Recent studies highlight the importance of the temporal domain in visual processing. Critical Flicker-Fusion Frequency (CFF), the frequency at which a flickering light is perceived as continuous, is widely used for evaluating visual temporal processing. However, substantial variability in the psychophysical paradigms, used for measuring CFF, leads to substantial variability in the reported results. Here, we report on a comprehensive comparison of CFF measurements through three different psychophysical paradigms: methods of limits; method of constant stimuli, and staircase method. Our results demonstrate that the CFF can be reliably measured with high repeatability by all three psychophysics methods. However, correlations (r = 0.92, p≪0.001) and agreement (Bland Altman test indicated 95% confidence limit variation of ±3.6 Hz), were highest between the staircase and the constant stimuli methods. The time required to complete the test was significantly longer for the constant stimuli method as compared to other methods (p < 0.001). Our results highlight the suitability of the adaptive paradigm for efficiently measuring temporal resolution in the visual system.

Aim: Longitudinal tracking of transplanted cells in clinical and experimental setups is crucial for evaluating the efficiency of retinal cell replacement therapies. Materials & methods: Gold nanopa...

Electrical vasoconstriction is a promising approach to control blood pressure or restrict bleeding in non-compressible wounds. We explore the neural and non-neural pathways of electrical vasoconstriction in-vivo. Charge-balanced, asymmetric pulses were delivered through a pair of metal disc electrodes. Vasoconstriction was assessed by measuring the diameter of rat saphenous vessels stimulated with low-voltage (20 V, 1 ms) and high-voltage (150 V, 10 μs) stimuli at 10 Hz for 5 min. Activation pathways were explored by topical application of a specific neural agonist (phenylephrine, alpha-1 receptor), a non-specific agonist (KCl) and neural inhibitors (phenoxybenzamine, 25 mg/ml; guanethidine, 1 mg/ml). Acute tissue damage was assessed with a membrane permeability (live-dead) fluorescent assay. The Joule heating in tissue was estimated using COMSOL Multiphysics modeling. During stimulation, arteries constricted to 41 ± 8% and 37 ± 6% of their pre-stimulus diameter with low- and high-voltage stimuli, while veins constricted to 80 ± 18% and 40 ± 11%, respectively. In arteries, despite similar extent of constriction, the recovery time was very different: about 30 s for low-voltage and 10 min for high-voltage stimuli. Neural inhibitors significantly reduced low-voltage arterial constriction, but did not affect high-voltage arterial or venous constriction, indicating that high-voltage stimuli activate non-neural vasoconstriction pathways. Adrenergic pathways predominantly controlled low-voltage arterial but not venous constriction, which may involve a purinergic pathway. Viability staining confirmed that stimuli were below the electroporation threshold. Modeling indicates that heating of the blood vessels during stimulation (< 0.2 °C) is too low to cause vasoconstriction. We demonstrate that low-voltage stimuli induce reversible vasoconstriction through neural pathways, while high-voltage stimuli activate non-neural pathways, likely in addition to neural stimulation. Different stimuli providing precise control over the extent of arterial and venous constriction as well as relaxation rate could be used to control bleeding, perfusion or blood pressure.

Non-compressible hemorrhage is the most common preventable cause of death on battlefield and in civilian traumatic injuries. We report the use of microsecond pulses of electric current to induce rapid constriction in femoral and mesenteric arteries and veins in rats. Electrically-induced vasoconstriction could be induced in seconds while blood vessels dilated back to their original size within minutes after stimulation. At higher settings, a blood clotting formed, leading to complete and permanent occlusion of the vessels. The latter regime dramatically decreased the bleeding rate in the injured femoral and mesenteric arteries, with a complete hemorrhage arrest achieved within seconds. The average blood loss from the treated femoral artery during the first minute after injury was about 7 times less than that of a non-treated control. This new treatment modality offers a promising approach to non-damaging control of bleeding during surgery, and to efficient hemorrhage arrest in trauma patients.