Electrophysiological evidence for a defect in the processing of temporal sound patterns in multiple sclerosis

Auditory evoked potentials in children and adolescents with multiple sclerosis and neuromyelitis optica spectrum disorders

BACKGROUND

In children, an acute demyelinating disease may evolve as a multiphasic disease with multiple relapses, such as multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD). The Brainstem Auditory Evoked Potentials (BAEP) and Long-Latency Auditory Evoked Potentials (LLAEP) contribute to the identification of either retrocochlear changes or other central auditory nervous system (CANS) changes.

OBJECTIVES

To characterize BAEP and LLAEP in children and adolescents with MS and NMOSD and verify the diagnostic values of these potentials in each of the demyelinating diseases.

METHODS

The 40 participants were divided into two study groups (SG1 - MS, SG2 - NMOSD) and two comparison groups (CG1 and CG2), matched for age (9 years-17 years and 11 months) and sex. Electrophysiological hearing assessment was performed with BAEP and LLAEP.

RESULTS

When SG1 and SG2 were compared with CG1 and CG2 regarding BAEP and LLAEP, both SG1 and SG2 presented a higher occurrence of changes. Also, individuals with MS had higher occurrences of BAEP changes, whereas individuals with NMOSD had a higher occurrence of LLAEP changes.

CONCLUSIONS

BAEP and LLAEP in children and adolescents with MS or NMOSD showed higher latencies and lower amplitudes of some components when these individuals were compared with their peers. These procedures were highly accurate to identify demyelinating diseases. BAEP results were more abnormal in individuals with MS, while LLAEP was so with NMOSD. These findings indicate that the auditory evoked potentials are important instruments for the differential diagnosis of MS and NMOSD, and valuable to monitor disease evolution.

Effects of Age and Type of Stimulus on the Cortical Auditory Evoked Potential in Healthy Malaysian Children

BACKGROUND AND OBJECTIVES

The cortical auditory evoked potential (CAEP) is a useful objective test for diagnosing hearing loss and auditory disorders. Prior to its clinical applications in the pediatric population, the possible influences of fundamental variables on the CAEP should be studied. The aim of the present study was to determine the effects of age and type of stimulus on the CAEP waveforms.

SUBJECTS AND METHODS

Thirty-five healthy Malaysian children aged 4 to 12 years participated in this repeated-measures study. The CAEP waveforms were recorded from each child using a 1 kHz tone burst and the speech syllable /ba/. Latencies and amplitudes of P1, N1, and P2 peaks were analyzed accordingly.

RESULTS

Significant negative correlations were found between age and speech-evoked CAEP latency for each peak (p< 0.05). However, no significant correlations were found between age and tone-evoked CAEP amplitudes and latencies (p>0.05). The speech syllable /ba/ produced a higher mean P1 amplitude than the 1 kHz tone burst (p=0.001).

CONCLUSIONS

The CAEP latencies recorded with the speech syllable became shorter with age. While both tone-burst and speech stimuli were appropriate for recording the CAEP, significantly bigger amplitudes were found in speech-evoked CAEP. The preliminary normative CAEP data provided in the present study may be beneficial for clinical and research applications in Malaysian children.

Impairment of frequency-specific responses associated with altered electrical activity patterns in auditory thalamus following focal and general demyelination

Multiple sclerosis is characterized by intermingled episodes of de- and remyelination and the occurrence of white- and grey-matter damage. To mimic the randomly distributed pathophysiological brain lesions observed in MS, we assessed the impact of focal white and grey matter demyelination on thalamic function by directing targeted lysolecithin-induced lesions to the capsula interna (CI), the auditory cortex (A1), or the ventral medial geniculate nucleus (vMGN) in mice. Pathophysiological consequences were compared with those of cuprizone treatment at different stages of demyelination and remyelination. Combining single unit recordings and auditory stimulation in freely behaving mice revealed changes in auditory response profile and electrical activity pattern in the thalamus, depending on the region of the initial insult and the state of remyelination. Cuprizone-induced general demyelination significantly diminished vMGN neuronal activity and frequency-specific responses. Targeted lysolecithin-induced lesions directed either to A1 or to vMGN revealed a permanent impairment of frequency-specific responses, an increase in latency of auditory responses and a reduction in occurrence of burst firing in vMGN neurons. These findings indicate that demyelination of grey matter areas in the thalamocortical system permanently affects vMGN frequency specificity and the prevalence of bursting in the auditory thalamus.

