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===== The fine-scale functional connectivity of striate cortex in sighted and blind people =====

This page presents the raw data described in this paper:

  *  OH Butt, NC Benson, R Datta, GK Aguirre (2013) "The fine-scale functional connectivity of striate cortex in sighted and blind people"

Please refer any questions to <aguirreg@mail.med.upenn.edu>.

=====Abstract=====

To what extent are spontaneous neural signals within striate cortex organized by vision? We examined the fine-scale pattern of striate cortex correlations within and between hemispheres in rest-state BOLD fMRI data from sighted and blind people. In the sighted, we find that cortico-cortico correlation is well modeled as a Gaussian point-spread function across millimeters of striate cortical surface, rather than degrees of visual angle. Blindness produces a subtle change in the pattern of fine-scale striate correlations between hemispheres. Across participants blind before the age of 18, the degree of pattern alteration covaries with the strength of long-range correlation between left striate cortex and Broca’s area. This suggests that early blindness exchanges local, vision-driven pattern synchrony of the striate cortices for long-range functional correlations potentially related to cross-modal representation.
=====Supplementary Information=====

====Replication and extension of Bedny et al., 2011====

In their 2011 paper, Bedny and her colleagues examined the resting state connectivity of the left lateral occipital cortex to other areas in blind and sighted individuals:
 
  *  Bedny M, Pascual-Leone A, Dodell-Feder D, Fedorenko E, Saxe R (2011) [[http://www.pnas.org/content/early/2011/02/18/1014818108|Language processing in the occipital cortex of congenitally blind adults]]. Proc Natl Acad Sci U S A. 108(11): 4429-34.

Bedny et al report a reduced left-right, whole-region correlation of the lateral occipital cortices in the blind as compared to sighted. We were unable to replicate this result in our age-matched population [two-tail t[22 df]= 0.79165, p = 0.437  (mean z': [1.13 1.03], diff = 0.0963)((LOC defined using the Destrieux et al., 2010 atlas)). There was, however, a trend toward decreased connectivity, and this comparison approaches significance (p=0.06) in our larger populations which are not age-matched.

Repeating our between-hemisphere, fine-scale analyses using lateral occipital as a seed region, we do not see a significant difference between age-matched blind and sighted subjects for a “LOC pattern similarity” measure: two-tail t[22 df]= 1.7654, p = 0.0914 (means: [0.125 0.0522], diff = 0.0728). LOC pattern similarity does not significantly correlate with striate pattern similarity for either the sighted (r = 0.27, p = 0.19) or blind populations (r = 0.16, p = 0.49).

Bedney et al also reported that the blind had a greater resting-state correlation between the left LOC and Broca's area as compared to sighted controls. We were able to replicate this finding. The figure below shows the whole-brain group difference in correlation for mean left LOC signal. Areas in red had a larger, on average, correlation with the left LOC in the blind group as compared to the sighted controls. To account for multiple comparisons, only regions with an FDR-corrected q of < 0.05 are displayed. No differences at this map-wise threshold were found either on the medial surface of the brain or the right hemisphere. 

^  Replication: "Changes in resting-state correlation from lateral occipital region (left LOC)"  ^
|  {{:public:papers:restv1:bedfig4.png?400|}}  |

====Direct Volumetric Distance Subject Matrices====

The following are representative scaled volumetric between-hemisphere distance matrices. In volumetric space, the gyral “peaks” of striate cortex are in very close proximity between the right and left hemisphere. Consequently, the first and last rows and columns of the matrix (which represent cortical surface points from the gyral ridge) have lower volumetric distances as compared to regions deep in the calcarine (center of the matrix). The color-scale represents scaled distance 0->1. 

^  Subject 3  ^  Sighted Subject 20  ^  Sighted Subject 22  ^
|  {{:public:papers:restv1:sighted-subject-3-vold.png?350|}}  |  {{:public:papers:restv1:sighted-subject-20-vold.png?350|}}  |  {{:public:papers:restv1:sighted-subject-22-vold.png?350|}}  |
|  {{:public:papers:restv1:sighted-subject-3-vold.pdf|}}  |  {{:public:papers:restv1:sighted-subject-20-vold.pdf|}}  |  {{:public:papers:restv1:sighted-subject-22-vold.pdf|}}  |
====Within vs. Between matrices====

In the striate cortex of sighted individuals, the fine-scale connectivity matrices within a given hemisphere closely resemble the between the hemisphere connectivity matrices after accounting for the digital image artifact. Furthermore, the blind within-hemisphere structure closely resembles and is statistically indistinguishable from the sighted-within hemisphere structure. This, however, is not the case for the blind between hemisphere structure. As such, while the sighted difference matrix should reveal minimal difference across the matrix, structured difference should be observed in the blind difference matrix. 

^  [Within - Between] connectivity matrix  ^^^
|  {{:public:papers:butt_2013_sighted-meandiff-whole.png?200|}}  |  {{:public:papers:butt_2013_blind-meandiff-whole.png?200|}}  |  {{:public:papers:restv1:DiffColorScale.png?85|}}  |
^  Sighted  ^  Blind  ^ ^  
====Matched Between Hemisphere Correlation - Line of 'exact partners'====


In adult human striate cortex, neurons with receptive fields close to the vertical meridian have monosynaptic, callosal connections (Clarke et al., 1990). 

We asked if the correlation between matched vertex positions between right and left hemisphere varies across polar angle. The mean correlation in 5° bins across polar angle was plotted against mean correlation (z') for the blind (red) and sighted (black) groups. Shaded regions represent ± 1 SEM across the groups.

No increased correlation was seen for the vertical meridian (0° and 180°) compared to the horizontal meridian (90°). Indeed, the trend appears to be in the opposite direction.

{{:public:papers:restv1:diagoncorrz.png?500|}}

====Pattern Matrices derived from a Phantom Water Jug====
{{:public:papers:restv1:jug-v1paper.png?500|}}\\
Eight functional scans of a phantom water jug were obtained and passed through the particular anatomical and image processing routines for 8 randomly selected subjects. The resulting pattern matrices for phantom data were averaged following a Fisher's r-to-z transformation. //**A**//  Structure about the diagonal of the matrix is readily apparent in the within-hemisphere matrix, which we termed “digital image structure.” The overall form strongly echos the simulated data matrices (**Figure 2**).  //**B**//  Minimal correlation is observed when comparing between hemispheres, again reminiscent of the simulated data plots.

=====Subject and Data Table=====

<csv public:papers:restv1.csv>>         <hdr_cols>=<1>       </csv>


NLP - no light perception, LP - best vision light perception only, HM - best vision hand-motion perception.
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