Composite brains: toward a systems theory of neural reconstruction.

The results of uncontrolled, open-label clinical trials indicate that reconstructive cellular therapies have the capacity to produce meaningful functional improvements in patients with brain disorders. However, the transplantation of fetal cells has not progressed to viable best practice treatment for any brain disorder. A conceptual approach, referred to as the Repair Model, has served as a useful heuristic for initiating research in the field and guiding the development of new practices. Analysis of evidence for the treatment of Parkinson's disease indicates that recovery following neural grafting is a complex process influenced by factors beyond the replacement of neurons. An alternative approach, the Composite Brain Model, is outlined to address limitations of the Repair Model. A hierarchical, open-system model is proposed, which aims to track the interactions between the grafted cells, the host brain, and the environment. The Composite Brain Model emphasizes the importance of the interactions between the patient, their physical and social environment, and the provision of rehabilitation during recovery. It is proposed that the Composite Brain Model is useful in providing an alternative perspective for research, theory building, and practice.