Somatosensory cortical map changes following digit amputation in adult monkeys

Abstract

The cortical representations of the hand in area 3b in adult owl monkeys were defined with use of microelectrode mapping techniques 2-8 months after surgical amputation of digit 3, or of both digits 2 and 3. Digital nerves were tied to prevent their regeneration within the amputation stump. Successive maps were derived in several monkeys to determine the nature of changes in map organization in the same individuals over time. In all monkeys studied, the representations of adjacent digits and palmar surfaces expanded topographically to occupy most or all of the cortical territories formerly representing the amputated digit(s). With the expansion of the representations of these surrounding skin surfaces (1) there were severalfold increases in their magnification and (2) roughly corresponding decreases in receptive field areas. Thus, with increases in magnification, surrounding skin surfaces were represented in correspondingly finer grain, implying that the rule relating receptive field overlap to separation in distance across the cortex (see Sur et al., '80) was dynamically maintained as receptive fields progressively decreased in size. These studies also revealed that: the discontinuities between the representations of the digits underwent significant translocations (usually by hundreds of microns) after amputation, and sharp new discontinuous boundaries formed where usually separated, expanded digital representations (e.g., of digits 1 and 4) approached each other in the reorganizing map, implying that these map discontinuities are normally dynamically maintained. Changes in receptive field sizes with expansion of representations of surrounding skin surfaces into the deprived cortical zone had a spatial distribution and time course similar to changes in sensory acuity on the stumps of human amputees. This suggests that experience-dependent map changes result in changes in sensory capabilities. The major topographic changes were limited to a cortical zone 500-700 micron on either side of the initial boundaries of the representation of the amputated digits. More distant regions did not appear to reorganize (i.e., were not occupied by inputs from surrounding skin surfaces) even many months after amputation. The representations of some skin surfaces moved in entirety to locations within the former territories of representation of amputated digits in every monkey studied. In man, no mislocation errors or perceptual distortions result from stimulation of surfaces surrounding a digital amputation.(ABSTRACT TRUNCATED AT 400 WORDS)

Two-point discrimination thresholds in spinal cord injured patients with dysesthetic pain

“…The findings indicate that SCI patients with DPS have greater sensitivity to somatosensory stimuli, particularly in skin areas with projections to We suggest that the cortical maps of deafferentated areas following SCI change similarly to the experimental demonstra tions of reorganization following amputa tion and deafferentation in monkeys. 29,44 The degree and quality of the reorganiza tion progressively changes over time and is influenced by pain and/or tactual stimula tion.46,47 The cortical representations of normally innervated skin surfaces, adjacent to the injured areas, slowly expand and occupy cortical territories that had previ ously represented the injured area. Accord ing to this view, it is reasonable to assume that innervated cortical regions in close proximity to deafferentated regions receive increased levels of stimulation causing more extensive reorganization.…”

More than skin deep: Body representation beyond primary somatosensory cortex

“…There is no intrinsic, hard-wired, link between a location in a somatotopic map and a body location. This is especially true given Body Beyond SI 9 the clear plasticity of somatotopic maps following peripheral trauma (Merzenich et al, 1984;Pons et al, 1991) and learning Pascual-Leone & Torres, 1993). While some referral of sensation between skin surfaces may occur following massive cortical reorganisation (e.g., Ramachandran, Rogers-Ramachandran, & Stewart, 1992) or in plasticity induced by simultaneous tactile co-activation of skin surfaces (Schweizer et al, 2001;Sterr et al, 1998), in most cases plastic changes in somatosensory cortex do not lead to mislocalsation of touch.…”

Extensive reorganization of primary somatosensory cortex in chronic back pain patients

“…Keywords: Back pain; Cortical reorganization; Magnetoencephalography; Source localization; Plasticity; Chronicity Research in animals [18,19] and humans [5,8,21] has shown that lesions of the afferent nerves may lead to extensive reorganization of the spinal and cortical zones that represent the deafferented body region. For example, in upper extremity amputees the cortical representation of the face was shown to 'invade' the representation of the hand and arm amputation zone [5,21] with the amount of reorganization observed being proportional to the magnitude of phantom limb pain [8].…”