Gerald P. Novak

Differentiation of negative event-related potentials in an auditory discrimination task ☆

Several different negative potentials elicited in auditory perceptual tasks make spatially and temporally overlapping contributions to the scalp-recorded event-related potential. Frequent non-target tones in a 2-stimulus oddball pitch discrimination task, when compared with the same stimuli in ignore or simple reaction time conditions, elicit a negative deflection with two peaks (NA1 and NA2) differing in their latency and topography from the exogenous N92-P156 deflections. Oddball tones, when compared with the frequent ones, elicit mismatch negativity (MMN) in both ignore and discrimination conditions; MMN displays a frontocentral-posterolateral polarity inversion. In the discrimination condition, MMN is followed by N2 and P3b; the former has a more central amplitude maximum than MMN, and no posterolateral polarity inversion. When the pitch discrimination task was made more difficult, there was no effect on NA1 or NA2, but the latency of MMN, N2, P3b, and reaction time all increased in parallel. It is hypothesized that MMN reflects the outcome of an automatic mismatch detection process, and that the subsequent processing of targets is related to the event of mismatch detection.

Cortical responses to speech sounds and their formants in normal infants: maturational sequence and spatiotemporal analysis

Cortical auditory evoked potentials (AEPs) to the synthesized syllables [da[ and [ta[ and to the isolated 3 formants of [da[ were obtained from 32 normal infants studied at monthly intervals from birth through 3 months and at 6 months of age. A bilateral array of 16 electrodes referenced to the mid-occiput permitted a topographic analysis of the cortical AEPs at selected latencies. A differential maturational sequence was seen: a predominantly negative cortical AEP wave form became positive, first over the frontocentral region (around term), and then over the temporal region (at 1-2 months). The timing of these electrophysiological changes coincides with a differential anatomical maturational sequence in the auditory cortex, as myelination and synaptogenesis are more advanced in primary than secondary auditory areas at term. All infants in this study followed this developmental sequence. However, there was no systematic effect of the center frequency of the formant stimuli on the maturational level of their respective cortical AEPs, suggesting a relative maturational equivalence in those regions of auditory cortex responding to stimuli across the frequency range present in human speech. In term infants, an initial midline positivity and bitemporal negativities were asynchronous in their peak and offset latencies. suggesting independent generators for each of these components. In infants from 3 to 6 months of age, cortical AEP wave forms consisted of 2 initial positive peaks followed by a negative peak. While the wave forms were similar over midline and lateral scalp, spatiotemporal analysis revealed differences in the latency of onset, duration and in the spatial extent of these components, again suggesting that 2 bilateral, temporally overlapping generators contribute to the cortical AEP. No systematic topographic difference was observed in the cortical AEPs elicited by each of the 3 formants, which differed in center frequencies.

The Role of Brain Computed Tomography in Evaluating Children with New Onset of Seizures in the Emergency Department

Summary: Background: The purpose of neuroimaging of a patient with new onset of seizures is to demonstrate cause and explore the prognosis. It was recently recommended that emergency brain computed tomography (CT) be performed only in adult seizure patients with an increased likelihood of life‐threatening lesions, i.e., those with new focal deficits, persistent altered mental status, fever, recent trauma, persistent headaches, history of cancer, history of anticoagulation, or suspicion of acquired immunodeficiency syndrome. The objective of this study was to determine the diagnostic utility of emergency brain CT in children who present to the emergency department with new onset of seizures.

The Value of Early Postictal EEG in Children with Complex Febrile Seizures

Summary: Purpose: To assess the usefulness of an early post‐ictal EEG in neurologically normal children with complex febrile seizures.

Lorazepam in the Treatment of Refractory Neonatal Seizures

We report the results of treatment of intractable seizures with lorazepam in seven neonates. All of the patients were part of a prospective study, who failed to respond to 40 mg/k of phenobarbital. Lorazepam was given intravenously at 0.05 mg/k and repeated up to a total dose of 0.15 mg/k if necessary. The diagnosis of seizures and the efficacy of treatment was assessed clinically and by EEG during the administration of lorazepam in three patients and on clinical grounds in four patients. Six patients were full term and one was premature; there were five males and two females. Four patients had hypoxic-ischemic encephalopathy, two had intracranial hemorrhage, and one had bacterial meningitis. Two patients received one dose of lorazepam, three received two doses, and two received three doses. Six patients responded with a complete cessation of seizures within three minutes of their last dose; the remaining patient (who received two doses) had a reduction in seizures. No patients developed apnea or hypotension during or immediately after the infusion of lorazepam and no other adverse effects were observed. Four patients remained seizure-free for the rest of the neonatal period and no other anticonvulsant medications were added. Seizures recurred in one patient at 16 hours; subsequent intermittent seizures were managed with additional phenobarbital. In another patient, seizures recurred at 12 hours and subsequent intermittent seizures were managed with phenytoin. In one patient, seizures continued with reduction of frequency and duration. We conclude that lorazepam may be effective in the treatment of neonatal seizures refractory to phenobarbital and that further treatment with intravenous phenytoin may be unnecessary under these circumstances. (J Child Neurol 1991;6:319-323).

MRI in neonatal dural sinus thrombosis

Dural sinus thrombosis in the newborn period is a rare but underrecognized condition which may cause seizures, macrocephaly, lethargy, and respiratory depression. A 10-day-old term infant with no pre- or perinatal risk factors for thrombosis presented with seizures and was found to have dural sinus thrombosis on computed tomography and magnetic resonance imaging (MRI). One week later, MRI revealed partial resolution and 3 weeks later disclosed a complete resolution of the thrombosis. Clinicians should consider the diagnosis of neonatal dural sinus thrombosis in infants presenting with seizures and/or increased intracranial pressure even in the absence of risk factors or when the cranial computed tomography is normal. MRI is the most sensitive diagnostic tool to establish the diagnosis and permit a noninvasive follow-up, contributing to our understanding of the natural history, associated pathology, and prognosis of this condition.

Ethanolamine kinase activity in purified myelin of rat brain

Abstract: Highly purified rat brain myelin showed a significant level of ethanolamine kinase, amounting to 17% of the specific activity of whole brain homogenate. This kinase level in myelin was an order of magnitude higher than that of lactate dehydrogenase, a marker for cytosol. Subcellular distribution studies revealed that in addition to myelin, this kinase was present in the P1, P2, P3, and cytosolic fractions with highest relative specific activity in the latter. The possibility that myelin activity resulted from adsorption of the soluble enzyme was unlikely since activity was retained in myelin that had been washed with buffered sodium chloride or taurocholate. Mixing experiments and repeated purification further indicated that the enzyme is intrinsic to myelin. Kinetic studies indicated similar Km values for ethanolamine in the microsomal, cytosolic, and myelin fractions but a significantly lower apparent Km for ATP in myelin. This and other differences suggested the possible existence of isozymes. Establishment of the presence of this kinase completes the list of phospholipid synthesizing enzymes needed to synthesize phosphatidylethanolamine from diacylglycerol within the myelin membrane.

Brainstem Glioma Presenting as Paroxysmal Headache

An unusual case of brainstem glioma is described. The distinctive features were long duration (at least six months) of headaches preceding the appearance of neurological signs, and the intermittent, paroxsymal nature of the symptoms, often precipitated by postural change. The mechanism of headache induced by brain tumor is discussed, and a possible cause for the headaches in this patient is suggested, involving intermittent obstruction of CSF flow.