Early Left-hemispheric Lesions Research Articles

Plasticity during Early Brain Development Is Determined by Ontogenetic Potential.

Two competing hypotheses address neuroplasticity during early brain development: the "Kennard principle" describes the compensatory capacities of the immature developing CNS as superior to those of the adult brain, whereas the "Hebb principle" argues that the young brain is especially sensitive to insults. We provide evidence that these principles are not mutually exclusive. Following early brain lesions that are unilateral, the brain can refer to homotopic areas of the healthy hemisphere. This potential for reorganization is unique to the young brain but available only when, during ontogenesis of brain development, these areas have been used for the functions addressed. With respect to motor function, ipsilateral motor tracts can be recruited, which are only available during early brain development. Language can be reorganized to the right after early left hemispheric lesions, as the representation of the language network is initially bilateral. However, even in these situations, compensatory capacities of the developing brain are found to have limitations, probably defined by early determinants. Thus, plasticity and adaptivity are seen only within ontogenetic potential; that is, axonal or cortical structures cannot be recruited beyond early developmental possibilities. The young brain is probably more sensitive and vulnerable to lesions when these are bilateral. This is shown here for bilateral periventricular white matter lesions that clearly have an impact on cortical architecture and function, thus probably interfering with early network building.

The Visual Word Form Area remains in the dominant hemisphere for language in late-onset left occipital lobe epilepsies: A postsurgery analysis of two cases

Automatic recognition of words from letter strings is a critical processing step in reading that is lateralized to the left-hemisphere middle fusiform gyrus in the so-called Visual Word Form Area (VWFA). Surgical lesions in this location can lead to irreversible alexia. Very early left hemispheric lesions can lead to transfer of the VWFA to the nondominant hemisphere, but it is currently unknown if this capability is preserved in epilepsies developing after reading acquisition. In this study, we aimed to determine the lateralization of the VWFA in late-onset left inferior occipital lobe epilepsies and also the effect of surgical disconnection from the adjacent secondary visual areas. Two patients with focal epilepsies with onset near the VWFA underwent to surgery for epilepsy, with sparing of this area. Neuropsychology evaluations were performed before and after surgery, as well as quantitative evaluation of the speed of word reading. Comparison of the surgical localization of the lesion, with the BOLD activation associated with the contrast of words–strings, was performed, as well as a study of the associated main white fiber pathways using diffusion-weighted imaging. Neither of the patients developed alexia after surgery (similar word reading speed before and after surgery) despite the fact that the inferior occipital surgical lesions reached the neighborhood (less than 1cm) of the VWFA. Surgeries partly disconnected the VWFA from left secondary visual areas, suggesting that pathways connecting to the posterior visual ventral stream were severely affected but did not induce alexia. The anterior and superior limits of the resection suggest that the critical connection between the VWFA and the Wernicke's Angular Gyrus cortex was not affected, which is supported by the detection of this tract with probabilistic tractography. Left occipital lobe epilepsies developing after reading acquisition did not produce atypical localizations of the VWFA, even with foci in the close neighborhood. Surgery for occipital lobe epilepsy should take this into consideration, as well as the fact that disconnection from the left secondary visual areas may not produce alexia.

IS-021 Functional Mri And Language Development In Infants And Children

Language is specific to the human and can, thus, not be studied in the animal. In the adult, there is a strong dominance of the left hemisphere for most aspects of language and stroke in language regions often leads to permanent aphasia. In contrast, lesions in similar locations acquired very early do not lead to an impaired language function in the affected child. With the advent of fMRI, the cerebral representation of language organisation can now be studied non-invasively even in smaller children. Questions 1. Language representation during development? 2. Early left hemispheric lesions and language representation? 3. If there is language reorganisation, does it affect right hemispheric functions? 4. How good is right hemispheric language? 5. What is the time frame for reorganisation? Answers Language representation is initially bilateral and increasingly left dominated during development. Early left hemispheric lesions may induce reorganisation to the right – in homotopic areas. This happens on the expense of right hemispheric functions. Language quality in reorganised language is not impaied for everyday language, but there are differences in complex linguistic aspects, which supports the idea of a genetic predisposition. The time frame for reorganisation is not very clear, but there is no evidence for successful reorganisation after preschool age. This work is supported by the German Research Council (DFG) and the University of Tubingen.

Language abilities after early left-hemispheric lesions – neural and cognitive compensation

Language abilities after early left-hemispheric lesions – neural and cognitive compensation

Language abilities after early left-hemispheric lesions – Production and comprehension of complex linguistic structures

Introduction: Normally language functions in the brain are organized in the left cerebral hemisphere. After pre- or perinatally acquired left hemisphere brain damage, language function can be saved by reorganization into the right hemisphere.

Left hemisphere regions are critical for language in the face of early left focal brain injury

A predominant theory regarding early stroke and its effect on language development, is that early left hemisphere lesions trigger compensatory processes that allow the right hemisphere to assume dominant language functions, and this is thought to underlie the near normal language development observed after early stroke. To test this theory, we used functional magnetic resonance imaging to examine brain activity during category fluency in participants who had sustained pre- or perinatal left hemisphere stroke (n = 25) and in neurologically normal siblings (n = 27). In typically developing children, performance of a category fluency task elicits strong involvement of left frontal and lateral temporal regions and a lesser involvement of right hemisphere structures. In our cohort of atypically developing participants with early stroke, expressive and receptive language skills correlated with activity in the same left inferior frontal regions that support language processing in neurologically normal children. This was true independent of either the amount of brain injury or the extent that the injury was located in classical cortical language processing areas. Participants with bilateral activation in left and right superior temporal-inferior parietal regions had better language function than those with either predominantly left- or right-sided unilateral activation. The advantage conferred by left inferior frontal and bilateral temporal involvement demonstrated in our study supports a strong predisposition for typical neural language organization, despite an intervening injury, and argues against models suggesting that the right hemisphere fully accommodates language function following early injury.

