The value of brain imaging in the study of development and its disorders

Attempts to understand the relationship between the brain and the mind began with the study of patients with lesions. Much has been learned through such studies about how psychological functions map onto specific cortical regions, particularly with regard to sensory and motor cortex. If the location and extent of the brain lesion is known it is often possible to predict the psychological effect of the lesion. But this approach only works if the mapping relationship is relatively static. This assumption clearly does not apply to the developing brain and recent evidence suggests that the adult brain is also not as static as we once supposed (e.g., Draganski et al., 2004). To study the developing brain we need to look at brain structure and function at different stages in development. The new, non-invasive, brain imaging techniques allow such examination in both healthy and damaged brains without any known risk in the case of magnetic resonance imaging (MRI), magentoencephalography (MEG) and electroencephalography (EEG). These techniques allow us to look at brain structure (location of grey and white matter), brain function (location and timing of changes in brain activity) and brain connectivity (tracing white matter tracts and detecting functional connectivity) (see Primer on Brain Imaging by D.S. Pine). In principle these methods should revolutionize our understanding of brain development and allow us to pinpoint deviations underlying abnormal development, but in practice progress has been slow.