Receptive Field (RF) Properties of the Macaque Second Somatosensory Cortex: RF Size, Shape, and Somatotopic Organization

Abstract

The detailed structure of multidigit receptive fields (RFs) in somatosensory cortical areas such as the SII region has not been investigated previously using systematically controlled stimuli. Recently (Fitzgerald et al., 2004), we showed that the SII region comprises three adjoining fields: posterior, central, and anterior. Here we characterize the RF structures of the 928 neurons that were reported in that study using a motorized oriented bar that was indented into the 12 finger pads of digits 2-5. Most (81%) of the neurons were responsive to the oriented bar stimuli, and 81% of those neurons had RFs that spanned multiple digits. Furthermore, the RFs varied greatly in size, shape, and complexity. Some RFs contained only excitatory finger pads, some contained only inhibitory pads, and some contained both types of pads. A subset of the neurons (23%) showed orientation tuning within one or more pads. The RFs spread across different digits more than within individual digits, and the responsive finger pads for a given neuron tended to cluster together within the hand. Distal and lateral finger pads were better represented than proximal and medial finger pads. Furthermore, neurons in the posterior, central, and anterior SII region fields contained different proportions of RF types. These results collectively indicate that most SII region neurons are selective for different stimulus forms either within single finger pads or across multiple pads. We hypothesize that these RFs represent the kernels underlying the representation of tactile shape.

Context effects in haptic perception of roughness

“…When using low-level stimulations, which are more representative of the signals that we receive from our natural environment, the input from two fingers produced additive or facilitatory interactions in the early component of the cerebral potential (Gandevia et al 1983). Furthermore, a number of studies have demonstrated the existence of multi-finger receptive fields in areas of the second somatosensory cortex (Fitzgerald et al 2006;Sinclair and Burton 1993). Together, these results suggest that spatial context should influence perception.…”

“…The spatial contextual effect in haptic roughness perception could be explained by a comparable mechanism in which signals from the index finger and from the inducer middle finger both fall within the centre of the same receptive field, producing the assimilation effect. These receptive fields could be the multi-finger receptive fields that were found at the level of the somatosensory cortex where integration of information received from different fingers occurs (Biermann et al 1998;Fitzgerald et al 2006;Forss et al 1995;Iwamura et al 1983;Sinclair and Burton 1993).…”

Congruency of body-related information induces somatosensory reorganization

“…Previous studies have identified the generators of this component in the upper wall of the Sylvian Sulcus in the secondary somatosensory area (SII; Allison et al, 1992Allison et al, , 1989bHämäläinen et al, 1990;Hari et al, 1990). Thus, one possibility is that whereas on-line modulation of SI organization seems to have a clear functional role in rapidly enhancing object perception on the body surface (Cardini et al, 2012;, off-line projectionsdirected instead towards secondary somatosensory regions -might perhaps be aimed at modulating more complex functions, such as tactile learning and memory processes (Fitzgerald et al, 2006a(Fitzgerald et al, , 2006bHari et al, 1990). …”

Posteromedial Parietal Cortical Activity and Inputs Predict Tactile Spatial Acuity

“…Some SA neurons in area 3b of macaque primary somatosensory cortex (SI) exhibit spatial response profiles isomorphic to stimulus patterns and possessing the spatial resolution to support tactile spatial acuity, whereas other neurons in area 3b, and neurons in area 1 of SI, represent stimulus patterns non-isomorphically (Phillips et al, 1988). Furthermore, the spatial receptive field properties of neurons in SI (DiCarlo et al, 1998;Sripati et al, 2006) and in the parietal operculum (Fitzgerald et al, 2006) are often quite complex. It remains unclear how these complex receptive fields and non-isomorphic representations relate to tactile spatial acuity.…”