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As the commentaries reveal, cognitive neuroscience's first steps toward a theory of development are marked by vigorous debate, ranging from basic points of definition to the fine details of mechanism. In this Response, we present the neural constructivist position on this broad spectrum of issues, from basic questions such as what sets constructivism apart from other theories (particularly selectionism) to its relation to behavioral theories and to its underlying mechanisms. We conclude that the real value of global theories at this stage of cognitive neuroscience is not just their answers but the new set of research questions they pose.

How do minds emerge from developing brains? According to 'neural constructivism,' the representational features of cortex are built from the dynamic interaction between neural growth mechanisms and environmentally derived neural activity. Contrary to popular selectionist models that emphasize regressive mechanisms, the neurobiological evidence suggests that this growth is a progressive increase in the representational properties of cortex. The interaction between the environment and neural growth results in a flexible of learning: 'constructive learning' minimizes the need for prespecification in accordance with recent neurobiological evidence that the developing cerebral cortex is largely free of domain-specific structure. Instead, the representational properties of cortex are built by the nature of the problem domain confronting it. This uniquely powerful and general learning strategy undermines the central assumption classical learnability theory, that the learning properties of a system can be deduced from a fixed computational architecture. Neural constructivism suggests that the evolutionary emergence of neocortex in mammals is a progression toward more flexible representational structures, in contrast to the popular view of cortical evolution as an increase in innate, specialized circuits. Human cortical postnatal development is also more extensive and protracted than generally supposed, suggesting that cortex has evolved so as to maximize the capacity of environmental structure to shape its structure and function through constructive learning. Keywords: cognitive development; constructivism; evolution; learnability; mathematical learning theory; neural development; selectionism

Van Gelder seeks to distinguish between the computational and the dynamical hypotheses primarily on the basis of ontic criteria - the kind of systems cognitive agents really are. I suggest that this meets with mixed success. By shifting to epistemic criteria - what kind of explanations we require to understand cognitive agents - I suggest there is an easier and more intuitive way to distinguish between these two competing views of cognitive agents.

The modular theory of cognitive development can be disproved by observations of neurobiological processes which show how areas in the brain acquire specific abilities due to patterns of stimulation imposed by the environment. These areas become centers of knowledge or ability only when afferent neural activity produce patterns that influence the creation of specific functional areas. Thus, abilities are not derived from prespecified areas of the cortex, and their development can be altered at early stages when infant brains are highly plastic and require environmental stimuli to acquire organization.