Effective Connectivity Differences During an Executive Control Task Between MS Subtypes and Healthy Individuals (P6.140)

OBJECTIVE:To examine differences in effective connectivity between regions involved in the Stroop interference task between healthy controls and multiple sclerosis (MS) patients. BACKGROUND:The Stroop interference task is a cognitively demanding task of executive control. The dynamic interactions between active brain regions during this task in MS patients have not been investigated yet. DESIGN/METHODS:The Stroop interference task was administered to 84 MS patients (34 relapsing-remitting [RR], 33 secondary progressive [SP] and 17 benign [B] MS) and 37 healthy controls. Group-level analysis was performed to determine common clusters of activation. Time series from 14 clusters of activation were extracted to analyze causal relationships during task performance. Effective connectivity analysis was performed using the Independent Multi-sample Greedy Equivalence Search and the Linear non-Gaussian Orientation, Fixed Structure. RESULTS:Compared to controls, all MS phenotypes exhibited extra connections. Out of the shared connections, compared to HC, RRMS patients had reduced connectivity between left and right posterior parietal lobule as well as stronger connections between the left ventromedial prefrontal and right inferior frontal gyrus, and between left and right dorsolateral prefrontal cortex. BMS showed stronger connections between right caudate nucleus and dorsal anterior cingulate and between left ventromedial prefrontal and right inferior frontal gyrus. SPMS patients showed few increased short-range connections within prefrontal and parietal regions. At the same time, in SPMS a loss of connections within frontal regions was observed. In RRMS and SPMS patients, abnormalities of connection strengths were significantly correlated with performance accuracy, disability scores and structural MRI measures of tissue damage. CONCLUSIONS:Our results suggest that, depending on the phenotype, MS patients might be using different compensation strategies in addition to relying on different network connections during Stroop task performance. Study Supported by:Partially supported by a grant from Italian Ministry of Health (GR-2009-1529671).