Ontogenesis of Neuronal Networks

Conclusion

Neuronal network ontogenesis proceeds in successive steps. The early stages (target recognition at regional, cellular and membrane levels) are activity-independent and appear to be exclusively controlled by intrinsic factors that determine the intracerebral gradients of chemotactic factors and recognition proteins. Morphogenetic genes, that orchestrate the initial stages of brain construction, appear to be good candidates for the control of these initial steps. However, by activation of the plasticity processes normally occurring during development, the epileptic activity could generate aberrant synaptic circuitry and further abnormal excitability.

Later stages consist of refinement of the initial neuronal circuitry under the control of synaptic activity. These events occur in humans during the perinatal period. As a consequence, occurrence of epileptic activity early during the neonatal period could alter the definitive neuronal pathway emergence. Moreover, the use of similar processes of activity-dependent construction of neuronal pathways during learning and memory could explain the frequent alterations of these cognitive functions in epileptic children.

In conclusion the developmental schedule of synaptogenesis represents a notable illustration of the complementary roles of both the expected and unexpected, the innate mechanisms and experience during brain construction.