The Effects of Ageing on Tactile Function in Humans

Abstract

Ageing is accompanied by a steady decline in touch sensitivity and acuity. Conversely, pleasant touch, such as experienced during a caress, is even more pleasant in old age. There are many physiological changes that might explain these perceptual changes, but researchers have not yet identified any specific mechanisms. Here, we review both the perceptual and structural changes to the touch system that are associated with ageing. The structural changes include reduced elasticity of the skin in older people, as well as reduced numbers and altered morphology of skin tactile receptors. Effects of ageing on the peripheral and central nervous systems include demyelination, which affects the timing of neural signals, as well as reduced numbers of peripheral nerve fibres. The ageing brain also undergoes complex changes in blood flow, metabolism, plasticity, neurotransmitter function, and, for touch, the body map in primary somatosensory cortex. Although several studies have attempted to find a direct link between perceptual and structural changes, this has proved surprisingly elusive. We also highlight the need for more evidence regarding age-related changes in peripheral nerve function in the hairy skin, as well as the social and emotional aspects of touch. Highlights • With age, touch sensitivity declines, and gentle touch becomes more pleasant. • Skin elasticity is reduced, and skin tactile receptors are reduced or altered. • Axonal loss and demyelination affect the amount and timing of neural signals. • The brain undergoes changes to somatotopic organisation, and many broad changes. • The link between perceptual and physiological age-related changes remains elusive.

Continuous Transition Impairs Discrimination of Electrotactile Frequencies

“…The values of JND found in the present study for timeseparated electrotactile frequency-modulated stimulation (12-14%) were similar [15] or lower than the values of JNDs reported by previous studies using the same stimulation strategy, i.e., approximately 10-30% at a baseline frequency of 20 Hz, and approximately 20-30% at a baseline frequency of 60 Hz [7], [19]. Such variations may be explained by the fact that the sensitivity of tactile discrimination depends on many factors including stimulation intensity [12], location and size of the electrode [27], age [28], skin type [29], as well as the amount of training given [30]- [32]. The values of the NDI were similar to those previously reported [10].…”

Underestimation in temporal numerosity judgments computationally explained by population coding model

“…A potential factor for the aging effect is temporal sensitivity. It is known that the sensitivity to tactile 55 – 61 and auditory temporal structure 57 , 62 declines with aging. One of the previous studies focused on the temporal discrimination threshold for a sequence of two vibrations and found that the threshold increased with aging 60 .…”

Oligomeric α-Synuclein induces skin degeneration in a reconstructed human epidermis model

“…CC-BY-NC-ND 4.0 International license made available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprint this version posted June 18, 2021. ; https://doi.org/10.1101/2021.06.17.448863 doi: bioRxiv preprint include reduced elasticity, as well as reduced numbers and altered morphology of tactile receptors, consequently impairing skin sensitivity and sensoriality in the elderly (McIntyre et al, 2021). α-Syn is poorly expressed in the RHE and, as a prion-like protein, it can be transported by cell-to-cell propagation.…”

“…Both cytokines IL-1β and TNF-α overexpression may be triggering positive feedback of inflammatory cytokines previously described in skin inflammaging studies (Grover and Grewal, 2008; Zhuang and Lyga, 2014; Fuller, 2019; Pilkington et al, 2021) resulting in keratinocyte loss, epidermal degeneration, and ultimately, fine lines and impaired mechanic skin properties. Aging skin structural changes include reduced elasticity, as well as reduced numbers and altered morphology of tactile receptors, consequently impairing skin sensitivity and sensoriality in the elderly (McIntyre et al, 2021).…”