Topographic reorganization in the striate cortex of the adult cat and monkey is cortically mediated

Abstract

In primary sensory and motor cortex of adult animals, alteration of input from the periphery leads to changes in cortical topography. These changes can be attributed to processes that are intrinsic to the cortex, or can be inherited from alterations occurring at stages of sensory processing that are antecedent to the primary sensory cortical areas. In the visual system, focal binocular retinal lesions initially silence an area of cortex that represents the region of retina destroyed, but over a period of months this area recovers visually driven activity. The retinotopic map in the recovered area is altered, shifting its representation to the portion of retina immediately surrounding the lesion. This effectively shrinks the representation of the lesioned area of retina, and expands the representation of the lesion surround. To determine the loci along the visual pathway at which the reorganization takes place, we compared the course of topographic alterations in the primary visual cortex and dorsal lateral geniculate nucleus (LGN) of cats and monkeys. At a time when the cortical reorganization is complete, the silent area of LGN persists, indicating that changes in cortical topography are due to alterations that are intrinsic to the cortex. To explore the participation of thalamocortical afferents in the reorganization, we injected a series of retrogradely transported fluorescent tracers into reorganized and surrounding cortex of each animal. Our results show that the thalamocortical arbors do not extend beyond their normal lateral territory and that this physical dimension is insufficient to account for the reorganization. We suggest that the long-range intrinsic horizontal connections are a likely source of visual input into the reorganized cortical area.

Pain and Plasticity: Is Chronic Pain Always Associated with Somatosensory Cortex Activity and Reorganization?

“…Others have reported similar decreases in S1 sensitivity to innocuous stimuli in patients with trigeminal neuropathic pain (Dancause et al, 2005), trigeminal neuralgia (Darian-Smith and Gilbert, 1995), and complex regional pain syndrome (Davis et al, 1998). It appears that chronic pain is associated with general reduction of S1 processing, indicating a long-term modulation of somatosensory function, even in patients who do not display changes in S1 organization, anatomy, or ongoing activity.…”

Large-scale remapping of visual cortex is absent in adult humans with macular degeneration

“…Such reallocation of cortical processing has also been demonstrated when early visual areas remap following congenital retinal lesions in human 6 . In adulthood the cortex is less plastic, but even so, remapping of the visual cortical representation has been inferred on the basis of ectopic receptive fields in the lesion projection zone in animal models [7][8][9][10][11][12][13] . This effect is however rather modest and has been called into question recently 19 .…”

“…This novel finding speaks more generally to the way in which ectopic receptive fields should be interpreted. Frequently, the existence of ectopic receptive fields has been taken as evidence for remapping [7][8][9][10][11][12][13] . That ectopic characteristics can be recorded from normally sighted controls challenges this notion, particularly in the context of fMRI research 15,26 .…”

“…showed that voxels with ectopic receptive fields were not restricted to the fringe of the lesion projection zone, where most electrophysiological measurements have been taken [7][8][9][10][11][12][13] . We propose, like others 19,30 , that each cortical location (voxel) contains many neurons, the responses of which can be influenced by stimuli at a range of locations, but that the overall population response is heavily weighted to a modal location.…”

“…Although brain plasticity is clearly possible when neural changes occur early in life, the adult brain also appears capable of plasticity. Experimentally-induced retinal lesions in adult animals can lead to a remapping of primary visual cortex to respond to inputs from nearby intact retina [7][8][9][10][11][12][13] . We undertook the present study to determine whether cortical remapping generalizes to humans who acquire retinal lesions in adulthood.…”