A Focus On: Neural Microcircuits
This drawing of the partly dissected head and brain is from Vesalius's Fabrica (1543). Image Taken From: The Cognitive System, by Swanson LW. In: Brain Architecture (2 ed.) : Understanding the Basic Plan (Swanson LW, Editor). Publisher: Oxford University Press. DOI:10.1093/med/9780195378580.001.0001 © OUP 2011.
How is the brain organized? Since the rise of modern neuroscience in the late nineteenth century the focus has been on the patterns of interconnection between different brain regions. Generations of medical students have memorized the long axon pathways that course within the spinal cord, carrying sensory signals up to the brain and motor signals down to control movements. Within the brain itself the white matter contains millions of axons that knit together the different regions of the cerebral cortex. Interruptions in these pathways due to stroke or epilepsy are the subjects of neurology and neurosurgery. Together, these pathways constitute what is called today the "connectome", the totality of the patterns of interregional interconnections.
These interconnections can be visualized by a variety of methods developed over the past century. Much more difficult to study are the interconnections within the regions. Current experimental and computational studies are leading to the concept of a neural "microcircuit", a specific pattern of connectivity between neurons within a region. A microcircuit carries out the specific kinds of processing of a region, such as direction sensitivity or contrast enhancement in the retina, or spatial maps in the hippocampus, or error coding in the prefrontal cortex.
Microcircuits are a new and exciting frontier in brain research. The methods of study range from the finest levels of recordings of ion movements in individual dendritic spines, to light activation of specific neuron types, to functional mapping of activity in cortical regions at ever higher magnetic strengths. As in the integrated silicon microcircuits that carry out the functions of a computer, so integrated neural microcircuits carry out the specific functions of different brain regions. Knitting together the "macroconnectome" between regions with the "microconnectome" of microcircuits within regions is one of the key challenges for the neuroscience of the future. Together they provide the basis for normal and disordered function in virtually all of the neuroscience titles in Oxford Medicine Online.
Dr. Gordon M. Shepherd, MD, DPhil, Department of Neurobiology, Yale University School of Medicine
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