component analysis of somatosensory evoked potentials in rats

Background  

Somatosensory evoked potential (SEP) signal usually contains a set of detailed temporal components measured and identified in a time domain, giving meaningful information on physiological mechanisms of the nervous system. The purpose of this study is to measure and identify detailed time-frequency components in normal SEP using time-frequency analysis (TFA) methods and to obtain their distribution pattern in the time-frequency domain.     

Development of cortical somatosensory evoked potentials in rats.

The development of the contra- and ipsilateral cortical potential evoked by electrical sciatic nerve stimulation was studied in 77 male albino rats aged 5 to 45 days. A contralateral response was already recorded, as double negativity, in the youngest animals, while an ipsilateral evoked potential was not reliably present until the 10th day. At this time, however, both responses started with an inconstant positive wave and their shape was practically the same. During subsequent development the responses differed only in respect to their dominant component: in the contralateral response, the N1 wave had the highest amplitude for most of the time, while in the ipsilateral response the delayed N2 wave was the largest component. The latent periods of contralateral responses were somewhat shorter than those of ipsilateral evoked potentials. During development we noticed a phase of abrupt shortening of the latent period, which took place before the 15th day in the contralateral response and before the 20th day in the ipsilateral response. We also found a difference in the fatigability of the responses, which was greater in immature rats than in adult animals; in the ipsilateral evoked potential it approached adult values more slowly. The development of the ipsilateral response is thus delayed compared with the development of the contralateral response.     

Prognostic value of p53 overexpression in head and neck carcinomas: a pilot study

OBJECTIVE: To correlate p53 overexpression in squamous cell carcinoma of the head and neck region with the outcome of treatment. STUDY DESIGN: Twenty-five biopsy-proven squamous cell carcinomas of the head and neck region, locally advanced and untreated, were studied. Before treatment, all patients underwent fine needle aspiration from primary and/or metastatic lesions. Smears were prepared from the aspirate for immunostaining, and p53 overexpression was measured semiquantitatively. All patients received a radical dosage of radiation equivalent to 60 Gy for 6 weeks in 30 fractions from a 6-MV linear accelerator. Local-regional disease control was studied, and the mean follow-up duration was one year. The pretreatment values of p53 overexpression were correlated with the outcome of treatment. RESULTS: Overexpression of p53 was found in 36% patients. At the end of 1 year, 6/9 patients showing overexpression were disease free as compared to 5/16 patients without overexpression. The difference was not significant (chi2 test, P>.05). CONCLUSION: Response to radiation therapy is not dependent on p53 overexpression in squamous cell carcinoma of the head and neck region. However, this was only a pilot study, and a large number of cases are needed to establish the prognostic value of p53 overexpression in locally advanced head and neck squamous cell carcinoma.     

Prognostic value of visual evoked potentials in occipital blindness following basilar artery occlusion.

Three patients suffering from sudden occipital blindness following basilar artery occlusion underwent electroretinography and visual evoked potential (VEP) examinations. The VEPs performed early in those blind patients and repeated later seem to be of prognostic value. Responses of normal shape and amplitude after monocular and binocular stimulation were followed by complete recovery of vision. Unequal and subnormal VEPs obtained following monocular stimulation, and even smaller responses reached after binocular stimulation, accompanied permanent unilateral occipital damage resulting in homonymous hemianopsia. Lack of VEP was proved to be a preceding sign of permanent blindness.     

Age-dependent changes of short-latency somatosensory evoked potentials in healthy adults

Age-dependent changes of short-latency somatosensory evoked potentials following median nerve stimulation in humans were investigated in two groups of healthy adults aged 20-30 and 50-60 years. Normative values for both age groups are given. Compared to the younger group, in the older one P27 latency and N20-P27 interpeak latency were about 2 ms longer, and P27-N35 and P27-P45 interpeak latencies were significantly decreased. These findings suggest that N20 and P27 are generated by different structures and that the subsequent components do not depend on P27.     

Naloxone decreases diurnal variation in pain sensitivity and somatosensory evoked potentials

A group of 35 normal subjects had somatosensory evoked potentials (EPs) recorded and were tested on a psychophysical pain judgment task in morning and afternoon sessions. Subjects tested in the morning were found to be significantly less pain sensitive than those tested in the afternoon on psychophysical judgments. EP measures were consistent with decreased sensitivity in the morning. In a second experiment, a group of 12 normal subjects also received naloxone (2 mg, iv) in a double blind trial, 6 in the morning and 6 in the afternoon. Naloxone hyperalgesia effects on the EP were present in the morning and absent in the afternoon. It has been recently demonstrated that beta-lipotropin, a possible precursor of the endogenous opiate beta-endorphin shares with ACTH a diurnal rhythm. Our results are consistent with the hypothesis that endorphins at least partially mediate diurnal variations in pain appreciation.     

