Early plasticity versus early vulnerability: the problem of heterogeneous lesion types

It's easier to relearn gross motor skills than learn them for the first time after injury: Empirical evidence informing the age at injury debate

The effect of age at injury on outcomes after brain injury has long been debated. Many have argued that the greater plasticity of the immature brain aids in its recovery from trauma, but others (notably Donald Hebb) have argued that early injury can impair the future ability of the brain to acquire new capabilities. This is difficult to assess empirically due to the presence of many age-dependent confounders. We performed Item Response Theory (IRT) analyses of two datasets of Gross Motor Function Measure (GMFM) observations, one in children with cerebral palsy (CP) and one in children with acquired brain injury (ABI) sustained at later ages. We used IRT to derive independent estimates of test item difficulty in the two populations. Additionally, where comparison between GMFM items and items in the Denver II Developmental Screening Test battery was possible we used the latter to obtain the ages at which these abilities are acquired in typically developing children. Item difficulty estimates for the two populations are highly correlated (adjusted r2=0.89, p<0.0005), but demonstrate significant bias with harder items (typically acquired at later ages) being more readily achieved by children with ABI compared to CP. These results support the Hebbian perspective that (when considering gross motor function) it is easier to maintain or recover previously established functions than to learn them for the first time in an injured brain. This argues for a more cautious outcome prognosis in injury at very young ages.

Implications of age at lesion onset for neuropsychological outcomes: A systematic review focusing on focal brain lesions

Theories of the relation between age at lesion onset and outcomes posit different views of the young brain: resilient and plastic (i.e., the so-called "Kennard Principle"), or vulnerable (i.e., the Early Vulnerability Hypothesis). There is support for both perspectives in previous research and questions about the "best" or "worst" times to sustain brain injury remain. Here, we present a systematic review investigating the influence of age at focal brain lesion onset on cognitive functioning. This systematic review identifies and qualitatively synthesizes empirical studies from 1985 to 2021 that investigated age at lesion onset as a variable of interest associated with neuropsychological outcomes. A total of 45 studies were identified from PubMed, PsycINFO, and CINAHL databases. Almost all studies indicated that brain injury earlier in the developmental period predicts worse cognitive outcomes when compared to onset either later in the developmental period or in adulthood. More specifically, the overwhelming majority of studies support an "earlier is worse" model for domains of intellect, processing speed, attention and working memory, visuospatial and perceptual skills, and learning and memory. Relatively more variability in outcomes exists for domains of language and executive functioning. Outcomes for all domains are influenced by various other age and injury variables (e.g., lesion size, lesion laterality, chronicity, a history of epilepsy). Continued interdisciplinary understanding and communication about the influence of age at lesion onset on neuropsychological outcomes will aid in promoting the best possible outcomes for patients.

Principles of early intervention

The great majority of children with neurodevelopmental challenges do not get specific intervention until after their second birthday. This worsens their outcomes, because a great part of the entire neuroplastic window for learning is misspent. There is emerging evidence that the impact on outcomes of early goal-directed training involving the parents in infants with neurodevelopmental disabilities is significantly superior to the results achieved in older children and adults, especially if intervention commences in the first months of life. This chapter outlines the common elements of neurodevelopment and early intervention. It includes an outline of some of the primary early intervention practices and the scientific evidence driving them.

Pediatric Stroke: Unique Implications of the Immature Brain on Injury and Recovery

Pediatric stroke causes significant morbidity for children resulting in lifelong neurological disability. Although hyperacute recanalization therapies are available for pediatric patients, most patients are ineligible for these treatments. Therefore the mainstay for pediatric stroke treatment relies on rehabilitation to improve outcomes. Little is known about the ideal rehabilitation therapies for pediatric patients with stroke and the unique interplay between the developing brain and our models of stroke recovery. In this review, we first discuss the consequences of pediatric stroke. Second, we examine the scientific evidence that exists between the mechanisms of recovery and how they are different in the pediatric developing brain. Finally, we evaluate potential interventions that could improve outcomes.

Plasticity following early-life brain injury: Insights from quantitative MRI

Over the last decade, the application of novel advanced neuroimaging techniques to study congenital brain damage has provided invaluable insights into the mechanisms underlying early neuroplasticity. The concept that is clearly emerging, both from human and nun-human studies, is that functional reorganization in the immature brain is substantially different from that of the more mature, developed brain. This applies to the reorganization of language, the sensorimotor system, and the visual system. The rapid implementation and development of higher order imaging methods will offer increased, currently unavailable knowledge about the specific mechanisms of cerebral plasticity in infancy, which is essential to support the development of early therapeutic interventions aimed at supporting and enhancing functional reorganization during a time of greatest potential brain plasticity.

