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PubMed1977

An objective indicant of binocular vision in humans: size-specific interocular suppression of visual evoked potentials.

Evoked cortical potentials (VEPs) to grid patterns flashed to one eye were suppressed in amplitude when grid patterns were continuously presented to the other eye. The degree of interocular suppression of VEPs was influenced by the stereoacuity of the subjects. VEPs were obtained to each of two grid sizes flashed to one eye (individual squares subtending 15 and 60 min of arc) and changes in amplitude of these VEPs were considered as a function of four stimuli continuously presented to the other eye (diffuse light, 15, 30, and 60 min of arc squares in grids). Interocular suppression of VEPs was greater (a) when the continuously presented grid was of high (38.00 mL) as compared to low (00.38 mL) intensity, (b) when the continuous and flashed grids were of the same as compared to different sizes, and (c) in six subjects who had good as compared to six subjects who had poor binocularity. Eleven of the twleve subjects could be classified correctly as having good or poor binocularity on the basis of statistically significant interocular suppression of VEPs. The results were interpreted in terms of centrally located binocular neurons responsive to specific grid sizes or spatial frequencies and the decreased functioning of such neurons in subjects with poor binocularity.

Evoked Potentials↗
PubMed1993

Correlation of motor-evoked potentials, somatosensory-evoked potentials, and the wake-up test in a case of kyphoscoliosis.

The ability to monitor the descending motor pathways of the spinal cord during surgery is an important goal in neurophysiologic monitoring of spinal deformities. This report describes a case of a severe spinal deformity for which instrumentation and reduction carried a significant risk of neurologic complications. During the procedure, changes in neurologic status were monitored simultaneously using both SSEPs and tcMMEPs. The reliability of these two complimentary modalities was then verified by concurrent wake-up tests. This case provides documentation of the reliability of tcMMEP responses when an accurate assessment of motor function was necessary.

Adult↗
PubMed2004

Monitoring of motor evoked potentials compared with somatosensory evoked potentials and microvascular Doppler ultrasonography in cerebral aneurysm surgery.

OBJECT: The aims of this study were to compare the efficiency of motor evoked potentials (MEPs), somatosensory evoked potentials (SSEPs), and microvascular Doppler ultrasonography (MDU) in the detection of impending motor impairment from subcortical ischemia in aneurysm surgery; to determine their sensitivity for specific intraoperative events; and to compare their impact on the surgical strategy used. METHODS: Motor evoked potentials, SSEPs, and MDU were monitored during 100 operations for 129 aneurysms in 95 patients. Intraoperative events, monitoring results, and clinical outcome were correlated in a prospective observational design. Motor evoked potentials indicated inadequate temporary clipping, inadvertent occlusion, inadequate retraction, vasospasm, or compromise to perforating vessels in 21 of 33 instances and deteriorated despite stable SSEPs in 18 cases. Microvascular Doppler ultrasonography revealed inadvertent vessel occlusion in eight of 10 cases and insufficient clipping in four of four cases. Stable evoked potentials (EPs) allowed safe, permanent vessel occlusion or narrowing despite reduced flow on MDU in five cases. Two patients sustained permanent and 10 showed transient new weakness, which had been detected by SSEPs in two of 12 patients and MEPs in 10 of 11 monitored cases. The surgical strategy was directly altered in 33 instances: by MEPs in 16, SSEPs in four, and MDU in 13. CONCLUSIONS: Monitoring of MEPs is superior to SSEP monitoring and MDU in detecting motor impairment, particularly that from subcortical ischemia. Microvascular Doppler ultrasonography is superior to EP monitoring in detecting inadvertent vessel occlusion, but cannot assess remote collateral flow. Motor evoked potentials are most sensitive to all other intraoperative conditions and have a direct influence on the course of surgery in the majority of events. A controlled study design is required to confirm the positive effect of monitoring on clinical outcome in aneurysm surgery.

Adult↗
PubMed2003

Effects of desflurane on spinal somatosensory-evoked potentials and conductive spinal cord evoked potential.

