John Fino

Premature temporal theta (PTθ)

Abstract A distinctive pattern called premature temporal theta (PTθ) was studied in 436 infants, ranging in age from 24 to 46 weeks. The pattern is seen in early prematurity, maximizes at 29–31 weeks and then diminishes and disappears near term. Usually the pattern is found independently on both temporal areas, but with a right-sided preference. Patients without PTθ or with a significantly low amount had either neurological or non-neurological (medical) conditions. With age there is a tendency for an increase in frequency and a decrease in amplitude. Five different peaks in the amount of this pattern are seen at approximately every month. Unilateral PTθ tends to be seen in older babies, more often on the right side and with an abnormal EEG. An abnormal EEG is usually associated with a delay in both the appearance and disappearance of this wave form. PTθ is also associated mainly with REM or active sleep. A polynomial rather than an exponential or power function best describes these data with changes of age. PTθ may arise from the inferior temporal gyrus and/or especially the transverse gyrus.

The importance of phase of stimulus and the reference recording electrode in brain stem auditory evoked potentials

In normal subjects the phase of the stimulus and the reference electrode of the brain stem auditory evoked potential (BAEP) were investigated. Compared to condensation (C), rarefaction (R) clicks produced longer latencies, especially for peaks IN, IIIN and IV and lower amplitudes, mainly for IIN. The amplitude of the initial phase of R clicks was lower in the acoustical wave form (with piezoelectric phones) than the succeeding higher amplitude C phase, but damping characteristics varied with recording conditions. In comparing Ipsi vs. Contra ear reference the Ipsi showed a shorter latency for II and IIN, a longer latency for III, IIIN and IV and a higher amplitude, except for II. The relative contribution of the central vertex (Cz) and of each ear to the standard Cz-ear linkage was determined by referring each to an indifferent electrode. The activity at the Ipsi ear was out of phase with Cz up to peak IV, especially I, IN and III (but not II) with a resulting high amplitude in the Cz-ear linkage; in-phase relationships were noted between Cz and the Contra ear resulting in a relatively low amplitude in the Cz-Contra ear linkage. Discussion of the latter points included the complex, but significant changes of the amplitude and latency of Cz activity by an ear reference.

Brainstem auditory evoked potentials - A review and modified studies in healthy subjects

Summary: The authors review the brainstem auditory evoked potential (BAEP), and present studies on 40 healthy subjects. In addition to the conventional click evoked BAEP, three modified BAEP examinations were performed. The modified BAEP tests include a 1,000 Hz tone-burst BAEP, and more rapid rate binaural click and 1,000 Hz tone-burst BAEPs–each of the last two studies performed at four diminishing moderate intensities. In addition to the usual parameters, the authors examined the Wave V to Vn interpeak latency, and stimulus intensity versus Wave V latency and amplitude functions in the rapid rate binaural studies. Studies were also repeated on healthy subjects in a dependant head position in an attempt to increase intracranial pressure. Discussion centers on the BAEP, its current utility in medicine, unique neurophysiology, and literature support that the above modifications could increase the practicality of the test in patients at risk with intracranial lesions and perhaps improve the feasibility for real-time continuous or frequent monitoring in the future.

The Visual Evoked Potentials to the Light Emitting Diode Compared to the flash and Pattern Reversal Stimulus

Light-emitting diode (LED), flash (FL) and pattern reversal (PR) stimuli were used to elicit visual evoked potentials (VEPs) in 16 normal subjects (32 eyes) and 39 patients (78 eyes) with signs of visual system abnormality. Latencies and amplitudes (plus standard deviations) of 5 components of each response, correlation coefficients of the normal and abnormal responses and false negatives and positives are presented for the 3 kinds of stimuli. The data show that responses to LED stimuli are very similar to those of FL stimuli and should be useful in the operating room to monitor the visual pathways, if various endogenous factors known to affect late responses can be stabilized.

The Significance of the Negativities in the Brainstem Auditory Evoked Potential (Baep)

This study was designed to investigate the negativities of the brainstem auditory evoked potential (BAEP), especially to determine if they represented a part of a composite waveform together with a given positivity. Subjects (10) and patients (56) provided the data, mainly in the form of correlation coefficients of latency and amplitude values, trace by trace comparisons of multiple responses from the same subject and the specific grouping of abnormal waves from the patient population. The results show that the strongest relationships of latency and amplitude involved completely different pairs of waves, that the negative and positive values often changed in opposite directions, and that no pair of waves of opposite polarity were typically abnormal together. Thus, the negativities are not generally associated with given positivities and likely have their own generators.

The effect of light sleep on the brainstem auditory evoked potential (BAEP).

This study dealt with the latency and amplitude changes in the brainstem auditory evoked potential (BAEP) measured during periods from wake to light sleep, after stimulating both ears of 16 subjects. All 13 latencies (positive and negative) increased from the central vertex electrode (referred C7 vertebra) with statistical significance from peak VI (and II), and 8 of 13 latencies increased from the (ipsilateral) ear electrode with statistical significance from negative peak V. Furthermore, a significant decrease in amplitude occurred in peak V (ear) and in peak VIII (Cz and ear). Finally, the more typical recording of vertex to ipsilateral ear showed all 13 latencies increasing in the sleep state and nonparametric statistics showed significance in 6 of these latencies. The assumption that the latencies and amplitudes do not change from the waking to the sleeping state should be reconsidered.

Electrocochleography recorded non-invasively from the external ear

A method is described to record cochlear evoked potentials in humans (ECochG) with a low impedance electrode on the external ear near the opening of the external auditory canal. A piezoelectric click stimulus was delivered to the ear through a polyethylene tube creating diminution of stimulus artifact and a signal delay. Wave forms resembling the cochlear microphonic (CM), summating potential (SP) and the eighth nerve action potential (N1) were differentially accentuated by changes in stimulation and recording parameters. The addition or subtraction of condensation and rarefaction click wave forms further clarified the N1 and SP, or the CM potential, respectively. These responses can be recorded with most contemporary evoked response equipment. This non-invasive method of ECochG lends itself well to the study of hearing loss and possibly other neurologic disorders, and may complement BAER examination especially when wave I is poorly delineated.

Brainstem Monitoring in the Neurocritical Care Unit: A Rationale for Real-Time, Automated Neurophysiological Monitoring

AbstractPatients with severe traumatic brain injury or large intracranial space-occupying lesions (spontaneous cerebral hemorrhage, infarction, or tumor) commonly present to the neurocritical care unit with an altered mental status. Many experience progressive stupor and coma from mass effects and transtentorial brain herniation compromising the ascending arousal (reticular activating) system. Yet, little progress has been made in the practicality of bedside, noninvasive, real-time, automated, neurophysiological brainstem, or cerebral hemispheric monitoring. In this critical review, we discuss the ascending arousal system, brain herniation, and shortcomings of our current management including the neurological exam, intracranial pressure monitoring, and neuroimaging. We present a rationale for the development of nurse-friendly—continuous, automated, and alarmed—evoked potential monitoring, based upon the clinical and experimental literature, advances in the prognostication of cerebral anoxia, and intraoperative neurophysiological monitoring.