I had spent three hours—no, make that three and a half hours—trying to get Daniel to sing one line. It had taken me about two minutes to learn it, but trying to translate the four lyrics and simple melody into Daniel’s brain was seeming like an impossible task, one that was not going to be accomplished in the mere four hours we spent together. Frustrated, I closed up my big red binder, tried to ask him about his upcoming birthday party, and drifted off to my own daydreams. In reality, I had given up.
I started tutoring middle school children when I was sixteen. While I enjoyed working with little kids, and always had, this job was different than most; these children had Asperger’s syndrome, a developmental disorder on the Autism spectrum. In other classes I had worked in, kids talked and laughed and played with each other. But in Daniel’s class, they didn’t, and I began to wonder why that was—why the term “Autism” correlated to these observable differences in social behaviors. Such a question was the impetus for my study of neuroscience, and I now believe that the answer of what makes Daniel different lies in his brain—more specifically, in his connectome.
But what is a connectome? Coined by Dr. Olaf Sporns as a play on the word “genome”, connectome refers to the complete mapping of all of the structural connections in the human brain (analogous to the genetic mapping of the genome). The brain is made up of 1011 cells called neurons, which form 1015 connections, or synapses, between them. These seemingly infinite connections form higher, specialized regions in the brain, which communicate with one another to produce human cognition: for example, light hitting the sensory receptors of our eyes sends information down the optic nerve to the lateral geniculate nucleus, which then synapses, or makes a connection, with the occipital lobe in the brain. The occipital lobe then communicates with more specialized regions, which altogether produce the ability to see. In a way, we are our synapses—without the microscopic connections between neurons, we would be unable to process any sensory information from the outside world, encode memories, or gain knowledge—they are what make us who we are. Using the connectome model and mapping the neuronal connections between large cortical areas on the human brain in 3D and 4D (with time, or brain development, as the fourth dimension), scientists may be able to fully understand the relationship between structure and function in the brain.
This is no small undertaking; brain networks can be defined at different scales, and there are many methods used to uncover the connections: at the cellular scale, or neuron-by-neuron, scientists are utilizing a new technique called Brainbow, in which they use fluorescent proteins to stain tissue slices of the cortex. This beautifully colorful labeling technique allows for distinct labeling of individual neurons, which they can then trace throughout the cortex. On a larger scale, imaging methods such as diffusion tensor imaging (DTI) are being utilized, which uses radio-frequency and magnetic-field gradient pulses to track the movement of water molecules throughout the brain. This allows researchers to map larger scale cortical connections. These results are also becoming available to the public through websites such as Brain Navigator (www.brainnav.com), in which one can search through the multitude of cortical connections already uncovered in the human brain.
But why go through all of that trouble? If we are our synapses, the mapping the synaptic connections in our brain may open doors to understanding how we think, see, and remember; an understanding of structure may lead to one of function. Which brings me back to my point: if scientist were able to map the connectome and see functional brain wiring, the potential for the understanding ‘miswring”, what is faulty in the brains children with Aspergers or Autism, is huge. Recent research shows that neurons in an autistic brain have underdeveloped dendrites, the parts of the cell that form connections with other neurons. Using the connectome as a comparison, scientists may fund underdeveloped neurons in regions such as the amygdala, which processes emotion, or in the cerebellum, which is responsible for fine motor movements---as many children with Aspergers jump or twitch regularly. Of course, we will not know this without understand the structure of a healthy brain, or the connectome.
As I sat with Daniel years ago, frustrated over not being able to teach him that song, I remember wishing I understood why. But with the recent advancements in understanding brain structure and function, the future of Aspergers may be very different. Perhaps scientists will find a way to stimulate missing connections, or discover ways to make dendrites grow in certain regions of the cortex. And when they do, we will have to thank the connectome.
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