An Ever-Changing Brain

Human brains -- like the climate -- never stop changing. Experiences sculpt their effects on the brain for good and for ill. Scientists at Washington University (St. Louis) and the University of Chieti (Italy) have demonstrated measurable changes in the brain's "background noise activity" just hours after the brain has learned a new task. The study is published in PNAS.

At the start of the experiment, Corbetta, graduate students Chris Lewis and Antonello Baldassarre and their colleagues in Italy used functional connectivity magnetic resonance imaging to scan the spontaneous brain activity of 14 volunteers as they sat quietly.

Next, researchers scanned the subjects as they spent one to two hours a day for five to seven days learning to watch a display inside the MRI scanner for the brief presence of an inverted "T" in a specific part of the screen. Two sets of brain areas were particularly active during the task: part of the visual cortex that corresponded to the portion of the visual field where subjects were looking for the "T", and areas in the dorsal part of the brain involved in directing attention to the location on the screen.

After the visual training, scientists again scanned the subjects' brains while they did nothing.

When the subjects rested at the start of the experiment, spontaneous activity in the two parts of the brain that are important to the visual task was either not linked or weakly correlated, with the two regions involved in the upcoming task only occasionally being active at the same time. After learning, though, each region was more likely to be active when the other region wasn't. Subjects who were more successful at the task exhibited a higher degree of this "anti-correlation" between the two regions after learning.

Corbetta suggests this learning-induced change in the brain's spontaneous activity may reflect what he calls a "memory trace" for the new skill. The trace makes it easier to use those parts of the brain together again when the same challenge recurs. _SD

Very interesting. By identifying the neural pattern of successful learning, researchers may well be laying the groundwork for advanced neurofeedback-based "superlearning" -- a potentially fruitful approach to breaking through the mental blocks of learning that stop so many promising young students.

Researchers at Rockefeller University's Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology have demonstrated changes in DNA methylation of rat hippocampal tissue following brief, 30 minute stressful exposures.

Richard Hunter, a postdoc in Rockefeller University's Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology, found that a single 30-minute episode of acute stress causes a rapid chemical change in DNA packaging proteins called histones in the rat hippocampus, which is a brain region known to be especially susceptible to the effects of stress in both rodents and humans.

The chemical change Hunter examined, called methylation, can either increase or decrease the expression of genes that are packaged by the histones, depending on the location of the methylation. He looked for methylation on three regions of histone H3 that have been shown to actively regulate gene expression. In experiments published this month in Proceedings of the National Academy of Sciences, he shows that methylation of one mark, H3K9 trimethyl, roughly doubled in the hippocampus. Methylation of a second mark, H3K27 trimethyl, dropped by about 50 percent in the same area. Changes associated with the third mark were minor.

"The hippocampus is involved in episodic memory, so you would expect it to be sensitive to episodic experiments like this, more so than the motor regions, for instance," says Hunter, who worked on the project with Rockefeller scientists Bruce S. McEwen and Donald W. Pfaff.... _SD

So we see once again, that experiences can alter gene expression -- sometimes permanently. Interestingly, Prozac was able to reverse some of the genetic changes associated with chronic stress. No doubt other pharmacological agents will prove superior for that purpose.

Al Fin Neuro-Behaviouralists prefer non-pharmacological approaches to therapy whenever possible -- such as electromagnetic stimulation, hypnosis, and neurofeedback, for example. But as better targeted drugs come along and better means of drug delivery are developed (nanotechnology), it is likely that pharmacology will be a big part of the better brains revolution.