Tayebi, B. | bioRxiv Science

bioRxiv2021

Adaptive spectroscopic visible-light optical coherence tomography for human retinal oximetry

Alterations in the retinal oxygen saturation (sO2) and oxygen consumption are associated with nearly all blinding diseases. A technology that can accurately measure retinal sO2 has the potential to improve ophthalmology care significantly. Recently, visible-light optical coherence tomography (vis-OCT) showed great promise for noninvasive, depth-resolved measurement of retinal sO2 as well as ultra-high resolution anatomical imaging. We discovered that spectral contaminants (SC), if not correctly removed, could lead to incorrect vis-OCT sO2 measurements. There are two main types of SCs associated with vis-OCT systems and eye conditions, respectively. Their negative influence on sO2 accuracy is amplified in human eyes due to stringent laser power requirements, eye motions, and varying eye anatomies. We developed an adaptive spectroscopic vis-OCT (Ads-vis-OCT) method to iteratively remove both types of SCs. We validated Ads-vis-OCT in ex vivo bovine blood samples against a blood-gas analyzer. We further validated Ads-vis-OCT in 125 unique retinal vessels from 18 healthy subjects against pulse-oximeter readings, setting the stage for clinical adoption of vis-OCT.

bioengineering↗

bioRxiv2020

Subcircuits of deep and superficial CA1 place cells support efficient spatial coding across heterogeneous environments

The hippocampus is thought to guide navigation by forming a cognitive map of space. However, the behavioral demands for such a map can vary depending on particular features of a given environment. For example, an environment rich in cues may require a finer resolution map than an open space. It is unclear how the hippocampal cognitive map adjusts to meet these distinct behavioral demands. To address this issue, we examined the spatial coding characteristics of hippocampal neurons in mice and rats navigating different environments. We found that CA1 place cells located in the superficial sublayer were more active in cue-poor environments, and preferentially used a firing rate code driven by intra-hippocampal inputs. In contrast, place cells located in the deep sublayer were more active in cue-rich environments and expressed a phase code driven by entorhinal inputs. Switching between these two spatial coding modes was supported by the interaction between excitatory gamma inputs and local inhibition.

neuroscience↗