Brain Neurons
Until relatively recently, scientists thought that no new neurons grew in the brains of adults and that every blow on the head or glass of wine after adolescence cut the number of brain cells. Over the past decade, though, neuroscientists have realised that young neurons do continue to appear in the brains of mature mammals. Many of these new brain cells are found in the hippocampus, a structure used to remember events, people and places. This suggested to Tracey Shors that the cells might be involved in forming such memories.
To learn the fate of these new neurons, Dr Shors and her team used a chemical tag that attaches itself to cells that are dividing. On a given day, the researchers injected this chemical into the brains of rats. As a result, only the new brain cells that were born that day were labelled and thus the team could follow a cohort of new neurons over time.
The rats were treated in three different ways. Some of them were killed one week after the chemical tag had been injected and their brains were examined. About 5,000 labelled cells were found in each hippocampus. Members of a second group were placed in a dull, unstimulating environment for a further week. When the brains of these rats were examined, the labelled cells had all died.
Dr Shors and her colleagues trained members of further groups to learn something new in their final week. The researchers played a sound and then, after a set period of time that varied between each group, blew a puff of air into the rats’ eyes, making them blink. After several repetitions, the animals learned to blink after hearing the noise in anticipation of the puff of air, and they timed their blinks to avoid it.
Looking at the brains of these animals, the researchers found that the labelled neurons had not only persisted but also appeared to mature into functionally wired neurons. Moreover, the rats that successfully completed the more difficult task, which involved a longer gap in time between the sound and the puff of air, had retained more new neurons than those assigned easier tasks, with shorter gaps.
“Use it or lose it,” The Economist