Solving Navigational Uncertainty Using Grid Cells on Robots

To successfully navigate their habitats, many mammals use a combination of two mechanisms, path integration and calibration using landmarks, which together enable them to estimate their location and orientation, or pose. In large natural environments, both these mechanisms are characterized by uncertainty: the path integration process is subject to the accumulation of error, while landmark calibration is limited by perceptual ambiguity. It remains unclear how animals form coherent spatial representations in the presence of such uncertainty. Navigation research using robots has determined that uncertainty can be effectively addressed by maintaining multiple probabilistic estimates of a robot's pose. Here we show how conjunctive grid cells in dorsocaudal medial entorhinal cortex (dMEC) may maintain multiple estimates of pose using a brain-based robot navigation system known as RatSLAM. Based both on rodent spatially-responsive cells and functional engineering principles, the cells at the core of the RatSLAM computational model have similar characteristics to rodent grid cells, which we demonstrate by replicating the seminal Moser experiments. We apply the RatSLAM model to a new experimental paradigm designed to examine the responses of a robot or animal in the presence of perceptual ambiguity. Our computational approach enables us to observe short-term population coding of multiple location hypotheses, a phenomenon which would not be easily observable in rodent recordings. We present behavioral and neural evidence demonstrating that the conjunctive grid cells maintain and propagate multiple estimates of pose, enabling the correct pose estimate to be resolved over time even without uniquely identifying cues. While recent research has focused on the grid-like firing characteristics, accuracy and representational capacity of grid cells, our results identify a possible critical and unique role for conjunctive grid cells in filtering sensory uncertainty. We anticipate our study to be a starting point for animal experiments that test navigation in perceptually ambiguous environments

Improving Adherence to Care Among “Hard to Reach” HIV-Infected Patients in Argentina

Many HIV-infected patients fail to achieve undetectable viral load and are not retained in care. This pilot study examined patients lost to care in public and private clinics in Buenos Aires, Argentina. The impact of patient and provider interventions was compared separately and collectively. In Phase 1, participants prescribed antiretrovirals (ARVs) and non-adherent to treatment in the prior 3 to 6 months (n = 60) were randomized to patient intervention or standard of care (SOC) and assessed over 12 months. In Phase 2, providers were trained in interviewing techniques and 60 additional patients were randomized to patient intervention or SOC condition. Averaged across patient intervention status, Phase 2 provider intervention patients reported the most improved adherence and viral suppression at 6 and 12 months. Adherence in “patient intervention only” improved at midpoint and returned to baseline at 12 months. Results suggest provider training sustained patient adherence and viral suppression among “hard to reach” patients