An investigation of auditory processing in relapsing-remitting multiple sclerosis.

Multiple sclerosis (MS) is one of the most common neurological diseases in North America and it is frequently associated with sensory processing difficulties, cognitive deficits, and psychiatric illness. While many studies have examined cognitive deficits in MS measured by behavioural responses and neuroimaging techniques, only a few studies have examined neurophysiological measures of auditory functioning in MS, such as the mismatch negativity (MMN). The MMN is an event-related potential that indicates automatic auditory change detection. This study examined whether MMN endpoints measured by electroencephalography (EEG) differ in individuals with relapsing-remitting MS compared to healthy controls and whether the symptomatology of MS, including symptoms of depression and fatigue, are related to MMN measures. A multi-feature MMN paradigm, which includes five distinct deviant tones, was used to assess auditory cortex function in MS. There were no significant differences in MMN amplitudes or latencies between the MS and control group (p < 0.05) and corresponding effect sizes were small. However, there was a correlation between reduced MMN amplitudes in response to an intensity deviant and physician-reported disability. The intensity MMN may be more sensitive to deterioration in this population. Ultimately, this study provides a comprehensive profile of early auditory processing abilities in MS and suggests that a reduction in the MMN response may be representative of disease severity in MS.

MMN-Indexed Auditory Change Detection in Major Depressive Disorder.

In major depressive disorder (MDD), event-related potentials that are involved in auditory cortex function (i.e. N100 and P300) often have greater latencies and decreased amplitudes. The auditory mismatch negativity (MMN) is thought to be produced by generators in the auditory cortex, as well as the frontal lobes. Reports on differences in MMN in those with MDD have been varied. It was hypothesized that the wide range of results in the literature may be due to the use of different deviant types in eliciting the MMN. To attempt and explain these inconsistencies, the current study employed a multifeature MMN paradigm with 5 deviant tone types in community-dwelling participants with a diagnosis of MDD. We found those with MDD had higher MMN amplitudes following tones that deviated in intensity and location, but no difference in MMNs elicted by the other deivants (relative to unaffected controls). Location MMN deviants were negatively correlated with depression severity scores (i.e. larger MMN with greater severity). We also found longer MMN latencies following the pitch deviant. These results suggest the early auditory change detection process is altered in MDD, but only following certain types of auditory stimuli. Potential explanations for these findings, including high levels of anxiety and the influence of tryptophan are explored. Equally, the current report highlights the importance of using various deviant types when examining the MMN in clinical populations.