After consuming 100 milligrams of caffeine, the equivalent of about two cups of coffee, volunteers in a recent study experienced increased activity in the frontal lobe, where working memory is centered, and the anterior cingulum, which controls attention.

Now a team of Austrian researchers using advanced brain imaging technology have discovered that caffeine makes people more alert by perking up part of the brain involved in short-term memory, the kind that helps focus attention on the tasks at hand.

And Americans seem most in need of concentrating their thoughts since their average daily consumption of 236 milligrams of caffeine, equivalent to more than 4.5 cups of coffee, is three times the world average.

More Able to Focus

"Almost all of us drink coffee or something with caffeine in it and we know why, because we want to be more awake or feel better," said Dr. Florian Koppelstaetter of the Medical University Innsbruck in Austria. "We wanted to know what effect one to two cups of coffee would have on short-term memory."

Reporting Wednesday at the Radiological Society of North America meeting in Chicago, Koppelstaetter said that functional magnetic resonance imaging, or fMRI, was used to measure brain function in 15 healthy volunteers before and after consuming coffee.

The findings revealed increased activity in the frontal lobe, where working memory is centered, and the anterior cingulum, which controls attention, in volunteers after consuming 100 milligrams of caffeine, the equivalent of about two cups of coffee. These areas showed no increased activity when the subjects drank the same fluid without caffeine in it.

"The increased activity means you are more able to focus," Koppelstaetter said. "You have more attention and your task management is better."

Short-term memory lasts about 30 to 45 seconds and stores a small amount of information for a limited amount of time. It's the kind of memory used to look up a telephone number and remember it long enough to dial it. Long-term memory, on the other hand, stores an unlimited amount of information for an unlimited amount of time.

"What is exciting is that by means of MRI we are able to see that caffeine exerts increases in neuronal activity in distinct parts of the brain going along with changes in behavior," Koppelstaetter said.

Marijuana Smoking and Schizophrenia

In another report presented at the meeting, researchers from New York's Albert Einstein Medical School found that marijuana smoking may increase the risk of schizophrenia in people who have a genetic susceptibility to the disease.

Using a special version of MRI technology called diffusion tensor imaging or DTI, Drs. Manzar Ashtari and Sanjiv Kumra found that marijuana smokers had brain abnormalities similar to those of schizophrenics.

The abnormalities occurred in a bundle of fibers called the arcuate fasciculus, which connects Broca's area in the left frontal lobe with Wernicke's area in the left temporal lobe, a fiber pathway linked to higher aspects of language and auditory functions.

The fibers in the arcuate fasciculus bundle are among the last parts of the brain to be formed during adolescence. DTI images, which can peer deep into the brain to reveal connections between neurons, found that connections in the arcuate fasciculus bundle were forming abnormally in marijuana smokers. These are the same fibers that the researchers showed were abnormal in schizophrenics.

The researchers studied normal youngsters in late adolescence who didn't smoke marijuana, adolescents who smoked marijuana, adolescents who had schizophrenia and adolescent schizophrenics who smoked marijuana.

The formation of the arcuate fasciculus bundle appeared normal in the adolescents who didn't smoke and showed some signs of abnormalities in those who did. The abnormalities were more pronounced in schizophrenics who didn't smoke marijuana and were the most pronounced in those who did.

Ashtari said the Albert Einstein team undertook the study because of population studies showing an association between marijuana smoking and schizophrenia.

The latest of these studies, reported in the May issue of the Journal of Addiction, involved 1,000 people followed for 25 years. It showed that the heaviest marijuana use was associated with a higher risk of schizophrenia and that schizophrenics who smoked marijuana had more relapses than schizophrenics who didn't smoke.

"We're not saying that anybody who smokes marijuana is going to get schizophrenia," Ashtari said. "However, we are saying that if you are genetically predisposed, because your uncle or aunt or father or somebody has schizophrenia in your family, then marijuana increases your risk of contracting the disease."