An expectation maximization algorithm for high-dimensional model selection for the Ising model with misclassified states.

We propose the misclassified Ising Model: a framework for analyzing dependent binary data where the binary state is susceptible to error. We extend previous theoretical results of a model selection method based on applying the LASSO to logistic regression at each node and show that the method will still correctly identify edges in the underlying graphical model under suitable misclassification settings. With knowledge of the misclassification process, an expectation maximization algorithm is developed that accounts for misclassification during model selection. We illustrate the increase of performance of the proposed expectation maximization algorithm with simulated data, and using data from a functional magnetic resonance imaging analysis.

Hippocampal state transitions at the boundaries between trial epochs.

The hippocampus encodes distinct contexts with unique patterns of activity. Representational shifts with changes in context, referred to as remapping, have been extensively studied. However, less is known about transitions between representations. In this study, we leverage a large dataset of neuronal recordings taken while rats performed an olfactory memory task with a predictable temporal structure involving trials and intertrial intervals (ITIs), separated by salient boundaries at the trial start and trial end. We found that trial epochs were associated with stable hippocampal representations despite moment-to-moment variability in stimuli and behavior. Representations of trial and ITI epochs were far more distinct than spatial factors would predict and the transitions between the two were abrupt. The boundary was associated with a large spike in multiunit activity, with many individual cells specifically active at the start or end of each trial. Both epochs and boundaries were encoded by hippocampal populations, and these representations carried information on orthogonal axes readily identified using principal component analysis. We suggest that the hippocampus orthogonalizes representations of the trial and ITI epochs and the activity spike at trial boundaries might serve to drive hippocampal activity from one stable state to the other.

A randomised controlled trial investigating the effects of dopexamine on gastrointestinal function and organ dysfunction in the critically ill.

OBJECTIVE: To determine whether an infusion of dopexamine for up to 7 days has an effect on gastrointestinal (GIT) absorption and permeability, renal function or organ dysfunction in the critically ill. DESIGN AND SETTING: Prospective, randomised controlled clinical trial in two general adult intensive care units. PATIENTS: 102 critically ill adult patients predicted to require organ support for at least 4 days. INTERVENTIONS: After resuscitation patients were randomly assigned to receive an infusion of up to 2 mcg/kg/min [corrected] per minute of dopexamine or control. MEASUREMENTS AND RESULTS: GIT absorption and permeability were measured using the ratio of absorbed rhamnose to 3- O-methyl- D-glucose and the ratio of lactulose to rhamnose on days 1, 4 and 7. Creatinine clearance was measured concurrently. Daily Sequential Organ Failure Assessment scores were calculated. Fifty-two patients received dopexamine. No significant difference between the two groups emerged on any of the measured parameters during the study period. CONCLUSIONS: No benefit was seen from a prolonged infusion of dopexamine in this group of critically ill patients in terms of GIT absorption and permeability, creatinine clearance or organ dysfunction.