STUDY DESIGN: Spinal somatosensory-evoked potential (interspinous-space-recorded evoked potentials after peripheral nerve or dermatomal stimulation) and conductive spinal cord evoked potential (interspinous-space-recorded evoked potentials after spinal cord stimulation) were analyzed in rats under different concentrations of the anesthetic desflurane. OBJECTIVES: To investigate and compare the effects of a new volatile anesthetic, desflurane, on the common intraoperative neuromonitoring models. SUMMARY OF BACKGROUND DATA: Intraoperative evoked potentials are sensitive to most anesthetics. Interpretation of the data becomes complicated because of a suppression effect caused by the anesthesia. Desflurane has become a valuable anesthetic in neurosurgery because of its pharmacokinetic advantages. METHODS: Fifteen rats were placed under general anesthesia, and vital signs were closely monitored. Needle recording electrodes were placed stereotactically into the thoracolumbar interspinous ligament; dermatomal somatosensory-evoked potential by L5 dermatome, mixed-nerve somatosensory-evoked potential by sciatic nerve stimulation, and spinal cord evoked potential of the same recording electrodes elicited by C2-C3 interspinous stimulation were obtained. The effects of desflurane were examined at end-tidal concentrations of 6% (1.05 minimal alveolar concentration), 9% (1.57 minimal alveolar concentration), and 12% (2.10 minimal alveolar concentration). RESULTS: Amplitude decreased and latency was delayed in all three kinds of potentials, and the more so with higher concentrations. Comparing 9% with 6% desflurane, the amplitude in dermatomal somatosensory-evoked potential, mixed-nerve somatosensory-evoked potential, and spinal cord evoked potential decreased to 84.3%, 88.9%, and 70.8%, respectively, values with no statistically significant difference. However, at 12%, again compared with 6%, the amplitude decreased further to 64.4%, 70.3%, 41.8%, respectively; mixed-nerve somatosensory-evoked potential and dermatomal somatosensory-evoked potential were significantly more preserved than spinal cord evoked potential (P = 0.04). CONCLUSIONS: The concentration of desflurane alters the amplitude of somatosensory-evoked potential and spinal cord evoked potential, and, to a lesser degree, delays the latency; spinal cord evoked potential is more liable to be suppressed than somatosensory-evoked potential. The dose-dependent suppression effect on amplitude should be considered when interpreting changes during surgery. Furthermore, the potential benefit of somatosensory-evoked potential elicited by direct major nerve stimulation should be considered because of its large amplitude and higher resistance, even with a greater concentration of volatile anesthetics.

Anesthetics, Inhalation↗
PubMed1976

Effects of morphine and barbiturate on the SI and SII potentials evoked by tooth pulp stimulation of rats.

The effects of morphine and barbiturate on the evoked potentials recorded from the primary and secondary somatic sensory areas of rats were investigated. The electric stimulation of contra- and ipsilateral tooth pulp (CTP and ITP) was used. The afferent impulse from dental pulp projected to the sensory face areas I and II (SI and SII). Morphine in doses of 2.5-10 mg/kg definitely inhibited SI and SII potentials evoked by CTP stimulation. Morphine also inhibited SII potentials evoked by ITP stimulation, while it rather enhanced SI potentials evoked by ITP stimulation. Pentobarbital sodium in doses of 4-16 mg/kg tended to inhibit SI potentials, but showed no effect or rather an enhancement on SII potentials evoked by CTP stimulation. Pentobarbital sodium enhanced SI and SII potentials evoked by ITP stimulation. In a large dose of 32 mg/kg, pentobarbital sodium inhibited SI and SII potentials evoked by ITP and CTP stimulations. The results suggest that SII is more closely related to the analgesia due to morphine than is SI.

Animals↗
PubMed1983

Brain-stem auditory evoked potentials and early somatosensory evoked potentials in neurointensively treated comatose children.

