The effect of thiopentone on somatosensory evoked responses and EEGs in comatose patients.

EEGs and somatosensory evoked responses from the brachial plexus, neck and scalp were recorded in seven comatose patients on continuous thiopentone infusion. Although pathological in five of the patients, the evoked responses were present in all. Additional amounts of thiopentone producing a full suppression of all spontaneous EEG activity had no effects either on the configuration of the evoked responses or on the central conduction times. This resistance of the somatosensory evoked responses to a deep and sustained thiopentone narcosis makes it a useful test in comatose patients receiving this treatment.     

Polysensory evoked potentials in rat parietotemporal cortex: combined auditory and somatosensory responses

A 64 channel microelectrode array was used to map auditory evoked potentials (AEP), somatosensory evoked potentials (SEP) as well as combined auditory and somatosensory evoked potentials (ASEP) from a 7 × mm² area in rat parietotemporal neocortex. Cytochrome oxidase (CO) stained sections of layer IV were obtained in the same animals to provide anatomical information underlying epicortical field potentials. Epicortical responses evoked by click or vibrissa stimuli replicated earlier findings from our laboratory, and appeared as a family of waveforms centered on primary auditory (AI) or somatosensory (SI) cortical areas as determined from CO histology. Selective microinjections of HRP to AI and SI further confirmed their specific sensory relay nuclei in the thalamus. A small polysensory area between AI and SI, responded uniquely with an enhanced negative sharp wave to combined auditory and somatosensory stimuli. HRP retrograde labeling revealed that the thalamocortical projections to this area were from the posterior nuclear group (Po) and medial division of the medial geniculate (MGm). These data establish close relationships between epicortical AEP, SEP, and especially ASEP and corresponding cortical structures and thalamocortical projections. The neurogenesis of unimodal and polysensory evoked potentials is discussed in terms of specific and non-specific systems.     

The prognostic value of somatosensory evoked potentials in traumatic primary and secondary brain stem lesions

To estimate the prognostic value of somatosensory evoked potentials elicited via stimulation of the median nerve (M-SSEP) in cases of primary and secondary brainstem lesions 126 patients with traumatic brainstem lesions (GCS < or = 6) were investigated on admission to our hospital. Various parameters of the patients' M-SSEP were compared with the corresponding data of 40 healthy persons. Latency and amplitude of the cervical (N14) and cortical (N20) derived potentials and the central conduction time (CCT) were taken into account. Changes or a loss of the N20 signal and of the CCT were related to clinical outcome for up to two years. All patients had a normal N14 bilaterally. Most patients with a primary brainstem lesion (n = 25) showed symmetrical N20 changes bilaterally. However, the majority of patients with a secondary brainstem lesion (n = 62) showed asymmetric N20 changes in M-SSEP which became more symmetrical in cases with marked progressive brainstem compression. Irrespective of a primary or secondary traumatic brainstem lesion, marked changes of N20 represented an unfavourable clinical prognosis. A loss of N20 was closely correlated with a very poor outcome (GOS 1-2) if the N20 potential had not recovered within 48 hours. The recovery of this potential, however, was not necessarily correlated to a recovery of the brain function.     

动态脑电图和脑干听觉诱发电位在昏迷预后判断中的应用

目的探讨昏迷病人动态脑电图（AEEG）和脑干听觉诱发电位（BAEP）表现及其对预后判断的临床意义。方法对96例昏迷病人行动态脑电图和脑干听觉诱发电位检查,并根据结果进行预后判断,与病人随访3个月时结果进行比较。结果AEEG＋BAEP对预后的评估敏感性为92．3％,特异性95．5％,准确率93．8％,错误率为2．1％,Glasgow评分敏感性为76．9％,特异性77.7％,准确率77．3％,错误率为10．4％,经x^2检验,差异有统计学意义（P〈0．05）。结论动态脑电图和脑干听觉诱发电位联合应用对昏迷病人临床顸后的判断有重要意义。     

Mismatch negativity and late auditory evoked potentials in comatose patients.

