Neuroplasticity

by Moheb Costandi

The brain contains various types of interneurons, but many of these have not yet been properly characterized, and we probably still do not fully appreciate their diverse forms and functions. But one type in particular—the large basket cells—are evidently responsible for plasticity in the developing visual system. Large basket cells are present in the primary visual cortex, but they mature slowly. When newborn mice first open their eyes, a protein called Otx2 is transported along the optic nerve from the retina to the visual cortex, where it accumulates inside the large basket cells. At this stage, the large basket cells are still immature, forming numerous weak inhibitory connections with their neighboring neurons. When the concentration of Otx2 reaches a certain level, the molecules enter the nucleus, where they activate a genetic program that promotes maturation of the large basket cells.15 As this program unfolds, the large basket cells begin to refine their connections. Certain synapses are stabilized and strengthened while others are eliminated by pruning. Meanwhile, the maturing network of large basket cells is gradually ensheathed by a net of extracellular matrix proteins, which strengthens the new synaptic connections further. Thus, sensory experience refines the microscopic structure of the visual cortex by driving maturation of the large basket cells, which puts the brakes on plasticity by consolidating the emerging circuitry at a time when its representation of ...