Recovery of function after brain injury in man.

Late after-effects of cerebral trauma are difficult to study because patients tend to be seen for persisting symptoms, and not simply for their lesions. We have tried to avoid this bias by recalling periodically, over the years, 520 men with known brain injuries incurred in World War II or in Korea or Vietnam. These men are seen irrespective of clinical need and all undergo intensive behavioural and neurological assessment, which still continues. For such groups, recovery is impressive, though one third shows persistent intellectual loss. In addition, some tasks reveal specific deficits enduring unchanged, after th first 2-3 yr, for the 20-30 yr of follow-up (e.g. visual field defects, certain auditory discrimination losses, trouble on various complex perceptual tasks). These lasting deficits are linked to the site and size of focal injury, often representing remnants of more severe initially-present disorders. The extent of recovery is correlated with age at the time of trauma, the youngest faring best. Extension of such studies to cases of early brain damage (birth to five years), as indicated by hemiparesis, shows the familiar 'escape' of language after early left-hemisphere lesions but this is achieved at a price, the price being borne by non-verbal functions that normally depend on the integrity of the right hemisphere.

Visuospatial deficits in patients with early left-hemispheric lesions and functional reorganization of language: Consequence of lesion or reorganization?

Introduction Patients with early left-hemispheric lesions have repeatedly been reported to show spared language functions (which are then mediated by the right hemisphere), but exhibit deficits in visuospatial functions. The “crowding hypothesis” explains these deficits by a neuronal scarcity in the right hemisphere for the original right hemispheric functions. An alternative hypothesis suggests direct lesion effects as the sole reason for the visuospatial impairments. The scope of this study was to examine the relations between visuospatial skills and hemispheric preference for language, and between visuospatial skills and cerebral lesion size. Methods In a sample of young adults with pre- or perinatally acquired focal lesions of the left hemisphere and unilateral spastic cerebral palsy on the right side, we assessed intelligence and neuropsychological functions in the verbal and visuospatial domains. The behavioural data was correlated with structural MRI information and language preference as assessed using fMRI. Results Patients with right hemispheric language production were impaired in visuospatial functions, compared not only to normal controls, but also to patients without right hemispheric language preference. Additionally, the degree of right hemispheric language correlated negatively with performance in visuospatial tasks. Lesion size correlated negatively only with performance IQ, which again correlated negatively with motor impairment of the patients and thus does not seem to reflect true cognitive deficits. Conclusion Visuospatial deficits in patients with early left-hemispheric lesions are a consequence of lesion-induced right hemispheric language organization, thus lending further support to the “crowding hypothesis”.

Cognitive outcome of children with epilepsy and malformations of cortical development.

To assess intellectual functioning (IQ) in 54 children and adolescents with intractable epilepsy who later underwent cortical resection due to unilateral malformations of cortical development acquired in utero. Lesion type was classified into circumscribed mass lesions and diffuse cortical dysplasia based on histopathologic analysis of surgical tissue. Cortical dysplastic lesions were further graded as mild, moderate, or severe according to specific microscopic features. Laterality of lesion was determined through neurologic examination and electrophysiologic and neuroradiologic procedures. Classification of lesion type was corroborated by its significant relationship with other disease-related variables known to be related to clinical severity (age at seizure onset, age at resection, and extent of lesion). Analyses of covariance revealed that circumscribed lesions had a less deleterious effect on nonverbal IQ than did diffuse cortical dysplasia, after controlling for age at seizure onset and extent of lesion. This effect was also found on verbal IQ measures, but only in subjects with right-sided lesions. Subjects with left-sided lesions performed significantly more poorly on verbal IQ measures than those with right-sided lesions. Additionally, younger age at onset and greater extent of lesion were associated with poorer cognitive outcome. Cortical dysplasia and early left hemisphere lesions have a significantly worse impact on cognitive functioning than circumscribed lesions or right hemisphere developmental lesions in children with epilepsy.

Right hemisphere restitution of language and memory functions in right hemisphere language-dominant patients with left temporal lobe epilepsy.

Concomitant with the right hemispheric restitution of language functions after early left hemisphere lesions, suppression effects on originally right hemispheric visuospatial/constructional functions have repeatedly been reported. The present study evaluated this issue in 10 right hemisphere language-dominant patients with temporal lobe epilepsy. Left hemisphere language-dominant patients with left (n = 10) or right (n = 10) temporal lobe epilepsy served as controls. The following results were obtained: in all but one of the right dominant patients, left hemisphere lesions, left hemisphere foci and histories of early left brain damage indicated that secondary language transfer rather than a genetically determination is the more likely cause of the right hemisphere dominance. Despite this transfer, the language functions (comprehension, fluency, reasoning) of the right dominant patients remained significantly impaired. Language generally appeared to be better preserved in patients with an onset of epilepsy before the third year of life or a circumscribed left hemisphere lesion. No suppression effects could be detected on the level of complex cortical language and non-language functions. In contrast, on the level of temporo-limbic memory functions, verbal learning and recognition were left largely intact, albeit mostly at the expense of visuo-spatial learning and memory. The findings of the study thus indicate that the cerebral plasticity of the right hemisphere differs according to the extent of the left-hemisphere lesion, the onset of structural/functional damage and the complexity of the functions requiring restitution. Assuming that language and memory represent neocortical and palaeocortical functions, respectively, the restitution process is seemingly governed by their status in a phylogenetically determined hierarchy of functional importance.