The extent to which individual experiences can shape our cognitive and emotional behaviour has
been an issue of intense debate and study for centuries, and the topic takes on different forms
depending on the field of study. Any form of behaviour will depend on the existence of functional
connections in the brain, linking inputs and outputs. If these connections are damaged, or in any way
silenced or suppressed, the related behaviour will be impaired, or modified accordingly. A large part
of ontogenesis is devoted to the formation of such connections within and between different brain
structures. Whereas the initial formation of connections is largely determined by chemical guidance
factors and thus genetically specified, the ensuing neuronal circuits remain ‘plastic’ or modifiable for
a prolonged period and, in some cases, throughout life. In this paper, I define notions of plasticity
from a neurobiological perspective. I use the example of experience-dependent plasticity in
multisensory convergence and integration in the brain, in order to illustrate the extent and limitations
of the role of experience in sculpting neuronal circuits. I then describe briefly the various
mechanisms that are thought to underlie experience-dependent changes in brain circuits during early
development. D 2002 Elsevier Science B.V. All rights reserved