Plasticity of sensory and motor maps in adult mammals.
TL;DR: This rev iew addresses questions about the capacity of sensory and motor maps in the brains of adul t mammals to change as a resul t of alterations in the effectiveness of inputs, the availability of effectors, and direct damage.
Abstract: This rev iew addresses questions about t he capacity of sensory and motor maps in the brains of adul t mammals to change as a resul t of alterations in the effectiveness of inputs, the availability of effectors, and d irect damage. The issue of the mutabil ity of maps in adults is important because sensory and motor representations occupy much of the brains of mammals, regardless of the complexity and extent of neocortex (e.g. Kaas 1988, Wall 1988, Maunsell & Newsome 1987); behavioral recovery occurs after damage to central representations (e.g. Bor nschlegl & Asanuma 1987, Diirsteler et a11987, Eidelberg & Stein 1974); and such changes may relate to improvements in sensory and motor skills with experience (e.g. Gibson 1953). Tn addition, features of reorganization that are apparent in sensory and motor maps may characterize less easily studied areas of the brain. Specific questions addr essed in this review are as follows:
Citations
More filters
TL;DR: The goal of the current paper is to review the fields of both synaptic and cortical map plasticity with an emphasis on the work that attempts to unite both fields, to highlight the gaps in the understanding of synaptic and cellular mechanisms underlying cortical representational plasticity.
Abstract: It has been clear for almost two decades that cortical representations in adult animals are not fixed entities, but rather, are dynamic and are continuously modified by experience. The cortex can preferentially allocate area to represent the particular peripheral input sources that are proportionally most used. Alterations in cortical representations appear to underlie learning tasks dependent on the use of the behaviorally important peripheral inputs that they represent. The rules governing this cortical representational plasticity following manipulations of inputs, including learning, are increasingly well understood. In parallel with developments in the field of cortical map plasticity, studies of synaptic plasticity have characterized specific elementary forms of plasticity, including associative long-term potentiation and long-term depression of excitatory postsynaptic potentials. Investigators have made many important strides toward understanding the molecular underpinnings of these fundamental plasticity processes and toward defining the learning rules that govern their induction. The fields of cortical synaptic plasticity and cortical map plasticity have been implicitly linked by the hypothesis that synaptic plasticity underlies cortical map reorganization. Recent experimental and theoretical work has provided increasingly stronger support for this hypothesis. The goal of the current paper is to review the fields of both synaptic and cortical map plasticity with an emphasis on the work that attempts to unite both fields. A second objective is to highlight the gaps in our understanding of synaptic and cellular mechanisms underlying cortical representational plasticity.
2,051 citations
Cites background from "Plasticity of sensory and motor map..."
...…reviews of cortical map reorganization in both developmental and adult studies, see Merzenich et al (1984, 1987, 1990a,b), Wall (1988), Kaas (1991), O’Leary et al (1994), Merzenich & Jenkins (1992), Gilbert (1992, 1996), Merzenich & Sameshima (1993), Weinberger (1995), and Merzenich &…...
[...]
...…in the spinal cord (Basbaum & Wall 1976, Devor & Wall 1981, Lisney 1983, Wilson & Snow 1987; but see Brown et al 1984, Pubols 1984), dorsal columns (see Devor & Wall 1981, Welker et al 1992, Florence & Kaas 1995), and the thalamus (Eysel et al 1981, Land & Akhtar 1987, Garraghty & Kaas 1991)....
[...]
TL;DR: The results suggest that the representation of different parts of the body in the primary somatosensory cortex of humans depends on use and changes to conform to the current needs and experiences of the individual.
Abstract: Magnetic source imaging revealed that the cortical representation of the digits of the left hand of string players was larger than that in controls. The effect was smallest for the left thumb, and no such differences were observed for the representations of the right hand digits. The amount of cortical reorganization in the representation of the fingering digits was correlated with the age at which the person had begun to play. These results suggest that the representation of different parts of the body in the primary somatosensory cortex of humans depends on use and changes to conform to the current needs and experiences of the individual.
1,821 citations
TL;DR: The results suggest that, after local damage to the motor cortex, rehabilitative training can shape subsequent reorganization in the adjacent intact cortex, and that the undamaged motor cortex may play an important role in motor recovery.
