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Results for “Experience-dependent plasticity”

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PubMed1995

Functional MRI evidence for adult motor cortex plasticity during motor skill learning.

Performance of complex motor tasks, such as rapid sequences of finger movements, can be improved in terms of speed and accuracy over several weeks by daily practice sessions. This improvement does not generalize to a matched sequence of identical component movements, nor to the contralateral hand. Here we report a study of the neural changes underlying this learning using functional magnetic resonance imaging (MRI) of local blood oxygenation level-dependent (BOLD) signals evoked in primary motor cortex (M1). Before training, a comparable extent of M1 was activated by both sequences. However, two ordering effects were observed: repeating a sequence within a brief time window initially resulted in a smaller area of activation (habituation), but later in larger area of activation (enhancement), suggesting a switch in M1 processing mode within the first session (fast learning). By week 4 of training, concurrent with asymptotic performance, the extent of cortex activated by the practised sequence enlarged compared with the unpractised sequence, irrespective of order (slow learning). These changes persisted for several months. The results suggest a slowly evolving, long-term, experience-dependent reorganization of the adult M1, which may underlie the acquisition and retention of the motor skill.

Adult↗

PubMed1988

Experience-dependent modifications of kitten striate cortex are not prevented by thalamic lesions that include the intralaminar nuclei.

It has been shown previously that surgical lesions of the antero-medial thalamus interfere with ocular dominance modifications that normally result from monocular deprivation in young kittens (Singer 1982). The aim of the present study was to determine whether this effect was due specifically to the destruction of the visual cortical projections of the anterior intralaminar nuclei. We report here that large excitotoxin lesions of the anterior dorsal thalamus have no effect on the cortical response to monocular deprivation. These data indicate that the intralaminar projection is not essential for ocular dominance plasticity.

Animals↗

PubMed1994

Spatial interactions in human vision: from near to far via experience-dependent cascades of connections.

Perceptual learning has been shown to affect early visual processes. Here, we show that learning induces an increase in the spatial range of lateral interactions. Using a lateral masking/facilitation paradigm and bandpass-localized stimuli, we measured the interaction range before and after extensive training on a threshold detection task. For naive observers, target threshold was found to be facilitated by mask presence at distances up to six times the target period. However, practice had the effect of increasing the facilitation range by at least a factor of three. We suggest that the induced longer-range facilitation is a result of internal response transmission via a cascade of local connections. The data presented also show that this chain can be broken. These results suggest a plasticity in early vision governed by Hebbian-like rules.

Humans↗

PubMed1991

Stimulation of phosphoinositide turnover by excitatory amino acids. Pharmacology, development, and role in visual cortical plasticity.

Theoretical analysis suggests that in the visual cortex during early postnatal development, afferent activity can yield either an increase or a decrease in synaptic strength depending on the pattern of EAA receptor activation in cortical neurons. This motivated us to study the mechanism of EAA-stimulated phosphoinositide turnover in visual cortex. Available evidence suggests that PI hydrolysis is stimulated by EAAs primarily at a single receptor site (Q2 receptor), and that this site is distinct from both the traditional quisqualate (Q1) receptor and the NMDA receptor. NMDA does, however, inhibit EAA-stimulated PI turnover in visual cortex, confirming that the Q2 receptor is on visual cortical neurons (as opposed to glia). We find that Q2 receptors in the neocortex are expressed transiently during postnatal development. The developmental time-course of EAA-stimulated PI turnover correlates precisely with the critical period when synaptic modifications are most readily elicited in visual cortex by changes in sensory experience. The compound AP3 can inhibit EAA-stimulated PI turnover, probably by acting as a partial Q2 agonist, and under some circumstances AP3 evidently can interfere with experience-dependent synaptic modifications. Increases in synaptic strength in visual cortex, as elsewhere, have been linked specifically to activation of NMDA receptors. We propose that decreases in synaptic strength may be specifically related to activation of the Q2 receptor. Further tests of this hypothesis will require the development of selective and potent antagonists.

Amino Acids↗

PubMed1992

Plasticity of binocular visual connections in the frog, Xenopus laevis: reversibility of effects of early visual deprivation.