Forty-three comatose children treated by invasive neurointensive care were examined by brain-stem auditory evoked potentials (BAEPs) and somatosensory evoked potentials (SEPs). The evoked potential (EP) results obtained were reviewed in conjunction with the clinical outcome. As a BAEP criterion, the V-I interpeak latency and, as an SEP criterion, the central conduction time (N20-N14 latency) were measured. A loss of BAEP and SEP components portended a poor prognosis. On the other hand, latency prolongations were seen in a third of patients who made a complete recovery. However, the SEP and BAEP have proved themselves as reliable methods in the judgment of the clinical state and the prognosis of intensively treated children with a hypoxic-ischemic encephalopathy or a head injury. The measurement of both BAEPs and SEPs was a more reliable prognostic aid than either EP measurement alone.

Adolescent↗
PubMed1994

EEG, auditory evoked potentials and evoked rhythmicities in three-year-old children.

According to our working hypothesis, the resonance properties of the brain systems play an important role in internal brain communications (e.g., Başar, 1992; Başar, Başar-Eroglu, Demiralp & Schürmann, 1992). It was assumed that evoked potentials (EPs) reflect brain resonance properties, showing enhancement, time and frequency-locking during the poststimulus period. All these phenomena might be referred to the spontaneous (intrinsic) EEG rhythms according to the excitability rule and the related concept of brain system response susceptibility: a brain system could react to internal or external stimuli producing those rhythms or frequency components, which have already been present in intrinsic or spontaneous activity (Başar, 1980). In order to test the hypothesis of response susceptibility, in the present paper we used an natural model--3-year-old children--to investigate how brain systems respond to external stimulation if their spontaneous rhythms are different in comparison to the spontaneous EEG rhythms in adults. For that purpose we used a combined time and frequency domain approach. The spectral characteristics of the spontaneous EEGs as well as the frequency components of auditory EPs elicited under identical auditory stimulation in 3-year-old children and adults aged 20-22 years were compared. Our observations support the hypothesis for response susceptibility; if in a given frequency channel the spontaneous brain rhythms are missing, they are also absent in the evoked and induced rhythmicities and vice versa: children at 3 years do not create alpha resonance upon sensory stimulation while they do not have developed EEG rhythms in the range of 8-15 Hz. Elicited under identical experimental conditions (auditory stimulation with fixed stimulus parameters) children and adult evoked rhythms differ. It was concluded that the AEPs recorded in 3-year-old children might be regarded mainly as a superposition of rhythmicities in delta and theta ranges. These rhythmicities are prolonged and delayed in comparison to the corresponding rhythms in adults.

Adult↗
PubMedDate not supplied

Abnormal brainstem evoked potentials in diabetes mellitus. Evoked potential testings and magnetic resonance imaging.

Brainstem auditory evoked potentials (BAEPs) and median nerve somatosensory evoked potentials (MN-SEPs) were measured in 53 diabetic patients. Magnetic resonance imaging (MRI) was performed 12 patients with abnormal BAEPs and/or MN-SEPs in order to confirm the existence of lesions in the central nervous system. Twenty-six percent of the diabetic patients had abnormal BAEPs and three had a prolongation of the central conduction time in the MN-SEPs. MRI findings of ten of the 12 patients with abnormal BAEPs or MN-SEPs showed multiple small lesions in the pons, thalamus, and centrum semiovale etc. Two of them showed small lesion in the pontine basis which could induce prolonged interpeak latencies of BAEPs. Our MRI study might suggest that abnormal brainstem evoked potentials in diabetic patients were induced by diabetic macroangiopathy or microangiopathy.

Adolescent↗
PubMed1995

[Efferent spinal evoked potentials by transcranial magnetic stimulation in dog].

