Evoked potentials during recovery from blindness recorded serially from an infant and his normally sighted twin

Visual evoked potentials (VEPs) elicited by diffuse field flashes wee recorded from a behaviourally blind infant with his twin as control. The patient was tested at ages 4, 5, 6, 8, 10 and 15 months. In spite of his behavioural blindness, clear VEPs were recorded from the patient at age 4 months, although the wave form was monophasic as contrasted with the multiphasic wave form recorded from his twin at the same age. Latency to first deflection and to first peak were considerably longer for the patient. The patient's VEP wave forM grew progressively more complex with age, paralleling recovery of useful vision. However, the VEP development anticipated behavioural recovery.     

Evoked potentials recorded during routine EEG predict outcome after perinatal asphyxia

Objective

To evaluate the added value of somatosensory (SEPs) and visual evoked potentials (VEPs) recorded simultaneously with routine EEG in early outcome prediction of newborns with hypoxic-ischemic encephalopathy under modern intensive care.

Early nociceptive evoked potentials (NEPs) recorded from the scalp

ObjectiveNeurophysiological investigation of nociceptive pathway has so far been limited to late cortical responses. We sought to detect early components of the cortical evoked potentials possibly reflecting primary sensory activity.MethodsThe 150 IDE micropatterned electrode was used to selectively activate Aδ intraepidermic fibres of the right hand dorsum in 25 healthy subjects and 3 patients suffering from trigeminal neuralgia. Neurographic recordings were performed to assess type of stimulated fibres and check selectivity. Cortical evoked potentials were recorded from C3′-Fz and Cz-Au1.ResultsNeurographic recordings confirmed selective activation of Aδ fibres. Early components were detected after repetitive stimulation (0.83/s rate and 250–500 averages); the first negative component occured at 40 ms (N40) on the contralateral scalp.ConclusionsThe provided data support the hypothesis that N40 could be the cortical primary response conducted by fast Aδ fibres.SignificanceThis is the first report of early, possibly primary, cortical responses in humans by nociceptive peripheral stimulation. Although not perfected yet to allow widespread diagnostic use, this is probably the only method to allow fully objective evaluation of the nociceptive system, with important future implications in experimental and clinical neurophysiology.     

Evoked potentials in spinal muscular atrophy

Visual evoked potentials, brainstem evoked responses, and somatosensory evoked potentials were evaluated in 22 children with spinal muscular atrophy, types I and II. Eleven of the children had the severe form of spinal muscular atrophy (type I) and 11 children had the intermediate form (type II). The results of visual evoked potentials, brainstem evoked responses, and somatosensory evoked potentials were compared with those obtained in a control group. Statistical analysis showed abnormalities in the different sensory modalities. A significant increase in the visual evoked potential latencies was observed and was found more often in patients with spinal muscular atrophy type I. Alterations of the somatosensory thalamocortical responses were also observed, as well as a delay in the central conduction time. Although spinal muscular atrophy is usually considered to be a purely motor disorder involving neurons of the spinal anterior horn and nuclei of the lower cranial nerves, lesions of the posterior roots, spinal ganglia, ascending tracts, lateral geniculated corpus, and thalamus have been reported. Our results suggest that sensory neuron degeneration occurs more commonly in spinal muscular atrophy than previously thought and that this process probably develops more slowly than motoneuron degeneration. Such degeneration may be associated with brain atrophy.     

Comparison of somatosensory evoked potentials recorded from the scalp and dorsal column nuclei to upper and lower limb stimulation in the rat.

Responses from the dorsal column nuclei (DCN) in the rat to stimulation of the upper limbs (median nerve) and lower limbs (sciatic nerve) showed a difference in the wave forms of the two responses. These results support results of earlier studies in the cat, monkey, and man that showed that only slow-conducting cutaneous afferents from the lower limbs travel in the dorsal column, while all afferents from the upper limbs travel in the dorsal column and synapse in the DCN. A comparison between the response from the DCN and that from the vertex to stimulation of the upper limbs showed correspondence between short-latency peaks, while no clear earlier waves could be discerned in the response from the vertex to stimulation of the lower limbs. Even when the dorsal column was transected on one side, the correspondence between the early peaks in the scalp and the DCN responses to stimulation of the upper limbs was maintained. The effect of the dorsal column lesion on the response recorded from the surface of the DCN to stimulation of the sciatic nerve was mainly a reduction in the number of peaks. Transection at the midbrain level resulted in elimination of the long-latency response in the scalp recording, but the initial negative peak was maintained, which corresponded to the initial negative peak of the DCN response to stimulation of the upper limbs.     

Loss of evoked potentials during spinal surgery due to spinal cord hemorrhage

The cortical somatosensory evoked potential (SEP) disappeared during corrective spinal surgery in a patient with muscular dystrophy. The patient died 18 hours after surgery. Autopsy revealed an intramedullary hemorrhage 4 mm in diameter in the posterior horn of the cervical spinal cord. Microscopically, hypoxic neurons were seen adjacent to the hemorrhagic area, implying that the lesion was at least 6 hours old. The hemorrhage corresponded to the loss of SEPs and confirms that spinal cord monitoring can detect such lesions.     

