title: Cortical state determines global variability and correlations in visual cortex.
abstract: The response of neurons in sensory cortex to repeated stimulus presentations is highly variable. To investigate the nature of this variability, we compared the spike activity of neurons in the primary visual cortex (V1) of cats with that of their afferents from lateral geniculate nucleus (LGN), in response to similar stimuli. We found variability to be much higher in V1 than in LGN. To investigate the sources of the additional variability, we measured the spiking activity of large V1 populations and found that much of the variability was shared across neurons: the variable portion of the responses of one neuron could be well predicted from the summed activity of the rest of the neurons. Variability thus mostly reflected global fluctuations affecting all neurons. The size and prevalence of these fluctuations, both in responses to stimuli and in ongoing activity, depended on cortical state, being larger in synchronized states than in more desynchronized states. Contrary to previous reports, these fluctuations invested the overall population, regardless of preferred orientation. The global fluctuations substantially increased variability in single neurons and correlations among pairs of neurons. Once this effect was removed, pairwise correlations were reduced and were similar regardless of cortical state. These results highlight the importance of cortical state in controlling cortical operation and can help reconcile previous studies, which differed widely in their estimate of neuronal variability and pairwise correlations.
authors.affiliation: UCL Institute of Ophthalmology, University College London, London EC1V 9EL, United Kingdom, and marieke.scholvinck@esi-frankfurt.de.
authors.forename: Marieke L
authors.initials: ML
authors.lastname: Schölvinck
authors.affiliation: UCL Institute of Ophthalmology, University College London, London EC1V 9EL, United Kingdom, and.
authors.forename: Aman B
authors.initials: AB
authors.lastname: Saleem
authors.affiliation: UCL Institute of Ophthalmology, University College London, London EC1V 9EL, United Kingdom, and.
authors.forename: Andrea
authors.identifier: http://orcid.org/0000-0002-7698-6289
authors.initials: A
authors.lastname: Benucci
authors.affiliation: UCL Institute of Ophthalmology, University College London, London EC1V 9EL, United Kingdom, and UCL Institute of Neurology and UCL Department of Neuroscience, Physiology & Pharmacology, London WC1E 6DE, United Kingdom.
authors.forename: Kenneth D
authors.identifier: http://orcid.org/0000-0002-5930-6456
authors.initials: KD
authors.lastname: Harris
authors.affiliation: UCL Institute of Ophthalmology, University College London, London EC1V 9EL, United Kingdom, and.
authors.forename: Matteo
authors.identifier: http://orcid.org/0000-0003-4880-7682
authors.initials: M
authors.lastname: Carandini
mesh_terms: D000818:Animals; D002415:Cats; D005260:Female; D009415:Nerve Net / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods*; D011897:Random Allocation; D014793:Visual Cortex / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology*
keywords: brain states; cerebral cortex; neural populations; thalamus; vision