Do we really use only 10 percent of our brains?

Barry L. Beyerstein, a psychologist in the Brain Behavior Laboratory at Simon Fraser University, Burnaby, B.C., offers this answer:

PERHAPS IT IS UNWELCOME news, but neuroscience has found no vast, unused cerebral reservoir for us to tap. In addition, a study of self-improvement products by a National Research Council panel found that no “brain booster” is a reliable substitute for practice and hard work when it comes to getting ahead in life.

Why would a neuroscientist immediately doubt that 90 percent of the average brain lies perpetually fallow? First of all, it is obvious that the brain, like all our other organs, has been shaped by natural selection. Brain tissue is metabolically expensive both to grow and to run, and it strains credulity to think that evolution would have permitted squandering of resources on a scale necessary to build and maintain such a massively underutilized organ.

Moreover, doubts are fueled by ample evidence from clinical neurology. Losing far less than 90 percent of the brain to accident or disease has catastrophic consequences. There does not seem to be any area of the brain that can be destroyed by strokes or other trauma without leaving the patient with some kind of functional deficit. Likewise, electrical stimulation of points in the brain during neurosurgery has so far failed to uncover any dormant areas where no perception, emotion or movement can be elicited by applying these tiny currents. (This can be done with conscious patients under local anesthetic because the brain itself has no pain receptors.)

With the aid of instruments such as EEGs, magnetoencephalographs, PET scanners and functional MRI machines, researchers have succeeded in localizing a vast number of psychological functions to specific centers and systems in the brain. With animals, and occasionally with human patients undergoing neurological treatment, recording probes can even be inserted into the brain itself. Despite this detailed reconnaissance, no quiet areas awaiting new assignments have emerged.

The 10 percent myth has undoubtedly motivated many people to strive for greater creativity and productivity in their lives—hardly a bad thing. The comfort, encouragement and hope that it has engendered helps to explain its longevity. But, like so many uplifting myths, the truth of the matter seems to be its least important aspect.

What causes headaches?

Mike A., Wilmington, Del.

Dawn A. Marcus, an associate professor in the departments of anesthesiology and neurology at the University of Pittsburgh School of Medicine, explains:

ALTHOUGH THEY MAY FEEL as if they are located in the brain, headaches actually arise because of irritation of nearby structures: skin, joints, muscles, nerves or blood vessels. Brain tissue, encased in the protective coating of the skull, has not evolved the ability to respond to pressure sensations.

Clinicians classify all headaches as either secondary or primary. Secondary headaches, which appear as symptoms of an underlying disorder, have no uniform cause. Anything from a pinched nerve to a sinus infection can lead to secondary head pain.

Most headaches, however, are primary, meaning that what is wrong is not a condition preceding the headache but the headache itself. Research suggests that this type—which includes tension headaches and migraines—may derive from a single, identifiable pathway.

The chain begins when pain centers in the brain are activated, at which point they produce neurotransmitters such as serotonin and norepinephrine. These chemicals call for expansion of meningeal blood vessels enveloping the brain, which results in increased blood flow. As the vessels swell, they stretch the nerves that surround them. These nerves, in turn, convey signals to the trigeminal system, an area of the brain that relays pain messages for the head and face, and we perceive pain.

Why the pathway is initiated at all is still an open question, although some circumstances seem to make headache onset more likely. These triggers may be internal (for example, hormonal changes during menstruation) or environmental (such as stress or sleep deprivation). So far most evidence for what factors are directly responsible is anecdotal, and the mechanism by which triggers are converted to chemical signals is little understood.

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