Functional imaging of developmental and adaptive changes in neurocognition

Abstract

Characterization of brain–behavior relationships through functional magnetic imaging (fMRI) within typically or atypically developing populations poses methodological and interpretational challenges. We consider theoretical, methodological, and artifactual factors that influence characterization of developmental and adaptive changes in childhood. Findings from anatomical and physiological brain development studies are highlighted as they may influence functional imaging results. Then, we consider several patterns of functional activation within the context of developmental processes as well as neurologic disease. Hypotheses regarding the development of cognitive networks are proposed to account for the individual differences seen in normal and atypical development. We also identify potential sources of unwanted variability related to experimental design and task performance and suggest possible solutions to help minimize these effects. Lastly, a challenge for current studies is a lack of group and individual analysis methods that can be reliably applied to capture and quantify factors that contribute to variability introduced by developmental and disease processes. We review current methods and propose potential solutions.

Introduction

Functional magnetic resonance imaging (fMRI) has permitted characterization of brain–behavior relationships with increasing precision. Characterization of those relationships within typically or atypically developing populations, however, poses methodological and interpretational challenges that differ from those pertinent to adult populations. Specifically, two factors distinguish investigation of child and adult neurocognition. First, characterization of the neural basis of cognition in children must be made against the backdrop of ongoing biological maturation. With variable rates of biological maturation, children of the same age are likely to differ more than adults of the same age. Thus, individual variability must be characterized more fully in investigation of developing rather than mature cognition. Second, adaptive changes following developmental or acquired disorders may differ in structural and functional characteristics relative to those following adult neurologic injury. As an end state of maturation, adulthood represents completed functional organization. Functional recovery following adult neurological injury, therefore, must be accomplished by compensatory processing enabled by neural reorganization. In contrast, as a state of ongoing maturation, childhood represents incomplete functional organization. Childhood disorders, therefore, alter the course of functional organization. Functional outcomes are likely to differ following adaptive changes in childhood relative to adulthood. Thus, models of functional organization gleaned from adult studies are limited in revealing adaptive changes in neurocognition. Taken together, these factors result in neurocognitive adaptive changes in children that are unlikely to be homogeneous because biological and experiential factors interact in a variety of ways. Consequently, there may be multiple variants of typical and atypical development.

This paper will consider theoretical, methodological, and artifactual factors that influence characterization of developmental and adaptive changes in childhood. Current functional neuroimaging methods are optimized for elucidating invariant properties of cognition as embodied in adulthood, and therefore, are limited in revealing a complete picture of developmental and adaptive variability in brain–behavior relationships. While others have considered some of these factors, the present discussion will focus on these issues as they pertain specifically to the investigation of developing populations.