Joan Stiles

The Basics of Brain Development

Over the past several decades, significant advances have been made in our understanding of the basic stages and mechanisms of mammalian brain development. Studies elucidating the neurobiology of brain development span the levels of neural organization from the macroanatomic, to the cellular, to the molecular. Together this large body of work provides a picture of brain development as the product of a complex series of dynamic and adaptive processes operating within a highly constrained, genetically organized but constantly changing context. The view of brain development that has emerged from the developmental neurobiology literature presents both challenges and opportunities to psychologists seeking to understand the fundamental processes that underlie social and cognitive development, and the neural systems that mediate them. This chapter is intended to provide an overview of some very basic principles of brain development, drawn from contemporary developmental neurobiology, that may be of use to investigators from a wide range of disciplines.

EARLY LEXICAL DEVELOPMENT IN CHILDREN WITH FOCAL BRAIN INJURY

Early lexical development in 27 children with focal brain injury was studied cross-sectionally and longitudinally. Data were obtained from children between 12 and 35 months of age who acquired their lesion prenatally or within the first 6 months of life. Results for the group as a whole provide clear evidence for delays in lexical comprehension and production, and for a larger number of comprehension/production dissociations than would be expected by chance. In addition, a significant number of children were observed having unusual difficulty mastering predication and/or using an atypically high proportion of closed class words (suggesting reliance on holistic/formulaic speech). Analyses by lesion type revealed no effect of lesion size. Analyses according to side of lesion revealed that children with right-hemisphere damage produced a higher proportion of closed class words, suggesting heavy reliance on well-practiced but under-analyzed speech formulae. Children with left-hemisphere damage were slightly better in comprehension than children with right-hemisphere damage. In addition, left posterior lesions were associated with greater delays in expressive language, and delays were more protracted in children with left posterior damage. No differential effects of left posterior damage were found for lexical comprehension.

Neural plasticity and cognitive development.

It has been well documented that the effects of early occurring brain injury are often attenuated relative to later occurring injury. The traditional neuropsychological account of these observations is that, although the developing neural system normally proceeds along a well-specified maturational course, it has a transient capacity for plastic reorganization that can be recruited in the wake of injury. This characterization of early neural plasticity is limited and fails to capture the much more pervasive role of plasticity in development. This article examines the role of neural plasticity in development and learning. Data from both animal and human studies show that plasticity plays a central role in the normal development of neural systems allowing for adaptation and response to both exogenous and endogenous input. The capacity for reorganization and change is a critical feature of neural development, particularly in the postnatal period. Subtractive processes play a major role in the shaping and sculpting of neural organization. However, plasticity is neither transient nor unique to developing organisms. With development, neural systems stabilize and optimal patterns of functioning are achieved. Stabilization reduces, but does not eliminate, the capacity of the system to adapt. As the system stabilizes, plasticity becomes a less prominent feature of neural functioning, but it is not absent from the adult system. The implications of this broader view of plasticity for our understanding of development following early brain damage are discussed.It has been well documented that the effects of early occurring brain injury are often attenuated relative to later occurring injury. The traditional neuropsychological account of these observations is that, although the developing neural system normally proceeds along a well-specified maturational course, it has a transient capacity for plastic reorganization that can be recruited in the wake of injury. This characterization of early neural plasticity is limited and fails to capture the much more pervasive role of plasticity in development. This article examines the role of neural plasticity in development and learning. Data from both animal and human studies show that plasticity plays a central role in the normal development of neural systems allowing for adaptation and response to both exogenous and endogenous input. The capacity for reorganization and change is a critical feature of neural development, particularly in the postnatal period. Subtractive processes play a major role in the shaping and sculpting of neural organization. However, plasticity is neither transient nor unique to developing organisms. With development, neural systems stabilize and optimal patterns of functioning are achieved. Stabilization reduces, but does not eliminate, the capacity of the system to adapt. As the system stabilizes, plasticity becomes a less prominent feature of neural functioning, but it is not absent from the adult system. The implications of this broader view of plasticity for our understanding of development following early brain damage are discussed.

