Increased Modularity of Resting State Networks Supports Improved Narrative Production in Aphasia Recovery

Abstract

The networks that emerge in the analysis of resting state functional magnetic resonance imaging (rsfMRI) data are believed to reflect the intrinsic organization of the brain. One key property of such complex biological networks is modularity, a measure of community structure. This topological characteristic changes in neurological disease and recovery. Nineteen subjects with language disorders after stroke (aphasia) underwent neuroimaging and behavioral assessment at multiple time points before (baseline) and after an imitation-based therapy. Language was assessed with a narrative production task. Group independent component analysis was performed on the rsfMRI data to identify resting state networks (RSNs). For each participant and each rsfMRI acquisition, we constructed a graph comprising all RSNs. We assigned nodal community based on a region's RSN membership, calculated the modularity score, and then correlated changes in modularity and therapeutic gains on the narrative task. We repeated this comparison controlling for pretherapy performance and using a community structure not based on RSN membership. Increased RSN modularity was positively correlated with improvement on the narrative task immediately post-therapy. This finding remained significant when controlling for pretherapy performance. There were no significant findings for network modularity and behavior when nodal community was assigned without consideration of RSN membership. We interpret these findings as support for the adaptive role of network segregation in behavioral improvement in aphasia therapy. This has important clinical implications for the targeting of noninvasive brain stimulation in poststroke remediation and suggests potential for further insight into the processes underlying such changes through computational modeling.

Re-emergence of modular brain networks in stroke recovery

“…Both of these changes are consistent with a reduction in network modularity, which has been observed in stroke patients, even in the unaffected hemisphere (Gratton, Nomura, Pérez, & D’Esposito, 2012). A recent study of aphasia patients found that improved narrative production following therapy correlated with an improvement in modularity of resting state networks (Duncan & Small, 2016). …”

Enhanced estimations of post‐stroke aphasia severity using stacked multimodal predictions

“…This is likely because performance does not depend solely on the “missing” parts of the brain, but also on the structural and functional integrity of the remaining tissue, which can support the functional reorganization of language processes [Carter et al, ; Corbetta et al, ; Crofts et al, ; Rorden and Karnath, ; Saur et al, ; Siegel et al, ; Turkeltaub et al, ; Wu et al, ]. Consequently, proper prediction of aphasia scores requires the integration of multiple neuroimaging modalities, each describing a different property, spanning from lesion maps to structural disconnections, and from pairwise connections to network properties [Carter et al, ; Crofts et al, ; Duncan and Small, ; Grefkes and Fink, ].…”

Advances in neurocognitive rehabilitation research from 1992 to 2017: The ascension of neural plasticity.

“…As noted above, Duncan and Small (2016) indicated that improvement in untrained narrative language samples was associated with increased network modularity from pre- to post-treatment. For a treatment designed using CATE principles,Sandberg et al (2015) found increased connectivity of left superior medial frontal and right inferior frontal cortices to other cortical nodes for participants whose training generalized from abstract to semantically related concrete words.…”

“…The nature and timing of the next wave of paradigm shifts is difficult to foresee, though many of them undoubtedly will relate to the ever evolving technosphere around us. A more modest, and perhaps achievable, objective would be to point to a few current trends from the current state of affairs that likely will accelerate: (a) With respect to neuroimaging and neural plasticity, imaging neural systems and their connectivity has found its way from the cognitive neuroscience laboratory into the neurocognitive rehabilitation literature (e.g., Duncan & Small, 2016), and this trend will only accelerate in the search to understand the neural underpinnings of this kind of rehabilitation. (b) Multi-modality neuroimaging research has already occurred in the neurocognitive rehabilitation arena.…”

“…For example, Duncan and Small (2016) gave patients with aphasia six weeks of an imitation treatment, which involved audio-visual presentation of words and phrases followed by repetition of these stimuli by the patients (Lee et al, 2010). Resting state fMRI scans were done at roughly 3-week intervals (3 pre-, 1 during, 3-post intervention).…”