OBJECTIVES: The purpose of this study was to assess the patterns of mismatch negativity (MMN) and N100 component in comatose patients and to evaluate their prognostic value vis-à-vis return of consciousness. METHODS: MMN and auditory (early, middle-latency and late) evoked potentials were recorded in 52 normals and in 128 comatose patients (comas due to neurosurgical and neurological problems). At the time of recording, all patients scored lower than 8 on the Glasgow scale. RESULTS: Visually detected N100 and MMN were confirmed by cross-correlation of sub-averages. The MMN was present in 33/128 patients and the N100 component in 84/128. The amplitudes of MMN and N100 waves detected in comatose patients were statistically different from those of normal subjects. By 3 months after the onset of coma, 95 patients had returned to consciousness, most of them with moderate to severe disability. A ratio of 30/33 patients with MMN and 70/84 with N100 had regained consciousness. The presence of a MMN together with a N100 component was more specific (90.9%) than the presence of a N100 component irrespective of MMN (57.6%) in terms of predicting return to consciousness, but its sensitivity was lower (respectively 31.6% for MMN and 73.7% for N100). The mean period that elapsed between the recording of evoked potentials and a return to consciousness was 6.3+/-4 days. MLAEPs were also highly specific, but BAEPs were not. CONCLUSION: MMN and auditory evoked potentials provide a reliable assessment of the functional status of comatose patients. When present, MMN and the N100 differ from those found in normal subjects in terms of latencies and amplitudes. As a predictor of return of consciousness MMN had high specificity and low sensitivity, whereas the N100 had high sensitivity and low specificity. This study demonstrates that the recording of MMN and the auditory N100 can be a very useful aid in the assessment of coma and in predicting whether or not a patient will regain consciousness.     

诱发电位与脑电图联合检测对脑血管病昏迷患者预后的评估

目的研究脑电图（EEG）、脑干听觉诱发电位（BAEP）、体感诱发电位（SEP）联合检测对脑血管病昏迷患者预后的判断。方法对60例脑血管病昏迷患者进行EEG、BAEP、SEP检测,并与预后结果进行分析。结果诱发电位与脑电图联合检测对预后评估的敏感性为96．9％,特异性96．4％,准确率96．7％,与glasgow评分组比较差异有统计学意义P〈0．05。结论EEG、BAEP及SEP联合检测对评价脑血管病昏迷患者脑功能状态,预测预后提供了客观可靠的依据。     

Two evoked responses with different recovery functions in the primary somatosensory cortex in humans.

OBJECTIVES: We investigated the recovery function of somatosensory evoked magnetic cortical fields (SEFs) to confirm the temporal aspects of the somatosensory process in humans. METHODS: SEFs were recorded following median nerve electrical stimulation in 6 healthy subjects. Double stimulation, with interstimulus intervals (ISIs) from 3 to 100 ms, was applied, and the SEF components for the second stimulation were analyzed. In a supplementary experiment, responses to single stimulations of various intensities from the sensory threshold to the motor threshold were studied. RESULTS: The first SEF component (1M) diminished when the ISI was less than 10 ms, while the second component (2M) remained even when the ISI was 3 ms. The two components showed a very similar attenuation with decrease of stimulus intensity. There was no significant difference in dipole location between 1M and 2M in the primary somatosensory cortex (SI). CONCLUSIONS: The results suggested that at least two independent pathways with different recovery functions exist in a similar area in the SI.     

40 Hz--middle latency auditory evoked response in comatose patients

Brain-stem auditory evoked response (BAER) and 40 Hz middle latency auditory evoked response (40 Hz AER) were elicited in 12 comatose patients. The concept of a midbrain generator of 40 Hz AER is being discussed.     

