Differences in age-related effects on myelinated and unmyelinated peripheral fibres: a sensitivity and evoked potentials study.

BACKGROUND: Experimental data regarding age effects on sensitivity and pain thresholds are not always consistent, with the type of stimulus being a major source of variability. This could suggest that some types of peripheral sensory fibres undergo more important modifications with age than others. We investigated whether ageing affects differently myelinated and unmyelinated fibres.
METHODS: Somatosensitivity and pain perception and recorded somatosensory evoked potentials (SEPs) were assessed in younger and older adults during the selective activation of either myelinated Aδ- or unmyelinated C-fibres.
RESULTS: Somatosensitivity for information transmitted and SEPs elicited by stimulation of C-fibres did not differ between both groups. In contrast, pain perception was lower in older than in younger adults, and older adults showed longer SEP latencies and reduced peak-to-peak amplitude, during selective stimulation of Aδ-fibres.
CONCLUSIONS: These findings suggest that myelinated Aδ-fibres are compromised by the normal ageing process, whereas unmyelinated C-fibres seem to remain unaltered or, at least, less affected.