Cool Videos: Starring the Wiring Diagram of the Human Brain

MRI videoThe human brain contains distinct geographic regions that communicate throughout the day to process information, such as remembering a neighbor’s name or deciding which road to take to work. Key to such processing is a vast network of densely bundled nerve fibers called tracts. It’s estimated that there are thousands of these tracts, and, because the human brain is so tightly packed with cells, they often travel winding, contorted paths to form their critical connections. That situation has previously been difficult for researchers to image three-dimensional tracts in the brain of a living person.

That’s now changing with a new approach called tractography, which is shown with the 3D data visualization technique featured in this video. Here, researchers zoom in and visualize some of the neural connections detected with tractography that originate or terminate near the hippocampus, which is a region of the brain essential to learning and memory. If you’re wondering about what the various colors represent, they indicate a tract’s orientation within the brain: side to side is red, front to back is green, and top to bottom is blue.

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Creative Minds: Reverse Engineering Vision

Networks of neurons in the mouse retina

Caption: Networks of neurons in the mouse retina. Green cells form a special electrically coupled network; red cells express a distinctive fluorescent marker to distinguish them from other cells; blue cells are tagged with an antibody against an enzyme that makes nitric oxide, important in retinal signaling. Such images help to identify retinal cell types, their signaling molecules, and their patterns of connectivity.
Credit: Jason Jacoby and Gregory Schwartz, Northwestern University

For Gregory Schwartz, working in total darkness has its benefits. Only in the pitch black can Schwartz isolate resting neurons from the eye’s retina and stimulate them with their natural input—light—to get them to fire electrical signals. Such signals not only provide a readout of the intrinsic properties of each neuron, but information that enables the vision researcher to deduce how it functions and forges connections with other neurons.

The retina is the light-sensitive neural tissue that lines the back of the eye. Although only about the size of a postage stamp, each of our retinas contains an estimated 130 million cells and more than 100 distinct cell types. These cells are organized into multiple information-processing layers that work together to absorb light and translate it into electrical signals that stream via the optic nerve to the appropriate visual center in the brain. Like other parts of the eye, the retina can break down, and retinal diseases, including age-related macular degeneration, retinitis pigmentosa, and diabetic retinopathy, continue to be leading causes of vision loss and blindness worldwide.

In his lab at Northwestern University’s Feinberg School of Medicine, Chicago, Schwartz performs basic research that is part of a much larger effort among vision researchers to assemble a parts list that accounts for all of the cell types needed to make a retina. Once Schwartz and others get closer to wrapping up this list, the next step will be to work out the details of the internal wiring of the retina to understand better how it generates visual signals. It’s the kind of information that holds the key for detecting retinal diseases earlier and more precisely, fixing miswired circuits that affect vision, and perhaps even one day creating an improved prosthetic retina.

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Making the Connections: Study Links Brain’s Wiring to Human Traits

The Human Connectome

Caption: The wiring diagram of a human brain, measured in a healthy individual, where the movement of water molecules is measured by diffuse tensor magnetic resonance imaging, revealing the connections. This is an example of the type of work being done by the Human Connectome Project.
Source: Courtesy of the Laboratory of Neuro Imaging and Martinos Center for Biomedical Imaging, Consortium of the Human Connectome Project

For questions about why people often think, act, and perceive the world so differently, the brain is clearly an obvious place to look for answers. However, because the human brain is packed with tens of billions of neurons, which together make trillions of connections, knowing exactly where and how to look remains profoundly challenging.

Undaunted by these complexities, researchers involved in the NIH-funded Human Connectome Project (HCP) have been making progress, as shown by some intriguing recent discoveries. In a study published in Nature Neuroscience [1], an HCP team found that the brains of individuals with “positive” traits—such as strong cognitive skills and a healthy sense of well-being—show stronger connectivity in certain areas of the brain than do those with more “negative” traits—such as tendencies toward anger, rule-breaking, and substance use. While these findings are preliminary, they suggest it may be possible one day to understand, and perhaps even modify, the connections within the brain that are associated with human behavior in all its diversity.

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Cool Videos: Reconstructing the Cerebral Cortex

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This colorful cylinder could pass for some sort of modern art sculpture, but it actually represents a sneak peak at some of the remarkable science that we can look forward to seeing from the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative. In a recent study in the journal Cell [1], NIH grantee Jeff Lichtman of Harvard University, Cambridge, MA and his colleagues unveiled the first digitized reconstruction of tissue from the mammalian cerebral cortex—the outermost part of the brain, responsible for complex behaviors.

Specifically, Lichtman’s group mapped in exquisite detail a very small cube of a mouse’s cerebral cortex. In fact, the cube is so tiny (smaller than a grain of sand!) that it contained no whole cells, just a profoundly complex tangle of finger-like nerve cell extensions called axons and dendrites. And what you see in this video is just one cylindrical portion of that tissue sample, in which Licthtman and colleagues went full force to identify and label every single cellular and intracellular element. The message-sending axons are delineated in an array of pastel colors, while more vivid hues of red, green, and purple mark the message-receiving dendrites and bright yellow indicates the nerve-insulating glia. In total, the cylinder contains parts of about 600 axons, 40 different dendrites, and 500 synapses, where nerve impulses are transmitted between cells.

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Creative Minds: Meet a Theoretical Neuroscientist

Sean Escola

Sean Escola

Most neuroscientists make their discoveries in a traditional laboratory or clinical setting. Sean Escola, a theoretical neuroscientist at Columbia University in New York, just needs a powerful computer and, judging from his photo, a good whiteboard.

Using data that he and his colleagues have recorded from living brain cells, called neurons, Escola crunches numbers to develop rigorous statistical models that simulate the activity of neuronal circuits within the brain. He hopes his models will help to build a new neuroscience that brings into sharper focus how the brain’s biocircuitry lights up to generate sensations and thoughts—and how it misfires in various neurological disorders, particularly in mental illnesses.

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