Brain waves are classified by how frequently the neurons fire in a single second. If they fire one to four times, that’s a delta wave, which occurs during deep sleep. If they fire 12 to 30 times, that’s a beta wave, which is typical of normal wakefulness. And if they do so 30 to 90 times, that’s a gamma wave, which has been linked to higher mental abilities, like memory, attention, and perception. Scientists have seen disrupted gamma waves in many types of brain disorders, including injuries, schizophrenia, and Alzheimer’s disease.
But by studying mice, Hannah Iaccarino and Annabelle Singer have shown that these disrupted gamma waves aren’t just a symptom of Alzheimer’s. By restoring normal gamma waves, Iaccarino and Singer actually managed to counteract a hallmark of the disease. In Alzheimer’s, a protein called beta-amyloid gathers in the spaces between neurons, and creates large, harmful plaques. But gamma can apparently mobilize the immune system to clear these plaques.
By simply exposing mice to lights that had been programmed to flicker at a specific frequency, they managed to induce gamma waves, excite the microglia, and reduce beta-amyloid levels. They even managed to clear beta-amyloid plaques in older mice that were further along in their disease. After looking at the flickering lights for just an hour a day, for seven days, the rodent’s plaque counts fell by two-thirds, as did the size of the remaining plaques.
A team led by geneticist Steven McCarroll of the Broad Institute, based in Cambridge, Mass., combed through genetic information from about 29,000 schizophrenia cases, 36,000 controls and 700 brain samples from deceased patients.
McCarroll found that patients who had certain variations of a gene called C4 were more likely to inherit the disease. In healthy brains, the gene helps prune unnecessary connections between cells. But when it runs amok, as it does in schizophrenia, the process destroys healthy brain tissue.
C4’s involvement might also explain why schizophrenia arises during the late teens into the 20s. “It’s a period in human development in which brain circuits change and reorganize and . . . vulnerabilities to many neuropsychiatric illnesses emerge,”