Getting wired — slowly — is good for our brains

All last week, I wrote about the debate over the extent to which our brains are different from other primate brains.

There is new empirical data, and there are scientists eager to integrate the emerging information into their own work.

According to an extensive new study, the cognitive capabilities of human brains may outstrip those of our primate relatives because of a combination of the brain’s plasticity and our longer childhoods.

The idea is that early neuronic connections are stimulated by experiences, and that the extra years that we humans spend as immature children give us significantly more opportunity than chimps and macaques have to “wire up.”

In a longitudinal study of synaptic connections in the prefrontal cortexes of the three species, researchers found that human PFC development lasts much longer than the equivalent growth in chimps and monkeys. While new PFC wiring quickly stalls in lower primates, in humans the growth spurt continues for the first five years of  life.

Even when the data are adjusted to include the differences in average life spans of individuals, human PFC growth outstrips that of the other two primates.

In “Human Brains Wire Up Slowly but Surely,” published online on February 1st by Science, reporter Jon Cohen writes that “We unhurriedly make synaptic connections through much of our early childhoods, and this plasticity enables us to slowly wire our brains based on our experiences.”

In a painstaking extension of the study, researchers counted the synapses visible in electron micrographs of the brains of the three species, discovering that “the number of synapses in macaques and chimpanzees skyrocketed shortly after birth but did not peak in humans until about 4 years of age.”

Reaction to the design and detail of the study has been swift and positive. And behavioural biologists have been equally quick to speculate about the possible implications of the research.

One group of scientists is interested in the new data, for “the differences they found may also separate us from Neanderthals, as evidence suggests that these extinct humans had faster cranial and dental development than modern humans.”

And Eric Courchesne, a University of California San Diego autism researcher, is intrigued because “the new findings also mesh with his own studies of autism and brain overgrowth. Courchesne has found that the brains of autistic children grow more quickly than normal, which he theorizes prevents them from having enough experiences to properly wire neurons.”

These scientists are suggesting possible new areas for research and not making highly speculative interpretations of the limited data just announced.

That’s the way that science works: new results suggest new experiments, leading to more results, and on to more experiments. Slowly, and not at all randomly, the evidence mounts for one interpretation or another, or for one or another group of related interpretations, and the science progresses.

This is a sensible and legitimate process, and it differs greatly from the sometimes wildly unjustified speculations that too often taint “soft” fields like biology and psychology — not to mention the social sciences.

It’s too bad that my math/chemistry friend doesn’t often read this blog. As he’s told me many times, it has too many words and not enough numbers for his taste.

He’d be so proud of me for labelling biology a “soft” science!