Edin, Benoni B. Quantitative analyses of dynamic strain sensitivity in human skin mechanoreceptors. J Neurophysiol 92: 3233-3243, 2004; doi:10.1152/jn.00628.2004. Microneurographical recordings from 24 slowly adapting (SA) and 16 fast adapting (FA) cutaneous mechanoreceptor afferents were obtained in the human radial nerve. Most of the afferents innervated the hairy skin on the back of the hand. The afferents' receptive fields were subjected to controlled strains in a ramp-and-hold fashion with strain velocities from 1 to 64% ⅐ s Ϫ1 , i.e., strain velocities within most of the physiological range. For all unit types, the mean variation in response onset approached 1 ms for strain velocities Ͼ8% ⅐ s Ϫ1 . Except at the highest strain velocities, the first spike in a typical SAIII unit was evoked at strains Ͻ0.5% and a typical SAII unit began to discharge at Ͻ1% skin strain. Skin strain velocity had a profound effect on the discharge rates of all classes of afferents. The "typical" peak discharge rate at the highest strain velocity studied was 50 -95 imp/s Ϫ1 depending on unit type. Excellent fits were obtained for both SA and FA units when their responses to ramp stretches were modeled by simple power functions (r 2 Ͼ 0.9 for 95% of the units). SAIII units grouped with SAII with respect to onset latency and onset variation but with SAI units with respect to dynamic strain sensitivity. Because both SA and FA skin afferents respond strongly, quickly, and accurately to skin strain changes, they all seem to be able to provide useful information about movement-related skin strain changes and therefore contribute to proprioception and kinesthesia.
I N T R O D U C T I O NIt has become increasingly apparent that mechanoreceptors in the hairy skin may play an important role in proprioception and motor control. Movements at nearby joints activate a majority of the fast-conducting afferents originating from skin mechanoreceptors on the back of the human hand (Edin and Abbs 1991). Moreover, the ways these afferents respond suggest that they provide high-fidelity information of both the static and dynamic aspects of joint movements. The static strain sensitivity of slowly adapting skin afferents from the back of the hand endow them with a static joint-position sensitivity at least on par with that reported for human muscle spindle afferents in the wrist and long finger extensor muscles (Cordo et al. 2002; Edin 1992). Grill and Hallet (1995) have reported also that the dynamic sensitivity of slowly adapting skin mechanoreceptors are comparable if not superior to those of muscle spindle primary and secondary afferents. Moreover, skin afferents from wide areas of the human thigh appear to provide high-fidelity information about knee-joint movements (Edin 2001). Skin mechanoreceptors thus seem suitable for providing proprioceptive information. Indeed, not only does electrical stimulation of the back of the hand induce movement illusions in a fair proportion of subjects but so do various spatial patterns of skin stretch applied t...