Effects of neurodevelopmental risk factors on brainstem maturation in premature infants

BACKGROUND

Interpeak latencies (IPL), as measured by the auditory brainstem-evoked responses (ABR) test, represent the conduction time, and therefore the maturation of the brainstem auditory pathway. We aimed to study the effect of various risk factors for the neurodevelopmental delay on the conduction time in the auditory pathway among normal hearing premature infants, at term postmenstrual age (PMA).

METHODS

Retrospective analysis of 239 premature infants (gestational age 32.5 ± 2.1 weeks, birth weight 1827 ± 483 g). Interpeak latencies, demographic data, and risk factors were recorded.

RESULTS

Sex, PMA at ABR test, being small for gestational age (SGA), intraventricular hemorrhage (IVH) or periventricular leukomalacia (PVL), and days of invasive ventilation were found to significantly affect the IPL's in the auditory pathway in a univariate analysis. Multivariable regression analysis revealed that male sex and less advanced PMA at the examination were independent factors associated with prolonged IPL's, while bronchopulmonary dysplasia, IVH or PVL and being SGA shortened the IPL's. Non-invasive mechanical ventilation, did not affect the caudal part of the auditory pathway, despite its high noise level.

CONCLUSIONS

Among various risk factors for the neurodevelopmental delay, male sex was associated with delayed, while IVH or PVL, BPD and SGA could be associated with accelerated auditory brainstem maturation.

IMPACT

Auditory brainstem-evoked response (ABR) test, among normal hearing infants, can serve as a clinical tool to assess brainstem auditory maturation. Different neurodevelopmental risk factors could have different effects on the maturity of the auditory pathway. Male sex is significantly associated with prolonged interpeak latencies (IPL) among preterm and term infants, while intraventricular hemorrhage or periventricular leukomalacia, bronchopulmonary dysplasia, and being small for gestation age may be associated with shortened IPL The corrected age at ABR testing is of significance, among preterm and term infants.

Programming effects of maternal and gestational obesity on offspring metabolism and metabolic inflammation

With the increasing prevalence of obesity in women of reproductive age there is a need to understand the ramifications of this on offspring. The purpose of this study is to investigate the programming effects of maternal obesity during preconception and the preconception/gestational period on adiposity and adipose tissue inflammation in offspring using an animal model. Adult female C57Bl/6J mice were assigned either normal diet, high fat diet (HFD) prior to pregnancy, or HFD prior to and through pregnancy. Some offspring were maintained on normal diet while others started HFD later in life. Offspring were assessed for body composition and metabolic responses. Lipid storing tissues were evaluated for expansion and inflammation. Male offspring from the preconception group had the greatest weight gain, most subcutaneous adipose tissue, and largest liver mass when introduced to postnatal HFD. Male offspring of the preconception/gestation group had worsened glucose tolerance and an increase in resident (CD11c⁻) adipose tissue macrophages (ATMs) when exposed to postnatal HFD. Female offspring had no significant difference in any parameter between the diet treatment groups. In conclusion, this study demonstrates that prenatal and pregnancy windows have independent programming effects on offspring. Preconception exposure affects body composition and adiposity while gestation exposure affects metabolism and tissue immune cell phenotypes.

Correlations between audiogram and objective hearing tests in sensorineural hearing loss

Owing to its subjective nature, behavioral pure-tone audiometry often is an unreliable testing method in uncooperative subjects, and assessing the true hearing threshold becomes difficult. In such cases, objective tests are used for hearing-threshold determination (i.e., auditory brainstem evoked potentials [ABEP] and frequency-specific auditory evoked potentials: slow negative response at 10 msec [SN-10]). The purpose of this study was to evaluate the correlation between pure-tone audiogram shape and the predictive accuracy of SN-10 and ABEP in normal controls and in patients suffering from sensorineural hearing loss (SNHL). One-hundred-and-fifty subjects aged 15 to 70, some with normal hearing and the remainder with SNHL, were tested prospectively in a double-blind design. The battery of tests included pure-tone audiometry (air and bone conduction), speech reception threshold, ABEP, and SN-10. Patients with SNHL were divided into four categories according to audiogram shape (i.e., flat, ascending, descending, and all other shapes). The results showed that ABEP predicts behavioral thresholds at 3 kHz and 4 kHz in cases of high-frequency hearing loss. Also demonstrated was that ABEP threshold estimation at 3 kHz was not affected significantly by audiogram contour. A good correlation was observed between SN-10 and psychoacoustic thresholds at 1 kHz, the only exception being the group of subjects with ascending audiogram, in which SN-10 overestimated the hearing threshold.

