Blame bad driving on bad genes?

Now you have a great excuse for hitting that fire hydrant with your Cadillac Escalade: You — and Tiger Woods — can blame it on bad genes.

According to a study published in the journal Cerebral Cortex earlier this fall, a certain common gene variation restricts the release of a protein called brain-derived neurotrophic factor (BDNF) that in turn affects the brain’s ability and rate of learning complicated tasks. Like driving.

As many as 30 percent of Americans carry this gene variation, says Dr. Steven Cramer, lead author of the study and an associate professor of neurology at the University of California at Irvine.

“Basically, BDNF affects the plasticity of the brain,” Dr. Cramer says.

Adds his co-author, Jeffrey A. Kleim, associate professor of neuroscience at the University of Florida: BDNF “is like fertilizer for the neurons.”

In other words, people without this particular “bad-driving gene” variant have more access to brain fertilizer.

So, not surprisingly, the lack of brain fertilizer (in people with the gene variant) affects not only driving, but also other complex tasks, Dr. Cramer says, adding that he chose to study driving ability because it’s a very common, complex task.

He and his fellow researchers enlisted 29 otherwise healthy persons - 22 without the bad-driving gene and seven with it. (The presence of the gene variant was checked easily with a genetic cheek swab, Dr. Cramer says.) The subjects then were asked to “drive” several laps using a simulator.

The track was slippery and curvy and required the study subjects to pay close attention and make quick adjustments, Mr. Kleim says.

“It tested everything from focus to reflexes,” he says.

While each person was taking the driving test, his or her head was MRI-scanned to determine brain activity. The test was repeated a few days later to see what knowledge and skills had been retained.

The outcome: Subjects with the gene variant that restricts the protein BDNF performed 20 percent worse on the test. They were 20 percent more likely to drive off the track - unable to adjust and react fast enough for the sudden twists, turns and slippery pavement.

But what possible evolutionary purpose could this bad-driving gene serve?

The flip side of plasticity is stability, Dr. Cramer explains, and with some brain conditions, such as Parkinson’s disease and other neurodegenerative diseases, the bad-driving gene gives stability to the brain, meaning it might slow the progression of the degenerative disease.

“This is a very exciting direction to think about,” Dr. Cramer says. “It may make the brain less vulnerable.”

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