dilation

Circadian regulation of reperfusion efficacy in acute ischemic stroke

Reperfusion with thrombectomy has changed the clinical landscape for ischemic stroke. Recently, some studies suggest that patients with “large cores” may still benefit from reperfusion. Why? If these “cores” represent dead brain, why should reperfusion help? One logical explanation is that currently used neuroimaging “cores”, do not always identify uniformly dead tissue. Our pilot data suggest that these “cores” include tissue with a wide range of injury, indicated as changes in relative CT Hounsfield Units (rHU). Importantly, circadian mechanisms may be involved. Ischemic tissue with less severe changes in rHU tend to occur in the morning (active phase) when responses to reperfusion are better. In mouse models of stroke, ischemic injury is also less severe when strokes occur during the nighttime (active phase for nocturnal animals). In contrast, more severe ischemic injury during the daytime (inactive phase for mice) is accompanied by dampened vasodilation and CBF response along with increased immunothrombosis and neutrophil extracellular traps (NETosis). Is it possible that understanding these circadian mechanisms may help identify patients who respond best to reperfusion? And is it possible that targeting these circadian mechanisms can help convert non- responders into responders? In this multi-PI project, we use a translational approach (clinical neuroimaging and biomarkers in stroke patients, mouse models of stroke, CT-PET imaging of tissue viability, molecular pharmacology) with three integrated aims that can be pursued in parallel. Aim 1 will use neuroimaging in stroke patients to show that less severe rHU values in reperfusion-responsive “cores” tend to occur in the morning, whereas more severe rHU values in reperfusion-non-responsive “cores” occur later. Aim 2 will use clinical biomarkers to show that more severe rHU “cores” that are not reperfusion-responsive correlate with circadian effects on vasodilation and immunothrombosis. Aim 3 will use mouse stroke models to test whether targeting these circadian mechanisms of vasodilation and immunothrombosis can convert reperfusion-non-responders into reperfusion-responders. Patients cannot choose when they have a stroke. So why should we pay attention to circadian mechanisms? There may be 2 reasons that are addressed by the present project. First, thrombectomy is resource-intensive, and in spite of the very low number-needed-to-treat, only 20% of “large core” patients do well after reperfusion. Our studies may help identify who (when) these responders are. Second, the pathophysiologic mechanisms of cerebral ischemia differ depending on time-of-day. Therefore, understanding and then targeting these circadian mechanisms may allow us to convert reperfusion non-responders into responders.

The Role of Spatial and Contextual Relations of real world objects in Interval Timing

In the real world, object arrangement follows a number of rules. Some of the rules pertain to the spatial relations between objects and scenes (i.e., syntactic rules) and others about the contextual relations (i.e., semantic rules). Research has shown that violation of semantic rules influences interval timing with the duration of scenes containing such violations to be overestimated as compared to scenes with no violations. However, no study has yet investigated whether both semantic and syntactic violations can affect timing in the same way. Furthermore, it is unclear whether the effect of scene violations on timing is due to attentional or other cognitive accounts. Using an oddball paradigm and real-world scenes with or without semantic and syntactic violations, we conducted two experiments on whether time dilation will be obtained in the presence of any type of scene violation and the role of attention in any such effect. Our results from Experiment 1 showed that time dilation indeed occurred in the presence of syntactic violations, while time compression was observed for semantic violations. In Experiment 2, we further investigated whether these estimations were driven by attentional accounts, by utilizing a contrast manipulation of the target objects. The results showed that an increased contrast led to duration overestimation for both semantic and syntactic oddballs. Together, our results indicate that scene violations differentially affect timing due to violation processing differences and, moreover, their effect on timing seems to be sensitive to attentional manipulations such as target contrast.

Separable pupillary signatures of perception and action during perceptual multistability

The pupil provides a rich, non-invasive measure of the neural bases of perception and cognition, and has been of particular value in uncovering the role of arousal-linked neuromodulation, which alters cortical processing as well as pupil size. But pupil size is subject to a multitude of influences, which complicates unique interpretation. We measured pupils of observers experiencing perceptual multistability -- an ever-changing subjective percept in the face of unchanging but inconclusive sensory input. In separate conditions the endogenously generated perceptual changes were either task-relevant or not, allowing a separation between perception-related and task-related pupil signals. Perceptual changes were marked by a complex pupil response that could be decomposed into two components: a dilation tied to task execution and plausibly indicative of an arousal-linked noradrenaline surge, and an overlapping constriction tied to the perceptual transient and plausibly a marker of altered visual cortical representation. Constriction, but not dilation, amplitude systematically depended on the time interval between perceptual changes, possibly providing an overt index of neural adaptation. These results show that the pupil provides a simultaneous reading on interacting but dissociable neural processes during perceptual multistability, and suggest that arousal-linked neuromodulation shapes action but not perception in these circumstances. This presentation covers work that was published in e-life

Revisiting neural basis of belief updating: P300, pupil dilation and beta rhythm as reliable indices of a unitary process

Using a pupil dilation metric to characterize the effect of trigeminal nerve stimulation