A major focus of neurobiology research is to understand the organization of the neocortex: the outer layers of the cerebral hemispheres that underlie that most complex mental capabilities. The neocortex is comprised of 6 layers of cells that are remarkably diverse in form and function and are highly interconnected to form complex networks with both local and long-range targets. To better understand the relationship between the layers of neocortical neurons, the Adesnik lab used optogenetics to photo-manipulate the main input layer of the primary sensory cortex: layer 4 (L4). Contrary to all existing models of neocortical organization, they discovered that L4 exerts a powerful, disynaptic inhibitory action onto the main output layer: layer 5. The functional consequence of this inhibition is a reduction in noise and a sharpening of sensory representations. Hence, neurons within layer 4 may act as a key node through which higher cortical areas dynamically sharpen stimulus representations according to behavioral demands.
Read the research article, “A direct translaminar inhibitory circuit tunes cortical output,” by Scott Pluta, Alexander Naka, Julia Veit, Gregory Telian, Lucille Yao, Richard Hakim, David Taylor & Hillel Adesnik, in Nature Neuroscience.
Read the associated article preview, “Rethinking canonical cortical circuits,” by Neel T Dhruv, also in Nature Neuroscience.
Image by Richard Hakim and Hillel Adesnik. Layer 4 neurons in the cortex expressing halorhodopsin, an optogenetic silencer of neuronal activity.