We have investigated the utility of transcranial magnetic stimulation for spinal cord monitoring, experimentally in dog. Experiment 1. Spinal cord potentials evoked by transcranial magnetic stimulation (TCMS) were recorded in the epidural space, using a bipolar mapping spinal electrode, and compared with potentials by transcranial electrical stimulation (TCES). Experiment 2. The effect of lateral compression on the spinal cord was observed, recording from 3 bipolar electrodes attached to the bilateral and dorsal midline epidural space. Experiment 3. The potentials evoked by TCMS were compared with the afferent potentials evoked by spinal electrical stimulation after lateral compression of the spinal cord. Efferent spinal cord potentials evoked by TCMS consisted of a 1 st component of high amplitude and short latency and a later polyphasic component with prolonged latency. The 1 st component was stable, and not affected by intravenous anesthesia. The potentials evoked by TCMS were similar to the potentials evoked by mild TCES, and the mean latency of the 1 st component by TCMS was very similar to that by mild TCES. After releasing the lateral compression, the amplitude recorded from the contralateral side of the spinal cord showed better recovery than that from the compression side. In experiment 3, for both potentials after good recovery, the latency was almost completely normalized, but the amplitude gradually decreased after two days. When there was relatively good recovery in the potentials by magnetic stimulation, the hind limbs resumed normal function. However when there was poor recovery in the potentials, the hind limbs showed a poor functional recovery. From these findings, we concluded that the potentials evoked by TCMS seem to reflect the function of the posterolateral portion of the spinal cord. These potentials were therefore a good indicator for monitoring the motor function of the spinal cord.

Animals↗
PubMed2002

Origins of surface potentials evoked by electrical stimulation of oculomotor nerves: are they related to electrooculographic or electromyographic events?

OBJECT: Evoked potentials elicited by electrical stimulation of the oculomotor nerve and recorded from surface electrodes placed on the skin around the eyeball reportedly originate in the eye and are represented on electrooculograms. Because evoked potentials recorded from surface electrodes are extremely similar to those of extraocular muscles, which are represented on electromyograms, the authors investigated the true origin of these potentials. METHODS: Evoked potentials elicited by electrical stimulation of the canine oculomotor nerve were recorded from surface electrodes placed on the skin around the eyeball. A thread sutured to the center of the cornea was pulled and the potentials that were evoked during the resultant eye movement were recorded. These potentials were confirmed to originate in the eye and to be represented on electrooculograms because their waveforms were unaffected by the administration of muscle relaxant. To eliminate the influence of this source, the retina, a main origin of standing potentials of the eyeball, was removed. This resulted in the disappearance of electrooculography (EOG) waves elicited by eye movement. Surface potentials elicited by oculomotor nerve stimulation were the same before and after removal of the retina. Again the oculomotor nerve was electrically stimulated and electromyography (EMG) response of the extraocular muscles was recorded at the same time that potentials were recorded from the surface electrodes. In their peak latencies, amplitudes, and waveforms, the evoked potentials obtained from surface electrodes were almost identical to EMG responses of extraocular muscles. CONCLUSIONS: Evoked potentials elicited by electrical stimulation of the oculomotor nerves and obtained from surface electrodes originated from EMG responses of extraocular muscles. These evoked potentials do not derive from the eye.

Abducens Nerve↗
PubMed1990

Cerebral electrical potentials evoked by balloon distention of the human esophagus.

UNLABELLED: Cerebral evoked potentials provide a technique for evaluation of central nervous processing of information derived from a variety of sensory modalities. Evoked potentials associated with balloon distention of the smooth muscle esophagus were studied in 14 adult volunteers. Stimulation was applied via repeated inflation and deflation of a balloon attached to a pressure pump that cycled at 0.2 Hz. Cortical electrical responses were recorded from scalp electrodes at Cz, Cz', and Pz of the international 10-20 System for electroencephalographic recording. The recording electrodes were referenced to Fpz and averaged over a 1-s period for 100 repetitions. Latencies, amplitudes, and waveforms of the evoked potentials were compared with controls consisting of pump on/balloon detached, auditory masking, and conventional somatosensory posterior tibial nerve stimulation. Polyphasic evoked potentials were obtained in all subjects, and maximum positive deflections occurring with latencies of 202-396 ms. Maximal amplitudes ranged from 2.5-8.3 microV. Latencies and amplitudes of the evoked responses were highly reproducible in each subject with considerable variation among subjects. CONCLUSIONS: (a) Reproducible evoked potentials with distinctive waveforms can be recorded in response to esophageal balloon distention in humans; (2) long latency of the evoked potentials suggests involvement of nonmyelinated visceral afferent pathways; (3) the evoked potentials are probably specific to mechanical stimulation rather than being nonspecific arousal responses; and (4) the results support this as a promising new method for investigation of the neurobiology of gastrointestinal sensation in humans that may help clarify pathological conditions of the irritable esophagus syndrome and esophagus-related chest pain.

