Leopold J. Streletz

Scalp recorded auditory evoked potentials and sonomotor responses: An evaluation of components and recording techniques ☆

Abstract Early (0–8 msec), middle (8–50 msec) and long (50–500 msec) latency auditory evoked potentials (AEPs) were recorded from the scalp, ear, nose and mastoid regions of normal adult subjects using a balanced sternovertebral non-cephalic reference system. This study intended to differentiate neurogenic from myogenic components. Components judged to be neurogenic were greatest in amplitude at frontocentral scalp recording locations and were recorded during sleep. Some of these potentials were also recorded from the ear, mastoid and nose which suggests that these locations are often not ideal reference sites for recording AEPs. Certain scalp recorded middle and long latency AEPs were characterized by progressive shifts in their peak latencies in the sagittal and coronal planes. This “traveling wave” phenomenon suggests that these potentials arise in multiple spacially fixed cerebral generators. Components judged to be myogenic had latencies of 8–60 msec, were widely distributed over the scalp and were of greatest amplitude in relationship to actively contracting scalp muscle groups. One of these potentials, the post-auricular response, was recorded from the ear, mastoid and postauricular region. Except for the post-auricular response, these potentials were not observed in sleeping subjects. This suggests that middle latency AEPs can be recorded free of evoked myogenic contamination in normal adults during sleep if the recording electrode is not placed in the vicinity of the ear.

Transcranial magnetic stimulation: Cortical motor maps in acute spinal cord injury

SummaryThis investigation examined the motor pathways of four, C5-6 spinal cord injured (SCI) patients within 6–17 days of injury. Mapping of the motor cortex was achieved by transcranial magnetic stimulation (TMS) applied to the scalp. Motor evoked potentials were recorded from target muscle groups (Biceps brachii and Abductor pollicis brevis m.). Evidence of an expanded cortical map of the preserved contralateral biceps muscle was demonstrated in these patients as early as 6 days. These findings suggested that early motor re-organization may occur following acute cervical spinal cord injury in man.

Computer analysis of EEG activity in dementia of the Alzheimer's type and Huntington's disease

Computer analysis of the EEG was obtained in the course of evaluation of 35 patients with Dementia of the Alzheimers Type (DAT) and Huntingtons disease (HD), and compared to 20 age-matched normal controls. On-line computer analysis of the EEG consisted of: 1) compressed spectral array (CSA) displays (2-6 channels); 2) relative frequency power (4 bands) and 3) an averaged frequency power function [( alpha/alpha + theta power (microV 2)] X 100 = % EEG Power function). Frequency power reflected increased theta, and reduced alpha components, in patient groups. Significant correlation was obtained between % EEG Power function, and clinical stage of dementia. This function correctly identified 17/25 DAT, and 7/10 HD patients, and gave additional quantification to the primary EEG.

Topographic mapping of human motor cortex with transcranial magnetic stimulation: Homunculus revisited.

SummanyThe purpose of this study was to non-invasively evaluate the homuncular organization of the motor cortex in man. We used transcranial magnetic stimulation to induce motor evoked potentials (MEPs) in Abductor Pollicis Brevis (APB) and Biceps Brachii (BB) muscles of 10 healthy volunteers. The practicality and accuracy of magnetic stimulation to scalp sites one cm apart was increased by the application to the scalp of a flexible nylon grid with grid size of 1×1 cm. Responsive scalp sites collectively contributed to distinct but overlapping muscle representational areas for the two muscles. The topography of these motor maps along and slightly anterior to the central fissure corresponds to the homuncular configuration as described by Penfield and Boldrey in 1937.

