IF YOU are a loner, you鈥檇 better get yourself some friends or else risk
losing precious brain cells. That鈥檚 the suggestion from a study into the brains
of songbirds, which found that birds living in large groups have more new
neurons and probably a better memory than those living alone.
How the brain stores long-term memory is a mystery, but some researchers
think it involves permanent changes in the gene expression of brain cells. So
animals like songbirds that have small brains and relatively long lifespans
would run out of neural 鈥渟pace鈥� to store new memories if they didn鈥檛 grow a
constant supply of new cells. Songbirds do grow new neurons, though most of
these die within three to five weeks and so can鈥檛 store memories for long. But
those that survive may provide space for new long-term memories.
Fernando Nottebohm of Rockefeller University in New York and his colleagues
decided to study adult zebra finches to see whether their social conditions
affect the survival rate of these new neurons. They injected the birds with a
radioactive form of thymidine鈥攁 marker to track new neurons鈥攁nd
placed the birds in three different settings: either alone, with another bird of
the opposite sex, or in a large group of about 45 other birds. After 40 days the
researchers examined three specific regions of the birds鈥� brains to check
development.
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The researchers found that compared with the other birds, those living in
large groups had about 30 per cent more new neurons in a region of the brain
involved in sound processing. Even more impressively, the male zebra finches,
who do all the singing, had twice as many new neurons in areas of the brain
involved in communication when living in large groups. That could be simply
because the birds are trying to remember every other bird鈥檚 distinctive song,
say the researchers in a paper to be published in the journal Behavioural Brain
Research.
Researchers have noticed before that social animals such as elephants tend to
have better memories than loners. But no one had actually seen a change in the
survival of neurons caused solely by the number of companions. 鈥淭his is exciting
stuff,鈥� says Arturo Alvarez-Buylla, an expert on neuronal growth from the
University of California, San Francisco. There is evidence that adult humans
also produce new neurons in their brains, so these results raise the possibility
that social interaction could help our neurons survive too, he says. And perhaps
that would even boost our memories.
But we can鈥檛 yet be sure. 鈥淲e really don鈥檛 know exactly where neurogenesis
occurs in humans, how much there is, or if it鈥檚 active throughout our life,鈥�
says Alvarez-Buylla.