Neuroscientists have long known that the brain needs proper sensory stimulation to develop correctly and that experience can induce plastical changes in the functional architecture of sensory cortices. Animals that grow up with one eye covered during a critical period of brain development lose some of their visual acuity and ability to respond to certain visual stimuli. In these experimental conditions, neuroscientist Gina Turrigiano and colleagues at Brandeis University explored the visual cortex circuit of young rats by recording electrical activity of neurons and their connections.

"We have found an important and novel mechanism involved in the loss of function of cortical circuits," said co-author neurophysiologist Arianna Maffei. "While our results directly apply to the loss of visual function secondary to sensory deprivation, they very likely represent a more general strategy for cortical networks to respond to experience."

The researchers showed that the lasting cortical shut-down induced by visual deprivation at early stages of development is the result of a massive increase of cortical inhibition. Specifically, the strength of inhibitory synaptic connections between two types of neurons in the layer receiving the input, the inhibitory fast-spiking basket cells and the excitatory star pyramidal neurons, increased 3-fold.

"Our data suggest a major revision of thinking about how experience works on our brains," noted Turrigiano. "Instead of targeting exclusively excitatory networks, a major locus of plasticity lies within the inhibitory networks. Our data show that inhibitory networks within the cortex are highly plastic, and that some pathological states arise through inappropriate activation of inhibitory plasticity."; Source: Brandeis University