Age-Related Reductions in Tactile and Motor Inhibitory Function Start Early but Are Independent

Marit F L Ruitenberg,Kaitlin E Cassady,Mark Tommerdahl,Rachael D Seidler,Patricia A Reuter-Lorenz

doi:10.3389/fnagi.2019.00193

Abstract

Aging is associated with declines in motor and somatosensory function. Some of these motor declines have been linked to age-related reductions in inhibitory function. Here we examined whether tactile surround inhibition also changes with age and whether these changes are associated with those in the motor domain. We tested a group of 56 participants spanning a wide age range (18–76 years old), allowing us to examine when age differences emerge across the lifespan. Participants performed tactile and motor tasks that have previously been linked to inter- and intra-hemispheric inhibition in the somatosensory and motor systems. The results showed that aging is associated with reductions in inhibitory function in both the tactile and motor systems starting around 40 years of age; however, age effects in the two systems were not correlated. The independent effects of age on tactile and motor inhibitory function suggest that distinct mechanisms may underlie age-related reductions in inhibition in the somatosensory and motor systems.

Highlights

Maintaining functional independence is a major concern in aging
Age-Related Reductions in Cortical Inhibition in the somatosensory cortex (Hicks and Dykes, 1983; Tremere et al, 2001). It is currently unclear how healthy aging affects this phenomenon, and whether potential age-related changes start to occur around the same time as those reported for changes in GABA concentration and for changes in bimanual coordination
Correlation analyses showed that information processing speed as reflected in Digit Symbol Substitution Test (DSST) scores and manual motor performance as reflected in Purdue pegboard scores declined with increasing age, while age was not significantly associated with general cognitive abilities as evaluated by the Montreal Cognitive Assessment (MoCA)

Summary

Introduction

Maintaining functional independence is a major concern in aging. Somatosensory and motor function have been linked to central nervous system changes with age including brain volumetric declines, altered patterns of brain functional activity and connectivity, and reductions in neurotransmission (for reviews see Seidler et al, 2010; Levin et al, 2014; Sala-Llonch et al, 2015; Heft and Robinson, 2017; Maes et al, 2017). Within the somatosensory tactile system, Von Békésy (1967) provided early evidence for cortical lateral inhibition of surrounding receptive fields upon skin contact. Such surround inhibition results in a sharper neural representation of stimuli and has been shown to extend to contralateral homologous representations (Halliday and Mingay, 1961). Age-Related Reductions in Cortical Inhibition in the somatosensory cortex (Hicks and Dykes, 1983; Tremere et al, 2001) It is currently unclear how healthy aging affects this phenomenon, and whether potential age-related changes start to occur around the same time as those reported for changes in GABA concentration (i.e., beginning in the third decade of life; Gao et al, 2013) and for changes in bimanual coordination (i.e., beginning in the fifth decade; Boisgontier et al, 2018). It has been well established that two-point tactile discrimination distance increases with age (Vieira et al, 2016), but this test assesses both peripheral and central sensory function

Methods

Results

Conclusion