Abstract: Substantial functional reorganization takes place in the motor cortex of adult primates after a focal ischemic infarct, as might occur in stroke. A subtotal lesion confined to a small portion of the representation of one hand was previously shown to result in a further loss of hand territory in the adjacent, undamaged cortex of adult squirrel monkeys. In the present study, retraining of skilled hand use after similar infarcts resulted in prevention of the loss of hand territory adjacent to the infarct. In some instances, the hand representations expanded into regions formerly occupied by representations of the elbow and shoulder. Functional reorganization in the undamaged motor cortex was accompanied by behavioral recovery of skilled hand function. These results suggest that, after local damage to the motor cortex, rehabilitative training can shape subsequent reorganization in the adjacent intact cortex, and that the undamaged motor cortex may play an important role in motor recovery.
1,821 citations
TL;DR: A global account of mechanisms involved in the induction of pain is provided, including neuronal pathways for the transmission of nociceptive information from peripheral nerve terminals to the dorsal horn, and therefrom to higher centres.
1,752 citations
Cites background from "Plasticity of sensory and motor map..."
...Further, such a retuning of DH synapses has been implicated in the reconstruction of cortical, somatosensory maps following peripheral nerve damage (Kaas, 1991)....
[...]
TL;DR: The finding that cocontracting muscles in the behavior come to be represented together in the cortex argues that, as in sensory cortices, temporal correlations drive emergent changes in distributed motor cortex representations.
Abstract: This study was undertaken to document plastic changes in the functional topography of primary motor cortex (M1) that are generated in motor skill learning in the normal, intact primate. Intracortical microstimulation mapping techniques were used to derive detailed maps of the representation of movements in the distal forelimb zone of M1 of squirrel monkeys, before and after behavioral training on two different tasks that differentially encouraged specific sets of forelimb movements. After training on a small-object retrieval task, which required skilled use of the digits, their evoked-movement digit representations expanded, whereas their evoked-movement wrist/forearm representational zones contracted. These changes were progressive and reversible. In a second motor skill exercise, a monkey pronated and supinated the forearm in a key (eyebolt)-turning task. In this case, the representation of the forearm expanded, whereas the digit representational zones contracted. These results show that M1 is alterable by use throughout the life of an animal. These studies also revealed that after digit training there was an areal expansion of dual-response representations, that is, cortical sectors over which stimulation produced movements about two or more joints. Movement combinations that were used more frequently after training were selectively magnified in their cortical representations. This close correspondence between changes in behavioral performance and electrophysiologically defined motor representations indicates that a neurophysiological correlate of a motor skill resides in M1 for at least several days after acquisition. The finding that cocontracting muscles in the behavior come to be represented together in the cortex argues that, as in sensory cortices, temporal correlations drive emergent changes in distributed motor cortex representations.
1,401 citations
Cites background from "Plasticity of sensory and motor map..."
..., somatotopic maps of the body surface) are altered by manipulations of their sensory inputs (for reviews, see Merzenich et al., 1988; Kaas, 1991) (see also Kalaska and Pomeranz, 1979; Kelehan et al....
[...]
References
More filters
TL;DR: 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.
Abstract: The cortical representations ofthe 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. Suc cessive 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 pal mar 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 aI., '80) was dynamically maintained as receptive fields progressively decreased in size. These studies also revealed that: (1) 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 representa tions (e.g., of digits 1 and 4) approached each other in the reorganizing map, implying that these map discontinuities are normally dynamically main tained. (2) 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. (3) The major topographic changes were limited to a cortical zone 500-700 JIm on either side of the initial boundaries of the representation of the amputated digits. More dis tant regions did not appear to reorganize (i.e., were not occupied by inputs from surrounding skin surfaces) even many months after amputation. (4) The representations of some skin surfaces moved in entirety to locations within the former territories of representation of amputated digits in every
1,327 citations
Additional excerpts
...(Merzenich et al 1984, Figure lI)....
[...]
TL;DR: Three recent developments that have yielded insight into information processing and flow within extrastriate cortex are focused on.
Abstract: The neuronal processes that lead to visual perception have attracted intense interest since Kuffier's studies of receptive field organization in cat retinal ganglion cells over three decades ago (Kuffier 1953). A variety of ana tomical and physiological approaches have been employed to analyze the organization of thc visual pathway between the retina and striate cortex (VI ) and the transformations of visual information that occur at each stage (see Hubel & Wiesel 1977, Stone 1 983, Shapley & Lennie 1985). The growth in understanding of the retinostriate pathway has been accompanied by increasing interest in visual processing in the expanse of extrastriate cortex beyond V I . Studies of extrastriate cortex in many spec ies showed that it comprises a mosaic of visual areas that can be dis tinguished by several anatomical and physiological criteria (reviewed by Kaas 1 978, Zeki 1 978, Cowey 1979, Van Essen 1 979, 1985, Wagor et al 1980, Tusa et al 1 98 1) . The literature in this field is large, and we do not attempt to review all relevant studies. Rather, we concern ourselves with three recent devel opments that have yielded insight into information processing and flow within extrastriate cortex. The first of these is the convergence of ana tom-
1,227 citations
TL;DR: These experiments demonstrate that functional cortical remodeling of the S1 koniocortical field, area 3b, results from behavioral manipulations in normal adult owl monkeys.
