Because serotonin is one of the primary chemicals the brain uses to influence mood and behavior, it is also the most common target of psychiatric drugs. To improve those drugs and to invent better ones, scientists need to know much more about how the molecule affects brain cells and circuits both in health and amid disease. In a new study, MIT researchers a working in a simple animal model present a comprehensive accounting of how serotonin affects behavior from the scale of individual molecules all the way to the animal’s whole brain. “There have been major challenges in rationally developing psychiatric drugs that target the serotonergic system,” says Steve Flavell, associate professor in The Picower Institute and MIT’s Department of Brain and Cognitive Sciences, and senior author of the study in Cell. “The system is wildly complex.”

Mutations of a gene called Foxp2 have been linked to apraxia, a speech disorder that makes it difficult to produce sequences of sound. A study from MIT and National Yang Ming Chiao Tung University sheds light on how this gene controls the ability to produce speech. The researchers found that the mutations disrupt the formation of dendrites and neuronal synapses in the brain’s striatum, which plays important roles in the control of movement. Mice with these mutations also showed impairments in their ability to produce the high-frequency sounds that they use to communicate. Those malfunctions arise because Foxp2 mutations prevent the proper assembly of motor proteins, which move molecules within cells. “This was an exciting finding,” says Ann Graybiel, a BCS and McGovern Institute professor and an author of the paper. “Who would have thought that a speech problem might come from little motors inside cells?”

For decades researchers believed the brain could learn to make sense of visual input only until age 7. Recent work from MIT Professor Pawan Sinha has shown that the picture is more nuanced than that. In many studies of children in India who had surgery to remove congenital cataracts beyond the age of 7, he has found that older children can learn visual tasks such as recognizing faces, distinguishing objects from a background, and discerning motion. In a new study, Sinha and his colleagues have discovered anatomical changes that occur in the brains of these patients after their sight is restored. These changes, seen in the structure and organization of the brain’s white matter, appear to underlie some of the visual improvements the researchers observed in these patients.