Recovery function of somatosensory evoked potentials in juvenile myoclonic epilepsy*

Abstract

Objective: We analysed the recovery function of somatosensory evoked potentials (SEPs) in juvenile myoclonic epilepsy (JME) patients. We hypothesized that there may be disinhibition in the recovery of SEPs at 20–100?ms intervals in JME patients.

Methods: We recorded SEPs and SEP recovery in 19 consecutive patients with JME admitted for a routine follow-up examination, and in a control group composed of 13 healthy subjects who were similar to the patient group regarding age and sex. The recovery function of SEPs was examined using paired stimuli at 30, 40, 60, and 100?ms intervals.

Results: The amplitudes of N20-P25 and P25-N33 components were higher in patients with JME. Ten patients had high-amplitude SEPs. By paired stimulation, there was inhibition of SEPs in both groups. The mean recovery percentages of N20-P25 and P25-N33 components at 30, 40, 60, and 100?ms were not different between healthy subjects and patients with JME.

Conclusions: The recovery function of SEP is normal in JME even in the presence of high-amplitude SEPs.     

Effect of body and foot positions on the somatosensory evoked potentials

Somatosensory evoked potentials in response to stimulation of the posterior tibial nerve at the ankle were recorded during sitting and standing with variable foot positions. During standing a decrease in the amplitude of the early positive component was observed. The deviation of the foot from a horizontal position was associated with an increase in the amplitude of the early negative component. The combined influence of body and foot positions showed a decrease in the amplitude of both early and late components. The standing position induced changes in more components than the varied foot positions. This suggests that maintenance of the standing posture is a more complex task than the maintenance of the foot position itself.     

Effect of selective attention on somatosensory evoked potentials in healthy people

The effect of selective attention on various waves of the somatosensory evoked potentials was studied in healthy people in the area of specific projection (sensorimotor) and the area of non-specific projection (occipital). Significant changes of the amplitude of waves with latency exceeding 55 msec were observed when attention was concentrated on the received stimulus (I and II group of subjects). In group I the process of attention concentration was associated with a phenomenon connected with the new yet unknown experimental situation (prevalence of amplitude increase), while in group II habituation was observed (prevailing amplitude fall). Waves M125 and N200 in the sensorimotor area and N200 and N235-255 in the occipital area seemed to be associated in a peculiar way with the process of attention concentration.     

Age-related dynamics of the parameters of somatosensory evoked potentials in healthy children

The purpose of this study was to evaluate the parameters of somatosensory evoked potentials (SSEPs) in healthy children of different age groups (n = 94). The amplitudes of the main cortical peaks and the central sensory conduction time (CSCT) from n. medianus and n. tibialis in children aged under 12 months, 1–12 years, and 12–17 years were estimated and compared. No significant cortical peaks were recorded from the tibial nerve in five children younger than 1 year (5 out of 23, 22%). Significant differences in CSCT were observed between the children younger than 1 year and two other groups. The amplitudes did not significantly differ between the groups. Thus, SSEPs may be used for the evaluation of somatosensory pathways in children aged one month to 17 years. CSCT differs significantly between children younger than 1 year and other age groups. Age-related reduction in CSCT and elevation of the cortical peak amplitudes may reflect the myelination of somatosensory pathways and the improvement in nervous system integration.     

Localization of sensorimotor cortex in neurosurgery by recording of somatosensory evoked potentials

The current method of localizing somatosensory and motor cortex during neurosurgical removal of abnormal tissue is Penfield's method of cortical stimulation. While useful, this method has drawbacks, in particular the need to operate under local anesthesia. Another method of localization, described here, involves intra-operative recording of short-latency somatosensory evoked potentials to stimulation of the contralateral median nerve, from electrodes placed directly on central cortex. Proper localization involves identification of potentials which invert in polarity across the central sulcus, identification of other potentials which are largest in the medial portion of the hand area of somatosensory cortex and do not polarity invert, and determination of the region of maximal potential amplitude. This method of localization works equally well whether the patient is under local or general anesthesia, but it occasionally fails in patients with tumors abutting or invading the hand area of sensorimotor cortex.