Examination of the Relationship between Startle Eyeblink Modulation and Perceived Fatigue in Multiple Sclerosis

Abstract

Multiple sclerosis (MS) is a neurodegenerative disorder from which fatigue is one of the most commonly reported symptoms. Recently, research into the underlying neural mechanisms of fatigue has focused largely on the relationship between perceived fatigue and neural efficiency. Imaging studies have shown correlations between self-reported fatigue measures and changes in the patterns of neural activation within the sensorimotor network (SMN), suggesting that disruptions of efficient processing within the SMN are related to fatigue perception. Extending this line of research, the present study investigated whether a psychophysiological measure of the sensorimotor network would correlate with perceived fatigue in a sample of individuals with MS. Startle Eyeblink Modulation (SEM), a measure that has been reliably shown to reflect the functioning of the SMN, indexes both the efficiency and timing of sensorimotor processing within the network. SEM involves the examination of the size and the speed of the startle eyeblink reflex elicited in the presence and absence of a non-startling “prepulse” stimulus that is paired with the startle stimulus. The effect of the prepulse is indexed by comparing the prepulse and non-prepulse (baseline) conditions, with changes in the size (amplitude) and timing (latency) of the startle eyeblink reflecting the efficiency of sensorimotor processing. In the current study, it was hypothesized that measures of SEM efficiency would significantly correlate with a measure of perceived fatigue for participants with MS. Individuals (n = 44) underwent SEM testing and completed an assessment of perceived fatigue. Results revealed that participants showed larger (i.e. slower) latencies of the startle eyeblink response, and that these latencies correlated with a self-report measure of perceived fatigue. These results contrasted with non-significant correlations between the same measures for a group of age-matched controls, who differed from the MS group on perceived fatigue measures. These results suggest that changes in the timing of these responses reflect disrupted sensorimotor gating, which is in turn related to the perception of fatigue for individuals with MS. Since startle eyeblink latency may represent an index of the initiation of stimulus processing, these results also provide support for research examining the relationship between fatigue and changes in processing efficiency within the sensorimotor network.