In the last two decades, research in developmental psychopathology and neuroscience has made considerable progress. Although we have learned a great deal about the time course of neural development and of psychopathology, some basic questions concerning the interaction between neurobiological and behavioral development still remain unanswered (Cicchetti, 1993). For example, we still do not know whether the emergence of a specific psychopathology requires activation of maladaptive processes during a time-critical window of vulnerability or whether simple alterations in the order or timing of neurobiological events during normal development are sufficient to induce psychopathology.

The differentiation of species, organ systems, and neural systems all involve sequencing the activation and suppression of a suite of genes and their products (Eisenberg, 1995). Changes in the endogenous timing mechanisms that regulate this programmed gene expression could affect the physical organization of the developing nervous system so that the organism's sensitivity to environmental stimuli is permanently enhanced or reduced. Altered sensitivity to the environment could then lead the organism to a developmental pathway that is atypical for the species. Alternatively, a change in timing may not be reflected in the physical organization of the developing nervous system, but advancing or delaying the deployment of a neural system could make a different system vulnerable to modification. In this view, the change in timing affects the developmental context of systems that are already in place, ultimately altering their function.