Download e-book Plasticity in Sensory Systems

Contents:

Activity-dependent axonal plasticity in sensory systems.

Sensory Deprivation and Brain Plasticity

Cross-modal plasticity has been demonstrated following visual and auditory deprivation since birth. In both cases, the deprived cortex becomes activated by one or more of the remaining senses, touch, audition, and olfaction in the case of blindness and visual stimulation in the case of deafness. There is a large body of evidence, based upon anatomical, metabolic, and behavioral findings, that the deprived sensory cortex acquires multiple sensory and cognitive functions, transforming itself therefore into a multimodal cortex.

In this issue, we have gathered a number of review and original papers on the topic of brain plasticity in humans and in animal models of unimodal sensory deprivation. We have welcomed not only papers dealing with various sensory systems such as vision, audition, touch, and olfaction but also those dealing with basic mechanisms of brain plasticity. Several papers present results on cross-modal plasticity and sensory substitution in humans and in animal models of sensory deprivation.

Using elegant methodologies, these studies highlight how other sensory modalities take over the deprived visual or auditory cortices in blind and deaf subjects, respectively.

Activity-dependent axonal plasticity in sensory systems.

Brain plasticity can also be triggered by changes in sensory experience. Neural reorganization will take place if the environment is modified during the early stages of development as is the case following cortical lesions of the visual cortical areas, visual deprivation through eyelid suturing, or dark-rearing M. As shown by J. Pietrasanta and coworkers describe how the interhemispheric connectivity between the visual cortices can be altered by visual deprivation.

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At the same time, functional alterations at the nanoscale such as expression or activation changes of channels and receptors contribute to the modulation of intrinsic excitability or input-output relationships. Subsequent research demonstrated that it was the minutes of engaged eye-hand coordination which improved the visual function in amblyopia, not the rotating stripes. Motor Adaptation and Proprioceptive Recalibration. Ptito and colleagues provide evidence that the functional segregation of the efferent projections of the primary visual cortex into a dorsal and a ventral stream is preserved in congenitally blind humans. Steeves , Laurence R.

The corpus callosum therefore seems to have a pivotal role in plasticity of the visual cortex. The papers by G. Dormal and colleagues and M. Ptito and colleagues provide evidence that the functional segregation of the efferent projections of the primary visual cortex into a dorsal and a ventral stream is preserved in congenitally blind humans.

Leo and colleagues focus on the purported role of the parietooccipital connections in conveying nonvisual information to the deprived visual cortex. Two papers focus on auditory deprivation and cross-modal plasticity. Allman show how the auditory cortex of deaf ferrets is reorganized by the somatosensory modality, whereas P.

Hirst and colleagues use a primate model to highlight cross-modal plasticity. To count them, you need very good control of your eye movements. You also need to see more than one line at a time to keep your place which requires the integration of information across your visual field which is a fundamental perceptual skill. Directing the eyes to a target prior to initiation of hand movement allows the central nervous system to obtain a high-resolution image of the target before the reach is initiated, which can facilitate programming of the reaching movement.

Sensory Deprivation and Brain Plasticity

In addition, when the eyes fixate on the target early during the trajectory, visual feedback can be used to update the initial motor plan…. In contrast, patients with mild or severe amblyopia initiated reaching prior to directing the eyes to the target in significantly more trials when viewing with the amblyopic eye. This behavior is not limited to children with amblyopia and is commonly seen in children with learning-related vision problems and in those who are viewed as clumsy.

These poorly learned skills can be enhanced with commensurate outcomes in performance.

The accuracy and precision of our movements depend on our ability to predict the consequences of our own actions and use sensory feedback. In directing movement, vision is actually predicting the future. The ways that you use vision to do this are endless. As examples, consider how vision functions to enable you to catch a ball or to drive a car.

Robert Hess presented a very unusual scientific paper. Hess was mentored by Fergus Campbell and in the s they developed a device based on sound theory to treat amblyopia. We purchased one right away and used it for a number of years in vision therapy. Hess discusses the device with a perspective and humility which is refreshing.

Neural Plasticity

This was the beginning of the CAM treatment of amblyopia which was to have an interesting, if not checkered, history over the next 40 years. The device consisted of a rotating wheel with stripes which were designed to stimulate edge detectors in the visual system. Edge detectors were discovered by Hubel and Weisel which changed the course of neuroscience and won them a Nobel Prize.

M13 6 plasticity of cortical representations

Subsequent research demonstrated that it was the minutes of engaged eye-hand coordination which improved the visual function in amblyopia, not the rotating stripes. The device worked, but for a serendipitous reason. In recent decades, numerous studies have shown that a range of visual functions in normal adult subjects can be improved as a result of intensive training termed perceptual learning.

Hess goes on to write: It has long been assumed that the primary problem in amblyopia is monocular loss of vision and that loss of binocularity is a secondary consequence. The traditional treatment is patching, which is directed to restore the vision in the amblyopic eye with the assumption, using the preceding logic, that binocular function will eventually follow suit. However, the binocular expectation is often not realized, and one is tempted to think that keeping a child monocular for a significant part of early visual development may not be the ideal way of going about restoring binocularity.

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Sue Barry is a neuroscientist who successfully became binocular with stereopsis for the first time at age 48 through vision therapy. This was assumed to be impossible by the scientific community and most of the medical community. We must ask whether poor success in establishing binocular vision in adult strabismics and amblyopes has resulted, not because of irreversible changes in neural circuitry, but because standard clinical treatments do not address the underlying causes of these disorders….

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The underlying problem in amblyopia is not poor acuity in one eye but rather a poor ability to use the two eyes together…. Surgery for the human patient is an entirely passive experience. Although an operation may reorient the eyes in the sockets in a way that makes fusion more likely, it does not teach the patient how to fuse….

Active learning must be involved.