Processing of Vibrotactile Inputs From Hairy Skin by Neurons of the Dorsal Column Nuclei in the Cat

Abstract

. The capacity of single neurons of the dorsal column nuclei (DCN) for coding vibrotactile information from the hairy skin has been investigated in anesthetized cats to permit quantitative comparison first with the capacities of DCN neurons responding to glabrous skin vibrotactile inputs and second with those of spinocervical tract neurons responding to vibrotactile inputs from hairy skin. Dynamically sensitive tactile neurons of the DCN the input of which came from hairy skin could be divided into two classes, one associated with hair follicle afferent (HFA) input, the other with Pacinian corpuscle (PC) input. The HFA-related class was most sensitive to low-frequency (Ͻ50 Hz) vibration and had a graded response output as a function of vibrotactile intensity changes. PCrelated neurons had a broader vibrotactile sensitivity, extending to Ն300 Hz and appeared to derive their input from the margins of hairy skin, near the footpads, or from deeper PC sources such as the interosseous membranes or joints. HFA-related neurons had phaselocked responses to vibration frequencies up to ϳ75 Hz, whereas PC neurons retained this capacity up to frequencies of ϳ300 Hz with tightest phaselocking between 50 and 200 Hz. Quantitative measures of phaselocking revealed that the HFA-related neurons provide the better signal of vibrotactile frequency up to ϳ50 Hz with a switchover to the PC-related neurons above that value. In conclusion, the functional capacities of these two classes of cuneate neuron appear to account for behavioral vibrotactile frequency discriminative performance in hairy skin, in contrast to the limited capacities of vibrotactile-sensitive neurons within the spinocervical tract system.

Vibrotactile Coding Capacities of Spinocervical Tract Neurons in the Cat

“…All responded to the first cycle of the vibration train, usually with a burst of two to six impulses at high frequency. However, in striking contrast to the behavior of DCN neurons that respond throughout the vibration train with high levels of impulse activity (Connor et al 1984;Douglas et al 1978;Ferrington and Rowe 1982;Ferrington et al 1987a-c;Sahai et al 2006;Zachariah et al 2001), the SCT neurons could not sustain their response throughout the 1-s vibration train at vibration frequencies Ͼ5-10 Hz. In Fig.…”

“…In brief, the recorded SCT impulse activity was displayed on an oscilloscope and fed to a discriminator from which standardized output pulses were relayed to a counter unit and a laboratory computer for the construction of impulse traces and response histograms from which quantitative measures of phaselocking, based on vector strength values (Sahai et al 2006), were derived for the vibrotactile responses of SCT neurons.…”

“…In the case of the dorsal column-lemniscal pathway, the individual DCN neurons display a striking capacity to code reliably for the various parameters of tactile stimuli applied either to the glabrous skin (Connor et al 1984;Douglas et al 1978;Ferrington and Rowe 1982;Ferrington et al 1987a) or to hairy regions of skin (Sahai et al 2006;Zachariah et al 2001). The dorsal column nuclei (DCN) neurons display sensitively graded stimulus-response relations as a function of changes in the intensity of both vibrotactile stimuli and static forms of skin indentation, and, in addition, retain a tightly phaselocked pattern of response to vibrotactile stimuli over a broad bandwidth of vibration frequencies extending up to ϳ400 Hz (Connor et al 1984;Douglas et al 1978;Ferrington and Rowe 1982;Sahai et al 2006;Zachariah et al 2001).…”

“…The dorsal column nuclei (DCN) neurons display sensitively graded stimulus-response relations as a function of changes in the intensity of both vibrotactile stimuli and static forms of skin indentation, and, in addition, retain a tightly phaselocked pattern of response to vibrotactile stimuli over a broad bandwidth of vibration frequencies extending up to ϳ400 Hz (Connor et al 1984;Douglas et al 1978;Ferrington and Rowe 1982;Sahai et al 2006;Zachariah et al 2001). The high security of synaptic transmission between tactile afferent fibers and their DCN target neurons (Coleman et al 2003a,b;Ferrington et al 1987a,b;Gynther et al 1995;Rowe 2002a,b;Vickery et al 1994;Zachariah et al 2001) enables the DCN neurons to retain, in their rates and patterns of impulse activity, a reliable signal of the intensity and periodicity parameters of vibrotactile perturbations encountered in either the glabrous or hairy skin.…”

“…In the present study in the cat, we have investigated quantitatively the response characteristics and tactile coding capacities of individual SCT neurons to permit precise comparison with their DCN counterparts (Connor et al 1984;Douglas et al 1978;Ferrington et al 1987a-d;Sahai et al 2006;Zachariah et al 2001), in particular, for the coding of information about the frequency and intensive components of vibrotactile stimuli applied to the hairy skin of the limbs.…”