Neural plasticity, the ability of the brain to generate new neurons and reshape its pathways, declines with age. Finding ways to temporarily reverse this decline and induce a more youthful state of plasticity may prove helpful in treating many conditions, but research is still at a fairly early stage of exploration:
Researchers have successfully re-created a critical juvenile period in the brains of adult mice. In other words, the researchers have reactivated brain plasticity - the rapid and robust changes in neural pathways and synapses as a result of learning and experience. The scientists achieved this by transplanting a certain type of embryonic neuron into the brains of adult mice. The transplanted neurons express GABA, a chief inhibitory neurotransmitter that aids in motor control, vision and many other cortical functions. Much like older muscles lose their youthful flexibility, older brains lose plasticity. But in the study, the transplanted GABA neurons created a new period of heightened plasticity that allowed for vigorous rewiring of the adult brain. In a sense, old brain processes became young again.
In early life, normal visual experience is crucial to properly wire connections in the visual system. Impaired vision during this time leads to a long-lasting visual deficit called amblyopia. In an attempt to restore normal sight, the researchers transplanted GABA neurons into the visual cortex of adult amblyopic mice. "Several weeks after transplantation, when the donor animal's visual system would be going through its critical period, the amblyopic mice started to see with normal visual acuity." These results raise hopes that GABA neuron transplantation might have future clinical applications. This line of research is also likely to shed light on the basic brain mechanisms that create critical periods.