FOR the first time the activities of individual brain cells have been monitored in real time, thanks to a new technique. The study has revealed striking differences between rats and cats in the part of the brain that enables them to spot movement.
The researchers injected a dye into the surface of an animal鈥檚 brain. Nerve cells absorb the dye and light up whenever they are active and awash with calcium ions. That makes it possible to monitor the activity of individual neurons near the surface of the brain with a microscope when the skull is opened. No other method for monitoring brain activity can resolve individual cells.
Clay Reid鈥檚 team at Harvard Medical School used the method to study the activity of brain cells in a small part of the visual cortex of rats and cats while they gazed at moving patterns. In cats, the cells responding to movement in a specific direction were organised into discrete zones, in complete contrast to the ways these cells are organised in rats (Nature, DOI: 10.1038/nature03274).
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鈥淎ll the neurons are carefully ordered in the cat, whereas in the rat they鈥檙e all mixed up,鈥� says Reid. 鈥淚t鈥檚 like salt and pepper versus absolute segregation.鈥� The difference could have arisen because spotting movement is a crucial skill for hunters such as cats.