Excitatory and inhibitory corticospinal responses to transcranial magnetic stimulation in patients with minor to moderate head injury

OBJECTIVES

The changes in excitatory and inhibitory responses to transcranial magnetic stimulation (TMS), as attested by motor evoked potential (MEP) and silent period (SP) parameters, were compared in patients who sustained minor to moderate head injury.

METHODS

A total of 38 patients with brain concussion, and diffuse, focal, and combined brain injury and 20 healthy volunteers were examined. The MEPs and SPs were recorded from the abductor pollicis brevis muscle after single pulse TMS 2 weeks after head trauma. The parameters assessed were the MEP resting threshold, the MEP/M wave amplitude ratio, the central motor conduction time (CMCT), the SP threshold, the interthreshold difference (ITD), and the SP duration (SPD).

RESULTS

The main finding was an increase in the ITD in patients with mild and moderate head injury due to the relatively greater augmentation of the MEP threshold. This was associated with a reduction of the MEP/M wave amplitude ratio. The degree of MEP and SP changes depended on severity of head injury and was not related to the type of brain lesions. The SPD did not differ significantly in brain concussion, or diffuse, focal and combined brain injury groups compared with the control group. The CMCT was prolonged in patients with diffuse and combined brain lesions. Among subjective complaints only fatigue was significantly related to ITD, MEP, and SP threshold abnormalities.

CONCLUSIONS

The results suggest that mechanisms involved in MEP and SP generation are differently affected in head injury, the first being impaired more severely. The increase of the ITD accompanied by reduction of the MEP/M wave amplitude ratio may reflect a dissociated impairment of inhibitory and excitatory components of central motor control in head trauma.

Results of otovestibular tests in mild head injuries

The neurotological workup of patients with minor head trauma was carried out prospectively. The preliminary results of the ongoing study were derived from 38 subjects (12 female, 26 male) at an average age of 33.5 years. All had been hospitalized after having suffered minimum head trauma followed by a temporary loss of consciousness, by amnesia, or by vomitting. The 38 subjects underwent the examination within 72 hours of the event and were summoned for a follow-up visit 3 months later. The anamnestic data show that the most frequent complaint was dizziness (81%). Tinnitus was noted in fewer than one-half of the patients, with a variety of descriptions. Twenty-six percent complained of hearing loss. The correlation between reported hearing loss and the finding on subsequent behavioral audiometry (within 72 hours after the event) was studied. The sensitivity of hearing loss (as complaint) was found to be only 40%, but its specificity was much higher at 83%. The overall equilibrium reflected in the composite score of the sensory testing in computed dynamic posturography actually worsened between tests. A good correlation was found between posturography results and symptomatology. We concluded that, after minor head trauma, most patients suffer from dizziness, and more than one-half complain of tinnitus or hearing loss. The unsteadiness does not subside within 3 months after concussion. A more protracted follow-up is required to summarize the outcome of head injury from a neurootological point of view. A clear correlation is found between complaints and posturography results. After minor head trauma, pure vestibular injuries are much less frequent than are central lesions. Motor dysfunction is less frequent than are the sensory abnormalities.

