Will talk about: Extracellular sheets and tunnels modulate glutamate diffusion in hippocampal neuropil
Terrence Sejnowski is a pioneer in computational neuroscience and his goal is to understand the principles that link brain to behavior. His laboratory uses both experimental and modeling techniques to study the biophysical properties of synapses and neurons and the population dynamics of large networks of neurons. New computational models and new analytical tools have been developed to understand how the brain represents the world and how new representations are formed through learning algorithms for changing the synaptic strengths of connections between neurons. He has published over 300 scientific papers and 12 books, including The Computational Brain, with Patricia Churchland.
He received his PhD in physics from Princeton University and was a postdoctoral fellow at Harvard Medical School. He was on the faculty at the Johns Hopkins University and he now holds the Francis Crick Chair at The Salk Institute for Biological Studies and is also a professor at the University of California, San Diego, where he is co-director of the Institute for Neural Computation and co-director of the NSF Temporal Dynamics of Learning Center. He is the President of the Neural Information Processing Systems (NIPS) Foundation, which organizes an annual conference attended by over 1000 researchers in machine learning and neural computation and is the founding editor-in-chief of Neural Computation published by the MIT Press.
An investigator with the Howard Hughes Medical Institute, he is also a fellow of the American Association for the Advancement of Science and the Institute of Electrical and Electronics Engineers. He has received many honors, including the Wright Prize for interdisciplinary research from Harvey Mudd College, the Neural Network Pioneer Award from the Institute of Electrical and Electronics Engineers and the Hebb Prize from the International Neural Network Society. He was elected to the Institute of Medicine in 2008 and to the National Academies of Science in 2010.
The extracellular space in the neuropil of the brain serves as an important channel for volume communication between cells. No method exists to accurately measure the geometry of the extracellular space in living brains and surprisingly little is known about the morphology of this space. We show here for the first time the three-dimensional geometry of the extracellular space in rat hippocampal neuropil reconstructed from serial electron microscope sections and corrected for tissue shrinkage from the in vivo state. In contrast to the accepted value of the extracellular width as uniformly 20 nm, the reconstruction revealed an interconnected network of large diameter tunnels, formed at the junction of three or more cellular processes, spanned by sheets between pairs of cell surfaces with nearly uniform width. The tunnels tended to occur around synapses and axons and the sheets were enriched around astrocytes. The rate of diffusion of neurotransmitter and other small molecules was slower in sheets than in tunnels based on Monte Carlo simulations of diffusion in the corrected reconstructions. Thus, the sheets and tunnels found in the extracellular space may have specialized functions for signaling and volume transmission.