Adult↗
PubMed1997

Assessment of the reliability of cerebral potentials evoked by electrical stimulation of the anal canal.

The aim of this study was to assess the reliability of cortical evoked potentials after electrical stimulation of the anal canal. Cortical evoked potentials were recorded on 243 patients presenting with perineal pain (28 patients), impotence (55 patients), anal incontinence (52 patients), urinary continence (30 patients), constipation (49 patients), and on 29 neurological patients, by stimulating the external anal sphincter and penis (or clitoris). The inter- and intra-observer reproducibility was studied by coding recordings interpreted by three different observers on two separate occasions. The influence of recording characteristics and clinical data were assessed. To study operator dependence, five operators investigated the patients. Only one of them was well trained in this technique. The interpretation of the coded curves by the observers was poorly reproducible in about 15% of cases, depending on time between the two readings and the quality of recordings. The interpretation of cerebral responses after anal stimulation were observer-dependent and influenced by the knowledge of clinical data. This was also observed with cortical evoked potentials after electrical stimulation of the penis or clitoris, but to a lesser extent. The cerebral evoked potentials method was also operator-dependent, mainly after anal stimulation. When a study of cortical evoked potentials by perineal stimulation is needed in clinical practice, it seems logical to prefer cortical evoked potentials by penile or clitoral stimulation as they seem easier to obtain than those evoked by anal stimulation if the investigators are not well trained for the performance of electrophysiological studies as the former are much less operator- and observer-dependent.

Adult↗
PubMed1983

Influence of drugs on evoked potentials in the cat cerebellum: II. Effects of morphine hydrochloride (1).

Effects of morphine hydrochloride on the cerebellum were examined in cats. Morphine (2.0 mg/kg, i.v.) decreased the potentials by superficial radial nerve (SR), nucleus reticularis lateralis (LRN), or nucleus olivaris inferior (ION) stimulation on the cerebellar cortices. These effects were antagonized by naloxone hydrochloride (0.4 mg/kg, i.v.). In the LRN or ION, morphine decreased the potentials evoked by SR stimulation. In the LRN- or ION-lesioned cat, morphine decreased the potentials evoked by SR stimulation on the cerebellar cortices. This opiate decreased the potentials evoked by tooth pulp stimulation on the vermis, and this effect was also antagonized by naloxone. Morphine slightly decreased the potentials evoked by SSA-1 stimulation on the cerebellar cortices. Furthermore, the potentials evoked by SR stimulation on the SAA-1 were slightly decreased by morphine. These results may suggest that the cerebellum plays an important role in not only the motor system, but also the sensation of pain.

Animals↗
PubMed1997

[Intraoperative pain stimuli change somatosensory evoked potentials, but not auditory evoked potentials during isoflurane/nitrous oxide anesthesia].

