1. Reliability of Negative BOLD in Ipsilateral Motor Cortex
K. M. McGregor, A. Sudhyadhom, B. Crosson, A.J Butler
Center for Visual and Neurocognitive Rehabilitation CVNR) Atlanta VA Medical Center
Emory University School of Medicine, Department of Neurology
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Abstract
Methods
Reliability Analysis
Research using functional magnetic resonance imaging has for numerous years now reported the existence of a negative blood oxygenation level dependent (BOLD) response. Based on accumulating evidence, this negative BOLD signal appears to represent an active inhibition of cortical areas in which it is found during task activity. However, to date, we are aware of no study that has tested the reliability of evoked negative BOLD in ipsilateral sensorimotor (M1S1) cortex in individuals across sessions. The current study employs a unimanual finger opposition task, previously shown to evoke negative BOLD in ipsilateral M1S1 cortex, across three sessions. Reliability metrics across sessions indicates that both the magnitude and location of ipsilateral M1S1 negative BOLD response is relatively stable over each of the three sessions. Moreover, the volume of negative BOLD in ipsilateral cortex was highly correlated with volume of positive BOLD activity in the contralateral primary M1S1. These findings show that the negative BOLD signal can be reliably evoked in unimanual task paradigms, and that the signal dynamic could represent an active suppression of the ipsilateral M1S1 cortex originating from the contralateral motor areas.
Regions of interest maps were computer for two ROI (Right and Left M1S1)
1) Intraclass Correlation Coefficient (ICC): ICC model (A, k) testing the degree of absolute agreement 2) Jaccard Coefficient: J = M11/(M01+M10-M11); where M11 represents the number of coactive sites/voxels in both comparisons sessions and both M01 and M10 represent sites/voxels active in only one of the two comparisons sessions, respectively 3) Intersession Magnitude Map: Intersession reliability map generated from binarized activity maps at FDR q<.05 across sessions.
7 right-handed able-bodied younger (18-31) adults participated in 3 fMRI sessions offset by 7 or 14 days.
fMRI: Two high spatial resolution (2mm x 2mm x 2mm) gradient echo EPI (4s= TR; TE = 30) axial fMRI runs were obtained in block design involving unimanual finger pinch of the right hand.
Data Processing: Intersession alignment of functional images: 1) The T1-weighted structural image from the initial fMRI session was aligned to the first EPI image acquisition of the same session using a local Pearson correlation procedure (Saad et al. 2009). 2) EPI acquisitions from the second and third session were then each zero-padded and center- aligned. 3) The second and third functional runs were each registered to the EPI-registered T1 image from the initial fMRI mapping session.
Results: Reliability
ICC Analysis:
Measure
Left M1S1 ICC
Right M1S1 ICC
Positive BOLD
Negative BOLD
Total Volume
.84**
.52*
CoM X
.98**
.68*
CoM Y
.97**
.66*
CoM Z
.81**
Results: Descriptive Stats
fMRI
Left M1S1 Positive BOLD
Right M1S1 Negative BOLD
fMRI Map Volume (µL)
Mapping Session 1
Mapping Session 2
Mapping Session 3
1970 (345) 1855 (507) 1977 (612)
808 (248) 1073 (825) 851 (533)
CoM X (Atlas Coordinate)
31.15 (4.9) (3.2) (2.95)
(6.9) (10.53) (6.07)
CoM Y (Atlas Coordinate)
CoM Z (Atlas Coordinate)
27.84 (5.88) (4.92) (3.94)
27.42 (9.1) (4.5) (1.79)
Mapping Session 3  
50.25 (2.1) (3.79) 52 (2.11)
51.43 (4.8) (7.63) (5.15)
Average CoM Shift (in mm)*
3.27 (1.98)
10.42 (4.68)
LM1 CoM
RM1 CoM
Jaccard Analysis:
Left Positive BOLD
Right Negative BOLD
Sessions
1-2
2-3
1-3
Average
0.61
0.49
0.55
0.62
0.44
0.56
.54
0.43
0.54
0.47
0.50
0.39
0.46
0.45
0.38
0.25
0.36
0.31
0.42
0.37
0.48
0.58
0.53
0.75
0.59
0.60
0.51
0.52
0.34
0.26
0.63
Intersession Reliability Map
The contents do not represent the views of the Department of Veterans Affairs or the United States Government. This work was supported by a Department of Veteran Affairs (VA) Rehabilitation R&D Center of Excellence #F2182C, Career Development Award Level-2 (KMM) and Senior Research Career Scientist (BC: #B6364L) awards.