Classification of brain-stem trigeminal evoked potentials in multiple sclerosis, minor head injuries and post-concussion syndrome pathologies by similarity measurements

In this study measurements obtained from brain-stem trigeminal evoked potentials (BTEP) are applied to the problem of diagnosing Multiple Sclerosis (MS) and Post-concussion syndrome (PCS). We present a simplistic model that depicts the BTEP waveform as the linear combination of a set of filters excited by a short stimulus. The relation between the BTEP latencies and the 1st to 4th harmonic components is shown. The performance of a fuzzy similarity measure based classifier is compared with that of human experts. The efficiency of the proposed classifier in conjunction with delay time and amplitude features is examined. Using this novel approach, a classification rate of 93.55% and 84.1% for MS and PCS pathologies, respectively, was achieved. This performance compares favorably to the classification rates of 84.28% for MS and 70.47% for PCS pathologies achieved by human experts.

Dissociation of somatosensory and motor evoked potentials in non-comatose patients after head injury

OBJECTIVES

This study was performed to evaluate the clinical value of combined use of somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) in patients with different brain lesions after head trauma.

METHODS

A total of 64 patients with minor and moderate head injury were investigated by means of SEPs recorded over the parietal and frontal areas and MEPs following single-pulse transcranial magnetic stimulation (sTMS) and slow-rate repetitive transcranial magnetic stimulation (rTMS).

RESULTS

In almost 50% of the patients, a dissociated impairment of somatosensory and motor evoked potentials was found. This dissociation was related to different distribution of SEP and MEP abnormalities in head injury subgroups. The higher threshold to sTMS and increased variability of the MEP amplitude during slow-rate rTMS were the most prominent features in patients with focal brain contusions, suggesting impairment of the cortical excitability. SEP abnormalities, as well as central conduction impairments, were more noticeable in patients with diffuse brain injury.

CONCLUSIONS

A combined analysis of SEPs and MEPs may improve the assessment of cortical dysfunctions and central conduction abnormalities in non-comatose patients with head injury. A slow-rate rTMS may be considered as a complementary technique to the evaluation of the threshold in assessment of the excitability of the motor cortex in minor and moderate head injury.

[Exhaustion of motor cortex after head injury--revealed by transcranial magnetic stimulation]

We evaluated the pattern of motor evoked potentials elicited by single-pulse and slow-rate (1 Hz) repetitive, transcranial, magnetic stimulation (RTMS) in minor head injuries. The motor response to a single magnetic stimulus in patients with minor head injury was characterized by a significantly higher threshold than in healthy subjects. However, central and peripheral motor conduction was normal in all patients. A stable pattern of MEP throughout the RTMS session was the most prominent feature in the control group. A progressive decrease in MEP amplitude and irregular alternation of large and very small MEPs over the course of RTMS was observed in minor head injury. The higher threshold of the motor response and the abnormal patterns of MEP behavior revealed by RTMS may reflect impaired excitability and enhanced exhaustion of the motor cortex in patients with minor head injuries, which improve with time.

Altered excitability of the motor cortex after minor head injury revealed by transcranial magnetic stimulation

This study attempts to find out whether the motor evoked potential (MEP) elicited by single pulse and slow-rate (1 Hz) repetitive transcranial magnetic stimulation (TMS) can disclose concealed subclinical impairments in the cerebral motor system of patients with minor head injury. The motor response to single pulse TMS (STMS) of the patient group was characterized by significantly higher threshold compared with that of the control group. The central motor conduction time, as well as the peripheral conduction time were normal in all patients pointing to cortical impairment. Two main patterns of MEP changes in response to repetitive TMS (RTMS) were observed in the patient group. A.--progressive decrease of the MEP amplitude throughout the stimulation session to a near complete abolition. B.--irregularity of the amplitude and the waveform of the MEP in a chaotic form. The MEP latency remained stable during the whole stimulation session. The MEP abnormalities recovered gradually over the period of a few months. The higher threshold of the motor response to STMS and the abnormal patterns of the MEP to RTMS seem to reflect transient impairment of cortical excitability or "cortical fatigue" in patients who sustained minor head injures. Further study is needed to evaluated the extent and the pathophysiological mechanisms of the central nervous system fatigue phenomenon following head injury.