PURPOSE: Evoked potentials are used for intraoperative monitoring to assess changes of cerebral function. This prospective randomised study assesses the influence of surgical stimulation on midlatency components of somatosensory (SEPs) and auditory evoked potentials (AEPs) in anaesthetised patients. METHODS: After approval of the Ethics Committee and written informed consent 36 orthopaedic patients (34 +/- 15 y, 73 +/- 14 kg. 1.71 +/- 0.07 m, ASA I-II) were randomly included in the study. Anaesthesia was induced with 1.5 micrograms/kg fentanyl, 0.3 mg/kg etomidate and 0.1 mg/kg vecuronium. The lungs were intubated and patients normoventilated in steady state anaesthesia with isoflurane (end-tidal 0.6%) and 66% nitrous oxide. 18 patients (group 1) were assigned to the SEP group: median nerve stimulation, recording at Erb, C 6 and the contralateral somatosensory cortex (N20, P25, N35) vs Fz. AEPs were recorded in group 2 (n = 18): binaural stimulation, recording at Cz versus linked mastoid (V, Na, Pa, Nb). Recordings were performed during 30 min before the start of surgery (baseline: BL), at skin incision (SURG1) and at the preparation of the periost (SURG2). Heart rate, mean arterial blood pressure, oxygen saturation, endtidal pCO2 and isoflurane (PetISO) concentrations were registered simultaneously. Data were analysed by one-way analysis of variance. Post hoc comparison were made by Mann-Whitney U-Wilcoxon Rank Sum Test with p < 0.05 significant. RESULTS AND DISCUSSION: During steady state isoflurane anaesthesia surgical stimulation (SURG2) resulted in significant increases of N20 P25 amplitudes compared with BL (BL: 1.4 +/- 0.7 microV; SURG2: 2.0 +/- 0.8 microV; p < 0.05). Latencies of SEPs and midlatency components of AEPs did not change over time. There were no differences in autonomic parameters between SEP and AEP groups. MAP increased from 76 +/- 6 mmHg at BL to 93 +/- 16 mmHg at SURG1 and 96 +/- 17 mmHg at SURG2 (n = 36; p < 0.05). HR increased from BL (60 +/- 8 beats/min) to SURG2 (76 +/- 12 beats/min). Increases of amplitudes of midlatency SEP amplitudes indicate increased nociceptive signal transmission which is not blunted by isoflurane-nitrous oxide anaesthesia. In contrast, unchanged AEPs indicate adequate levels of the hypnotic components of anaesthesia.

Adult↗
PubMed2006

Brainstem auditory evoked potentials and flash visual evoked potentials in Vietnamese miniature pot-bellied pigs.

Brainstem auditory evoked potentials (BAEP) and flash visual evoked potentials (VEP) were recorded from juvenile (5-7 weeks of age) and adult Vietnamese miniature pot-bellied pigs to provide normative data for clinical applications. BAEP responses were collected in response to stimulus intensities of 85, 95, and 105 dB nHL. VEP responses were collected in response to flashes of white light in a darkened room. Left-right ear and left-right eye responses did not differ significantly, and were combined for analysis, with each animal providing two data points for each response. BAEP responses in juvenile subjects were mature, and in all subjects showed the typical pattern of decreasing peak latencies and increasing peak amplitudes with increasing stimulus intensity. VEP responses in juvenile subjects were near to mature values, but the latencies still exceeded those of adults. Differences in response maturation between precocial and altricial species are discussed.

Aging↗
PubMed1993

Magnetic fields normalize visual evoked potentials and brainstem auditory evoked potentials in multiple sclerosis.

The present communication concerns a 46 year old woman with a 10 year history of chronic progressive multiple sclerosis (MS) in whom external application of magnetic fields (MF) (7.5 picoTesla; 5 Hz) during a period of remission resulted in a rapid and dramatic improvement in symptoms including vision, cerebellar symptomatology (ataxia and dysarthria), mood, sleep, bowel and bladder functions as well as fatigue. Improvement in the patient's symptoms was associated with normalization of the pretreatment latencies of the visual evoked potentials and brainstem auditory evoked potential responses within a week after initiation of magnetic treatment. This report demonstrates that treatment with picoTesla MF is an effective, nonpharmacological modality in the management of MS and for the first time documents reversal of abnormal evoked potential responses by this treatment. The pineal gland is a magnetosensor. As MF affect the release of the pineal gland's principal hormone, melatonin, it is hypothesized that the effects of picoTesla MF in MS are partly mediated by the pineal gland which has recently been implicated in the pathogenesis of MS (Sandyk, 1992 a; b).

Electromagnetic Fields↗