In frogs, each lobe of the midbrain optic tectum receives two spatially aligned maps of binocular visual space, one through each eye. The map from the contralateral eye is the product of direct retinal input to the tectum, while that from the ipsilateral eye is mediated by a commissural system of connections that relays binocular visual information from one tectal lobe to the other. In Xenopus laevis, dark-reared from early life, the visuotectal map through the ipsilateral eye exhibits significant signs of disorder indicating that the normal development of the underlying "intertectal" system involves experience-dependent processes. Here we investigate the potential of this system for recovery from such deprivation-induced disruption. Three groups of animals were first dark-reared from embryonic stages until 3 months, 12 months or 2 years after metamorphosis. These short-, medium- and long-term periods of visual deprivation are associated with a progressive disturbance of the intertectal system (Grant and Keating 1989b). The animals then experienced 12-18 months in a normal visual environment, before an electrophysiological mapping experiment was carried out to reveal the status of their intertectal system. Quantitative analyses of the visuotopic order in the ipsilateral visuotectal map and of its spatial alignment with the map derived from the contralateral eye revealed that these features were completely normal in all 3 experimental groups. It is concluded that defects present in the intertectal system of dark-reared Xenopus can be repaired by subsequent visual experience, and that the reparative capacity is not limited either by the animal's age or by the existing degree of prior disruption.

Animals↗

PubMed1995

Differential rearing alters spine density on medium-sized spiny neurons in the rat corpus striatum: evidence for association of morphological plasticity with early response gene expression.

Morphological plasticity of medium-sized spiny neurons of the striatum was examined in Long-Evans hooded rats reared in complex or individual cage environments. Rat pups, aged 28-32 days, were housed either individually in standard laboratory cages or as a group in a large toy- and object-filled environment for 30 days. The spine density on dendrites of medium-sized spiny neurons in the dorsolateral striatum was then examined using the Golgi-Cox method. Rats reared in the complex environment displayed an increase of approximately 30% in spine density relative to those reared individually. These results demonstrate experience-dependent changes in neural structure in the striatum and suggest that the mechanisms for information storage in response to experience may be more widespread in the forebrain than previously believed.

Animals↗

PubMed1996

Distribution and localization of NMDA receptor subunit 1 in the visual cortex of strabismic and anisometropic amblyopic cats.

ACTIVATION of NMDA (N-methyl-D-aspartate) receptors has recently been proposed as a prerequisite for the induction of experience-dependent modification of visual cortical neurones seen during early postnatal development. A new monoclonal antibody to the NMDA receptor subunit 1 (NMDA-R1) has been used to localize and compare the distribution of the receptors in the primary visual cortex of normal cats and those raised with either amblyopia induced by monocular optical blur or monocular esotropic strabismus. Although all three groups showed densest labelling in layers II-III, a comparison of immunopositive cells at any depth below the cortical surface showed a significantly lower frequency in strabismic and anisometropic cats than in normal cats, but a greater frequency in anisometropic cats that in strabismic animals. There appears to be no direct relationship between the expression of NMDA-R1 receptors and the level of excitability, binocularity or neuronal acuity known to exist in either of these two cat models of amblyopia, thus raising further questions as to the precise nature of the role of NMDA receptors in the processes of visual cortical plasticity.

Amblyopia↗

PubMed1984

Somatosensory cortical map changes following digit amputation in adult monkeys.

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)

Afferent Pathways↗

PubMed1990

Ocular dominance plasticity and developmental changes of 5'-nucleotidase distributions in the kitten visual cortex.

