Reduced task adaptation in alternating motion rate tasks as an early marker of bulbar involvement in amyotrophic lateral sclerosis

The identification of robust biomarkers to detect the onset of amyotrophic lateral sclerosis (ALS) has been an ongoing challenge. Recent evidence from multiple studies suggests that speech changes are a reliable early indicator of ALS particularly during physically demanding speaking tasks such as alternating motion rate (AMR). However, it has also been found that individuals make various behavioral adaptations to meet the maximum rate requirement in AMR. In this study, we explored the extent to which persons with early-stage ALS are capable of adapting to challenging speech-like tasks. Speech motor performance of 14 healthy controls was compared to that of 18 patients at the early stage of ALS during standard (unconstrained) and fixed-target (constrained) AMR tasks. Fixed-target tasks were designed to impose high demands on the speech motor system. Although habitual speaking rate was maintained within normal limits, findings revealed that task adaptation was reduced at the early stage of ALS. Furthermore, the difference between the number of cycles in the fixed-target task and standard task showed higher sensitivity than habitual speaking rate to detect early decline in bulbar function. The inability to adapt to the fixed-target task was a good early indicator of bulbar motor involvement due to ALS.