Challenges for identifying the neural mechanisms that support spatial navigation: the impact of spatial scale.

Spatial navigation is a fascinating behavior that is essential for our everyday lives. It involves nearly all sensory systems, it requires numerous parallel computations, and it engages multiple memory systems. One of the key problems in this field pertains to the question of reference frames: spatial information such as direction or distance can be coded egocentrically-relative to an observer-or allocentrically-in a reference frame independent of the observer. While many studies have associated striatal and parietal circuits with egocentric coding and entorhinal/hippocampal circuits with allocentric coding, this strict dissociation is not in line with a growing body of experimental data. In this review, we discuss some of the problems that can arise when studying the neural mechanisms that are presumed to support different spatial reference frames. We argue that the scale of space in which a navigation task takes place plays a crucial role in determining the processes that are being recruited. This has important implications, particularly for the inferences that can be made from animal studies in small scale space about the neural mechanisms supporting human spatial navigation in large (environmental) spaces. Furthermore, we argue that many of the commonly used tasks to study spatial navigation and the underlying neuronal mechanisms involve different types of reference frames, which can complicate the interpretation of neurophysiological data

Increased uptake of early initiation of antiretroviral therapy and baseline drug resistance testing in San Francisco between 2001 and 2015

BackgroundEarly initiation of antiretroviral therapy (eiART) can improve clinical outcomes for persons with HIV and reduce onward transmission risk. Baseline drug resistance testing (bDRT) can inform regimen selection upon subsequent treatment initiation. We examined the uptake of eiART and bDRT within 3 months and 30 days of HIV diagnosis.MethodsWe analyzed a population-based sample from the San Francisco Department of Public Health HIV/AIDS Case Registry of newly-diagnosed HIV/non-AIDS individuals between 2001 and 2015 who received care at publicly-funded facilities (N = 3,124).ResultsUptake of eiART within 3 months of diagnosis increased significantly from 2001 to 2015 (pConclusionsObserved increases in eiART and bDRT uptake from 2010 to 2015 may reflect the adoption of treatment as prevention and a local public health policy statement in 2010 recommending treatment initiation at time of diagnosis irrespective of CD4 count. Concerns about stigma may underlie disparities in eiART, however such concerns would not bear as directly on a provider-initiated laboratory test like bDRT

What is the role of spatial processing in the decline of episodic memory in Alzheimer's disease? The "mental frame syncing" hypothesis

The current theories on episodic memory suggest a crucial role of spatial processing for an effective retrieval. For a successful episodic recall, the long-term allocentric scene has to be translated into an egocentric scene. Here, we argue that a crucial role for an episodic retrieval is played by a "mental frame syncing" between two kinds of allocentric representations. This neurocognitive process allows an effective retrieval of our past experiences by synchronizing the allocentric view-point independent representation with the allocentric view-point dependent representation. If the "mental frame syncing" stops, even momentarily, it is difficult to reconstruct a coherent spatial scaffold upon which to effectively retrieve our previous events within an egocentric perspective. This is what apparently happens in Alzheimer's disease: a break in the "mental frame syncing" between these two kinds of allocentric representations, underpinned by damage to the hippocampus, may contribute significantly to the early deficit in episodic memory