Abstract: 1. Multiple microelectrode maps of the hand representation within and across the borders of cortical area 3b were obtained before, immediately after, or several weeks after a period of behaviorally controlled hand use. Owl monkeys were conditioned in a task that produced cutaneous stimulation of a limited sector of skin on the distal phalanges of one or more fingers. 2. Analysis of microelectrode mapping experiment data revealed that 1) stimulated skin surfaces were represented over expanded cortical areas. 2) Most of the cutaneous receptive fields recorded within these expanded cortical representational zones were unusually small. 3) The internal topography of representation of the stimulated and immediately surrounding skin surfaces differed greatly from that recorded in control experiments. Representational discontinuities emerged in this map region, and "hypercolumn" distances in this map sector were grossly abnormal. 4) Borders between the representations of individual digits and digit segments commonly shifted. 5) The functionally defined rostral border of area 3b shifted farther rostralward, manifesting either an expansion of the cutaneous area 3b fingertip representation into cortical field 3a or an emergence of a cutaneous input zone in the caudal aspect of this normally predominantly deep-receptor representational field. 6) Significant lateralward translocations of the borders between the representations of the hand and face were recorded in all cases. 7) The absolute locations--and in some cases the areas or magnifications--of representations of many skin surfaces not directly involved in the trained behavior also changed significantly. However, the most striking areal, positional, and topographic changes were related to the representations of the behaviorally stimulated skin in every studied monkey. 3. These experiments demonstrate that functional cortical remodeling of the S1 koniocortical field, area 3b, results from behavioral manipulations in normal adult owl monkeys. We hypothesize that these studies manifest operation of the basic adaptive cortical process(es) underlying cortical contributions to perception and learning.
906 citations
"Plasticity of sensory and motor map..." refers background in this paper
...When monkeys were trained to maintain contact with a rotating disk with one or two digits, there was evidence for an expansion of the cortical representation of these digits (Jenkins et al 1990)....
[...]
TL;DR: Without needing to make any elaborate assumptions about its structure or about the operations its elements are to carry out, it is shown that the mappings are set up in a system- to-system rather than a cell-to-cell fashion.
Abstract: An important problem in biology is to explain how patterned neural connections are set up during ontogenesis. Topographically ordered mappings, found widely in nervous systems, are those in which neighbouring elements in one sheet of cells project to neighbouring elements in a second sheet. Exploiting this neighbourhood property leads to a new theory for the establishment of topographical mappings, in which the distance between two cells is expressed in terms of their similarity with respect to certain physical properties assigned to them. This topographical code can be realized in a model employing either synchronization of nervous activity or exchange of specific molecules between neighbouring cells. By means of modifiable synapses the code is used to set up a topographical mapping between two sheets with the same internal structure. We have investigated the neural activity version. Without needing to make any elaborate assumptions about its structure or about the operations its elements are to carry out we have shown that the mappings are set up in a system-to-system rather than a cell-to-cell fashion. The pattern of connections develops in a step-by-step and orderly fashion, the orientation of the mappings being laid down in the earliest stages of development.
808 citations
TL;DR: Data support the hypothesis that crucial variables for the expression of activity-dependent synaptic modifications are a critical level of postsynaptic activation and calcium entry through ion channels linked to NMDA receptors.
Abstract: Intracortical infusion of the "N-methyl-D-aspartate" (NMDA) receptor blocker D,L-2-amino-5-phosphonovaleric acid (APV) renders kitten striate cortex resistant to the effects of monocular deprivation. In addition, 1 week of continuous APV treatment (50 nanomoles per hour) produces a striking loss of orientation selectivity in area 17. These data support the hypothesis that crucial variables for the expression of activity-dependent synaptic modifications are a critical level of postsynaptic activation and calcium entry through ion channels linked to NMDA receptors.
807 citations
Additional excerpts
...The NMDA receptor has been implicated in use-dependent development plasticity in the visual cortex (Gruel et al 1988, Kleinschmidt et al 1987, Bear et al 1987), and the receptor may have a similar role in adult plasticity....
[...]