The distribution of the adenosine-producing ecto-enzyme 5'-nucleotidase was investigated histochemically in the visual cortex of normally reared and monocularly deprived kittens and cats. In normally reared kittens aged between 11 to 44 days, 5'-nucleotidase activity formed a band of intense neuropil staining throughout cortical layer IV of areas 17 and 18. The other layers were almost devoid of reaction product. Between the 4th and 6th week, this band had a patchy appearance in area 17, the center-to-center spacing of 5'-nucleotidase patches being approximately 1 mm. Monocular enucleation accentuated these patches of enhanced 5'-nucleotidase activity or made them reappear at developmental stages at which they had normally faded. Simultaneous visualization of ocular dominance columns by transneuronal transport of intraocularly injected 3H-proline showed that the patches of enhanced 5'-nucleotidase activity coincided with the territories of afferents from the intact eye. With increasing age and normal visual development, the patches disappeared and 5'-nucleotidase activity spread to the supra- and infragranular layers. The adult pattern was characterized by dense staining of all cortical laminae in both areas 17 and 18 and was established at about 8 weeks of age. At approximately 7 weeks of age, when the patches in layer IV had disappeared in the course of normal development, monocular enucleation caused a reappearance of the discontinuous pattern of 5'-nucleotidase activity in layer IV. These results reveal a close relation between the distribution of 5'-nucleotidase and the time course of the developmental phase during which the visual cortex is susceptible to experience-dependent alterations. As suggested by the correlation between sites of enzyme activity and eye dominance columns, the expression of 5'-nucleotidase patches in layer IV appears to be associated with the remodelling of ocular dominance territories that occurs both in normal development and after manipulation of afferent retinal input. Thus, 5'-nucleotidase is likely to serve a function in activity-dependent modifications of cortical circuitry. Moreover, 5'-nucleotidase activity is the only endogenous marker known to date that exhibits a columnar pattern in cat visual cortex.

5'-Nucleotidase↗

PubMed1996

Transient expression of NADPH diaphorase activity in the mouse whisker to barrel field pathway.

Development of the topographic map of the somatosensory cortex of rodents appears to depend on fine-tuned patterns of neuronal activity. Nitric oxide (NO) has been described as a potent messenger in the modulation of neural activity associated with synaptic plasticity. To evaluate the role of NO in the murine somatosensory pathway, we investigated NO synthase activity by NADPH diaphorase histochemistry at crucial developmental stages. At birth, NADPH diaphorase activity was detected in the cortical plate of the developing somatosensory cortex. At day 3, diffuse NADPH diaphorase activity increased within the emerging layer 4 in the future barrel field hollows. This staining was most intense at day 6 in the barrel field hollows and became undetectable by the end of the second postnatal week. The appearance of the diffuse NADPH diaphorase staining pattern was also observed in a similar time course and topography in the ascending relays of the somatosensory cortex, specifically in the barreloids within the ventrobasal nucleus of the thalamus and the barrelettes of the trigeminal nucleus of the brainstem. Lesioning the C row of whiskers at day 1 (i.e. during the critical period of barrel formation) led to fused C barrels of diffuse NADPH diaphorase activity in the barrel fields. In addition, highly NADPH diaphorase activity-positive individual cells present in the deeper layers of the somatosensory cortex at days 0 and 3 became visible in the upper layers at day 6 and remained until day 15. In layer 4, these cells were predominantly localized in the septa at day 6 and 9. No positive individual cells were detected in barrelettes or barreloids at any age. We conclude that NADPH diaphorase activity is present during experience-dependent consolidation of synaptic contacts in the somatosensory pathway.

Aging↗

PubMed1992

Agonists of cholinergic and noradrenergic receptors facilitate synergistically the induction of long-term potentiation in slices of rat visual cortex.

Acetylcholine (ACh) and noradrenaline (NA) have been shown to facilitate experience-dependent modifications of synaptic connectivity during postnatal development of the kitten visual cortex. To further investigate the mechanisms of this facilitation we studied the effects of these neuromodulators in an in vitro model of use-dependent synaptic plasticity. We have chosen long-term potentiation (LTP) in rat visual cortex slices because it shares several features with the in vivo model. In both cases induction of synaptic modifications requires that postsynaptic activation reaches a critical threshold and in both cases changes are induced more easily in young animals and when N-methyl-D-aspartate (NMDA) receptor-gated conductances are activated. Intracellular recordings were obtained from regular spiking cells in supragranular layers of rat visual cortex and LTP was induced by tetanic stimulation of the underlying white matter. Both cholinergic and noradrenergic agonists raised the probability that tetanic stimuli induced LTP and as in vivo they acted synergistically. These effects were mediated by agonists of muscarinic and beta-receptors, respectively. The agonists of both receptor systems enhanced the depolarizing response to the tetanus and increased NMDA receptor-gated conductances during this response. We suggest that this mode of action also accounts for the facilitatory effects which ACh and NA have on use-dependent synaptic plasticity in the developing visual cortex.

Acetylcholine↗

PubMed1996

A synaptic basis for memory storage in the cerebral cortex.

