A systematic analysis of neurons with large somatosensory receptive fields covering multiple body regions in the secondary somatosensory area of macaque monkeys

Abstract

Receptive fields (RFs) of the secondary somatosensory cortex of Japanese monkeys were analyzed. We found large RFs, mostly bilateral ones, covering more than one body region when the entire body was divided into the four: forelimb, hindlimb, trunk, and head. Two tendencies of RF enlargement—interconnecting limb extremities and the mouth and expansion of the trunk RF toward limb extremities to cover the entire body—were found. Neurons with either tendency were distributed in a specific subregion.

Feeling a Touch to the Hand on the Foot

“…On the sensory homunculus of primary somatosensory cortex (SI), neurons with receptive fields on different limbs are distant from each other [1], excluding overlapping representations in SI [29] as a source of phantom errors. However, the limbs are represented in close proximity in secondary somatosensory areas [30][31][32], and cortically-distant limb representations in several somatosensory areas are interconnected via subcortical pathways [33][34][35]. Spreading of activation along such neural connections could explain phantom errors, analogous to accounts of tactile referral in amputees and neurological patients [8,36].…”

Secondary somatosensory cortex of primates: beyond body maps, toward conscious self-in-the-world maps

“…This experiment was first aimed at detecting changes in the intraparietal sulcus, where neurons' RFs adapt to code the tool as an extension of body parts; thus, SII expansion was unexpected. Despite this, the result is reasonable when assuming that the coding and manipulation of images and schemas of body parts (Corradi-Dell'Acqua et al 2009) is the crucial principle for tool usage, and such a body image (accounting for the tool) is formed through the integration of somatosensory and visual information (Taoka et al 2016), being possibly related to self-awareness and consciousness (Tsakiris et al 2007). On the other hand, this finding also implies that information processing in SII is capable of plastic and dynamical changes, depending on situations and environmental requirements, rather than a precise and fixed mode depending on intrinsic bodily structures.…”

“…In humans, skin palpation activates the contralateral SI and bilateral parietal operculum including SII, but regions that contribute particularly to tactile perception are (Taoka et al 2016). b Distribution in the SII of anterograde tracers injected into closely related cutaneous responsive sites in macaque (Burton et al 1995).…”

“…Then, how could tactile response properties relate to visual responses? Taoka et al (2016) examined RFs of SII neurons under this perspective (i.e., how the RFs of SII neurons spread across four major body regions: head, trunk, forelimb, and hindlimb). About 25% of the RFs of recorded neurons (total of 1099 from nine hemispheres of six monkeys) covered combined body regions, and among those, 90% had RFs on bilateral body parts.…”

Neural Basis of Touch and Proprioception in Primate Cortex

“…For neurons with bilateral RFs, stimulation of the ipsilateral side typically exerts a modulatory effect on the response evoked by contralateral stimulation (87, 88). About half of LPC neurons respond to cutaneous stimulation and half to deep stimulation (355). Both S2 and PV receive projections from all four APC areas (34, 216, 295) as evidenced by the fact that lesioning individual areas reduces the responsiveness of their downstream targets (35, 132, 284): selective removal of proprioceptive input (areas 3a and 2) or cutaneous input (areas 3b et 1) selectively reduces proprioceptive and cutaneous responses in LPC, respectively (285) (Fig.…”