Finding | Publication | Potential components | Comments | |
---|---|---|---|---|
Within area correlations | ||||
Fine-scale | V1-V3 cortico-cortico correlation modeled as a Gaussian point-spread function across millimeters of striate cortex | Butt et al., 2013; Butt et al., 2015 | Local or retinotopic | Consistent with any organization where response similarity falls off smoothly as a function of cortical distance, including the spatial spread inherent to the BOLD signal (Engel et al., 1997; Parkes et al., 2005) |
Similar when accounting for the size of the cortical sheet* | ||||
Ipsilateral, across area | ||||
Areal | Correlations higher between corresponding regions. Clustering algorithm could distinguish correlation patterns associated with upper versus lower visual field seeds | Butt et al., 2015; Striem-Amit et al., 2015 | Local or retinotopic | |
Similar in blind and sighted subjects* | ||||
Eccentricity | Butt et al. (2015) found higher correlations between iso-eccentric regions of cortex. Striem-Amit et al. (2015) found a clustering algorithm could distinguish the patterns created from foveal versus peripheral seed ROIs | Butt et al., 2015; Striem-Amit et al., 2015 | Local and iso-eccentric, or retinotopic | Butt et al. (2015) found no evidence of polar angle organization within areas. The analyses by Striem-Amit et al. (2015) left this aspect of organization unexplored |
Striem-Amit et al. (2015) found no overall differences between blind and sighted subjects. However, Butt et al. (2015) previously showed that, in early blind individuals, iso-eccentric correlations between corresponding regions had higher amplitude and spread more broadly, whereas the opposite pattern was found for homotopic regions* | ||||
Across-hemisphere correlations | ||||
Areal | Across-hemisphere correlations weaker than within-hemisphere but stronger between cortical homologs. Striem-Amit et al. (2015) found that a clustering algorithm could distinguish correlations patterns from left versus right seed ROIs | Butt et al., 2015; Striem-Amit et al., 2015 | Local and bilaterally iso-eccentric | Inconsistent with retinotopic organization because it represents higher correlations between cortical areas representing symmetric regions of visual space. Butt et al. (2015) found no evidence of within-area polar angle organization |
Across-hemisphere correlations are weaker in early blind individuals across occipital cortex, although no difference in clustering algorithm accuracy* | ||||
Eccentricity | Correlations enhanced for iso-eccentric regions | Butt et al., 2015 | Bilaterally iso-eccentric | |
Subtle differences blind and sighted* |
↵aAll previous findings can be explained in terms of a combination of local and iso-eccentric components of the resting-state signal. Corresponding regions refer to those representing similar regions of visual space (e.g., left hemisphere V1v, V2v, and V3v). Homotopic regions refer to paired quarters of the same visual area (e.g., V2v and V2d). Cortical homologs refer to regions that represent symmetric regions of visual space (e.g., left and right V3v).
↵*Differences between blind and sighted subjects.