Threaded on a wire one-fifth the thickness of a human hair, these tiny seeds of light can be injected to activate special networks of light-sensitive neurons.

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Researchers at Stanford University and MIT's Picower Institute for Learning and Memory had activated light-sensitive neurons in the brain's hippocampus involved in the memory of fright.

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This, Dr Silver is convinced, is because the activity in the light-sensitive neurons somehow activated a latent nerve pathway that spans both sides of the spinal cord, allowing them to synchronise.

ECONOMIST: Neurology

It involves using proteins that are sensitive to light, derived from other organisms such as algae, and putting them into neurons.

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