Short latency potentials recorded from the neck and scalp following median nerve stimulation in man.

Short latency evoked potentials were recorded from sites overlying the cervical and thoracic vertebrae, the clavicles, mastoid processes and cerebral cortex, following percutaneous stimulation of median nerve fibres at the elbow, wrist and fingers in 23 normal subjects. At least four major early components each with simultaneous positive and negative constituents, plus the first component (N20) of the cortical response, were all found to be mediated by sensory afferent fibres with conduction velocity 65--75 m/sec in the forearm of one subject. Study of the distribution of these potentials, using reference electrodes located at Fz or over the lower part of the spine, has led to the proposal of generator sites in the brachial plexus (N9), spinal roots or dorsal columns (N11), spinal grey matter or brain stem (N13), and brain stem or thalamus (N14). Comparison with intrathecal recordings in man lends support to the view that N11 and N13 are generated in or adjacent to the spinal cord. It is hoped the findings may extend the clinical applications of a non-invasive technique for investigating the afferent sensory pathways in man.     

The relationship between human long-latency somatosensory evoked potentials recorded from the cortical surface and from the scalp.

In scalp recordings, stimulation of the median nerve evokes a number of long-latency (40-300 msec) somatosensory evoked potentials (SEPs) whose neural origins are unknown. We attempted to infer the generators of these potentials by comparing them with SEPs recorded from the cortical surface or from within the brain. SEPs recorded from contralateral sensorimotor cortex can be characterized as "precentral," "postcentral," or "pericentral." The scalp-recorded P45, N60 and P100 potentials appear to correspond to the pericentral P50, N90 and P190 potentials and are probably generated mainly in contralateral area 1 of somatosensory cortex. The scalp-recorded N70-P70 appear to correspond to the precentral and postcentral N80-P80 and are generated mainly in contralateral area 3b of somatosensory cortex. The scalp-recorded N120-P120 appear to correspond to the intracranial N100-P100 and are probably generated bilaterally in the second somatosensory areas. N140 and P190 (the "vertex potentials") are probably generated bilaterally in the frontal lobes, including orbito-frontal, lateral and mesial (supplementary motor area) cortex. The supplementary sensory area probably generates long-latency SEPs, but preliminary recordings have yet to confirm this assumption. Most of the proposed correspondences are speculative because the different conditions under which scalp and intracranial recordings are obtained make comparison difficult. Human recordings using chronically implanted cortical surface electrodes, and monkey studies of SEPs which appear to be analogs of the human potentials, should provide better answers regarding the precise generators of human long-latency SEPs.     

Characterization and processing of surface recorded spinal somatosensory evoked potentials

Somatosensory evoked potentials were recorded from the skin surface overlying the spinal cord, from the lower lumbar to the lower cervical regions. The recorded responses did not vary over time in any one individual and at each level a consistent wave shape was obtained across all individuals tested. Since the initial signal-to-noise ratio (SNR) for the evoked response recorded at any cord level is very low, the signal data must be processed. In this study, bandpass filtering or matched filtering was used together with ensemble averaging to obtain a usable signal in a reasonable processing time. SNR was improved approximately 1.5 X with bandpass filtering and 2 X with matched filtering. Although the output of the matched filter is a distorted version of the input signal, detection of information is enhanced and processing time using the matched filter and ensemble averaging can be reduced to 1/4 that required for ensemble averaging alone.     

Evoked potentials and contingent negative variation during treatment of multiple sclerosis with spinal cord stimulation.

Cervical somatosensory evoked potentials, brainstem evoked potentials, visual evoked potentials, and the cerebral contingent negative variation were recorded in patients with definite multiple sclerosis before, during, and after spinal cord stimulation. Improvements were seen in the cervical somatosensory and brainstem evoked potentials but neither the visual evoked potential nor the contingent negative variation changed in association with spinal cord stimulation. The results indicate that spinal cord stimulation acts at spinal and brainstem levels and that the clinical improvements seen in patients are caused by an action at these levels rather than by any cerebral arousal or motivational effect. The evoked potentials were not useful in predicting which patients were likely to respond to stimulation.     

Evoked potentials recorded from brain-stem nuclei in awake cat: interaction of tone bursts and continuous tone.