Association between somatosensory evoked potentials and EEG in comatose patients after cardiac arrest

ObjectiveTo analyze the association between SSEP results and EEG results in comatose patients after cardiac arrest, including the added value of repeated SSEP measurements.MethodsContinuous EEG was measured in 619 patients during the first 3–5 days after cardiac arrest. SSEPs were recorded daily in the first 55 patients, and on indication in later patients. EEGs were visually classified at 12, 24, 48, and 72 h after cardiac arrest, and at the time of SSEP. Outcome at 6 m was dichotomized as good (Cerebral Performance Category 1–2) or poor (CPC 3–5). SSEP and EEG results were related to outcome. Additionally, SSEP results were related to the EEG patterns at the time of SSEP.ResultsAbsent SSEP responses and suppressed or synchronous EEG on suppressed background ≥24 h after cardiac arrest were invariably associated with poor outcome. SSEP and EEG identified different patients with poor outcome (joint sensitivity 39% at specificity 100%). N20 responses were always preserved in continuous traces at >8 Hz. Absent SSEPs did not re-emerge during the first five days.ConclusionsSSEP and EEG results may diverge after cardiac arrest.SignificanceSSEP and EEG together identify more patients without chance of recovery than one of these alone.     

Functional MRI study of the primary somatosensory cortex in comatose survivors of cardiac arrest

It is difficult to assess cerebral function in comatose patients. Because earlier functional neuroimaging studies demonstrate associations between cerebral metabolism and levels of consciousness, fMRI in comatose survivors of cardiac arrest could provide further insight into cerebral function during coma. Using fMRI, cerebral activation to somatosensory stimulation to the palm of the hand was measured in 19 comatose survivors of cardiac arrest and in 10 healthy control subjects and was compared to somatosensory-evoked potential (SSEP) testing of the median nerve. Changes in the blood oxygenation-level dependent signal (BOLD) in the primary somatosensory cortex (S1) contralateral to the stimulated hand were quantified. Clinical outcome was assessed using the Glasgow Outcome Scale (GOS) and the modified Rankin Scale at 3 months post-cardiac arrest. Five out of 19 patients were alive at 3 months. Patients who survived cardiac arrest showed greater BOLD in S1 contralateral to somatosensory stimulation of the hand compared to patients who eventually did not. Greater BOLD was also seen in S1 of patients who retained their SSEP N20 waveforms. There were also positive correlations between BOLD in S1 with both levels of consciousness and measures of outcome at 3 months. In summary, this study demonstrates that BOLD in the S1 contralateral to somatosensory stimulation of the hand varies with clinical measures of the level of consciousness during coma.     

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.     

Contribution of somatosensory cortex to evoked cerebellar blood flow responses

Projections from the trigeminocerebellar pathway and the somatosensory cortex coincide spatially in the granule cell layer of Crus I/II of the cerebellar hemisphere. A biphasic field potential was seen: one peak at 10 ms (trigeminal input) and another at 20 ms (somatosensory input). Linear correlation analysis revealed only a weak coupling between somatosensory input and cerebellar blood flow responses to infraorbital nerve stimulation. In separate experiments, cortical spreading depression attenuated the field potential peak at 20 ms while blood flow responses remained unaltered. Thus, trigeminocerebellar activity explained the evoked blood flow responses. Our data provide further evidence that activity-dependent blood flow responses are context-sensitive and that interaction between excitatory neuronal circuits targeting the same cells may occlude vascular responses.     

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.     

Central somatosensory conduction time in comatose patients.

Somatosensory conduction time between the dorsal column nuclei and the cerebral cortex may be measured following median nerve stimulation by recording evoked potentials from both scalp and neck. Central conduction times were significantly increased relative to normal (5.6 +/ 0.5 msec) in 11 of 24 comatose patients. Results within 10 and 35 days of onset of coma were correlated with the final clinical outcome. Conduction times were independent of serum phenobarbital (0 to 630 mumol per liter) and of central body temperature (35.0 to 38.5 degrees C). Serial studies in coma demonstrated (1) short-term increases during temporary metabolic disorders, and (2) sustained increases with gradual recovery over many months, particularly after head injury.     

Somatosensory evoked magnetic fields from the primary somatosensory cortex (SI) in acute stroke.

