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Fluorescent protein lets us read a fish’s thoughts

The zebrafish spots its lunch. What goes through its brain? Now, for the first time, we can see exactly what it is thinking, thanks to a new way of studying single neurons that lets researchers track patterns of brain activity in a live animal.

A standard way to achieve detailed imaging of cellular activity is by genetically altering cells to express green fluorescent proteins (GFPs) which light up when calcium concentrations rise – such as occurs when neurons are activated.

To try to see activity in individual neurons, Koichi Kawakami at the National Institute of Genetics in Shizuoka, Japan, and colleagues created a super-sensitive GFP and tested it in zebrafish larvae between four and seven days old, when they are transparent.

The researchers focused on capturing activity in the zebrafish’s tectum – a region of the brain that processes vision. They set up an LCD screen that displayed a blinking dot to one side of an immobilised zebrafish larva. As the dot appeared and disappeared, they saw corresponding flashes of light from the tectum, reflecting neural activity.

When the team moved the dot from left to right and top to bottom, they saw horizontal and vertical movement of brain signals in the tectum, revealing what is known as the visuotopic map. Visual information from each eye is processed in the opposite hemisphere of the brain, so movement seen by the right eye was replicated in the left side of the tectum and vice versa.

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