An Investigation of the Neural Basis of Changes in Tactile Acuity during Healthy Ageing and its Impact on Emotional Wellbeing

The sense of touch refers to the perception of tactile stimuli through mechanoreceptors in the skin and joints, combining both tactile and proprioceptive input 1,2. During tactile exploration, humans use their hands, which are innervated by a dense population of mechanoreceptors 3,4. These receptors transduce incoming tactile information, giving the hand high sensory acuity. However, as humans age their tactile acuity decreases 5-23, influencing haptic interactions with external stimuli.
The age-related decline in passive tactile acuity is linked to changes in the peripheral nervous system, including reductions in receptor populations and neurons 24-26. However, tactile perception through active exploration declines later than passive stimulation 27. This suggests that decreased tactile acuity during active touch may be more closely correlated with central, rather than peripheral, mechanisms.
Aging negatively impacts motor control 30, influencing how individuals interact with their environment. The inhibitory neurotransmitter gamma-aminobutyric acid (GABA) has been found to decline with age in healthy populations 28-30, which has been linked to age-related reduction in neural oscillatory activity during movement 31-35. These findings suggest that later decline in tactile acuity observed in older adults during active touch, relative to passive touch, may not result from an optimised exploratory procedure but rather suggests there may be a compensatory neural processing mechanism. However, the complete impact of aging on tactile processing within the central nervous system has yet to be fully elucidated.
Recently, we published research on brain activation during active exploration and the associated hedonic properties of tactile stimuli 36-38. These findings enhance our understanding of active touch mechanisms by employing cutting-edge force plate and EEG data fusion. However, the research did not specifically address age-related declines in tactile acuity. The well-established link between touch and hedonic preference 39,41-47 suggests that the age-related decline in tactile acuity may affect emotional well-being, akin to other sensory modalities 39,40. Our project aims to address this scientific gap by characterising the central mechanisms underlying age-related decline in tactile acuity, improving our understanding of the fundamental bioscience, and potentially informing translational research to improve the quality of life during healthy aging.
Primary objectives
1. Quantify contributions of peripheral and central mechanisms to age-related tactile acuity loss during active touch, including the investigation of peripheral mechanisms in healthy aging through sensory assessment and explore age-related haptic exploration pattern differences.
2. Multimodal neuroimaging to quantify brain activity within key processing areas, highlighting differences between young and old populations to uncover age-related compensatory mechanisms in the brain.
3. Explore the impact of declining tactile acuity on emotional wellbeing.
Hypotheses
1. Sensory assessments will reveal age-related changes in tactile acuity due to peripheral mechanisms. Age-related differences in haptic exploration patterns may compensate for declining peripheral mechanisms.
2. Differences in brain activation between aging and young adults will be due to compensatory mechanisms in central processing, or differences in exploratory behaviour due to peripheral mechanisms.
3.Declining tactile acuity in aging will negatively impact emotional well-being.
Methodologies
1. Sensory assessments of peripheral mechanisms, e.g., two-point discrimination.
2. Force plate for quantifying haptic exploration.
3. Electroencephalographic (EEG) time-frequency analysis.
4. fMRI for brain activity and network connectivity.
5. Subjective measures of wellbeing.