A cardinal feature of neurons in the cerebral cortex is stimulus selectivity, and experience-dependent shifts in selectivity are a common correlate of memory formation. We have used a theoretical "learning rule," devised to account for experience-dependent shifts in neuronal selectivity, to guide experiments on the elementary mechanisms of synaptic plasticity in hippocampus and neocortex. These experiments reveal that many synapses in hippocampus and neocortex are bidirectionally modifiable, that the modifications persist long enough to contribute to long-term memory storage, and that key variables governing the sign of synaptic plasticity are the amount of NMDA receptor activation and the recent history of cortical activity.

Animals↗

PubMed1995

The effects of early postnatal modification of body shape on the somatosensory-visual organization in mouse superior colliculus.

Different regions of the body of an animal have their own shape and location within visual space. Accordingly, in the superior colliculus there are somatosensory-visual bimodal neurons receiving tactile and visual input from the same region of space. In newborn mice, we changed the position of some body parts within visual space in order to see what happened to the alignment of the somatosensory and visual receptive fields of superior colliculus bimodal neurons. To do this, we modified the shape of the head by displacing the superior vibrissae and the ears, normally in the superior portion of visual space, into the inferior visual space. Analogously, we bent the inferior vibrissae into the superior visual space. At the sixth postnatal week we recorded from somatosensory-visual bimodal neurons of the deep layers of the superior colliculus and found that the tactile and visual receptive fields were aligned. Neurons receiving tactile input from the downward-displaced superior vibrissae and ears showed visual receptive fields in the inferior portion of visual space, whereas neurons receiving input from the upward-displaced inferior vibrissae showed visual receptive fields in the superior visual space. These results show that an experience-dependent interaction between visual and somatosensory inputs occurs during development, and that early exposure to abnormal visual-somatosensory experience modifies the organization of multisensory neurons in the superior colliculus.

Animals↗

PubMed1996

Brain-derived neurotrophic factor reversed experience-dependent synaptic modifications in kitten visual cortex.

During a critical period of early postnatal development the functional architecture of the visual cortex is shaped by experience-dependent circuit selection following a Hebbian mechanism. One consequence is that monocular deprivation (MD) leads to competitive repression of the input from the deprived eye. Recently it has been proposed that this process might involve activity-dependent competition for neurotrophic substances because the synthesis of brain-derived neurotrophic factor (BDNF) is regulated by visual input. Here we investigate the effects of intracortical infusion of BDNF and nerve growth factor (NGF) on MD effects in the visual cortex. Neuronal responses were monitored with optical and single unit recording techniques in the visual cortex of kittens that had been infused intracortically either with BDNF, NGF or cytochrome C while subjected to MD for 1 week during the peak of the critical period. NGF or cytochrome C had no effect on the consequences of MD. After BDNF treatment, by contrast, ocular dominance (OD) shifted towards the deprived eye in a zone extending 2.5-3.5 mm from the infusion cannula, and neurons lost their orientation selectivity. At intermediate distances both eyes activated the cortex equally well and responses were again tuned for orientation; at still larger distances OD was shifted towards the normal eye. Thus, BDNF antagonizes the functional effects of MD and at high concentrations causes paradoxical disconnection of non-deprived afferents and a loss of orientation selectivity.

Animals↗

PubMed1996

Newly learned auditory responses mediated by NMDA receptors in the owl inferior colliculus.

Alignment of auditory and visual receptive fields in the optic tectum of the barn owl (Tyto alba) is maintained through experience-dependent modification of auditory responses in the external nucleus of the inferior colliculus (ICX), which provides auditory input to the tectum. Newly learned tectal auditory responses, induced by altered visual experience, were found to be pharmacologically distinct from normal responses expressed at the same tectal sites. N-methyl-D-aspartate (NMDA) receptor antagonists administered systemically or applied locally in the ICX reduced learned responses more than normal responses. This differential blockade was not observed with non-NMDA or broad-spectrum antagonists. Thus, NMDA receptors preferentially mediate the expression of novel neuronal responses induced by experience during development.

2-Amino-5-phosphonovalerate↗

PubMed1991

Synaptic plasticity in visual cortex: comparison of theory with experiment.