Onset and course of the first schizophrenic episode

Schizophrenia seems to occur with equal frequency in all countries and cultures. The ecological and social disparity of prevalence rates in open societies is not due to social causes, but to selection processes. At what point in the course of the disease social disadvantage begins and on account of which mechanisms is a question of both theoretical and practical importance. In a representative sample of 232 first episodes the true onset of schizophrenia is assessed by means of a standardized interview (IRAOS). The onset is 3 to 4 years later in women than in men, which is a result of the protective effect of estrogens as confirmed by animal experiments and by a controlled clinical study. For women the distribution of disease onset across the entire age range shows a delayed increase in adolescence and a second peak in the age group 40-45, presumably due to the fading effect of estrogen around menopause. For three quarters of all schizophrenias the onset lies between 15 and 30 years of age, the period of steepest social development. The distribution of the social biography through the psychosis, which occurs on average 3-4 years earlier in males than in females, determines the social starting conditions of the disorder and affects the early social course. Nearly 75% of the total cases begin with a prodromal phase of 5 years on average. The psychotic prephase lasts 1.1 years. The mainly negative prodromal symptoms are often associated with social and cognitive deficits already at this stage. In a case control study social stagnation or decline occur already during the prodromal phase. After the end of the first episode the mean values of social disability and the objective social status remain fairly stable over a period of at least three years. So far treatment and rehabilitation measures are not started until after first admission, which means after several years' duration of the disease when the majority of social deficits have already become manifest.

Brain-stem trigeminal and auditory evoked potentials in multiple sclerosis: physiological insights

Thirty-six patients with multiple sclerosis were evaluated by means of brain-stem trigeminal and auditory evoked potentials. The brain-stem auditory evoked potentials (BAEPs) were abnormal in 26 patients (72.2%). Brain-stem trigeminal evoked potentials (BTEPs) yielded similar results, showing distorted waveforms and/or prolonged latencies in 25 patients (69.4%). As expected, the MRI proved to be the most efficient single test, revealing plaques in 86.4% of the patients evaluated. However, the diagnostic accuracy of MRI was lower than that provided by the combination of the BTEP and BAEP (88.9%). Moreover, in patients having signs of brain-stem involvement, the BTEP, alone and in combination with the BAEP, proved to be more sensitive than the MRI in revealing brain-stem lesions. Correlation between clinical and BTEP findings could be found only in those patients who presented with signs of trigeminal involvement such as trigeminal neuralgia or dysesthesiae. The analysis of the BTEP waveforms showed two distinct types of abnormality-a peripheral type and a central type-suggesting plaques in distinct locations. Both the BTEP and the BAEP demonstrated a correlation with the clinical course of the disease and the condition of the patient at the time of the evaluation. Relapse of the disease was associated with a marked prolongation of the central conduction time in the BTEP and in the BAEP, suggesting the application of such studies to the monitoring of unstable patients in the evaluation of new therapeutic protocols.

[Motor potentials evoked by magnetic stimulation--a tool for objective assessment of motor conduction along the spinal cord and its roots]

Magnetic stimulation of the motor cortex and nerve roots in conjunction with F-wave recording was used for assessment of central and peripheral motor conduction times in 98 patients suffering from myelopathy and cervical or lumbo-sacral radiculopathy. Significant prolongation of the central motor conduction times was found in the myelopathy group. The Motor Evoked Potential was of low amplitude and distorted shape. The amplitude of the F-wave was markedly increased. The main feature of the radiculopathy group was prolonged motor root conduction time as evident by delayed F-wave. Motor evoked potentials proved to be a reliable objective tool in the functional evaluation of conduction along the spinal cord and its roots.

Intracranial recording from the brain-stem and the trigeminal nerve following upper lip stimulation

Short latency evoked potentials following stimulation of the upper lip were recorded intracranially during neurosurgical procedures in 14 patients. In 10 patients, a suboccipital craniectomy provided direct access to the trigeminal root and the pons at the root entry zone. Direct recordings from the trigeminal root were characterized by a large triphasic potential at 2.4-2.7 msec. The latency of this potential increased as a result of moving the recording electrode proximally towards the brain-stem. The same potential could be recorded from the brain-stem surface at a latency suggesting an intra-axial presynaptic origin. A second component, N4.7, was recorded from over the most rostral aspect of the brain-stem in 3 patients and from the tentorium free edge in 4 patients. This potential of smaller amplitude did not show significant difference in latency or polarity at various electrode locations, suggesting a deep diencephalic origin remote from the recording electrode.

