Scientists have long known that brains need neural activity to mature and that sensory input is most important during a specific window of time called the "critical period" when the brain is primed for aggressive learning.
Vision, hearing and touch all develop during such critical periods, while other senses, such as the olfactory system, maintain lifelong plasticity. The visual system provides an exemplary model for studying developmental plasticity, however, because of the pioneering work of Nobel prize-winning HMS researchers David Hubel and Torsten Wiesel describing the visual system's structure, prerequisite knowledge for investigating its flexibility. Although visual plasticity has been studied for over 40 years, exactly how sensory experience interacts with the built-in machinery that permits the brain to change its circuits is only beginning to be understood.
A new study focusing on the molecular roots of plasticity has found that visual stimulus turns up the expression of some genes and turns down the expression of others, somewhat like a conductor cueing the members of an orchestra. The study also found that during different stages of life in rodents, distinct sets of genes spring into action in response to visual input. These gene sets may work in concert to allow synapses and neural circuits to respond to visual activity and shape the brain, reports the May issue of Nature Neuroscience.
The investigators' identification of many distinct sets of activity-dependent genes follows a shift in neuroscience research toward a more holistic view of the role of genes in neural development and plasticity. "What we found opens science up to a more global look at genes, from studying one gene at a time to looking at families of genes acting together," said first author Marta Majdan, HMS research fellow in neurobiology. These findings suggest that genetic therapies for neurodegenerative diseases, some of which are largely limited to treatment focused on a single gene, will require more extensive knowledge of molecular pathways and gene interactions to be successful
Majdan and co-author Carla Shatz, HMS Nathan Marsh Pusey Professor of Neurobiology, studied rodents during the critical period in which visual input stimulates aggressive plasticity, shaping the mesh of neural connections in the cortex and tuning the strengths of messages relayed by synapses. In mice, this period begins shortly after they open their eyes and begin to see. Previous research had determined that visual activity changes the level of expression of, or regulates, individual genes such as Brain-derived neurotrophic factor (Bdnf).