R. Clay Reid: 2011 Allen Institute for Brain Science Symposium

R. Clay Reid, Harvard Medical School "Functional and structural imaging of cortical circuits"

What does a neural circuit do? How is it wired up? These are the big questions Dr. Reid is tackling through cutting-edge technology that is suitable for scale-up to industrial size. Dr. Reid described the concept of a brain observatory, where neuronal activity can be viewed in an actively behaving mouse using 2-photon calcium imaging. By this technique, neurons can be imaged in a wide view of several hundred or a narrow view of a dozen or fewer neurons. Another technique Dr. Reid described is a serial sectioning approach to electron microscopy, which has the advantageous property of allowing one to visualize all the subcellular components of neurons in a circuit in exquisite detail. This method, which is currently highly labor-intensive, will be improved in the future with new automated tracing techniques to increase the speed by a thousand times or more. Dr. Reid also revealed preliminary data on two specific questions: whether excitatory pyramidal cells are connected randomly to other excitatory cells, and whether inhibitory neurons (interneurons) receive functionally random input from nearby excitatory cells. His preliminary answer to the former question indicates that although only 10% of excitatory cells are connected to each other in a given area, the network of connections is likely made up of cells that are similar to each other, with similar functions or synchronous activity. A preliminary answer to the latter question is yes, and the likelihood of connection is perhaps more related to proximity rather than specific function. Dr. Reid's approaches to unraveling cortical circuits are complementary to genetic, molecular, and connectivity studies that are currently aimed at assembling the functional parts list of brain circuits.