Beyond Blink Physiology: Reinterpreting Voluntary Rapid Blinking Rate as a Motor–Cognitive Performance Measure

Dear Editor,

Bahsi et al. [1] report that the voluntary rapid blinking rate (VRBR) at baseline was inversely associated with the future development of neurodegenerative disease over 7 years, introducing a simple, non‐invasive measure with potential value for early detection. The prospective design and operational simplicity of the test represent a meaningful contribution to a field in which clinically accessible prodromal indicators are required. The interpretation of this association may depend on whether performance on the 60‐s task reflects blink physiology alone or a broader combination of motor and cognitive functions.

The task described by Bahsi et al. requires participants to blink as rapidly as possible without interruption for 60 s after observing a 15‐s demonstration. Successful performance is likely to depend on more than just rapid eyelid movement. It may require instruction comprehension, prompt motor initiation, rapid repetitive output, and sustained attention throughout the task. These task demands, together with the authors' own observations, suggest that VRBR may reflect motor–cognitive performance in addition to blink physiology. The exclusion of four individuals who stopped blinking because of poor concentration suggests that task non‐completion may reflect attentional or cognitive difficulties rather than blink capacity alone [1]. Francis et al. [2] found that rapid voluntary blinking distinguished patients with Parkinson's disease (PD) more effectively than spontaneous blinking, supporting the view that voluntary and spontaneous blinking impose different demands on motor control. If VRBR depends on attentional and executive processes as well as motor output, reduced scores may reflect impairment across several functional domains. We therefore suggest that low VRBR may represent a broader pattern of motor–cognitive impairment rather than a blink‐specific phenomenon, and we would welcome the authors' interpretation of this possibility.

Bahsi et al. [1] combined dementia (n = 14) and PD (n = 4), including one participant who developed both conditions, into a single neurodegenerative outcome. This introduces interpretive complexity as the mechanisms underlying reduced VRBR may differ between conditions. Indeed, the fact that VRBR was numerically lower in both groups may itself suggest that the task captures a broader motor–cognitive construct rather than disease‐specific blink physiology alone. In PD, reduced blinking has been associated with bradykinesia and dopaminergic dysfunction, and abnormalities in eyelid movement have been demonstrated in early‐stage disease [3]. Reduced VRBR in PD may directly reflect disease‐related motor impairment—bradykinesia, impaired initiation, and a diminished capacity to sustain rapid motor output. In individuals who subsequently develop dementia, however, a similarly low VRBR may also reflect declining sustained attention, executive control, task comprehension, or subtle apraxia—the cognitive components of the task. Thus, the same observable reduction in VRBR may arise from partly different motor and cognitive mechanisms across conditions. The authors cite evidence that spontaneous blink rate may serve as a marker of mild cognitive impairment [4]. However, spontaneous blinking and voluntary rapid blinking are not equivalent constructs. Because they differ substantially in volitional and task‐related demands, spontaneous blink rate cannot be assumed to represent the same construct as that measured by VRBR. Direct extrapolation between the two warrants caution, particularly since dementia is highly heterogeneous, and the association between dementia and VRBR may not be fully explained by dopaminergic mechanisms across all subtypes. Information on dementia subtypes would help clarify whether reduced VRBR reflects a shared mechanism or different impairments producing a similar observable result.

The authors' focus on blink performance is clinically meaningful, and the use of the 15‐s VRBR in the regression analysis suggests that the temporal features of task performance warrant further investigation [1]. Future studies could report not only cumulative blink counts at 15, 30, and 60 s, but also temporal patterns within the task, including delayed initiation, progressive slowing, abrupt cessation, and inability to complete the task. Such information could help distinguish motor from cognitive contributions to low scores and determine whether VRBR represents a unitary blink biomarker or different forms of motor–cognitive impairment across neurodegenerative disorders. VRBR may ultimately prove to be not only a blink biomarker but also a brief motor–cognitive performance measure. Recognizing this possibility may help clarify the mechanisms underlying reduced performance and strengthen its future clinical application.

Author Contributions

Miyuki Imazawa drafted the manuscript. Kohei Kajiwara conceived the central interpretation presented in the correspondence and critically revised the manuscript. Both authors approved the final version of the manuscript.

Funding

This work was supported by the Japan Society for the Promotion of Science (grant No. 26K13889).

Ethics Statement

The authors have nothing to report.

Consent

The authors have nothing to report.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

Data sharing not applicable to this article as no datasets were generated or analyzed during the current study.