Utility of serial EEGs in neonates during extracorporeal membrane oxygenation

We found electroencephalographic (EEG) studies to be useful for monitoring cerebral function, for confirming seizure activity, and for limited prediction of short-term outcome in 145 neonates who required extra-corporeal membrane oxygenation (ECMO) of reversible respiratory failure. The EEG tracings were classified as normal or as mildly, moderately, or markedly abnormal; abnormal recordings were further classified as focal, diffuse, or predominantly lateralized. A significant decrease in frequency and degree of EEG abnormalities was observed in recordings obtained after ECMO compared to those obtained prior to (P = .001) or during ECMO (P = .001). There was no significant increase in marked EEG abnormalities when recordings obtained before and during ECMO were compared (P = 0.41). Of 11 infants with electrographic seizures during ECMO, 7 (64%) either died during their nursery courses or were developmentally handicapped at age 1 year which is a significantly greater adverse outcome than that observed in infants without EEG seizure activity (P less than .003). No consistently lateralized EEG abnormalities were observed during or after ECMO when compared to tracings obtained before cannulation of the right common carotid artery. There was no acute change in EEG rhythm or amplitude over the right cerebral hemisphere during right common carotid artery cannulation. Our observations support the value of serial EEG in the assessment of cerebral function in critically ill infants undergoing ECMO. They further suggest that, in this patient population, cannulation of the right common carotid artery is a safe procedure that does not result in lateralized abnormalities of cerebral electrical activity.

Visual evoked potentials in sarcoidosis

The visual evoked potential to pattern reversal was recorded in 50 patients with sarcoidosis. Abnormalities of latency and amplitude were found in 15 patients (30%), including all 4 patients with clinically evident brain disease and 4 of 17 patients with overt ocular disease. Twenty-nine patients had no clinical evidence of ocular or neurologic disease, and 7 of them (24%) had abnormalities of the VEP, implying subclinical sarcoid lesions in structures at the base of the brain.

Right common carotid artery reconstruction after extracorporeal membrane oxygenation : vascular imaging, cerebral circulation, electroencephalographic, and neurodevelopmental correlates to recovery

OBJECTIVE Right common carotid artery (RCCA) ligation after extracorporeal membrane oxygenation by venoarterial bypass may contribute to lateralized cerebral injury. Reconstruction of this artery after extracorporeal membrane oxygenation has proved feasible but has not been evaluated for neurologic outcome in any substantial series of infants. METHODS We evaluated RCCA reconstruction in 47 infants treated with ECMO and compared their cerebrovascular and neuroanatomic imaging findings, electroencephalograms, and developmental outcomes with those of 93 infants who had no reconstruction. SUMMARY RESULTS: Color Doppler blood flow imaging revealed that carotid artery patency was usually obtained after RCCA reconstruction. Right internal carotid and bilateral anterior and middle cerebral arterial blood flow velocities were generally higher, and were more symmetrically distributed in infants with reconstructed RCCA. Electroencephalography did not disclose an increased risk of deterioration or marked abnormalities in infants after reconstruction, nor were neuroimaging findings consistent with an increased number of either focal or generalized abnormalities. Neurodevelopmental follow-up revealed no differences in the incidence of delays between those with a reconstructed RCCA and those with a ligated RCCA during the first year of life. CONCLUSIONS Reconstruction of the RCCA after extracorporeal membrane oxygenation may facilitate normal distribution of cerebral blood flow through the circle of Willis, and may augment both left and right middle cerebral artery blood flow immediately after decannulation. The long-term consequences of either ligation or reconstruction of the RCCA will require careful scrutiny, however, before either course is recommended routinely.

Sensitivity and specificity of the neonatal brain-stem auditory evoked potential for hearing and language deficits in survivors of extracorporeal membrane oxygenation.

