Diagnostic Performance of the Herder Model in Veterans Undergoing PET Scans for Pulmonary Nodule Evaluation.

British Thoracic Society (BTS) guidelines recommend using the Herder model to risk-stratify lung nodules after positron emission tomography (PET). However, this approach has not been adequately evaluated, particularly among Veterans. A single-center retrospective cohort study was carried out in U.S. Veterans with pulmonary nodules assessed by PET to validate the Herder model; decision analysis using risk thresholds from the BTS guidelines was performed. One hundred subjects met inclusion criteria. Area under the curve of the Herder model for predicting malignancy was 0.87 for all lung nodules and 0.90 for newly discovered nodules. For low- and high-risk lung nodules, BTS guidelines would have recommended appropriate care in this patient cohort.

Unmasking the CA1 ensemble place code by exposures to small and large environments: more place cells and multiple, irregularly arranged, and expanded place fields in the larger space.

In standard experimental environments, a constant proportion of CA1 principal cells are place cells, each with a spatial receptive field called a place field. Although the properties of place cells are a basis for understanding the mammalian representation of spatial knowledge, there is no consensus on which of the two fundamental neural-coding hypotheses correctly accounts for how place cells encode spatial information. Within the dedicated-coding hypothesis, the current activity of each cell is an independent estimate of the location with respect to its place field. The average of the location estimates from many cells represents current location, so a dedicated place code would degrade if single cells had multiple place fields. Within the alternative, ensemble-coding hypothesis, the concurrent discharge of many place cells is a vector that represents current location. An ensemble place code is not degraded if single cells have multiple place fields as long as the discharge vector at each location is unique. Place cells with multiple place fields might be required to represent the substantially larger space in more natural environments. To distinguish between the dedicated-coding and ensemble-coding hypotheses, we compared the characteristics of CA1 place fields in a standard cylinder and an approximately six times larger chamber. Compared with the cylinder, in the chamber, more CA1 neurons were place cells, each with multiple, irregularly arranged, and enlarged place fields. The results indicate that multiple place fields is a fundamental feature of CA1 place cell activity and that, consequently, an ensemble place code is required for CA1 discharge to accurately signal location.