Predicting Ventriculoperitoneal Shunt Dependence in High Grade Aneurysmal Subarachnoid Hemorrhage.

INTRODUCTION: Aneurysmal subarachnoid hemorrhage (aSAH) commonly presents with hydrocephalus due to obstruction of cerebrospinal fluid (CSF) passage across the ventricular system in the brain. Placement of an external ventricular device (EVD) and in some cases ventriculoperitoneal shunt (VPS) are often necessary for patients requiring prolonged CSF diversion. The study aimed at evaluating critical factors that play a role in determining the need for extended extraventricular drainage. METHODS: We performed a retrospective observational cohort study of two groups of patients with radiological imaging confirmed high grade aSAH (Hunt & Hess grades 3-5) who required VPS placement, shunt-dependent group, and who did not require long term CSF diversion, non-shunt-dependent group. We collected and analyzed data regarding the daily CSF output for 10 days following EVD placement, daily EVD height, intracranial pressure (ICP) and cerebral perfusion pressure (CPP), indicators of hydrocephalus, and CSF characteristics. RESULTS: The cohort, comprising of 8 patients in the shunt-dependent group and 32 patients in the non-shunt-dependent group, displayed median daily CSF output of 275.1 mL/day and 193.4 mL/day, respectively (P = .0005). ROC curve for CSF drainage for the two groups showed an area under the curve (AUC) of 0.71 with a 95% confidence interval (CI) 0.65 to 0.77. Qualitative analysis of CSF characteristics revealed that the shunt-dependent group had more proteinaceous, darker red color, and greater proportion of red blood cells (RBCs) although not statistically significant. CONCLUSIONS: Determinants of prolonged CSF drainage requirements in patients with high grade aSAH are not fully elucidated to this date and there is no standardized protocol for CSF diversion. Our study revealed potential markers that can be used in the assessment for the need for long term CSF diversion. Our limited sample size necessitates further research to establish clear correlations and cutoffs of these parameters in predicting long term CSF diversion requirements.

Neural arbitration between social and individual learning systems.

Decision making requires integrating knowledge gathered from personal experiences with advice from others. The neural underpinnings of the process of arbitrating between information sources has not been fully elucidated. In this study, we formalized arbitration as the relative precision of predictions, afforded by each learning system, using hierarchical Bayesian modeling. In a probabilistic learning task, participants predicted the outcome of a lottery using recommendations from a more informed advisor and/or self-sampled outcomes. Decision confidence, as measured by the number of points participants wagered on their predictions, varied with our definition of arbitration as a ratio of precisions. Functional neuroimaging demonstrated that arbitration signals were independent of decision confidence and involved modality-specific brain regions. Arbitrating in favor of self-gathered information activated the dorsolateral prefrontal cortex and the midbrain, whereas arbitrating in favor of social information engaged the ventromedial prefrontal cortex and the amygdala. These findings indicate that relative precision captures arbitration between social and individual learning systems at both behavioral and neural levels.