title: Equalizing excitation-inhibition ratios across visual cortical neurons.
abstract: The relationship between synaptic excitation and inhibition (E/I ratio), two opposing forces in the mammalian cerebral cortex, affects many cortical functions such as feature selectivity and gain. Individual pyramidal cells show stable E/I ratios in time despite fluctuating cortical activity levels. This is because when excitation increases, inhibition increases proportionally through the increased recruitment of inhibitory neurons, a phenomenon referred to as excitation-inhibition balance. However, little is known about the distribution of E/I ratios across pyramidal cells. Through their highly divergent axons, inhibitory neurons indiscriminately contact most neighbouring pyramidal cells. Is inhibition homogeneously distributed or is it individually matched to the different amounts of excitation received by distinct pyramidal cells? Here we discover that pyramidal cells in layer 2/3 of mouse primary visual cortex each receive inhibition in a similar proportion to their excitation. As a consequence, E/I ratios are equalized across pyramidal cells. This matched inhibition is mediated by parvalbumin-expressing but not somatostatin-expressing inhibitory cells and results from the independent adjustment of synapses originating from individual parvalbumin-expressing cells targeting different pyramidal cells. Furthermore, this match is activity-dependent as it is disrupted by perturbing pyramidal cell activity. Thus, the equalization of E/I ratios across pyramidal cells reveals an unexpected degree of order in the spatial distribution of synaptic strengths and indicates that the relationship between the cortex's two opposing forces is stabilized not only in time but also in space.
authors.affiliation: 1] Neurobiology Section, Division of Biological Sciences, Center for Neural Circuits and Behavior, University of California, San Diego, La Jolla, California 92093-0634, USA [2] Department of Neuroscience, University of California, San Diego, La Jolla, California 92093-0634, USA [3] Department of Neuroscience, Baylor College of Medicine, Houston, Texas 77030, USA, and Jan and Dan Duncan Neurological Research Institute at Texas Children's Hospital, Houston, Texas 77030, USA.
authors.forename: Mingshan
authors.initials: M
authors.lastname: Xue
authors.affiliation: Champalimaud Neuroscience Programme, Champalimaud Centre for the Unknown, Lisbon 1400-038, Portugal.
authors.forename: Bassam V
authors.initials: BV
authors.lastname: Atallah
authors.affiliation: 1] Neurobiology Section, Division of Biological Sciences, Center for Neural Circuits and Behavior, University of California, San Diego, La Jolla, California 92093-0634, USA [2] Department of Neuroscience, University of California, San Diego, La Jolla, California 92093-0634, USA [3] Howard Hughes Medical Institute, University of California, San Diego, La Jolla, California 92093-0634, USA.
authors.forename: Massimo
authors.initials: M
authors.lastname: Scanziani
mesh_terms: D000818:Animals; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D051379:Mice; D009433:Neural Inhibition / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D017966:Pyramidal Cells / Q000502:physiology; D013569:Synapses / Q000502:physiology; D014793:Visual Cortex / Q000166:cytology* / Q000502:physiology*