Receptive Field Properties of the Macaque Second Somatosensory Cortex: Evidence for Multiple Functional Representations

Abstract

The detailed functional organization of the macaque second somatosensory cortex (SII) is not well understood. Here we report the results of a study of the functional organization of the SII hand region that combines microelectrode mapping using hand-held stimuli with single-unit recordings using a motorized, computer-controlled tactile oriented bar. The data indicate that the SII hand region extends ϳ10 mm in the anteroposterior (AP) dimension, primarily within the upper bank of the lateral sulcus. Furthermore, we find evidence that this region consists of multiple functional fields, with a central field containing neurons that are driven well by cutaneous stimuli, flanked by an anterior field and a posterior field that each contain neurons that are driven well by proprioceptive stimuli and less well by cutaneous stimuli. The anterior field extends ϳ4 -5 mm AP, the central field extends ϳ3-4 mm, and the posterior field extends ϳ3 mm. Data from the motorized stimulator indicate that neurons in the central field are more responsive to oriented bars, more frequently exhibit orientation tuning, and have larger receptive fields than neurons in the anterior and posterior fields. We speculate that the three putative fields play different functional roles in tactile perception; the anterior and posterior fields process information that involves both proprioceptive and cutaneous input such as sensorimotor integration or stereognosis, whereas the central field processes primarily cutaneous information.

Receptive Field Properties of the Macaque Second Somatosensory Cortex: Nonlinear Mechanisms Underlying the Representation of Orientation Within a Finger Pad

“…For a detailed description of the recording methods and an illustration of the stimulator that was used to indent the bar into the skin, see Fitzgerald et al (2004). Briefly, we recorded from single neurons in the SII hand region of four hemispheres of two rhesus monkeys (Macaca mulatta).…”

“…Stimulus duration was 500 ms, with an indentation force of 10 g. The bar was approximately the width of a monkey's finger and had rounded ends; its short axis was a 90°wedge, and its long axis was circular with an 8 mm radius, effectively producing a length of ϳ7 mm. The responses obtained from this protocol were used to determine the receptive field (RF) size of the neuron and to determine which finger pads were orientation tuned (Fitzgerald et al, 2004(Fitzgerald et al, , 2006a.…”

“…Electrode tracks, which had been marked with fluorescent dyes (DiCarlo et al, 1996), were reconstructed in Neurolucida and AutoCAD to confirm that the recordings were made in the SII region. We classified each neuron as belonging to the SII region posterior, central, or anterior field based on the subjective multiunit response properties (Fitzgerald et al, 2004).…”

“…In the second, Fitzgerald et al (2006a) found many neurons in the second somatosensory (SII) region that had multiple orientation tuned finger pads, and, for those neurons when the bar was indented in the center of their pads, the preferred orientation tended to be highly similar. In the current study, we investigated whether the responses were position invariant at different locations within a single pad and studied in more detail a subset (n ϭ 61) of the 928 neurons that were reported in the studies by Fitzgerald et al (2004Fitzgerald et al ( , 2006a. We repeatedly indented a motorized oriented bar (eight orientations, 22.5°increments) at nine positions per orientation into a single tuned distal finger pad (see Fig.…”

Properties of tactile responses of neurons in rat thalamic ventroposterolateral nucleus

“…The reason for the apparent absence of complex interaction of various receptor inputs at thalamic and cortical levels in previous studies was probably due to the lack of controlled mechanical stimuli and the deep anesthesia to the animals [4,5] . Increasing studies on the dorsal column lemnisco-thalamic pathway in the mammalian brain, however, indicated that there were the convergences of sensory information in the somatosensory cortex [6][7][8] . In addition, thalamic ventrobasal (VB) nucleus was also involved in converging sensory information in cat, raccoon and monkey [9][10][11] .…”