Theta-phase-specific modulation of dentate gyrus memory neurons.

The theta rhythm, a quasi-periodic 4-10 Hz oscillation, is observed during memory processing in the hippocampus, with different phases of theta hypothesized to separate independent streams of information related to the encoding and recall of memories. At the cellular level, the discovery of hippocampal memory cells (engram neurons), as well as the modulation of memory recall through optogenetic activation of these cells, has provided evidence that certain memories are stored, in part, in a sparse ensemble of neurons in the hippocampus. In previous research, however, engram reactivation has been carried out using open-loop stimulation at fixed frequencies; the relationship between engram neuron reactivation and ongoing network oscillations has not been taken into consideration. To address this concern, we implemented a closed-loop reactivation of engram neurons that enabled phase-specific stimulation relative to theta oscillations in the local field potential in CA1. Using this real-time approach, we tested the impact of activating dentate gyrus engram neurons during the peak (encoding phase) and trough (recall phase) of theta oscillations. Consistent with previously hypothesized functions of theta oscillations in memory function, we show that stimulating dentate gyrus engram neurons at the trough of theta is more effective in eliciting behavioral recall than either fixed-frequency stimulation or stimulation at the peak of theta. Moreover, phase-specific trough stimulation is accompanied by an increase in the coupling between gamma and theta oscillations in CA1 hippocampus. Our results provide a causal link between phase-specific activation of engram cells and the behavioral expression of memory.

Evaluation of a novel virtual care platform for remote monitoring of LVAD patients.

The aim of this study was to evaluate a novel virtual care platform created for use in Left Ventricular Assist Device (LVAD) patients. The platform included a daily log of LVAD parameters and medication adherence, two-way messaging with providers, and educational resources. To test the feasibility of this application, we recruited 25 patients between 2017 and 2019 and followed them for 6 months post discharge. Feedback concerning the platform was very positive with an average score of 4.5 ± 0.6 (out of 5) on usability and/or satisfaction and 8.1 ± 1.8 (out of 10) on likelihood to recommend the platform. In addition, our platform was well utilized with median (IQR) engagement rates of 87 (53,100)% at 30 days and 73 (49,95)% overall. We found that patients using the platform attended significantly less outpatient visits at the 6 month mark, however there was no difference in 30-day readmission rates compared to the overall LVAD cohort.