A handful of families from around the world with a rare brain malformation called polymicrogyria have led scientists to discover a new gene that helps us speak and swallow.
The gene, SCN3A, is turned “on” primarily during fetal brain development. When it’s mutated, a language area of the brain known as the perisylvian cortex develops multiple abnormally small folds, appearing bumpy. People with polymicrogyria in this region often have impaired oral motor development, including difficulties with swallowing, tongue movement and articulating words — especially if the polymicrogyria affects both sides of the brain.
The new study, published today in Neuron, ties together human genetics, measurements of electrical currents generated by neurons, studies of ferrets and more to start to connect the dots between SCN3A, the brain malformation and the oral motor impairment. …
Babies can hear and respond to sounds, including language, before birth. In fact, research shows that babies learn to recognize words in the womb. Now, an advanced MRI technique called diffusion tensor imaging is providing a fine-tuned view of when different brain areas mature, including the areas that process sound. And the findings suggest that babies born prematurely may have disruptions in auditory brain development and in speech.
Investigators at Boston Children’s Hospital, Brigham and Women’s Hospital, Washington University School of Medicine in St. Louis and University College London analyzed advanced MRI brain images from 90 preterm infants and 15 infants born at full term (40 weeks). Fifty-six of the preterm infants were imaged at multiple time points. As shown above, the team focused on a particular fold in the brain called Heschl’s gyrus (HG). This area contains the primary auditory cortex, the first part of the auditory cortex to receive sound signals, and the non-primary auditory cortex, which plays a higher-level role in processing those stimuli.
As seen in these sample images, the primary cortex has largely matured at 28 weeks’ postmenstrual age (PMA), whereas the non-primary auditory cortex has had a surge in development between 28 and 40 weeks’ PMA. Both regions appeared underdeveloped in the premature infants as compared with the infants born at term.
The study further found that disturbed maturation of the non-primary cortex was associated with poorer expressive language ability at age 2. The team suggests that this area may be especially vulnerable to disruption in a premature birth because it is undergoing such rapid change.
The study was published in eNeuro, an open-access journal from the Society for Neuroscience. Jeffrey Neil, MD, PhD, of Boston Children’s Department of Neurology, was senior author on the paper. First author Brian Monson, PhD, is now at the University of Illinois at Urbana-Champaign. Read more in the university’s press release.
Five people with an unusual pattern of brain folds have afforded a glimpse into how the human brain may have evolved its language capabilities.
How the human brain develops its hills and valleys—expanding its surface area and computational capacity—has been difficult to study. Mice, the staple of scientific research, lack folds in their brains.
Christopher Walsh, MD, PhD, head of the Division of Genetics and Genomics at Boston Children’s Hospital, runs a brain development and genetics clinic and has spent 25 years studying people in whom the brain formation process goes awry. Some brains are too small (microcephaly). Some have folds, or gyri, that are too broad and thick (pachygyria). Some are smooth, lacking folds altogether (lissencephaly). And some have an abnormally large number of small, thin folds—known as polymicrogyria.
In 2005, studying people with polymicrogyria, Walsh and colleagues identified a mutation in a gene known as GPR56, a clue that this gene helps drive the formation of folds in the cortex of the human brain.
In a study published in today’s issue of Science, Walsh and his colleagues focused on five people whose brain MRIs showed polymicrogyria, but just in one location—near a large, deep furrow known as the Sylvian fissure, which includes the brain’s primary language area. …