Brainstem lesions and click lateralization in patients with multiple sclerosis

Area of Science:

• Neuroscience
• Auditory Neuroscience
• Clinical Neurology

Background:

• Auditory lateralization relies on precise processing of interaural time differences (ITD) and interaural level differences (ILD).
• Multiple sclerosis (MS) can affect the central auditory pathways, potentially impacting sound localization abilities.
• Understanding the relationship between MS lesions and auditory deficits is crucial for diagnosis and management.

Purpose of the Study:

• To investigate the effects of brainstem lesions in multiple sclerosis (MS) patients on the ability to lateralize dichotic sounds using interaural time delays (ITD) and interaural level differences (ILD).
• To correlate specific lesion locations within the auditory pathway with deficits in auditory lateralization.

Main Methods:

• Psychoacoustical testing of dichotic click lateralization using ITD and ILD in seven MS subjects with normal audiograms.
• Magnetic resonance imaging (MRI) of the brainstem to identify and localize MS lesions.
• Matching MRI scans with a computerized brainstem atlas to determine affected auditory pathway structures.

Main Results:

• Two MS subjects with no auditory pathway lesions performed normally on both ITD and ILD tasks.
• Two MS subjects with trapezoid body lesions lateralized sounds normally with ILD but not ITD.
• Three MS subjects with unilateral lateral lemniscus lesions failed to lateralize sounds using either ITD or ILD.

Conclusions:

• Auditory lateralization deficits in MS patients are associated with specific brainstem lesion locations.
• Lesions in the trapezoid body may selectively impair ITD processing.
• Unilateral lesions of the lateral lemniscus appear to disrupt both ITD and ILD processing, suggesting a critical role in binaural hearing.