We recorded somatosensory evoked magnetic fields (SEFs) to median nerve stimulation from 15 patients in the acute stage (1-15 days from the onset of the symptoms) of their first-ever unilateral stroke involving sensorimotor cortical and/or subcortical structures in the territory of the middle cerebral artery (MCA). Neuronal activity corresponding to the peaks of the N20m, P35m and P60m SEF deflections from the contralateral primary somatosensory cortex (SI) was modelled with equivalent current dipoles (ECDs), the locations and strengths of which were compared with those of an age-matched normal population. Four patients with pure motor stroke had symmetric SEFs. In one of the 4 patients with pure sensory stroke, and in 5 of the 7 patients with sensorimotor paresis, the SEFs were markedly attenuated or missing. All except one patient with abnormal SEFs had deficient two-point discrimination ability; especially the attenuation of N20m was more clearly correlated with two-point discrimination than with joint-position or vibration senses. Of the different SEF deflections, P35m and P60m were slightly more sensitive indicators of abnormality than N20m, the former being affected in two patients with symmetric N20m. Three patients with pure sensory stroke and lesions in the opercular cortex had normal SEFs from SI. We conclude that the SEF deflections N20m, P35m and P60m from SI are related to cutaneous sensation, in particular discriminative to touch. The results also demonstrate that basic somatosensory perception can be affected by lesions in the opercular cortex in patients with functionally intact SI.     

Gamma synchronization in human primary somatosensory cortex as revealed by somatosensory evoked neuromagnetic fields

Cortical sensory neurons synchronize their activity at multiple frequency bands after an external stimulation. In the somatosensory cortical areas, previous reports describe more discrete and somatotopically specific neural synchronization at the gamma band. Therefore, an efficient gamma synchronization of the neurons in primary somatosensory cortex (S1) may be expected to characterize the stimulus processing from the thumb, i.e. the hand's most skillful area. To test this hypothesis, neuromagnetic fields were evoked over human S1 by the electrical stimulation of the contralateral thumb or little finger. Neuronal synchronization was indexed by the spectral coherence of the evoked neuromagnetic fields overlying S1. The frequencies of interest were the beta (16-32 Hz) and gamma (36-46 Hz) bands. The global amount of the coherence was defined as the total event-related coherence (ERCoh) among all magnetic sensors overlying the S1. Results showed prevalent increment of beta ERCoh (20-32 Hz) after the little finger stimulation and of gamma ERCoh (36-44 Hz) after the thumb stimulation. These results suggest that the neural synchronization in S1, as revealed by the ERCoh, may vary in frequency as a function of the finger stimulated. In this framework, the neural synchronization at gamma band may characterize the cortical representation of thumb, functionally prevalent with respect to little finger in humans.     

Changes of brainstem auditory and somatosensory evoked

Objective: to investigate the characteristics and clinical value of evoked potentials in late infantile form of metachromatic leukodystrophy. Methods: Brainstem auditory, and somatosensory evoked potentials were recorded in 6 patients, and compared with the results of CT scan. Results: All of the 6 patients had abnormal results of BAEP and MNSEP. The main abnormal parameters in BAEP were latency prolongation in wave I, inter-peak latency prolongation in Ⅰ-Ⅲ and Ⅰ-Ⅴ. The abnormal features of MNSEP were low amplitude and absence of wave N9, inter-Peak latency prolongation in Ng-N13 and N13-N20, but no significant change of N20 amplitude. The results also revealed that abnormal changes in BAEP and MNSEP were earlier than that in CT. Conclusion: The detection of BAEP and MNSEP in late infantile form of metachromatic leukodystrophy might early reveal the abnormality of conductive function in nervous system and might be a useful method in diagnosis.     

Visual and auditory evoked responses in patients with Parkinson's disease.

Visual evoked responses were obtained in 47 Parkinsonian patients and 26 age-matched controls. The stimulation to binocular and uniocular latency of the major positive peak was longer in the Parkinsonian patients and its amplitude was smaller than in the control subjects. There was a large interocular difference suggesting that at least part of the delay occurs at prechiasmatic level. The latency and amplitude varied markedly following ingestion of levodopa as Sinemet. Auditory evoked potentials were obtained in 16 Parkinsonian patients and 11 age-matched controls. The latency of the NV wave was prolonged in the former although the amplitude was the same, suggesting that the abnormality may be a widespread one.