Plasticity of the visual system after early brain damage

Abstract

The aim of this review is to discuss the existing evidence supporting different processes of visual brain plasticity after early damage, as opposed to damage that occurs during adulthood. There is initial evidence that some of the neuroplastic mechanisms adopted by the brain after early damage to the visual system are unavailable at a later stage. These are, for example, the ability to differentiate functional tissue within a larger dysplastic cortex during its formation, or to develop new thalamo-cortical connections able to bypass the lesion and reach their cortical destination in the occipital cortex. The young brain also uses the same mechanisms available at later stages of development but in a more efficient way. For example, in people with visual field defects of central origin, the anatomical expansion of the extrastriatal visual network is greater after an early lesion than after a later one, which results in more efficient mechanisms of visual exploration of the blind field. A similar mechanism is likely to support some of the differences found in people with blindsight, the phenomenon of unconscious visual perception in the blind field. In particular, compared with people with late lesions, those with early brain damage appear to have stronger subjective awareness of stimuli hitting the blind visual field, reported as a conscious feeling that something is present in the visual field. Expanding our knowledge of these mechanisms could help the development of early therapeutic interventions aimed at supporting and enhancing visual reorganization at a time of greatest potential brain plasticity.Brain plasticity consists of the modifications to the central nervous system in response to environmental stimulation, which allow us to learn new skills, remember new information, and recover from brain injury. 1 Mechanisms of neuronal plasticity are more powerful during early development. For example, children are faster than adults in learning a new language or in achieving complex skills such as playing a musical instrument. 2 Similarly, children lacking proper environmental inputs early in life are more susceptible to an abnormal development of the functions related to those inputs (the principle of sensitive periods 3 ).The presence of more powerful mechanisms of neuronal plasticity during early development should imply that recovery from brain damage is more effective after early lesions than after lesions occurring later in life. This principle was first suggested by Paul Broca in 1865 4 and then more systematically explored by Margaret Kennard in the late 1930s. 5 Since then, most of the studies of different species have supported this general principle, although describing a more complex picture, which takes into consideration several other aspects beyond timing of the insult, including the location and extension of injury (e.g. focal versus diffuse), the clinical phenotype (e.g. presence of seizures), or the genetic susceptibility of the individual. 6 Today, there is general agreement that the way the bra...

Involvement of the visual pathway is not a risk factor of visual field deficits in patients with occipital arteriovenous malformations: an fMRI study

“…We would speculate that from early gestation, the trajectories of the optic radiations in the affected hemisphere may deviate from their normal course, bypass the AVMs, and reach their final target in the occipital lobe. A similar process can be observed in the visual system of patients with unilateral peri-ventricular brain damage early in the third trimester of gestation [9]. Our speculation is also consistent with animal studies [13,20,21] and postmortem findings in human fetuses [10] which showed that developing geniculo-striate axons after mid-gestation "wait" in the subplate for weeks before entering the cortical plate.…”

“…We can also conclude that as a congenital disease, many AVMs might have coexisted with the optic radiation and visual cortex from very early phases of development and the visual pathway may modify continuously by virtue of brain plasticity to maintain normal VFs. This can also be observed from the findings of Guzzeta et al One patient in their study showed normal VFs despite a large lesion of the left peri-ventricular white matter involving most of the tissue where optic radiations would normally sit [9]. Most occipital AVMs may present with normal VFs unless a hemorrhage occurs.…”

Advanced Fiber Tracking in Early Acquired Brain Injury Causing Cerebral Palsy

“…Some case reports show diffusion tensor tractograms of thalamocortical connections that are displaced by lesions but still reach cortical areas in individuals with early acquired brain lesions (eg, Staudt et al 30 ; Guzzetta et al 31 ). With our method, we observed, in several cases and in all lesion types, that both the CST and TRS1 on the lesion side have altered paths when passing lesion-affected areas.…”

Cerebral versus Ocular Visual Impairment: The Impact on Developmental Neuroplasticity

“…Indeed, clinical editorials have highlighted that the relationship between observed clinical manifestations and the extent of brain damage in CVI is complex and not yet fully understood (Guzzetta et al, 2010). Additionally, attention has been called to the value of advanced neuroimaging techniques in helping to better understand the relationship between brain maldevelopment and visual impairment in CVI (Good, 2001; Edmond and Foroozan, 2006; Murakami et al, 2008).…”