CF-GNNExplainer: Counterfactual Explanations for Graph Neural Networks

Given the increasing promise of graph neural networks (GNNs) in real-world applications, several methods have been developed for explaining their predictions. Existing methods for interpreting predictions from GNNs have primarily focused on generating subgraphs that are especially relevant for a particular prediction. However, such methods are not counterfactual (CF) in nature: given a prediction, we want to understand how the prediction can be changed in order to achieve an alternative outcome. In this work, we propose a method for generating CF explanations for GNNs: the minimal perturbation to the input (graph) data such that the prediction changes. Using only edge deletions, we find that our method, CF-GNNExplainer, can generate CF explanations for the majority of instances across three widely used datasets for GNN explanations, while removing less than 3 edges on average, with at least 94\% accuracy. This indicates that CF-GNNExplainer primarily removes edges that are crucial for the original predictions, resulting in minimal CF explanations.Comment: Accepted to AISTATS 202

Ampk regulates IgD expression but not energy stress with B cell activation.

Ampk is an energy gatekeeper that responds to decreases in ATP by inhibiting energy-consuming anabolic processes and promoting energy-generating catabolic processes. Recently, we showed that Lkb1, an understudied kinase in B lymphocytes and a major upstream kinase for Ampk, had critical and unexpected roles in activating naïve B cells and in germinal center formation. Therefore, we examined whether Lkb1 activities during B cell activation depend on Ampk and report surprising Ampk activation with in vitro B cell stimulation in the absence of energy stress, coupled to rapid biomass accumulation. Despite Ampk activation and a controlling role for Lkb1 in B cell activation, Ampk knockout did not significantly affect B cell activation, differentiation, nutrient dynamics, gene expression, or humoral immune responses. Instead, Ampk loss specifically repressed the transcriptional expression of IgD and its regulator, Zfp318. Results also reveal that early activation of Ampk by phenformin treatment impairs germinal center formation but does not significantly alter antibody responses. Combined, the data show an unexpectedly specific role for Ampk in the regulation of IgD expression during B cell activation

Gait analysis and functional outcome in patients after Lisfranc injury treatment

Introduction: Lisfranc injuries involve any bony or ligamentous disruption of the tarsometatarsal joint. Outcome results after treatment are mainly evaluated using patient-reported outcome measures (PROM), physical examination and radiographic findings. Less is known about the kinematics during gait.Methods: Nineteen patients (19 feet) treated for Lisfranc injury were recruited. Patients with conservative treatment and surgical treatment consisting of open reduction and internal fixation (ORIF) or primary arthrodesis were included. PROM, radiographic findings and gait analysis using the Oxford Foot Model (OFM) were analysed. Results were compared with twenty-one healthy subjects (31 feet). Multivariable logistic regression was used to determine factors influencing outcome.Results: Patients treated for Lisfranc injury had a significantly lower walking speed than healthy subjects (P &lt;0.001). There was a significant difference between the two groups regarding the range of motion (ROM) in the sagittal plane (flexion-extension) in the midfoot durieng the push-off phase (p &lt;0.001). The ROM in the sagittal plane was significantly correlated with the AOFAS midfoot score (r2 = 0.56, p = 0.012), FADI (r(2) = 0.47, p = 0.043) and the SF-36-physical impairment score (r(2) = 0.60, p = 0.007) but not with radiographic parameters for quality of reduction. In a multivariable analysis, the best explanatory factors were ROM in the sagittal plane during the push-off phase (beta = 0.707, p = 0.001), stability (beta = 0.423, p = 0.028) and BMI (beta = -0.727 p = &lt;0.001). This prediction model explained 87% of patient satisfaction.Conclusions: This study showed that patients treated for Lisfranc injury had significantly lower walking speed and significantly lower flexion/extension in the midfoot than healthy subjects. The ROM in these patients was significantly correlated with PROM, but not with radiographic quality of reduction. Most important satisfaction predictors were BMI, ROM in the sagittal plane during the push-off phase and fracture stability. (c) 2017 European Foot and Ankle Society. Published by Elsevier Ltd. All rights reserved.</p