title: Effective connectivity in the neural network underlying coarse-to-fine categorization of visual scenes. A dynamic causal modeling study.
abstract: According to current models of visual perception scenes are processed in terms of spatial frequencies following a predominantly coarse-to-fine processing sequence. Low spatial frequencies (LSF) reach high-order areas rapidly in order to activate plausible interpretations of the visual input. This triggers top-down facilitation that guides subsequent processing of high spatial frequencies (HSF) in lower-level areas such as the inferotemporal and occipital cortices. However, dynamic interactions underlying top-down influences on the occipital cortex have never been systematically investigated. The present fMRI study aimed to further explore the neural bases and effective connectivity underlying coarse-to-fine processing of scenes, particularly the role of the occipital cortex. We used sequences of six filtered scenes as stimuli depicting coarse-to-fine or fine-to-coarse processing of scenes. Participants performed a categorization task on these stimuli (indoor vs. outdoor). Firstly, we showed that coarse-to-fine (compared to fine-to-coarse) sequences elicited stronger activation in the inferior frontal gyrus (in the orbitofrontal cortex), the inferotemporal cortex (in the fusiform and parahippocampal gyri), and the occipital cortex (in the cuneus). Dynamic causal modeling (DCM) was then used to infer effective connectivity between these regions. DCM results revealed that coarse-to-fine processing resulted in increased connectivity from the occipital cortex to the inferior frontal gyrus and from the inferior frontal gyrus to the inferotemporal cortex. Critically, we also observed an increase in connectivity strength from the inferior frontal gyrus to the occipital cortex, suggesting that top-down influences from frontal areas may guide processing of incoming signals. The present results support current models of visual perception and refine them by emphasizing the role of the occipital cortex as a cortical site for feedback projections in the neural network underlying coarse-to-fine processing of scenes.
authors.affiliation: Univ. Grenoble Alpes, LPNC, F-38040 Grenoble, France; CNRS, LPNC UMR 5105, F-38040 Grenoble, France. Electronic address: louise.kauffmann@upmf-grenoble.fr.
authors.forename: Louise
authors.initials: L
authors.lastname: Kauffmann
authors.affiliation: Univ. Grenoble Alpes, LPNC, F-38040 Grenoble, France; CNRS, LPNC UMR 5105, F-38040 Grenoble, France.
authors.forename: Alan
authors.initials: A
authors.lastname: Chauvin
authors.affiliation: Univ. Grenoble Alpes, LPNC, F-38040 Grenoble, France; CNRS, LPNC UMR 5105, F-38040 Grenoble, France.
authors.forename: Cédric
authors.initials: C
authors.lastname: Pichat
authors.affiliation: Univ. Grenoble Alpes, LPNC, F-38040 Grenoble, France; CNRS, LPNC UMR 5105, F-38040 Grenoble, France.
authors.forename: Carole
authors.initials: C
authors.lastname: Peyrin
mesh_terms: D001288:Attention / Q000502:physiology*; D001499:Bayes Theorem; D001931:Brain Mapping; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009415:Nerve Net / Q000502:physiology*; D009778:Occipital Lobe / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D017397:Prefrontal Cortex / Q000502:physiology*; D013702:Temporal Lobe / Q000502:physiology*; D055815:Young Adult
keywords: Inferior frontal gyrus; Inferotemporal cortex; Occipital cortex; Orbitofrontal cortex; Spatial frequencies; Top-down facilitation