Fourth finger dependence of high-functioning autism spectrum disorder in multi-digit force coordination

Shunta Togo,Hiroshi Imamizu,Nobumasa Kato,Ryuichiro Hashimoto,Chang Cai,Chieko Kanai,Takashi Itahashi

doi:10.1038/s41598-018-38421-6

Abstract

A number of studies have reported that the digit ratio 2D:4D (length of the second finger divided by length of the fourth finger) is smaller (longer fourth digit) in autism spectrum disorder (ASD) than in typically developed (TD) controls. Because form and function are closely related in biological systems, we hypothesized that the 4D dominance occurs in not only finger morphology but also physical performance in ASD. Individuals with ASD and TD controls participated in a multi-digit force-producing task. Individuals with ASD showed a significant 4D dependence compared to TD controls in the task. We found a significant correlation between 4D dependence and scores of the standard diagnostic instrument across individuals with ASD. Our analysis of functional connectivity in resting-state functional MRI suggests that connectivity between the visual cortex and the cerebellum contributes to the 4D dependence. Collectively, these results extend the 2D:4D ratio beyond being a morphological marker to being involved in motor functions in the form of 4D dependence in a multi-digit force task.

Highlights

A number of studies have reported that 2D:4D is smaller in autism spectrum disorder (ASD) or ASD-affected individuals than in unaffected controls[1,2]
Twenty male individuals with ASD and twenty male typically developed (TD) controls participated in the experiments
We gave no instruction on the relative contribution of each finger to the total force, so the fingers’ contributions were arbitrary determined by participants

Summary

Introduction

A number of studies have reported that 2D:4D (length of the second finger divided by length of the fourth finger) is smaller in autism spectrum disorder (ASD) or ASD-affected individuals than in unaffected controls[1,2]. We hypothesized that the small 2D:4D ratio is observed in finger morphology and physical performance (motor function) in ASD Our rationale for this hypothesis is that form and function are closely related in biological systems[9], suggesting the possibility of 4D dominance in morphology and function. To examine this hypothesis, we adopted a multi-digit force-sharing task to investigate the relationships among physical performances of individual fingers[10,11,12]. Connectivity between the visual cortex and the cerebellum may contribute to the distinct force-sharing pattern in ASD during the visual feedback control phase

Methods

Results

Conclusion