Mapping the Brain’s Genome

The functional complexity of the human brain is pretty well understood at this point. Science has charted out those regions responsible for memory, speech, the five senses, and my inability to do math. Studies continue to draw finer and finer distinctions within these domains, yet one area that has remained poorly understood is that of this layout’s structure at the genetic and molecular level. A study from the NIH, published in the May 2012 issue of Science, has helped to better characterize the origins of the brain’s complexity within the human genome.

The study compared the brains of 406 twins, both fraternal and identical (or mono- and dizygotic), to identify those areas whose growth is controlled by the same genes. Using fuzzy cluster analysis (where data is grouped in “clusters,” in this case called “fuzzy” because each data point can belong to more than one cluster, and not, unfortunately, because they are any cuddlier than other clusters), they grouped these areas together based on how much their surface area had increased as a result of gene expression. What they found is that these groups tended to coincide with the already established functionally defined regions of the brain.

The cluster analysis grouped data by similarity alone and did not include any information regarding the function of those regions of the brain being examined. Despite that, there was an overwhelming connection between the similarity in growth and in function. This indicates that areas which have similar functions are coded for by the same regions of an individual’s genome. Beyond this, the analysis showed that those areas of the brain responsible for those behaviors so unique to humans, such as high functioning motor skills and speech, emerged from the fundamental lobe structure that is shared by all mammals. They call this organization hierarchical, as each successive genetic advancement falls within the more general functional distinctions, creating nested subdivisions that form a hierarchy of function. All of this supports the idea that much of the human brain’s higher functions are based upon the basic mammalian brain, that humans simply possess highly specialized versions of the essential mammal mind.

According to its authors, what this study produced, in effect, was a genetic atlas of the human brain, tracing the development of highly complex neural pathways from the basic functional structure found in all mammals. This project is part of a general movement in neurobiology to map out the “connectome,” much like researchers mapped out the human genome. The connectome is the entirety of the myriad neural connections within the brain and mapping it will help to shed light on both how the brain functions and how it decays. Having a comprehensive map of the human brain would allow for a more in-depth and nuanced approach to diseases such as Alzheimer’s or dementia. Studies like this can help to better define those diseases brought on by complications in the development of the brain while also demonstrating how the human mind’s complexity arose.

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