New technologies that allow scientists to trace the fine wiring of the brain more accurately than ever before could soon generate a complete wiring diagram, including every tiny fiber and miniscule connection, of a piece of brain. Dubbed connectomics, these maps could uncover how neural networks perform their precise functions in the brain, and they could shed light on disorders thought to originate from faulty wiring, such as autism and schizophrenia.
With an estimated 100 billion neurons and 100 trillion synapses in the human brain, creating an all-encompassing map of even a small chunk is a daunting task. Using standard methods, it would take roughly three billion person years to generate the wiring diagram of a single cortical column.
But neuroscientists at M.I.T. have now developed a new technique to make more fine-scaled wiring maps using electron microscopy. Starting with a small block of brain tissue, the researchers bounce electrons off the top of the block to generate a cross-sectional picture of the nerve fibers in that slice. They then take a very thin (30-nanometer) slice off the top of the block and repeat the process. Scientists go through the images slice by slice to trace the path of each nerve fiber.