OBJECTIVE We determined the sensitivity and specificity of neonatal brain-stem auditory evoked potentials (BAEP) as markers for subsequent hearing impairment and for developmental problems found later in infancy and childhood. METHODS BAEP studies were performed before discharge in infants treated with extracorporeal membrane oxygenation (ECMO), and two specific abnormalities were analyzed: elevated threshold and delayed central auditory conduction. Behavioral audiometry was repeated during periodic follow-up until reliable responses were obtained for all frequencies, and standardized developmental testing was also conducted. The sensitivity and specificity of an elevated threshold on the neonatal BAEP for detecting subsequent hearing loss, and the relationship of any neonatal BAEP abnormality to language or developmental disorders in infancy, were calculated. RESULTS Test results for 46 ECMO-treated infants (57.5%) were normal, and those for 34 infants (42.5%) were abnormal, with either elevated wave V threshold, prolonged wave I-V interval, or both on neonatal BAEP recordings. Most significantly, 7 (58%) of the 12 children with subsequent sensorineural hearing loss had left the hospital after showing normal results on threshold tests. There was no significant difference in the frequency of hearing loss between subjects with abnormal (5/21, or 24%) and those with normal BAEP thresholds (7/59, or 12%; Fisher Exact Test, p = 0.28). Therefore the sensitivity of neonatal BAEP testing for predicting subsequent hearing loss was only 42%. Neonatal BAEP specificity for excluding subsequent hearing loss was 76%. In contrast, on language development testing, 19 children demonstrated receptive language delay. Of these children, 12 (63%) had abnormal neonatal BAEP recordings and 7 (37%) had a normal BAEP threshold, normal central auditory conduction test results, or both (p = 0.04). CONCLUSIONS Neonatal BAEP threshold recordings were of limited value for predicting subsequent hearing loss common in ECMO-treated survivors. However, an abnormal neonatal BAEP significantly increased the probability of finding a receptive language delay during early childhood, even in those with subsequently normal audiometry findings. Because neonatal ECMO is associated with a high risk of hearing and receptive language disorders, parents should be counseled that audiologic and developmental follow-up evaluations in surviving children are essential regardless of the results of neonatal BAEP testing.

Predictive value of neonatal electroencephalograms before and during extracorporeal membrane oxygenation

We studied the prognostic significance of electroencephalograms recorded serially at 2- to 4-day intervals during the acute neonatal course of 119 near-term infants with severe respiratory failure treated by venoarterial extracorporeal membrane oxygenation (ECMO). A poor prognosis was defined as early death (n = 27), an abnormally low developmental assessment score (n = 14), or cerebral palsy (n = 14) at 12 to 45 months of age. The only electroencephalographic abnormalities that were significantly related to a poor prognosis were burst suppression (B-S) and electrographic seizure (ES). The 30 infants with two or more recordings of B-S or ES, when compared with the 58 neonates without such electroencephalographic abnormalities, had an odds ratio for a poor prognosis of 6.6 (95% confidence limits, 2.2 to 20.2). The 31 infants with a single ES or B-S recording did not have a significantly increased risk for a poor prognosis. Cardiopulmonary resuscitation immediately before ECMO (n = 8) and the lowest systolic blood pressure before or during ECMO were significantly related to the occurrence of ES or B-S recordings. There was no significant predilection of ES for either cerebral hemisphere. We conclude that in near-term neonates with respiratory failure, serial electroencephalographic recordings are of predictive value, and may facilitate clinical care including the decision to initiate or to continue ECMO.

Motor evoked potentials and central motor conduction: studies of transcranial magnetic stimulation with recording from the leg

To determine central conduction times in the corticospinal pathways of humans using magnetic stimulation, we have developed a method for consistently recording conduction times between the motor cortex and the L4-5 level of the spinal cord. In 30 subjects, motor evoked potentials (MEPs) were recorded from the tibialis anterior muscle following contralateral motor cortex and peroneal nerve stimulation. In 18 of these subjects, the L4-5 intervertebral space was stimulated. The stimuli consisted of single, painless, short-duration magnetic pulses. In 12 subjects, measurements were made during voluntary ankle dorsiflexion, and during vibration of the TA tendon at rest. All subjects had measureable MEP latencies of 30.3 +/- 2.2 msec (mean +/- S.D.). The central motor conduction time (CMCT) was calculated using both a direct as well as an indirect method. The direct method in 18 subjects had a mean value of 16.2 +/- 1.7 msec, while the indirect method in all 30 subjects was 13.8 +/- 1.8 msec. No significant correlation of the CMCT was found with either age or height in these subjects. Ankle dorsiflexion significantly reduced the MEP latency and increased the amplitude, whereas vibration of the TA tendon significantly increased the amplitude alone. We conclude that MEPs may be consistently and painlessly measured in the lower extremity using magnetic stimulation in adults. Facilitation of the MEPs was produced more consistently by voluntary contraction than by vibratory stimulation of the tibialis anterior muscle tendon. Finally, CMCT was independent of both age and height in our study population.