Hemispheric asymmetries in global and local processing: evidence from fMRI

FUNCTIONAL magnetic resonance imaging (fMRI) was used to explore the brain substrate associated with global and local processing of visuospatial patterns. Systematic differences in activation, consistent with differences observed in reaction time data collected under conditions of visual hemifield presentation, were found in occipitotemporal regions of the right and left hemispheres. Within the right hemisphere, area of activation and fractional signal changes were greater under conditions of global processing than under local processing conditions. In the left hemisphere, activation to global and local input was high and comparable.

Cognitive development following early brain injury: evidence for neural adaptation.

Over the past few decades a large body of work from developmental neurobiology has shown that mammalian brain development is the product of dynamic and adaptive processes operating within highly constrained, but continually changing, biological and environmental contexts. The recent study of children with prenatal focal brain injury supports this dynamic view of development for humans. Childrens injuries often affect substantial portions of one cerebral hemisphere, resulting in damage that would compromise cognitive ability in adults. However, longitudinal behavioral studies of this population have revealed only mild deficits. It is suggested here that childrens capacity for adaptation reflects normal developmental processes operating against a backdrop of serious neural perturbation. Data from three behavioral domains--linguistics, spatial cognition and affective development--illustrate this complex profile of change.

Functional MRI of Global and Local Processing in Children

Functional magnetic resonance imaging was used to examine developmental change in hemispheric biases for globally and locally directed analysis of hierarchical forms. In a previous reaction time (RT) study, which presented hierarchical stimuli to the visual hemifields, children 7 to 14 years of age demonstrated an emerging pattern of hemispheric differences. Initially children analyzed local elements more slowly, without a strongly lateralized advantage for local or global level processing. With age, childrens development was marked by a left hemisphere advantage for local level processing that resembled an adults and a trend toward a right hemisphere advantage for global. In the current study, 20 children 12 to 14 years old were imaged during attend-global and attend-local conditions to determine whether the developmental change in cognitive measures corresponded to a change in distribution of functional activation. Children formed two groups based on their RT performance, immature-bilateral (IB) or mature-lateralized (ML). The volume of task-related activation within lateral temporo-occipital regions of interest was compared for global and local conditions between the two groups. The IB children showed greater activation overall for local level processing, comparable activation across the two hemispheres for the global condition, and a trend of right greater than left hemisphere activation for local. In contrast, the ML children displayed right greater than left hemisphere activation during global analysis and the opposite during local processing. Importantly these patterns of functional activation mirror the profiles of RT performance. Together they demonstrate a shift from undifferentiated, bilateral processing toward hemispheric lateralization.

Spatial grouping activity in young children with congenital right or left hemisphere brain injury

Spatial grouping abilities were examined in 20 preschool-aged children with right or left hemisphere congenital focal brain injury, and a group of age-matched normal control children. Children were presented with a series of spontaneous grouping tasks in which they were given small sets of blocks and asked to play with them. Although the children with focal brain injury played as actively with the blocks as normal children, the constructions they produced differed systematically. Across eight measures of spatial grouping both children with right and left hemisphere injury were delayed compared to normal children. In addition, the behavioral profiles for the two groups of children with focal brain injury were qualitatively different. Data for the children with RH injury suggested difficulty organizing objects into coherent spatial groupings, while data from the children with LH injury suggested difficulty with local relations within the spatial arrays. These findings are consistent with data reported for adults on spatial construction tasks. Developmental trajectories in the 3- to 4-year age period suggest, further, that the spatial integrative deficits observed in the children with RH injury are persistent. When the children began to produce spatial constructions using complex grouping procedures, those constructions were heaps or disordered clusters. In contrast, when children with LH injury began to use complex procedures, they generated the types of constructions usually associated with those procedures in normal children, e.g., arches, enclosures, and symmetries. These data were found within a cross-sectional study of 20 children and confirmed in a series of six longitudinal case study reports of three children with RH and three with LH injury. The data confirm our previous reports of spatial integrative deficit associated with early RH injury and present the first indication of spatial encoding deficits in children with LH injury.