Do Frenzel glasses have a place in the modern electronystagmography laboratory?

Electronystagmography (ENG) is generally performed with the patient's eyes closed to prevent visual fixation. In this way, direct observation of eye movements is impossible. By means of Frenzel glasses (FG), the direct observation of eye movements is possible, but the effectiveness of visual fixation suppression and the diagnostic contribution of FG must still be studied. One hundred seven patients with vertigo participated in this study. Each patient underwent a complete ENG test under two fixation modalities: (a) closed eyes and (b) open eyes with FG. The spontaneous nystagmus and the Hallpike test did not show any significant difference between the two fixation modalities. The slow-phase velocity of nystagmus with the caloric test was significantly greater with closed eyes, but the pattern of nystagmus with FG fixation was more tooth-shaped and regular than that with closed eyes. It is concluded that using FG when performing an ENG may improve its diagnostic value.

Trigeminal and auditory evoked responses in minor head injuries and post-concussion syndrome

Forty patients who sustained minor head trauma were investigated by brainstem trigeminal and auditory evoked potentials (BTEP, BAEP) and middle-latency auditory evoked potentials (MLAEP). The patients were evaluated within the first 48 h following their admission and at 3 months after the injury. Outcome was scored at the follow-up examination according to six complaints: failure to resume previous professional activity, headache, memory disorders, dizziness and vertigo, behavioural and emotional disturbances, and other symptoms of a neurological nature. Post-concussion syndrome (PCS) was defined by the presence of four or more of the listed features. All three evoked potential modalities showed significantly increased latencies at the initial assessment, disclosing disseminated axonal damage. Unlike the BTEPs and the BAEPs, the MLAEPs proved to correlate to outcome at 3 months, especially in its psychocognitive aspects. These findings suggest that organic diencephalic-paraventricular primary damage may account for the occurrence of PCS.

Motor and somatosensory conduction in cervical myelopathy and radiculopathy

STUDY DESIGN

Motor and sensory conduction times were measured in patients with cervical myelopathy and radiculopathy. The results were compared with those of control subjects.

OBJECTIVE

To evaluate the clinical value of the combined use of motor-evoked potentials with F wave recording and somatosensory-evoked potentials in cervical myelopathy and radiculopathy.

SUMMARY OF BACKGROUND DATA

Electromyography and somatosensory-evoked potentials provide only indirect information on the motor pathways. The development of magnetic transcranial stimulation has provided a direct and reliable physiologic insight into the motor system.

METHODS

Magnetic stimulation of the motor cortex and nerve roots with F wave recording was used to assess central and peripheral motor conduction times. Somatosensory conduction was evaluated by somatosensory-evoked potentials.

RESULTS

Significant prolongation of the central sensory and motor conduction times was found in the group with myelopathy. These findings were much more pronounced in patients who had multiple level spondylotic stenosis of the spinal canal than in those harboring a single disc herniation compressing the spinal cord. In contrast to somatosensory-evoked potentials, motor-evoked potentials combined with F wave recording showed marked impairment of peripheral conduction in patients with radiculopathy.

CONCLUSION

Motor-evoked potentials associated with F wave recording was suitable for the evaluation of patients with radiculopathy. The severity of conduction impairment in patients with myelopathy can be assessed by combined motor-evoked potentials and somatosensory-evoked potentials.

