title: Dynamic gamma frequency feedback coupling between higher and lower order visual cortices underlies perceptual completion in humans.
abstract: To perceive a coherent environment, incomplete or overlapping visual forms must be integrated into meaningful coherent percepts, a process referred to as "Gestalt" formation or perceptual completion. Increasing evidence suggests that this process engages oscillatory neuronal activity in a distributed neuronal assembly. A separate line of evidence suggests that Gestalt formation requires top-down feedback from higher order brain regions to early visual cortex. Here we combine magnetoencephalography (MEG) and effective connectivity analysis in the frequency domain to specifically address the effective coupling between sources of oscillatory brain activity during Gestalt formation. We demonstrate that perceptual completion of two-tone "Mooney" faces induces increased gamma frequency band power (55-71Hz) in human early visual, fusiform and parietal cortices. Within this distributed neuronal assembly fusiform and parietal gamma oscillators are coupled by forward and backward connectivity during Mooney face perception, indicating reciprocal influences of gamma activity between these higher order visual brain regions. Critically, gamma band oscillations in early visual cortex are modulated by top-down feedback connectivity from both fusiform and parietal cortices. Thus, we provide a mechanistic account of Gestalt perception in which gamma oscillations in feature sensitive and spatial attention-relevant brain regions reciprocally drive one another and convey global stimulus aspects to local processing units at low levels of the sensory hierarchy by top-down feedback. Our data therefore support the notion of inverse hierarchical processing within the visual system underlying awareness of coherent percepts.
authors.affiliation: Department of Basic Psychology I, Complutense University of Madrid (UCM), 28223 Pozuelo de Alarcón, Madrid, Spain; Laboratory for Clinical Neuroscience, Centre for Biomedical Technology, Technical University of Madrid (UPM), Campus Montegancedo, 28223 Pozuelo de Alarcón, Madrid, Spain. Electronic address: smoratti@psi.ucm.es.
authors.forename: S
authors.initials: S
authors.lastname: Moratti
authors.affiliation: Laboratory for Clinical Neuroscience, Centre for Biomedical Technology, Technical University of Madrid (UPM), Campus Montegancedo, 28223 Pozuelo de Alarcón, Madrid, Spain; CEI Campus Moncloa, UCM-UPM, Avenida Complutense s/n, 28040 Madrid, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Méndez-Bértolo
authors.affiliation: Laboratory for Cognitive and Computational Neuroscience, Centre for Biomedical Technology, Technical University of Madrid (UPM), Campus Montegancedo, 28223 Pozuelo de Alarcón, Madrid, Spain.
authors.forename: F
authors.initials: F
authors.lastname: Del-Pozo
authors.affiliation: Laboratory for Clinical Neuroscience, Centre for Biomedical Technology, Technical University of Madrid (UPM), Campus Montegancedo, 28223 Pozuelo de Alarcón, Madrid, Spain.
authors.forename: B A
authors.initials: BA
authors.lastname: Strange
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D058256:Brain Waves / Q000502:physiology*; D025461:Feedback, Physiological / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009415:Nerve Net / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*
keywords: Dynamic causal models; Feedback; Gamma band activity; Perceptual completion; Reverse hierarchical visual processing