Over the next three months, the Dana Foundation blog is pleased to host a new blog series, “Tales from the Lab,” featuring two neuroscience graduate student guest bloggers: Tim Balmer from Georgia State University and Grace Lindsay from Columbia University. Tim’s contributions will focus on life as a neuroscience graduate student and Grace will focus on neuroplasticity. This is Grace’s first blog in the series.
Infancy is a tumultuous time for the brain. A set of neurons with connections in constant flux are working to process an onslaught of sensory signals; yet the connections themselves are guided by the very signals they’re processing. Despite the apparent chaos, we all end up with roughly the same hardware: an occipital lobe for seeing, a temporal lobe for hearing, parietal lobe for sensing touch, etc.
But what happens when those brain-shaping signals can’t get into the brain? For example, in the case of Leber’s congenital amaurosis (LCA), a genetic mutation disrupts the function of cells in the eye, leaving people with LCA essentially blind from birth. This lack of visual input throws a wrench into the brain’s normal plan of development, and it shows in the brain anatomy of adults with these kinds of disorders. Without visual information to process, the occipital lobe is reassigned to other tasks. PET and fMRI studies of congenitally blind humans have shown activation of the occipital lobe during processing of sounds, smells, and touch (such as braille). Such activation is not seen when imaging the brains of sighted people, or even those who lost their vision later in life. These findings demonstrate the remarkable plasticity of the developing brain to adapt its activity and structure in order to best process the signals it receives.
But how does the developing brain do it? What could drive a bunch of cells containing information about sounds, for example, to send projections to an area generally dedicated to vision? Well it turns out that isn’t such a problem. In fact, excessive connections across different sense areas is normal in the infant brain; but these connections get pruned away during the developmental process. It is hypothesized that visual input is needed to drive the pruning of these connections in the occipital lobe, resulting in blind people retaining connections that are normally cut.
So, the ability to adapt is clearly a function of the developing brain, and is rooted in its inherent plasticity. Such a function allows for the appropriate response to a developmental disorder. But what happens in a different kind of developmental genetic disorder, a disorder that affects the plasticity itself? Fragile X Syndrome (FXS) is one such disease, and it highlights the huge role of plasticity in normal development. In FXS, a repeated portion of DNA on the FMR1 gene prevents the expression of the FMR protein. Animal studies suggest that this protein is necessary for the proper pruning of synapses during development as well as the fine tuning of connection strengths later on. Without it, people with FXS exhibit developmental delay, mental retardation, and seizures. The self-organizational skills of the infant brain are thus immensely important for its proper function. So while the developing brain may be a storm of misguided inputs and ever-changing connections, it is a storm with a purpose, without which appropriate information processing could never occur.
– Grace Lindsay
Grace Lindsay is a first-year Ph.D. student in the Neurobiology and Behavior Program at Columbia University. She got her BS in neuroscience from the University of Pittsburgh in 2011 and then spent a year doing research at the Bernstein Center in Freiburg, Germany. She blogs about all things neuroscience at neurdiness.wordpress.com.