1. The aim of this work was to assess whether a form of synaptic modification based on the theory of Bienenstock, Cooper, and Munro (BCM) can, with a fixed set of parameters, reproduce both the kinetics and equilibrium states of experience-dependent modifications cortex. 2. According to the BCM theory, the connection strength of excitatory geniculocortical synapses varies as the product of a measure of input activity (d) and a function (phi) of the summed postsynaptic response. For all postsynaptic responses greater than spontaneous but less than a critical value called the "modification threshold" (theta), phi has a negative value. For all postsynaptic responses greater than theta, phi has a positive value. A novel feature of the BCM theory is that the value of theta is not fixed, but rather "slides" as a nonlinear function of the average postsynaptic response. 3. This theory permits precise specification of theoretical equivalents of experimental situations, allowing detailed, quantitative comparisons of theory with experiment. Such comparisons were carried out here in a series of computer simulations. 4. Simulations are performed by presenting input to a model cortical neuron, calculating the summed postsynaptic response, and then changing the synaptic weights according to the BCM theory. This process is repeated until the synaptic weights reach an equilibrium state. 5. Two types of geniculocortical input are simulated: "pattern" and "noise." Pattern input is assumed to correspond to the type of input that arises when a visual contour of a particular orientation is presented to the retina. This type of input is said to be "correlated" when the two sets of geniculocortical fibers relaying information from the two eyes convey the same patterns at the same time. Noise input is assumed to correspond to the type of input that arises in the absence of visual contours and, by definition, is uncorrelated. 6. By varying the types of input available to the two sets of geniculocortical synapses, we simulate the following types of visual experience: 1) normal binocular contour vision, 2) monocular deprivation, 3) reverse suture, 4) strabismus, 5) binocular deprivation, and 6) normal contour vision after a period of monocular deprivation. 7. The constraints placed on the set of parameters by each type of simulated visual environment, and the effects that such constraints have on the evolution of the synaptic weights, are investigated in detail.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

The formation of cooperative cell assemblies in the visual cortex.

During a critical period of postnatal development of the mammalian visual cortex, synaptic connections are susceptible to use-dependent modifications. Synaptic connections strengthen if pre- and postsynaptic elements are active simultaneously and postsynaptic depolarization is sufficient to allow for the activation of N-methyl-D-aspartate (NMDA)-receptor-gated conductances. By contrast, synaptic gain decreases if postsynaptic activation exceeds a critical threshold and presynaptic afferents are not capable of activating NMDA-receptor-dependent conductances. These processes lead to selective stabilization of connections between neuronal elements which often exhibit correlated activity and thus modify connectivity according to functional criteria. It is suggested that such experience-dependent selection of circuits serves different purposes at different levels of visual processing. At the input stage to the striate cortex it contributes to optimize the match between the representations of the two eyes. At a later stage of processing it participates in the development of selective connections between cortical columns and thereby serves to establish neuronal representations for frequently occurring constellations of features. Use-dependent changes of synaptic gain can also be induced in the mature visual cortex. These modifications follow the same rules as those occurring during early development and appear to depend on similar molecular mechanisms. However, in the adult the changes of synaptic gain do not seem to be followed by major rearrangements of connectivity. This suggests developmental alterations in mechanisms responsible for growth, removal and stabilization of synaptic connections. Actually, many of the cellular mechanisms thought to be involved in use-dependent synaptic plasticity change during development but it is still unclear which of them are responsible for the definitive stabilization of functionally confirmed pathways.

Aging↗

PubMed1994

The flexible fly: experience-dependent development of complex behaviors in Drosophila melanogaster.

We demonstrate that Drosophila melanogaster provides a rich model system for studying behavioral development. Two additions to the many well-known advantages of this species are exploited here. First, as in mammals and higher vertebrates, early experience affects behavioral development of Drosophila. Second, the affected behaviors are complex and yet readily studied in the laboratory. Thus, Drosophila can be used to study the developmental mechanisms by which organisms can optimize their behavioral repertoires to enhance their chances for survival. Evidence that early experience affects female responsiveness to courting males is reviewed; in each case, experience modifies responses to behavioral targets. Our results demonstrate that developmental plasticity allows adjustment of intrinsically determined responses to visual targets so that they can take into account the actual characteristics of the developing animal's environment. Furthermore, plasticity makes it possible to introduce 'cultural' and 'social' elements into courtship and mate choice in insects. This previously unrecognized role for developmental plasticity in insects has broad theoretical and practical implications.

Animals↗