Evaluation of two-point discrimination in children: reliability, effects of passive displacement and voluntary movements.
Menier C, Forget R, Lambert J.
Dev Med Child Neurol. 1996 Jun;38(6):523-37.
"The threshold values for children are similar to those of adults" (Menier et al).
Establishing normal values of moving two-point discrimination in children and adolescents.
Hermann RP, Novak CB, Mackinnon SE.
Dev Med Child Neurol. 1996 Mar;38(3):255-61.
"Adult normal values for fingertip moving 2pd have already been established as 2 to 4 mm in the median and ulnar nerve distribution. This study has confirmed statistically that the normal values for individuals aged from four to 18 years is also 2mm to 4mm." (Hermann et al).
Based on these two studies I don't think it would be appropriate to state that 2 pt discrimination is "more powerful" in the child than the adult. I don't know of any studies that have tested children below 4 years of age.
1. Tactile sensitivity of children: effects of frequency, masking, and the non-Pacinian I psychophysical channel. Guclu and Oztek, J.
Experimental Child Psychology, 98(2), 2007, 113:130.
In this study, the tactile thresholds of children (ages 7–11 years) were measured and compared with the thresholds of young adults (ages
21–27 years). The stimuli consisted of sinusoidal bursts of mechanical displacements, which were applied to the left index fingertips of the participants by using a cylindrical probe. The study concludes that there were no significant differences between the tactile thresholds of children and those of young adults at key frequencies: 40 Hz for the Pacinian and non-Pacinian I channels and 250 Hz for the Pacinian channel. These findings contradict the hypothesis that there is gradual loss of tactile sensitivity starting from childhood to early adulthood.
The loss of sensitivity due to aging probably is more abrupt and occurs at a later age.
2. Tactile Sensitivity as a function of age. Thornbury and Mistretta, J. Gerontology, 36(1) 34-39.
In this study, in order to learn whether tactile sensitivity is decreased in elderly adults, the authors measured touch thresholds on the pad of the index finger in individuals aged 19 to 88 years.
Semmes-Weinstein aesthesiometer filaments were used. Tactile thresholds increased significantly with age. A large proportion of elderly individuals had thresholds that were higher than the average for young adults, although older people varied widely in touch sensitivity. Neither reported illness nor medication use was significantly related to tactile threshold.
This question seems based on the accepted view that no new sensory neurons are formed after birth, and that neurons in the peripheral nervous system are lost continuously due to the ravages of aging. Thus, it would make sense that two point discrimination and other measures of tactile sensitivity and innervation density would be less in young adults than in children. However, the prevailing view is that age-related changes in peripheral sensory innervation do not occur to any significant degree until about the 6th or 7th decades, at which point tactile sensitivity declines rather precipitously. There is some evidence that age-associated sensory loss involves preferentially the loss of structural and functional integrity of the large myelinated fibers and associated receptors, perhaps due to reduction of neurotrophins in the skin and/or neurotrophin receptors on the primary sensory neurons. (Although corneal innervation density and sensitivity also decline rapidly in the sixth and seventh decades, and the cornea is innervated exclusively by unmyelinated and small myelinated fibers).
The age-associated decline in peripheral sensitivity was once thought to be due to the loss of primary sensory neurons in the spinal ganglia; however, the literature on this subject remains contradictory (e.g, Bergman and Ulfhake, 1998, Loss of Primary Sensory Neurons in the Very Old Rat... J. Comparative Neurology 396:211-222.)
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