[Short-latency, brainstem, trigeminal evoked-potentials]

Short-latency, evoked-potentials were recorded from over the scalp in response to electrical stimulation of the upper lip, using the Microshev 4000 equipment (Microshev Co., Efrat). Normative data were obtained from 35 normal volunteers. The brain-stem, trigeminal evoked-potentials (BTEP) consisted of 4 distinct, well-reproduced waves evoked in less than 10 msec. The waves, named after their respective latencies, are thought to be generated in the preganglionic trigeminal nerve (T1), the postganglionic nerve entry zone (T2), in the trigeminal nucleus (T3) and the upper brainstem (T5). BTEP was recorded in nearly 200 patients suffering from various lesions in the peripheral trigeminal parts, tumors affecting the brainstem (before, during and after surgery) and in varying degrees of post-traumatic coma. BTEP proved to be a reliable tool for evaluating the brainstem trigeminal system; changes in its pattern reliably reflected altered activity of that system. It can be used for diagnosis as well as for intraoperative monitoring of brainstem function.

New perspectives in the epidemiology of schizophrenia

It was with great pleasure that I accepted the invitation to contribute to the present symposium in honour of my friend Jules Angst. It gives me the opportunity to pay tribute to his outstanding scientific work. The topic of my presentation has been inspired by the genius loci. In his foreword to a proceedings volume entitled 'Die Entstehung der Schizophrenie' (The Origin of Schizophrenia), which he edited on the occasion of the 100th anniversary of the Psychiatric University Hospital Zurich in 1970, Jules Angst pointed out that two former heads of the 'Burgholzli', Eugen and Manfred Bleuler, who had held that office longest, had dedicated their life's work to schizophrenia, which had received its name from Eugen Bleuler. Jules Angst's most successful research field has been psychiatric epidemiology. I therefore thought it appropriate to talk about new perspectives in the epidemiology of schizophrenia.

Prevalence and course of depression among elderly residential home admissions in Mannheim and Camden, London

A longitudinal study based on consecutive admissions to all residential homes for the elderly was conducted in the industrial city of Mannheim (Germany) and in the London borough of Camden (England). Inclusion criteria were that the elderly persons (65 years old and older) came directly from their own home or, if transferred from a hospital, had been there for less than 3 months. At each site, 60 home residents were interviewed at admission and 3 months and 8 months later. Depression and dementia were assessed with the aid of the Brief Assessment Scale. The prevalence of depression (Mannheim: 34.6%; Camden: 47.9%) was already high at admission and did not change significantly over time. Residents in Camden were more demented and more impaired in their activities of daily living at the time of admission, and the percentage of those who died or were transferred to a hospital or nursing home within 8 months thereafter was higher in Camden (30%) than in Mannheim (5%). Multiple regression analysis revealed that, in both study areas, depression at baseline was the best predictor for depression 3 months and 8 months later. This relationship was particularly strong in Camden, where a high percentage of the depressed at admission showed a chronic course of illness. Sex, age, home visits, social isolation, activities of daily living, cognitive impairment, and somatic symptoms at the time of admission were not significantly associated with depression 3 months later. Eight months after admission, a similar pattern was found in Mannheim. In Camden, however, in addition to depression, a lack of home visits by relatives and friends, and somatic symptoms at baseline, were significant predictors of depression 8 months after admission.

Intra- and extra-uterine development of neonatal 3-channel Lissajous' trajectory of auditory brainstem evoked potentials

This study compared intra- and extra-uterine maturation of the auditory pathway, using auditory brainstem evoked potentials (ABEPs), recorded with three orthogonal differential electrode configurations. From the three records of each subject, 3-channel Lissajous' trajectories (3CLTs) were derived and analyzed. 107 newborns were compared at the same gestational and post-conceptional (gestational+postnatal) age, from 29 weeks (wks) up to 43 wks. In addition, we explored the effects and neurophysiological consequences of early exposure to extra-uterine life, on the peripheral and central portions of the auditory pathway. Our findings indicate that exposure of premature infants to the extra-uterine environment is associated with advanced peripheral development, but slower central conduction compared to intra-uterine development.