Long-term influences of a preterm birth on movement organization and side specialization in children at 4-8 years of age

This study explored upper-limb and head kinematics during unimanual goal-directed movements in children born preterm (PT) and full-term (FT) aged 4-8 years. Further, functional lateralization was investigated through side-specific kinematics and hand preference observations. Altogether, 141 children were included, divided into three sub-groups based on gestation week at birth (GW). Children born FT (38-41 GW) and moderately PT (33-35 GW) showed faster, smoother, and shorter movement trajectories than children born very PT (V-PT < 33 GW). Only children born FT expressed evident side differences that were characterized by smoother movements with the preferred side. Regarding hand preference, the children born V-PT showed increased rates of non-right-handedness compared with the other groups. Regardless of hand preference, the children born V-PT showed less well organized movements compared with the other groups. These findings suggest that spatio-temporal movement organization and side specialization at pre-/early school-age are affected by a PT birth, and more frequently so for children born before 33 GWs, indicating long-lasting influences on neuromotor development and specialization.

Age, plasticity, and homeostasis in childhood brain disorders

It has been widely accepted that the younger the age and/or immaturity of the organism, the greater the brain plasticity, the young age plasticity privilege. This paper examines the relation of a young age to plasticity, reviewing human pediatric brain disorders, as well as selected animal models, human developmental and adult brain disorder studies. As well, we review developmental and childhood acquired disorders that involve a failure of regulatory homeostasis. Our core arguments are as follows:

Establishing, versus maintaining, brain function: a neuro-computational model of cortical reorganization after injury to the immature brain

The effect of age at injury on outcome after acquired brain injury (ABI) has been the subject of much debate. Many argue that young brains are relatively tolerant of injury. A contrasting viewpoint due to Hebb argues that greater system integrity may be required for the initial establishment of a function than for preservation of an already-established function. A neuro-computational model of cortical map formation was adapted to examine effects of focal and distributed injury at various stages of development. This neural network model requires a period of training during which it self-organizes to establish cortical maps. Injuries were simulated by lesioning the model at various stages of this process and network function was monitored as "development" progressed to completion. Lesion effects are greater for larger, earlier, and distributed (multifocal) lesions. The mature system is relatively robust, particularly to focal injury. Activities in recovering systems injured at an early stage show changes that emerge after an asymptomatic interval. Early injuries cause qualitative changes in system behavior that emerge after a delay during which the effects of the injury are latent. Functions that are incompletely established at the time of injury may be vulnerable particularly to multifocal injury.

Multisite trial comparing the efficacy of constraint-induced movement therapy with that of bimanual intensive training in children with hemiplegic cerebral palsy: postintervention results

OBJECTIVE

The aim of this study was to compare the effects of modified constraint-induced movement therapy (mCIMT; restraint of unaffected limb combined with unimanual intensive rehabilitation) with those of a bimanual intensive rehabilitation treatment (IRP) in children with hemiplegic cerebral palsy after a 10-wk practice vs. standard treatment (ST).

DESIGN

This study is a multicenter, cluster-randomized controlled clinical trial of tested groups of children with hemiplegic cerebral palsy treated using mCIMT, IRP, or ST. For 10 wks, in mCIMT and IRP, the intensive practice lasted 3 hrs/day, 7 days/wk; in ST, 1-hr sessions twice a week were provided. The primary outcomes are upper limb/hand function (Quality of Upper Extremity Skills Test) and activities of daily living (Besta Scale), which are assessed before and after treatment. One hundred five patients were recruited, 39 to the mCIMT group, 33 to the IRP group, and 33 to the ST group.

RESULTS

IRP and mCIMT significantly improved paretic hand function both in the Quality of Upper Extremity Skills Test and in the Besta Scale, whereas ST did not. mCIMT improved grasp more than IRP did (P < 0.01), whereas bimanual spontaneous use in play increased more with IRP (P = 0.0005). Activities of daily living in 2- to 6-yr-olds improved more with IRP (P < 0.0001) than with mCIMT (P = 0.011). Unaffected limb improved more from bimanual practice (IRP; P = 0.02).

CONCLUSIONS

More advantages resulted from intensive practice than in the standard one, in mCIMT for grasp and in IRP for bimanual spontaneous use and activities of daily living in younger children.

Margaret Kennard (1899-1975): not a 'principle' of brain plasticity but a founding mother of developmental neuropsychology

According to the 'Kennard Principle', there is a negative linear relation between age at brain injury and functional outcome. Other things being equal, the younger the lesioned organism, the better the outcome. But the 'Kennard Principle' is neither Kennard's nor a principle. In her work, Kennard sought to explain the factors that predicted functional outcome (age, to be sure, but also staging, laterality, location, and number of brain lesions, and outcome domain) and the neural mechanisms that altered the lesioned brain's functionality. This paper discusses Kennard's life and years at Yale (1931-1943); considers the genesis and scope of her work on early-onset brain lesions, which represents an empirical and theoretical foundation for current developmental neuropsychology; offers an historical explanation of why the 'Kennard Principle' emerged in the context of early 1970s work on brain plasticity; shows why uncritical belief in the 'Kennard Principle' continues to shape current research and practice; and reviews the continuing importance of her work.