Published in: Berkeley Neuroscience News | October 27, 2015
Layer 4 neurons in the cortex expressing halorhodopsin, an optogenetic silencer of neuronal activity. By Richard Hakim and Hillel Adesnik.
Layer 4 neurons in the cortex expressing halorhodopsin, an optogenetic silencer of neuronal activity. By Richard Hakim and Hillel Adesnik.

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.

Additional Information:

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.