Images of the brain have changed from the second century to the 21st. In a lecture at the New York Academy of Science last night, Carl Schoonover, a Ph.D. candidate at Columbia and the author of the critically acclaimed Portraits of the Mind, described how these images are a window into technological advances, the state of neuroscientific knowledge, and the challenges still to come.
Until Leonardo DaVinci came up with a way to dissect the brain without it falling apart in the process—he used hot wax to determine the shapes of ventricles, or empty spaces in the brain, then thought to be the areas of importance—everything about the brain’s structure was conjecture. But it was not until the mid 19th century that some truly exciting advances occurred.
This is when two important steps were made nearly simultaneously: microscope lenses improved greatly and staining techniques were invented. Camillo Golgi famously developed the stain named for him, which significantly reduces the number of neurons one sees on a microscope slide. Santiago Ramón y Cajal would use the stain and view samples through his microscope each morning, drawing them from memory in the afternoon. He had the remarkable ability to isolate individual neurons from his microscope view.
Stains have changed a lot since the time of Golgi and Ramón y Cajal. Researchers now use fluorescent stains to light neurons from within. Different types of neurons are now known to have genetic signatures; scientists can combine genetic fingerprinting tools and colors to begin teasing apart convoluted neural structures.
Microscopes have changed a lot, too. Confocal microscopes send planes of light through samples. Two-photon microscopes allow scientists to view structures in live samples without harming the animals being observed. Electron microscopes uncover levels of detail not previously observable and are allowing for a new generation of microscope pioneers. Imaging advances like fMRI and diffusion MRI have allowed scientists to uncover brain functions and structures, so far in research, not medical, settings.
What’s next? Engineers, physicists, and mathematicians are entering the field to map interactions and connections among neurons and structures. Models are being built to simulate brain regions—at best, Schoonover said, people can only record the activity of 100 neurons; there are 10 to 100 billion neurons in the human brain. Simulations of networks are a way to overcome these limitations.
Clearly, brain scientists are and always have been limited by the technology available at the time of their research. In 10 to 20 years, Schoonover believes, we will have new ways to select, light, and visualize neurons, an exciting prospect that could lead to entirely new portraits of mind.