A physiological coma scale: grading of coma by combined use of brain-stem trigeminal and auditory evoked potentials and the Glasgow Coma Scale

Forty-five comatose patients were prospectively studied by means of clinical examination and evoked potentials. In each patient, clinical data included Glasgow Coma Scale (GCS) score, age, pupillary response to light, corneal reflex, and eye movements. Neurophysiological evaluation was based on brain-stem trigeminal evoked potentials (BTEPs) and brain-stem auditory evoked potentials (BAEPs). For each physiological test, a progressive grading system was designed. This system was based on the evaluation of central conduction times along the trigeminal and the auditory pathways within the brain-stem. The accuracy of the clinical and the neurophysiological indicants in predicting "favorable" or "unfavorable" outcome was assessed singly and in combination. Of the clinical indicants, the GCS provided the most accurate prognosis (80%). Similar results were provided by the BAEP and the BTEP, with significant improvement in the confidence of outcome prediction. No significant difference in the accuracy of outcome predictions could be found between combined clinical data and neurophysiological data. However, the combination of clinical and neurophysiological data markedly increased both the accuracy and the confidence of outcome prediction, reaching 86% correct predictions at the over 90% confidence level with only 2% false pessimistic errors. According to these findings, a clinical-physiological coma scale, the trigeminal-auditory Glasgow (Coma Scale) score (TAG score) was designed. The TAG score demonstrated the highest accuracy at each confidence level as compared to other single indicants. We concluded that the TAG score may improve the evaluation of deep comatose patients and assist the physician in the management of such patients.

Monitoring of brain-stem trigeminal evoked potentials. Clinical applications in posterior fossa surgery

Brain-stem trigeminal evoked potentials (BTEPs) were monitored intraoperatively in 17 patients during posterior fossa surgery. Satisfactory BTEP recording was performed in all patients without technical problems or interfering with the activity of the operating team. The BTEP was not altered by anesthetic agents or muscle relaxants. Intraoperative monitoring of the BTEP showed wave form alterations or increasing peak latencies in 10 patients. Among these patients, the BTEP demonstrated a dynamic correlation with the surgical process in 8 instances. Two major causative surgical manipulations were identified: cerebellar retraction in 4 cases and tumor dissection from the brain-stem in 6 cases. Withholding the dissection of the tumor, readjusting a cerebellar retractor or further modifying the surgical attitude resulted in partial or complete return of the wave form in 7 patients. The BTEP at the end of surgery proved to correlate with the immediate surgical outcome in most instances. We concluded that the intraoperative monitoring of the BTEP was feasible and suggested, despite the small number of patients, a potential value in the survey of brain-stem functions during posterior fossa surgery.

Critical ages in brainstem development revealed by neonatal 3-channel Lissajous' trajectory of auditory brainstem evoked potentials

Auditory brainstem evoked potentials (ABEPs) were recorded from 91 newborns from 7 age groups between 26 to 43 weeks of gestation. In addition to the widely used vertex-mastoid derivation, potentials were recorded from three orthogonal electrode configurations, and represented in 3 dimensional voltage-space as three-channel Lissajous' trajectories (3CLTs). ABEPs were evoked by alternating polarity, monaural 75 dBnHL clicks presented at rates of 10/s, 55/s and 80/s. Potentials were also recorded to 45 dBnHL and 15 dBnHL clicks presented at 10/s. 3CLT point by point (apex latencies, amplitudes and orientation) as well as planar segment (planar segment position and duration) descriptors, along with peak latencies of the vertex-mastoid peaks, were followed for effects of age, stimulus intensity and rate. ABEPs began to appear consistently at 29 weeks of gestation to high stimulus intensities, with a rapid decrease of ABEP thresholds up to 34 weeks. At 35 weeks, thresholds stabilized approximately at adult values. The results indicate a significant effect of stimulus rate and intensity as well as of gestational age group on apex latencies. The findings also showed changes in apex orientations associated with stimulus rate and intensity interacting with gestational age. 3CLT descriptors enhanced the understanding of these results in relation to developmental and maturational aspects of the auditory system. The results may be explained by maturational change in relative contributions of constituents of the complex ABEP generators.

