Dr. McGurk,

I have heard that meningitis has an influence on IQ level. What are the components of an IQ test and how do they negate learned knowledge?

Sorry about the delay in response.

The usual teaching is that bacterial meningitis, which causes a lot of inflammation and swelling and disrupts circulation can cause neurologic complications, from damage to cranial nerves (eg deafness, blindness) to damage to brain function (cognitive processing, seizures, etc). Viral meningitis, on the other hand, usually does not cause changes in neurologic function. Occasionally a viral infection of the CNS may be encephalitis (eg herpes) rather than being confined to the meninges. Encephalitis often does cause long term residual damage.

The question about IQ testing is a little harder to answer in writing, and I would like to speak with you if you would contact me at beeper 3580. Otherwise, I should say that there are numerous different IQ tests which all attempt to measure intelligence, all imperfectly. Ability to learn, ease or rate of learning, memory,capacity (for one's age) to manipulate abstract concepts, to learn and use arbitrary decoding systems, to assemble scenes in an order that tells a rational story, to complete puzzles, to copy geometric figures, to count...These are among the abilities that are considered intelligence, neurologically determined, and different IQ tests attempt to measure different selections of them. It is probably impossible to separate IQ entirely from learned knowledge, for a number of reasons. Some learned knowledge is assumed to be absorbed from the usual environment by the normal person. For example, fund of information about eg days of the week is measured on the WISC. If a child has been locked in a room for years or has been deaf-blind since birth, the usual criteria wouldn't apply. For one thing, experience is a source of intellectual development-and I mean ability to learn, not just information. Intellectual potential is not fixed for life, but may increase or decline under different circumstances. The degree to which stimulation of a young brain can alter its potential is of course one of the great unresolved issues driving the debate about funding for pre-school education.

Unless injury or illness occurs, IQ tests should remain in the same range through life, but the numbers are not at all exact . Testing in younger children is also less accurate and should be understood in more general terms.

If you would like to see specific IQ tests and discussion of their interpretation, you might go online to www.pedicases.org and look at the cases of development. "Tommy's Testing" shows the kind of detail I think you want.

Yours, Harriet McGurk