Changes in functional connectivity between the left fusiform gyrus and the right hemisphere homologues of the orthographic processing network in acquired dysgraphia
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1
Johns Hopkins University, United States
The left mid-fusiform Visual Word Form Area (VWFA) has been identified as a key region for orthographic processing in both reading and spelling. However, while a great deal of neuroimaging research has examined local activity in orthographic processing areas, only recently have researchers begun to investigate the network properties of the brain areas that support orthographic processing (Ellenblum et al., 2019). In general, brain network properties are evaluated in terms of the functional connectivity between network regions. In the case of orthographic processing, these include: left fusiform gyrus (L-FG), left inferior frontal gyrus (L-IFG), left intraparietal sulcus (L-IPS) and left superior temporal sulcus (L-STS). One analytic approach to evaluating functional connectivity is “variance partitioning”. Variance partitioning evaluates how much of the variance of the functional time series of one brain region can be uniquely explained by the time series of some other brain region. In the context of acquired deficits, there is great interest in understanding the role of right hemisphere regions in the recovery of function. Accordingly, we examined how the functional connectivity relationships between L-FG and the right hemisphere homologues of the orthographic processing network are affected by lesion and recovery in acquired dysgraphic patients.
Methods and Results. Twenty-two participants who suffered acquired dysgraphia due to a left hemisphere stroke participated in a spelling treatment and were scanned while carrying out a spelling task during fMRI at pre- and post- treatment time-points. Another group of twenty-four individuals served as healthy controls. Background functional connectivity (Norman-Haignere et al., 2012) was quantified using the residual time-series of the GLM, after regressing out the task effect. To perform the variance partitioning analysis (Oksanen et al., 2007), we first extracted the average residual time-series in the L-FG and each right hemisphere orthographic processing homologue region. We then evaluated the degree of unique variance of the L-FG that was explained by each of the right hemisphere ROI time series.
First, in the dysgraphic group: the L-FG/R-FG connectivity was significantly greater than the connectivity between the L-FG and all other right ROIs (F(3,266)=303, p<0.001). Second, the pre- and post- treatment connectivity changes were greatest for the L-FG/R-FG connection compared to the L-FG connections with all other right ROIs (F(1,266)=4.69, p=0.03). Third, in terms of pre-post treatment change, while all other connectivities with the L-FG increased or stayed the same, the L-FG/R-FG connectivity decreased further (F(2,266)=2.52, p=0.083).
Discussion. In summary, we found that the connectivity between left and right fusiform areas was greater than that between the L-FG and all other right hemisphere orthographic processing homologues. Further, in the context of recovery-based changes, we found that while connectivity between L-FG and right ROIs moved towards normalization, the L-FG/R-FG connectivity exhibited anti-normalization. Although the connectivity between L-FG and R-FG has not been previously investigated, prior fMRI research (Cohen et al., 2003) does indicate that the R-FG is a right hemisphere area that is often activated during orthographic processing. Our findings provide evidence that connectivity changes between the L-FG and R-FG may play a significant role in recovery.
Acknowledgements
We are grateful for NIH support (DC012283) for its support of this research.
References
Norman-Haignere, S. V., McCarthy, G., Chun, M. M., & Turk-Browne, N. B. (2011). Category-selective background connectivity in ventral visual cortex. Cerebral Cortex, 22(2), 391-402.
Oksanen, J., Kindt, R., Legendre, P., O’Hara, B., Stevens, M. H. H., Oksanen, M. J., & Suggests, M. A. S. S. (2007). The vegan package. Community ecology package, 10, 631-637.
Cohen, L., Martinaud, O., Lemer, C. et al.,(2003) visual word recognition ain the left and right hemipsheres: Anatomical and functional correlates of peripheral alexias. Cerebral Cortex, 13 (12) 1313-1333.
Keywords:
functional connectivity,
Orthographic processing networks,
dysgraphia,
fusiform gyrus,
normalization
Conference:
Academy of Aphasia 57th Annual Meeting, Macau, Macao, SAR China, 27 Oct - 29 Oct, 2019.
Presentation Type:
Poster presentation
Topic:
Eligible for student award
Citation:
Li
S,
Tao
Y and
Rapp
B
(2019). Changes in functional connectivity between the left fusiform gyrus and the right hemisphere homologues of the orthographic processing network in acquired dysgraphia.
Front. Hum. Neurosci.
Conference Abstract:
Academy of Aphasia 57th Annual Meeting.
doi: 10.3389/conf.fnhum.2019.01.00083
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Received:
07 May 2019;
Published Online:
09 Oct 2019.
*
Correspondence:
Mr. Shi Pui Li, Johns Hopkins University, Baltimore, United States, shipui2005@hotmail.com