Territorial Displays of the Ctenophorus decresii Complex: A Story of Local Adaptations

Closely related species make for interesting model systems to study the evolution of signaling behavior because they share evolutionary history but have also diverged to the point of reproductive isolation. This means that while they may have some behavioral traits in common, courtesy of a common ancestor, they are also likely to show local adaptations. The Ctenophorus decresii complex is such a system, and comprises six closely related agamid lizard species from Australia: C. decresii, C. fionni, C. mirrityana, C. modestus, C. tjanjalka, and C. vadnappa. In this study, we analyze the motion displays of five members of the C. decresii complex in the context of their respective habitats by comparing signal structure, habitat characteristics and signal contrast between all species. Motor pattern use and the temporal sequence of motor patterns did not differ greatly, but the motion speed distributions generated during the displays were different for all species. There was also variation in the extent to which signals contrasted with plant motion, with C. vadnappa performing better than the other species at all habitats. Overall, this study provides evidence that members of the C. decresii complex exhibit local adaptations in signaling behavior to their respective habitat, but they also maintain some morphological and behavioral traits in common, which is likely a consequence from the ancestral state.

Critically coupled Fabry–Perot cavity with high signal contrast for refractive index sensing

Perfect absorption at a resonance wavelength and extremely low absorption at the wavelength range of off-resonance in a one-port optical cavity is required for refractive index (RI) sensing with high signal contrast. Here, we propose and analyze an absorption-enhanced Fabry–Perot (MAFP) cavity based on a critical coupling condition in a near-infrared wavelength range. For a one-port cavity, a thick bottom Au is used as a mirror and an absorber. To achieve the critical coupling condition, a top dielectric metasurface is employed and tailored to balance the radiation coupling and the absorption coupling rates, and the one-port cavity is theoretically analyzed using temporal coupled-mode theory. We investigate two types of MAFP structures for gas and liquid. The gas MAFP cavity shows a sensitivity of ~ 1388 nm/RIU and a full-width at half-maximum of less than 0.7 nm. This MAFP cavity resolves the RI change of 5 × 10−4 with a reflectance signal margin of 50% and achieves a signal contrast of ~ 100%. The liquid MAFP cavity shows a sensitivity of ~ 996 nm/RIU when RI of liquid changes from 1.30 to 1.38. With tailoring the period of the metasurface maintaining its thickness, a signal contrast of ~ 100% is achieved for each specific RI range.

Myelin Imaging Using 3D Dual-echo Ultra-short Echo Time MRI with Rosette k-Space Pattern

Purpose: This study aimed to develop a new 3D dual-echo rosette k-space trajectory, specifically for applications of ultra-short echo time (UTE) magnetic resonance imaging (MRI). The direct imaging of the myelin bilayer, which has ultra-short transverse relaxation time (uT2), was acquired to test the performance of the proposed UTE sequence. Theory and Methods: The rosette trajectory was developed based on rotations of a "petal-like" pattern in the kx-ky plane, with oscillated extensions in kz-direction for 3D coverage. Five healthy volunteers were recruited and underwent ten dual-echo rosette UTE scans with varied echo times (TEs). Dual-exponential model fitting was performed to separate uT2 signals, with the output of uT2 fraction, uT2 value and long T2 value. Results: The reconstructed images' signal contrast between white matter (WM) and grey matter (GM) increased with longer TEs. The WM regions had higher uT2 fraction values than GM (10.9% ± 1.9% vs. 5.7% ± 2.4%). The uT2 value was about 0.12 milliseconds in WM. Conclusion: The higher uT2 fraction value in WM compared to GM demonstrated the ability of the proposed sequence to capture rapidly decaying signals.

Variable utility in the enigmatic presence of ultraviolet reflectance in conspicuous aposematic signals

Warning signals are often characterized by highly contrasting, distinctive and memorable colors. Both chromatic (hue) and achromatic (brightness) contrast contribute to signal efficacy, making longwave colored signals (red and yellow) that generate both chromatic and achromatic contrast common. Shortwave colors (blue and ultraviolet) do not contribute to luminance perception, yet are also common in warning signals. The presence of UV aposematic signals is paradoxical as UV perception is not universal, and evidence for its utility is at best mixed. We used visual modeling to quantify how UV affects signal contrast in aposematic butterflies and frogs. We found that UV only appreciably affected visual contrast in the butterflies. As the butterflies, but not the frogs, have UV-sensitive vision these results support the notion that UV reflectance is associated with intraspecific communication, but appears to be non-functional in frogs. Consequently, we should be careful when assigning a selection-based benefit from UV reflectance.

Large-scale voltage imaging in the brain using targeted illumination

Recent improvements in genetically encoded voltage indicators enabled high precision imaging of single neuron's action potentials and subthreshold membrane voltage dynamics in the mammalian brain. To perform high speed voltage imaging, widefield microscopy remains an essential tool to record activity from many neurons simultaneously over a large anatomical area. However, the lack of optical sectioning makes widefield microscopy prone to background signal contamination. We implemented a simple, low cost, targeted illumination strategy based on a digital micromirror device (DMD) to restrict illumination to the cells of interest to improve background rejection, and quantified optical voltage signal improvement in neurons expressing the fully genetically encoded voltage indicator SomArchon. We found that targeted illumination, in comparison to widefield illumination, increased SomArchon signal contrast and reduced background cross-contamination in the brains of awake mice. Such improvement permitted the reduction of illumination intensity, and thus reduced fluorescence photobleaching and prolonged imaging duration. When coupled with a high-speed sCMOS camera, we routinely imaged tens of spiking neurons simultaneously over several minutes in the brain. Thus, the DMD-based targeted illumination strategy described here offers a simple solution for high-speed voltage imaging analysis of large scale network at the millisecond time scale with single cell resolution in the brains of behaving animals.

