Temporal correspondence in perceptual organization: Reciprocal interactions between temporal sensitivity and figure-ground segregation.

How do visual representations account for time? Is it the case that they represent time by themselves possessing temporal properties (temporal mirroring) or by atemporal markers/tags (temporal tagging)? This question has been asked for the past 5 decades and more, in neuroscience, philosophy, and psychology. To address this debate, we designed a study to test temporal correspondence. We tested whether a temporal property (flicker frequency) could influence figure-ground segregation, and in turn, reciprocally, whether a figure-ground segregation would alter a temporal property (here, temporal resolution). We manipulated flicker frequency of dots on either side of an ambiguous edge in Experiment 1 and asked participants to indicate the figural region. In Experiment 2, we measured temporal sensitivity using a temporal order judgment (TOJ) task in both figural and ground regions. We showed temporal correspondence by showing specifically that figure-ground segregation depends on flicker frequency differences between two regions in ambiguous displays, where slow-flickering regions are seen as figural (Experiment 1). Reciprocally, in Experiment 2, we showed that participants performed a temporal-order judgment task better when the task had to be performed on a region seen as background compared with the same region seen as a figure. We show how relatively slower flickering regions are seen as figural, and correspondingly, seeing a region as figural is associated with a poorer temporal resolution. Our results collectively allow us to demonstrate a tight temporal correspondence in figure-ground perception, which could be explained using the parvocellular and magnocellular pathways, the two major retino-geniculo-cortical pathways.

Finite element modeling of the human cervical spinal cord and its applications: A systematic review.

Background Context: Finite element modeling (FEM) is an established tool to analyze the biomechanics of complex systems. Advances in computational techniques have led to the increasing use of spinal cord FEMs to study cervical spinal cord pathology. There is considerable variability in the creation of cervical spinal cord FEMs and to date there has been no systematic review of the technique. The aim of this study was to review the uses, techniques, limitations, and applications of FEMs of the human cervical spinal cord. Methods: A literature search was performed through PubMed and Scopus using the words finite element analysis, spinal cord, and biomechanics. Studies were selected based on the following inclusion criteria: (1) use of human spinal cord modeling at the cervical level; (2) model the cervical spinal cord with or without the osteoligamentous spine; and (3) the study should describe an application of the spinal cord FEM. Results: Our search resulted in 369 total publications, 49 underwent reviews of the abstract and full text, and 23 were included in the study. Spinal cord FEMs are used to study spinal cord injury and trauma, pathologic processes, and spine surgery. Considerable variation exists in the derivation of spinal cord geometries, mathematical models, and material properties. Less than 50% of the FEMs incorporate the dura mater, cerebrospinal fluid, nerve roots, and denticulate ligaments. Von Mises stress, and strain of the spinal cord are the most common outputs studied. FEM offers the opportunity for dynamic simulation, but this has been used in only four studies. Conclusions: Spinal cord FEM provides unique insight into the stress and strain of the cervical spinal cord in various pathological conditions and allows for the simulation of surgical procedures. Standardization of modeling parameters, anatomical structures and inclusion of patient-specific data are necessary to improve the clinical translation.

Pinless Electromagnetic Neuronavigation During Awake Craniotomies: Technical Pearls, Pitfalls, and Nuances.

BACKGROUND: Awake craniotomies are often performed with rigid pin fixation to support optical neuronavigation. Newer electromagnetic (EM) neuronavigation technology now enables unpinned cranial neurosurgery while maintaining robust intraoperative image guidance. Here, we share technical nuances, operative pearls, and lessons learned from our institutional experience using Curve EM neuronavigation during awake, unpinned craniotomies. METHODS: We describe our process for patient positioning, instrumentation setup, system registration, intraoperative navigation, and surgical adjunct use (e.g., intraoperative neuromonitoring and intraoperative magnetic resonance imaging) in detail. At each step, we provide pearls for success and tips for pitfall avoidance based on our experience. RESULTS: Ten patients underwent awake pinless intra-axial tumor resection using Curve EM neuronavigation from May 2021 to August 2022 with a single surgeon. Postoperative transient neurological deficits were seen in 8 of 10 cases (80.0%), as all resections were taken to functional margins. Of the 9 patients with a 3-month follow-up visit at the time of publication, all 9 (100%) had improved or stable preoperative symptoms. No surgical complications, clinically appreciable inaccuracies, intraoperative losses of registration, unexpected postoperative magnetic resonance imaging findings, or errors related to the use of EM neuronavigation occurred. CONCLUSIONS: The technical pearls outlined here will help interested neurosurgeons integrate EM neuronavigation into awake craniotomies. In our experience, using unpinned neuronavigation during awake cases provides many advantages to the patient, surgeon, and entire operative team. It has thus become the standard practice at our institution.

