Brain doesn't allow math, memory to mix
There is a limit to multi-tasking after all. The brain is not wired to allow you to balance your chequebook while introspecting, say researchers who have practically wire-tapped a hard-to-reach region of the brain.
The research showed that groups of nerve cells in a structure called the posterior medial cortex, or PMC, are strongly activated during a recall task such as trying to remember whether you had coffee yesterday. However, these groups of nerve cells are also just as strongly suppressed when you're engaged in solving a math problem.
The PMC, situated roughly where the brain's two hemispheres meet, is of great interest to neuroscientists because of its central role in introspective activities, the journal "Proceedings of the National Academy of Sciences", reports.
"This brain region is famously well-connected with many other regions that are important for higher cognitive functions," said Josef Parvizi, associate professor of neurology and neurological sciences at the Stanford University Medical Centre. "But it's very hard to reach. It's so deep in the brain that the most commonly used electrophysiological methods can't access it."
Parvizi and his Stanford colleagues found a way to directly and sensitively record the output from this ordinarily anatomically inaccessible site in human subjects, according to a Stanford statement.
By doing so, they learned that particular clusters of nerve cells in the PMC that are most active when you are recalling details of your own past are strongly suppressed when you are performing mathematical calculations. Parvizi co-authored the study with postdoctoral scholars Brett Foster and Mohammed Dastjerdi.
Much of our understanding of what roles different parts of the brain play has been obtained by techniques such as functional magnetic resonance imaging, which measures the amount of blood flowing through various brain regions as a proxy for activity in those regions.
But changes in blood flow are relatively slow, making functional magnetic resonance imaging a poor medium for listening in on the high-frequency electrical bursts (approximately 200 times per second) that best reflect nerve-cell firing.
For this study, the Stanford scientists employed a highly sensitive technique to demonstrate that introspective and externally focused cognitive tasks directly interfere with one another, because they impose opposite requirements on the same brain circuitry.