Short latency trigeminal evoked potentials: normative data and clinical correlations

A very short latency trigeminal evoked potential (STEP) to electrical stimulation of the upper lip has been recorded from over the scalp. This potential consists of 5 distinct peaks within the 12 msec range. Normative data were obtained from 25 healthy volunteers. The impact of the stimulus rate and intensity on the response was studied in each subject. These results were compared to those of 19 patients suffering from lesions involving the trigeminal system in its peripheral aspect or the brain-stem. The STEP was consistently abnormal whenever the involved side was stimulated. Changes in peak latencies and in interpeak latency differences (IPLD) correlated well with clinical and radiological findings and improved with the removal of the offending lesion. The STEP proved to be a reliable method for evaluating the trigeminal system in its peripheral and central pathways; it may thus serve as an additional parameter for studying brain-stem functions.

Development of auditory brainstem evoked potentials in newborn infants: a three-channel Lissajous' trajectory study

Auditory brainstem evoked potentials (ABEP) were recorded from 50 newborns (35-43 weeks gestational age), using three orthogonal differential electrode pairs, in addition to the widely used vertex-mastoid derivation. Potentials were evoked by alternating polarity, 75 dBnHL clicks presented monaurally at a rate of 10/s. From the records of the three orthogonal electrode pairs (nasion-inion; vertex-spinous cervical process VII; left-right mastoids), Three-channel Lissajous' trajectories (3CLT) were derived and analyzed. 3CLT point-by-point, as well as segmental descriptors were compared with peak latencies of the vertex-mastoid derivation. Point-by-point 3CLT descriptors included apex amplitude, latency and orientation. Segmental descriptors included planar segment beginning latencies, duration and orientation. The interpretation of these results in relation to developmental aspects of the auditory system, as well as to the question of ABEP generators, is enhanced by using 3CLT descriptors of ABEP, which are more comprehensive than their single-channel counterparts. 3CLT apices correlated well with the Vertex-Mastoid defined peaks. Both peak and apex latency changes indicate that at the developmental stages surveyed in this study, development takes place in the more central portions of the pathway, whereas the peripheral portion is already relatively mature. The results also indicate a maturational change in the relative contributions of constituent generators of ABEP components.

Auditory brainstem evoked potentials in evaluating the efficacy of surgical ventilation of the middle ear

Conductive hearing loss in children is most commonly associated with Secretory otitis media (S.O.M.). Since auditory brainstem evoked potentials (ABEP) reflect conductive damage in prolonged peak latencies, the present study evaluated the efficacy of surgery for ventilating the middle ear, by comparing changes in peak latencies. These changes were compared in 4 groups of children (4-12 years old): children with S.O.M. in the past, who recovered as a result of conservative treatment; children with S.O.M. in the past, who had been operated on with insertion of ventilation tubes (V.T.); children with S.O.M. in the past, who had been operated on and who still had V.T. at the time of study, and a control group with healthy ears. In all, 183 ears were tested. The results indicate that there is no significant audiometric and electrophysiological difference between the groups who recovered with or without V.T.

Auditory brainstem evoked potentials in evaluating the central effects of middle ear effusion

Auditory brainstem evoked potentials (ABEP) were recorded to determine whether children who suffered in the past, or suffered at time of examination from Secretory otitis media (S.O.M.), exhibited slowed conduction along their auditory brainstem. Five groups of subjects were examined: children with active S.O.M. during the examination, children with S.O.M. in the past who were treated non-surgically and recovered, children with S.O.M. in the past who were treated surgically and recovered, children who were treated by insertion of ventilating tubes (V.T.), and had S.O.M. during the examination (recurrent S.O.M.), and a control group of neurologically and audiologically normal, age-matched children with no history of S.O.M. 205 ears were tested in all. Each of the groups was subdivided according to the severity of hearing loss, duration and type of treatment. These parameters were evaluated within and between groups, and in relation to the control group. Significant increases of interpeak latency differences (IPLD) between peaks V and III as well as V to I were found in the S.O.M. groups compared to the control group. The duration of the disease was found to be the dominant factor slowing central conduction. These findings confirm the suggestion that attenuation in auditory stimulation at an early age affects central conduction.