Developmental Trends in Visuospatial Analysis and Planning: I. Copying a Complex Figure

An existing scoring system was used to assess the accuracy of the childrens ability to copy the Rey-Osterrieth Complex Figure. The authors also developed additional measures to more precisely describe the process used by children in copying this figure. The findings suggest that children between the ages of 6 and 9 break the figure up into simple components but improve in their ability to integrate the figure with age. Younger children demonstrated a similar pattern of performance when copying the main features of the Rey-Osterrieth Complex Figure in isolation. The results of this study suggest that when faced with tasks requiring more advanced types of spatial analysis, children adopt strategies that proved successful when they were younger. Children have a variety of spatial analytic strategies available by age 6, but the strategy that they use is a function of pattern complexity and the capabilities of the child. The Rey-Osterrieth Complex Figure was designed more than 50 years ago for assessing visuospatial construction, planning, and memory in both adults and children (Osterrieth, 1944; Rey, 1941; see Corwin & Bylsma, 1993, for a translation). There have been several attempts to describe developmental change in copying the Rey-Osterrieth Complex Figure, but the complexity of the form has made this a difficult task. Four published studies have reported that until approximately age 9, most children use a piecemeal approach (Karapetsas & Kantas, 1991; Kirk, 1985; Osterrieth, 1944; Waber & Holmes, 1985). In this approach, details are juxtaposed, one next to the other without any apparent overall plan, yet the figure is often globally recognizable. After age 9, productions have been described as more configurational; that is, most participants start their drawing with the base rectangle or a detail that adjoins the rectangle and complete the large rectangle before drawing the rest of the figure. Although these are valid and useful descriptions of performance in the school-age period, they present an incomplete picture of childrens performance on the figure in terms of both the range of strategies children adopt in copying this complex visual pattern at each age and the systematic patterns of developmental change evident across the age span. Examination of the existing developmental data from the figure suggests that by age 6, children attend to and attempt to reproduce both the elements and the overall configuration of the pattern (Karapetsas & Kantas, 1991; Kirk, 1985; Oster

Face and place processing in Williams syndrome: evidence for a dorsal-ventral dissociation

Individuals with Williams syndrome (WMS) show an interesting dissociation of ability within the visuospatial domain, particularly between face perception and other visuospatial tasks. In this population, using tasks matched for stimuli, required response, and difficulty (for controls) is critical when comparing performance across these areas. We compared WMS individuals with a sample of typically developing 8- and 9-year-old children, and with a sample of adults, closer to the WMS participants in chronological age, in order to investigate performance across two precisely matched perceptual tasks, one assessing face processing and the other assessing proficiency in processing stimuli location. The pattern of performance seen in WMS, but not in controls, implicates a specific deficit of dorsal stream functioning in this syndrome.

The impact of early unilateral brain injury on perceptual organization and visual memory

Studies of young children with early unilateral brain injury have suggested that while hemispheric differences in visuospatial processing appear to be present early in development, the young brain is better able to compensate for injury than when the injury occurs later, after networks have been established. The aim of this study was to determine if this pattern continues later in development when these children are given a challenging task: the Rey-Osterrieth Complex Figure. Experiment 1 included longitudinal data from ten children with early left hemisphere (LH) injury and nine children with early right hemisphere (RH) injury. Injury was presumed to be due to a prenatal or perinatal stroke. Compared with typically developing children, both groups were poorer in copying the figure. With development, these children produced reasonably accurate drawings but continued to use the most immature and piecemeal strategy. In Experiment 2, copy and immediate memory drawings from the 19 children with early unilateral brain injury were collected at a single age (11-14 years). Eight of the ten children with LH injury organized their memory reproductions around the core rectangle but included relatively few additional details. In contrast, only two of the nine children with RH injury organized their memory reproductions around the core rectangle and all but one produced the figure in a piecemeal manner. The results from both studies demonstrate the continuation of subtle deficits in visuospatial analysis with development but also the continued capacity for compensation.