title: The direct, not V1-mediated, functional influence between the thalamus and middle temporal complex in the human brain is modulated by the speed of visual motion.
abstract: The main visual pathway that conveys motion information to the middle temporal complex (hMT+) originates from the primary visual cortex (V1), which, in turn, receives spatial and temporal features of the perceived stimuli from the lateral geniculate nucleus (LGN). In addition, visual motion information reaches hMT+ directly from the thalamus, bypassing the V1, through a direct pathway. We aimed at elucidating whether this direct route between LGN and hMT+ represents a 'fast lane' reserved to high-speed motion, as proposed previously, or it is merely involved in processing motion information irrespective of speeds. We evaluated functional magnetic resonance imaging (fMRI) responses elicited by moving visual stimuli and applied connectivity analyses to investigate the effect of motion speed on the causal influence between LGN and hMT+, independent of V1, using the Conditional Granger Causality (CGC) in the presence of slow and fast visual stimuli. Our results showed that at least part of the visual motion information from LGN reaches hMT+, bypassing V1, in response to both slow and fast motion speeds of the perceived stimuli. We also investigated whether motion speeds have different effects on the connections between LGN and functional subdivisions within hMT+: direct connections between LGN and MT-proper carry mainly slow motion information, while connections between LGN and MST carry mainly fast motion information. The existence of a parallel pathway that connects the LGN directly to hMT+ in response to both slow and fast speeds may explain why MT and MST can still respond in the presence of V1 lesions.
authors.affiliation: Laboratory of Clinical Biochemistry and Molecular Biology, Department of Surgical, Medical, Molecular Pathology and Critical Area, University of Pisa, Italy; Laboratory for Cognitive Brain Mapping, RIKEN Brain Science Institute, Wakoshi, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Gaglianese
authors.affiliation: Laboratory for Cognitive Brain Mapping, RIKEN Brain Science Institute, Wakoshi, Japan; IMAGO 7 Magnetic Resonance Center, IRCCS Stella Maris, Calambrone, Pisa, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Costagli
authors.affiliation: Support Unit for Functional Magnetic Resonance Imaging, RIKEN Brain Science Institute, Wakoshi, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Ueno
authors.affiliation: Laboratory of Clinical Biochemistry and Molecular Biology, Department of Surgical, Medical, Molecular Pathology and Critical Area, University of Pisa, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Ricciardi
authors.affiliation: Laboratory of Clinical Biochemistry and Molecular Biology, Department of Surgical, Medical, Molecular Pathology and Critical Area, University of Pisa, Italy; Clinical Psychology Branch, Pisa University Hospital, Pisa, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Bernardi
authors.affiliation: Laboratory of Clinical Biochemistry and Molecular Biology, Department of Surgical, Medical, Molecular Pathology and Critical Area, University of Pisa, Italy; Clinical Psychology Branch, Pisa University Hospital, Pisa, Italy. Electronic address: pietro.pietrini@med.unipi.it.
authors.forename: P
authors.initials: P
authors.lastname: Pietrini
authors.affiliation: Laboratory for Cognitive Brain Mapping, RIKEN Brain Science Institute, Wakoshi, Japan; Support Unit for Functional Magnetic Resonance Imaging, RIKEN Brain Science Institute, Wakoshi, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Cheng
mesh_terms: D001931:Brain Mapping; D002560:Cerebrovascular Circulation / Q000502:physiology; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D010100:Oxygen / Q000097:blood; D010775:Photic Stimulation / Q000379:methods; D013702:Temporal Lobe / Q000502:physiology*; D013788:Thalamus / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology*; D055815:Young Adult
chemical_list: D010100:Oxygen
keywords: Conditional Granger Causality; fMRI; hMT+; speeds; thalamus; visual motion