Scientists Discover Fundamental Rule of Brain Plasticity

Source: Picower Institute at MIT

Summary: A new study by the researchers provides an explanation of how synaptic strengthening and weakening combine in neurons to produce plasticity.

Our brains are famously flexible, or “plastic,” because neurons can do new things by forging new or stronger connections with other neurons. But if some connections strengthen, neuroscientists have reasoned, neurons must compensate lest they become overwhelmed with input. In a new study in Science, researchers at the Picower Institute for Learning and Memory at MIT demonstrate for the first time how this balance is struck: when one connection, called a synapse, strengthens, immediately neighboring synapses weaken based on the action of a crucial protein called Arc. The team discovered a simple, fundamental rule at the core of such a complex system as the brain, where 100 billion neurons each have thousands of ever-changing synapses. The study findings were published in the journal Science.


A dendrite and its spines, reconstructed with electron microscopy (right) after it was imaged with two-photon microscopy in the intact brain (left). Credit: Mriganka Sur, et. al.

In one key experiment, they invoked plasticity by changing a neuron’s “receptive field,” or the patch of the visual field it responds to. Neurons receive input through synapses on little spines of their branch-like dendrites. To change a neuron’s receptive field, the scientists pinpointed the exact spine on the relevant dendrite of the neuron, and then closely monitored changes in its synapses as they showed the mouse a target in a particular place on a screen that differed from the neuron’s original receptive field. The neuron had been genetically engineered to be activated by light flashes, a technique called “optogenetics.”

Senior author, Mriganka Sur said, “Collective behaviors of complex systems always have simple rules,” and further added, “When one synapse goes up, within 50 micrometers there is a decrease in the strength of other synapses using a well-defined molecular mechanism.”

More Information: Sami El-Boustani et al, “Locally coordinated synaptic plasticity of visual cortex neurons in vivo” Science (2018). DOI: 10.1126/science.aao0862

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