Abstract
As described elsewhere in this special issue, recent advances in neuroimaging over the last decade have led to a rapid expansion in our knowledge of anatomical and functional correlations within the normal and abnormal human brain. Here, we review how early blindness has been used as a model system for examining the role of visual experience in the development of anatomical connections and functional responses. We discuss how lack of power in group comparisons may provide a potential explanation for why extensive anatomical changes in cortico-cortical connectivity are not observed. Finally we suggest a framework—cortical specialization via hierarchical mixtures of experts—which offers some promise in reconciling a wide range of functional and anatomical data.
Highlights
OCCIPITAL CORTEX The effects of blindness on ipsilateral functional correlations between visual areas are not clear. Burton et al (2014) found that blindness had relatively little effect on ipsilateral occipital cortex correlations, especially when compared to the effect on inter-hemispheric correlations. Bedny et al (2010) found a decrease in ipsilateral correlations between middle temporal area (MT) and Brodmann area 18 (V2)–3, between Brodmann area 17 (V1) and V2–3, and between lateral occipital cortex (LO and MT) and inferior temporal cortex (Figures 2A,B: MT and lateral occipital area (LO) ↔ fusiform gyrus (FG)) in the left hemisphere
The main effect of early blindness on functional correlations seem to be reduced inter-hemispheric functional correlations within occipital and parietal regions, decreased functional correlations between occipital and ipsilateral and contralateral sensorimotor cortex, decreased functional correlations between visual areas and ipsilateral and contralateral temporal regions associated with auditory processing, and increased functional correlations between early visual areas and areas associated with higher level cognitive functions including parietal, prefrontal and frontal cortex
Crossmodal responses in occipital cortex in blind individuals tend to be larger when attention is engaged (Stevens et al, 2007; Weaver and Stevens, 2007) or the task contains a working memory component (Burton et al, 2010; see Burton et al (2014), for a review). This is generally true of sensory cortex, and robust auditory and tactile responses have been observed in occipital cortex as a result of early blindness which cannot be explained as representing attentional, cognitive control or working memory operations (Mahon et al, 2009; Collignon et al, 2011; Huber et al, 2014; Jiang et al, 2014)
Summary
“ there was among the Thebans a soothsayer, Tiresias, son of Everes and a nymph Chariclo, of the family of Udaeus, the Spartan, and he had lost the sight of his eyes . . . Pherecydes says that he was blinded by Athena; for Chariclo was dear to Athena. . . and Tiresias saw the goddess stark naked, and she covered his eyes with her hands, and so rendered him sightless. In contrast to the relatively small effect on ipsilateral occipital connectivity, a variety of studies have shown that early blindness (Bedny et al, 2011; Qin et al, 2013; Burton et al, 2014) and anophthalmia (Watkins et al, 2012) results in a decrease in inter-hemispheric functional correlations for resting state signals within occipital cortex between both homologous and non-homologous areas, with the difference between subject groups tending to increase across the visual hierarchy (Figure 3B: CAL ↔ CAL, LO, MOG, MT, SOG; LO ↔ LO; MT ↔ MT; SOG ↔ SOG, IOG). PRE-FRONTAL AND FRONTAL CORTICES a wide variety of studies have found increased functional correlations between visual areas (especially higher order areas) and ipsilateral and contralateral prefrontal (Sani et al, 2010; Bedny et al, 2011; Collignon et al, 2011; Watkins et al, 2012; Burton et al, 2014; Renier et al, 2014; Figures 2C,D: MT, FG, MOG, OTG and LO-IFG, 44–45, 47) and frontal (Liu et al, 2007; Bedny et al, 2010, 2011; Sani et al, 2010; Collignon et al, 2011; Watkins et al, 2012; Burton et al, 2014) cortex (Figures 2C,D: FG, IOG, SOG, LO, MT and OTG-46, 6, 8, 9, IFG, MFG, SFG)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
