Column: Once More into the Scanner


by Guy McKhann, M.D.

November 20, 2008

From a clinical perspective the major advances in how we diagnose and treat neurological diseases are in brain imaging. Structural information is used to detect brain tumors, strokes, dementia, brain trauma, developmental defects and more. Images of brain function are used less in clinical situations and more for research in areas where our understanding is poor.

A structural image obtained by a computerized tomography (CT) scan or magnetic resonance imaging (MRI) gives precise information about the brain. If a similar study is performed a week later, the brain image should be the same, unless some intervening changes have occurred. Functional studies such as functional MRI (fMRI) or positron emission tomography (PET) are based on small changes in regional blood flow or metabolism in response to the activity of nerve cells. They are often based on data comparing one group of subjects with another—using these methods to draw conclusions from a single subject is difficult because of individual variation. Furthermore, the stability of the response—that is, the ability of a subject to respond in the same way on repeated examinations—is often not known.

Nevertheless, functional brain imaging studies, usually with fMRI because it is cheaper, more readily available and faster than PET, are increasingly used in studies of brain behavior. Recent news stories report on several examples: studies of decision making (“Your Brain’s Secret Ballot”), the use of imaging data in court (“New Window into the Mind Worries Some Legal Experts” in a recent San Francisco Chronicle, not available online), the effect on the brain of Internet use versus reading (“Internet ‘Speeds Up Decision-Making and Brain Function’ ”) and, lastly, comparison of normal and abnormal readers (“Learning about Learning”).

The first two of these articles (decision making and applications in court) indicate how far we still have to go in understanding underlying brain mechanisms. Making choices and giving truthful versus non truthful answers are complicated brain processes that we are just beginning to understand, using very simple paradigms. The application to complex behavior may be premature. In addition, brain imaging is in the early stages of development, which adds another layer of uncertainty.

The next article reports on comparison studies. In one, brain activation during an Internet search is compared with activation during reading. The former employs the brain more widely, the research suggests. This should not be a surprise. An Internet search is an active, investigative process, while reading can be quite passive.

Is this type of activation good or bad for the developing brain? We don’t know, but the issue is not going to go away. I heard a commentary recently about the next wave of games and other programs that will be available on your cell phone. The challenge to parents will be to get kids to carry out a conversation or occasionally read a good book.

The last reveals that comparing good and impaired readers is getting closer to providing new knowledge we really need. How does the processing of information differ between the groups? As poorer readers get older, do they develop new compensatory strategies? Are our attempts at therapy doing anything? Educators have been flying blind for years. They have been quite willing to accept that one fourth-grader is a foot taller than another, but they have not had the information to recognize that two fourth-grade brains might also differ significantly. A developing field, “Neuroeducation,” is bringing together educators and developmental neuroscientists, to the benefit of both.