Lower Locus Coeruleus MRI intensity in patients with late-life major depression

Background The locus coeruleus (LC) is the major noradrenergic source in the central nervous system. Structural alterations in the LC contribute to the pathophysiology of different neuropsychiatric disorders, which may increase to a variable extent the likelihood of developing neurodegenerative conditions. The characterization of such alterations may therefore help to predict progression to neurodegenerative disorders. Despite the LC cannot be visualized with conventional magnetic resonance imaging (MRI), specific MRI sequences have been developed to infer its structural integrity. Methods We quantified LC signal Contrast Ratios (LCCRs) in late-life major depressive disorder (MDD) (n = 37, 9 with comorbid aMCI), amnestic Mild Cognitive Impairment (aMCI) (n = 21, without comorbid MDD), and healthy controls (HCs) (n = 31), and also assessed the putative modulatory effects of comorbidities and other clinical variables. Results LCCRs were lower in MDD compared to aMCI and HCs. While no effects of aMCI comorbidity were observed, lower LCCRs were specifically observed in patients taking serotonin/norepinephrine reuptake inhibitors (SNRIs). Conclusion Our results do not support the hypothesis that lower LCCRs characterize the different clinical groups that may eventually develop a neurodegenerative disorder. Conversely, our results were specifically observed in patients with late-life MDD taking SNRIs. Further research with larger samples is warranted to ascertain whether medication or particular clinical features of patients taking SNRIs are associated with changes in LC neurons.

Effects of Long-Term Meditation Practices on Sensorimotor Rhythm-Based Brain-Computer Interface Learning

Sensorimotor rhythm (SMR)-based brain–computer interfaces (BCIs) provide an alternative pathway for users to perform motor control using motor imagery. Despite the non-invasiveness, ease of use, and low cost, this kind of BCI has limitations due to long training times and BCI inefficiency—that is, the SMR BCI control paradigm may not work well on a subpopulation of users. Meditation is a mental training method to improve mindfulness and awareness and is reported to have positive effects on one’s mental state. Here, we investigated the behavioral and electrophysiological differences between experienced meditators and meditation naïve subjects in one-dimensional (1D) and two-dimensional (2D) cursor control tasks. We found numerical evidence that meditators outperformed control subjects in both tasks (1D and 2D), and there were fewer BCI inefficient subjects in the meditator group. Finally, we also explored the neurophysiological difference between the two groups and showed that the meditators had a higher resting SMR predictor, more stable resting mu rhythm, and a larger control signal contrast than controls during the task.

Measuring arterial pulsatility with Dynamic Inflow MAgnitude Contrast (DIMAC)

Poor arterial health is increasingly recognised as an independent risk factor for cerebrovascular disease, however there remain relatively few reliable methods for assessing the function and health of cerebral arteries. In this study, we outline a new MRI approach to measuring pulsatile flow in cerebral arteries that is based on the inflow phenomenon associated with fast gradient-recalled-echo acquisitions. Unlike traditional phase-contrast techniques, this new method, which we dub Dynamic Inflow MAgnitude Contrast (DIMAC), does not require velocity-encoding gradients as sensitivity to flow velocity results purely from the inflow effect. We achieved this desired effect using a highly accelerated single slice EPI acquisition with very short TR (15 ms) and a 90 degree flip angle, thus maximising inflow contrast. Simulating the spoiled GRE signal in the presence of large arteries and perform a sensitivity analysis to demonstrate that in the regime of high inflow contrast it shows much greater sensitivity to flow velocity over blood volume changes. We support this theoretical prediction with in-vivo data collected in two separate experiments designed to demonstrate the utility of the DIMAC signal contrast. We perform a hypercapnia challenge experiment in order to experimentally modulate arterial tone within subjects, and thus modulate the arterial pulsatile flow waveform. We also perform a thigh-cuff release challenge, designed to induce a transient drop in blood pressure, and demonstrate that the continuous DIMAC signal captures the complex transient change in the pulsatile and non-pulsatile components of flow. In summary, this study proposes a new role for a well established source of MR image contrast, and demonstrate its potential for measuring both steady-state and dynamic changes in arterial tone.

In Vivo Assessment of Burn Depth and Wound Healing Using a Handheld Terahertz Hyperspectral Scanner

The accuracy of clinical assessment in partial-thickness burn injuries has remained as low as 50-75%. Depending on the depth and environmental factors in the wound, such as reactive oxygen species, inflammation, and autophagy, partial-thickness burns can heal spontaneously or require surgical intervention. In this study, we demonstrate that Terahertz Time-Domain Spectral Imaging (THz-TDSI) is a promising tool for in vivo quantitative assessment of burn injuries. We used a novel handheld THz-TDSI scanner to characterize burn injuries in a porcine scald model with histopathological control. Prior work used THz reflectivity (representation of tissue hydration) as the only source of signal contrast. However, we used the spectral amplitude and the spectral slope of the terahertz electric field to distinguish the different severities of burns, suggesting that the energy loss due to electromagnetic scattering from skin constituents serves an additional metric to quantitatively assess burn injuries. Statistical analysis (n = 40) indicates that THz-TDSI can accurately differentiate between partial-thickness and full-thickness burn injuries (1-way ANOVA, p < 0.05) and monitor the healing process of partial thickness burns. THz-TDSI has the potential to improve burn care outcomes by helping surgeons to make objective decisions for early excision.