Connecting the Human Brain to the Mind

For almost a decade now, we have had the technology to map the entire DNA sequence of human beings. The price of having one’s own genome sequenced drops dramatically every year, and soon we will all have our genetic code deciphered. But even with the blueprint in hand, what can our DNA sequence tell us about who we are? Identical twins have the same genome, yet their personalities are unique.

Modern neuroscience tells us that our personalities emerge from our brains – that we are our brains. What in our brains determines who we are? We have the same anatomical structures and pathways, the same kinds of neurons. The distinctive feature is our brain’s organization. The neurons of the brain form thousands of connections with one another called synapses, through which they communicate information. These tiny and ubiquitous connections make two brains distinct.

This is why some neuroscientists aspire to map the connectome. A complete connectome would show the full set of synaptic connections in a human brain: the full biological organization that is a person’s mind. The brain’s fine structure is the reason rigid genomes can give rise to flexible people that are shaped by their experiences: our DNA gets our brain up and running and prepared to be molded by the world via synaptic changes. Scientists are hoping that access to the brain’s system of connections will help us discover how the peculiarities of being a person come from the peculiarities of our synapses.

Mapping the billions of connections in the human brain is too large a project right now, but neuroscientists are engaged in smaller tasks that can be stepping-stones toward the final goal. Researchers are currently building connectomes with coarser levels of detail than that of individual synaptic connections. A common design feature of the brain is that functionally related groups of neurons send their outputs collectively. A map of these major pathways would be like a roadmap: though containing only the highways, it still shows you most of what you need to know to navigate in the country.

At the fine-grained level, researchers are making connectomes of tiny regions of brain tissue. This requires making ultrathin brain slices, capturing images of the slices with electron microscopes, and analyzing the images to detect individual neurons. The shapes of neurons are traced from slice to slice in order to build 3-D models of the paths they take and the connections they make in the brain. These relatively slow methods will someday need to be replaced if we are to construct the human connectome in its entirety.

Connectomics may someday help us understand how the basic features of our everyday experience – thinking, remembering, feeling – reflect the organization of our brain and, importantly, effect changes in that organization. Whereas our genome is a finalized blueprint, our connectome is an unfinished draft, continuously working on itself. If you want to understand how your biology is linked to these changes, stay informed about progress in the human connectome project.