Regulation of conduction time along axons

Timely delivery of information is essential for proper functioning of the nervous system. Precise regulation of nerve conduction velocity is needed for correct exertion of motor skills, sensory integration and cognitive functions. In vertebrates, the rapid transmission of signals along nerve fibers is made possible by the myelination of axons and the resulting saltatory conduction in between nodes of Ranvier. Myelin is a specialization of glia cells and is provided by oligodendrocytes in the central nervous system. Myelination not only maximizes conduction velocity, but also provides a means to systematically regulate conduction times in the nervous system. Systematic regulation of conduction velocity along axons, and thus systematic regulation of conduction time in between neural areas, is a common occurrence in the nervous system. To date, little is understood about the mechanism that underlies systematic conduction velocity regulation and conduction time synchrony. Node assembly, internode distance (node spacing) and axon diameter - all parameters determining the speed of signal propagation along axons - are controlled by myelinating glia. Therefore, an interaction between glial cells and neurons has been suggested. This review summarizes examples of neural systems in which conduction velocity is regulated by anatomical variations along axons. While functional implications in these systems are not always clear, recent studies on the auditory system of birds and mammals present examples of conduction velocity regulation in systems with high temporal precision and a defined biological function. Together these findings suggest an active process that shapes the interaction between axons and myelinating glia to control conduction velocity along axons. Future studies involving these systems may provide further insight into how specific conduction times in the brain are established and maintained in development. Throughout the text, conduction velocity is used for the speed of signal propagation, i.e. the speed at which an action potential travels. Conduction time refers to the time it takes for a specific signal to travel from its origin to its target, i.e. neuronal cell body to axonal terminal.

Central auditory evaluation in multiple sclerosis: case report

Herein, we report a case of multiple sclerosis in which peripheral and central hearing, were evaluated through early (brainstem), middle and late auditory evoked potentials before and after corticosteroid therapy. Auditory evaluation revealed better performance on all post-treatment tests. In this case, central auditory function tests (behavioral and electrophysiological) identified the location of the impairment (brainstem), which was in agreement with the patient complaint. The speech in noise test and brainstem auditory evoked potentials are definitely appropriate in confirming brainstem lesions.

The effects of auditory distraction on visual cognitive performance in multiple sclerosis

BACKGROUND

A subset of individuals with multiple sclerosis (MS) endures degradation of cognitive function during disease progression. The purpose of this study was to compare visual cognitive reaction time performance during three conditions of auditory distraction (four-talker babble; word repetition; babble combined with word repetition) to a quiet, undistracted condition.

METHODS

Twenty-two patients with mild relapsing-remitting MS (Expanded Disability Status Scale mean of 3.0) and 17 age-matched and education-matched control subjects free of neurologic disease were tested on four cognitive visual processing subtests of simple reaction time, choice reaction time, and visual working memory for same and sequential digits concurrently during three conditions of auditory distraction.

RESULTS

When reaction times for MS and control participants were pooled across all four cognitive tests, the scores of the MS patients in quiet (528 ms) were significantly slower than those of the control subjects (459 ms). The auditory distraction condition of word repetition combined with four-talker babble degraded cognitive performance more than most of the other distraction conditions in both groups.

CONCLUSIONS

Even in mild MS, subtle visual cognitive processing deficits may be elicited by auditory distraction.