Previous work indicated that components of the auditory thalamocortical potential evoked by a brief binaural tone burst could be enhanced by certain stimulus combinations, e.g., a brief tone burst in the presence of a continuous tone. The principal questions of the present study were whether enhanced components could be obtained caudal to thalamocortex and whether monaural stimuli would be effective in producing enhancement. Eight cats received permanent electrodes in cochlear nucleus and the nucleus of the inferior colliculus. Custom earmolds were made for each ear of each animal. The median attenuation produced by the earmolds was 35 dB and the use of a single earmold approximated monaural stimulation. Auditory evoked potentials were recorded from the electrodes while the animals were unanesthetized but comfortably restrained. Brief 6.25 kHz tone bursts were presented against a background of silence or of a 4.96 kHz continuous tone. In the presence of the continuous tone, enhanced components were obtained from a majority of the electrodes in inferior colliculus but from none of the electrodes in cochlear nucleus. The late negative component in the colliculus potential was increased in amplitude while other components were reduced in amplitude by the continuous tone. The latencies of all components from all electrodes were increased by the presence of the continuous tone. It was concluded that enhancement effects could be obtained at the level of inferior colliculus, and that binaural stimulation does not appear to be necessary to produce enhanced components.     

Scalp recorded P13 and spinal recorded N13 in short latency somatosensory evoked potentials

Using non-cephalic reference and by median nerve stimulation, P 13 component and N 13 component are recorded on the scalp (scalp P 13) and the posterior neck (spinal N 13), respectively, in the short latency somatosensory evoked potentials (SSEP). The purpose of this study is to disclose the origin, characteristics and clinical significance of these two components. Ten healthy volunteers served for normal subjects. Ten patients with pontine lesion or brain death were studied. The effect of barbiturate was also studied in additional 5 patients during anesthesia for cranioplastic surgeries. Electrical stimuli of 0.2 msec square wave pulse were used in routine examination. To confirm the effects of stimulation frequency, 3, 6, 9, 12, 15, 18, 21, 24 and 27 Hz were also used in normal subjects. Recording electrodes were placed in the following sites. (1) Scalp electrode at the Shagass' point contralateral to the stimulated side (Par.). (2) Posterior neck electrode on the spinous process of the fifth cervical vertebrae (Cv5), (3) Anterior neck electrode on the thyroidal cartilage (Ant. C). (4) Erb's electrode just above the mid-clavicular point ipsilateral to the stimulation. Erb's electrode contra-lateral side of stimulation was used as a reference. Spinal N 13 on posterior neck reversed its polarity into P 13 (spinal P 13) on the anterior cervical electrode. A study with different stimulus rates revealed that the latency of scalp P 13 significantly prolonged at 24 Hz stimulation. On the other hand, the latency of spinal N 13-P 13 easily prolonged even at 18 Hz. This suggested that spinal N 13-P 13 were generated polysynaptically.(ABSTRACT TRUNCATED AT 250 WORDS)     

Unusual scalp recorded somatosensory evoked potentials after removal of a large intraventricular meningioma

Very unusual scalp recorded SEPs were seen in a case after removal of a large intraventricular meningioma. One day before death (ten days after surgery) when the patient was moribund, SEPs from the clinically and radiologically affected hemisphere in which a hematoma and thalamic infarct were found, had a normal latency and were decreased in amplitude. SEPs from the clinically and radiologically nonaffected hemisphere, where only minimal findings were seen, had an abnormally short latency (16.9 msec) and the CCT was only 3.1 msec. We do not offer any logical explanation of these unusual SEP findings from both hemispheres shortly before death.     

Evoked potentials during REM sleep reflect dreaming.

Polygraphic recordings were collected for 11 normal subjects during sleep and wakefulness in order to investigate characteristics of the rapid eye movement (REM) associated potentials. EEGs were averaged using 5 different triggering points: (1) saccade onset under the normal ambient illumination, (2) saccade onset in the total darkness, (3) onset of REMs during REM sleep, (4) flash during REM sleep, and (5) flash during stage 2 sleep. In the central area, positive potentials appeared with waking saccades under the normal ambient illumination (P240L) and REMs (P185R). The latency of P185R associated with REMs was significantly shorter than that of P240L associated with waking saccades. These findings suggest that P185R is evoked by PGO waves occurring just before the REM. A small positive potential appeared in the occipital area with waking saccade under the normal ambient illumination (P260L) and REMs in the total darkness (P250R). Conspicuous absence of these waves for waking saccades in the total darkness suggests that P250R accompanied with REMs reflects activities involved with the cognitive processes occurring when a subject scans a dream image during REM sleep.     

Event-related potentials recorded from the scalp and nasopharynx. II. N2, P3 and slow wave

Scalp and nasopharyngeal recordings of the N2, P3 and slow wave components were compared in a target-detection task. The effects of probability, interstimulus interval, intensity, discrimination difficulty, attention, stimulus omission and modality were evaluated. Waves of opposite polarity to the scalp N2 and P3 components were recorded in the nasopharynx. The scalp and nasopharyngeal N2 components showed different patterns of variation across experimental conditions. These findings indicate that there are two different cerebral processes occurring at the latency of the scalp N2. The scalp and nasopharyngeal P3 components consistently covaried across conditions, suggesting a single underlying process. The slow wave was observed only in the scalp recordings.