Coffee delivers jolt deep in the brain
Caffeine strengthens electrical signals in rats’ hippocampus
Most caffeine addicts would tell you that coffee sharpens the mind. It turns out that in rodents, a single dose of caffeine does indeed strengthen brain cell connections in an underappreciated part of the brain, scientists report online November 20 in Nature Neuroscience.
A clearer idea of caffeine’s effect on the brain could allow scientists to take advantage of its stimulating effects and perhaps even alleviate some symptoms of brain disorders. “Caffeine is something people are very interested in,” says neuroscientist Susan Masino of Trinity College in Hartford, Conn., who was not involved in the study.
So far, most of caffeine’s effects have been illuminated by studies using doses much higher than an average person’s morning cup of joe, says study coauthor Serena Dudek of the National Institute of Environmental Health Sciences in Research Triangle Park, N.C.
Dudek and her team looked at the effects of smaller hits of caffeine on a small part of the hippocampus. In humans, this seahorse-shaped structure is buried deep in the brain behind the ears. After feeding rats the equivalent of two human cups of coffee (two milligrams of caffeine per kilogram of body weight), the team measured the strength of nerve cells’ electrical messages in slices of brain tissue. Nerve cells in this particular nook — a brain region called CA2 — got a major jolt from caffeine, showing a bigger burst of electrical activity when researchers stimulated the cells. Nerve cells in a neighboring part of the hippocampus didn’t show this sensitivity.
And the higher the caffeine dose, the stronger the effect. A caffeine dose 10 times higher — a dose reached by only die-hard caffeine consumers — caused an even bigger response in nerve cells in the CA2 region.
The team found similar effects when they applying caffeine directly to CA2 nerve cells in a dish, a result that rules out effects from post-caffeine changes in blood flow. After five minutes of caffeine exposure, the synapses stayed amped up for three hours.
“We don’t know what it looks like in humans, but in rodents, we think this is the area most sensitive to caffeine,” Dudek says.
These strengthened synapses in the hippocampus may have a role in learning and memory, which makes sense because one of the main jobs of the hippocampus is to form spatial memories. (After navigating London’s labyrinthine roads for years, for instance, cab drivers have larger hippocampi than normal folks.)
Though the results are the first to establish CA2 as a caffeine hot spot, it’s too early to say how the research will apply to people, says psychologist Harris Lieberman of the U.S. Army Research Institute of Environmental Medicine in Natick, Mass. “It’s hard to jump from these kinds of studies to direct application to humans.”