title: AICHA: An atlas of intrinsic connectivity of homotopic areas.
abstract: BACKGROUND
  Atlases of brain anatomical ROIs are widely used for functional MRI data analysis. Recently, it was proposed that an atlas of ROIs derived from a functional brain parcellation could be advantageous, in particular for understanding how different regions share information. However, functional atlases so far proposed do not account for a crucial aspect of cerebral organization, namely homotopy, i.e. that each region in one hemisphere has a homologue in the other hemisphere.
  
  
  METHODS
  We present AICHA (for Atlas of Intrinsic Connectivity of Homotopic Areas), a functional brain ROIs atlas based on resting-state fMRI data acquired in 281 individuals. AICHA ROIs cover the whole cerebrum, each having 1-homogeneity of its constituting voxels intrinsic activity, and 2-a unique homotopic contralateral counterpart with which it has maximal intrinsic connectivity. AICHA was built in 4 steps: (1) estimation of resting-state networks (RSNs) using individual resting-state fMRI independent components, (2) k-means clustering of voxel-wise group level profiles of connectivity, (3) homotopic regional grouping based on maximal inter-hemispheric functional correlation, and (4) ROI labeling.
  
  
  RESULTS
  AICHA includes 192 homotopic region pairs (122 gyral, 50 sulcal, and 20 gray nuclei). As an application, we report inter-hemispheric (homotopic and heterotopic) and intra-hemispheric connectivity patterns at different sparsities.
  
  
  CONCLUSIONS
  ROI functional homogeneity was higher for AICHA than for anatomical ROI atlases, but slightly lower than for another functional ROI atlas not accounting for homotopy.
  
  
  CONCLUSIONS
  AICHA is ideally suited for intrinsic/effective connectivity analyses, as well as for investigating brain hemispheric specialization.
authors.affiliation: GIN, UMR 5296, CNRS, CEA, Bordeaux University, Bordeaux, France. Electronic address: marc.joliot@u-bordeaux.fr.
authors.forename: Marc
authors.initials: M
authors.lastname: Joliot
authors.affiliation: GIN, UMR 5296, CNRS, CEA, Bordeaux University, Bordeaux, France.
authors.forename: Gaël
authors.initials: G
authors.lastname: Jobard
authors.affiliation: GIN, UMR 5296, CNRS, CEA, Bordeaux University, Bordeaux, France.
authors.forename: Mikaël
authors.initials: M
authors.lastname: Naveau
authors.affiliation: GIP CYCERON, UMS 3408, Caen F-14000, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Delcroix
authors.affiliation: GIN, UMR 5296, CNRS, CEA, Bordeaux University, Bordeaux, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Petit
authors.affiliation: GIN, UMR 5296, CNRS, CEA, Bordeaux University, Bordeaux, France.
authors.forename: Laure
authors.initials: L
authors.lastname: Zago
authors.affiliation: GIN, UMR 5296, CNRS, CEA, Bordeaux University, Bordeaux, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Crivello
authors.affiliation: GIN, UMR 5296, CNRS, CEA, Bordeaux University, Bordeaux, France.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Mellet
authors.affiliation: GIN, UMR 5296, CNRS, CEA, Bordeaux University, Bordeaux, France.
authors.forename: Bernard
authors.initials: B
authors.lastname: Mazoyer
authors.affiliation: GIN, UMR 5296, CNRS, CEA, Bordeaux University, Bordeaux, France.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Tzourio-Mazoyer
mesh_terms: D000293:Adolescent; D000328:Adult; D001271:Atlases as Topic; D001921:Brain / Q000033:anatomy & histology / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods; D005260:Female; D007839:Functional Laterality; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D009434:Neural Pathways / Q000033:anatomy & histology / Q000502:physiology; D012146:Rest; D012815:Signal Processing, Computer-Assisted; D055815:Young Adult
keywords: Atlas; Brain parcellation; Homotopy; Intrinsic connectivity; Resting state; fMRI