Case report: Two unique cases of co-existing primary brain tumors of glial origin in opposite hemispheres.

Background: Primary CNS tumors are rare. Coexistence of two glial tumors of different histological origins in the same patient is even rarer. Here we describe two unique cases of coexisting distinct glial tumors in opposite hemispheres. Cases: Patient 1 is a 38-year-old male who presented with a seizure in February/2016. MRI showed a left parietal and a right frontal infiltrating nonenhancing lesions. Both lesions were resected revealing an oligodendroglioma WHO grade-2 and an astrocytoma WHO grade-2. Patient 2 is a 34-year-old male who presented with a seizure in November/2021. MRI showed a left frontal and a right mesial temporal lobe infiltrating nonenhancing lesions. Both lesions were resected revealing an oligodendroglioma WHO grade-2 and a diffuse low-grade glioma, MAPK pathway-altered (BRAF V600E-mutant). Patient 1 underwent adjuvant treatment. Both patients are without recurrence to date. Discussion: Two histologically distinct glial tumors may coexist, especially when they are non-contiguous. Pathological confirmation of each lesion is imperative for appropriate management. We highlight the different management of gliomas based on the new CNS WHO 2021 classification compared to its 2016 version, based on NCCN guidelines. Although more molecular markers are being incorporated into glioma classification, their clinical impact of it is yet to be determined.

A wrinkle in and of time: Contraction of felt duration with a single perceptual switch.

The way we represent and perceive time has crucial implications for studying temporality in conscious experience. Contrasting positions posit that temporal information is separately abstracted out like any other perceptual property through specialized mechanisms or that time is represented through the temporality of experiences themselves. To add to this debate, we investigate alterations in felt time in conditions where only conscious visual experience is altered through perceptual switches while a bistable figure remains physically unchanged. We predicted that if perceived time is a function of temporally evolving conscious content, then a break in it (here via a perceptual switch) would also lead to a break in felt time. In three experiments, we showed participants a Necker cube that was manipulated to induce a perceptual switch (experiments 1(a) and 1(b)) or left to switch on its own (experiment 2). We asked participants to report both perceptual switches and felt durations (experiments 1(a) and 2) or only estimate time (experiment 1(b)). Over these three experiments, we find evidence of contraction of felt time in trials with a perceptual switch, consistent with the idea that perceived time is a function of temporally evolving conscious experience. Additionally, we present a phenomenological demonstration to support our empirical data. Overall, the study provides evidence for temporal mirroring and isomorphism in visual experience, arguing for a link between the timing of experience and time perception.

Is perceptual learning always better at task-relevant locations? It depends on the distractors.

The role of attention in task-irrelevant perceptual learning has been contested. Attention has been studied in the past using distractor-type manipulations. Hence, during an initial exposure phase, we manipulated distractor similarity within a set of six gratings, to study its effects on perceptual learning at task-relevant and task-irrelevant locations. Of these six gratings, one was at a task-relevant location, one at a task-irrelvant location, which shared the orientation with the task-relevant grating, and the rest (four) were distractor gratings. The orientations of the distractor gratings were all either the same (homogeneous) or different from each other (heterogeneity). We hypothesized that learning at the task-irrelevant location would be worse than learning at the task-relevant location when distractors are heterogeneous and vice versa when the distractors are homogeneous. Participants were initially exposed to a grating set; they reported contrast changes at only one prespecified task-relevant location. This grating was grouped based on orientation with a task-irrelevant grating presented at the furthermost distractor location and presented alongside four control-distractors (homogeneous or heterogeneous). In the testing phase, orientation discrimination performance was measured at task-relevant, task-irrelevant (grouped), and control-distractor locations. Participants were exposed and tested sequentially, each day for 5 days. Participants learned and performed better at the task-irrelevant location compared to the task-relevant location with homogenous distractors and vice versa with heterogenous distractors. The poorer learning at the task-relevant location compared to the task-irrelevant location challenges current models of perceptual learning. Selection mechanisms driven by the nature of distractors influence perceptual learning at both task-relevant and task-irrelevant locations.

Time and time again: a multi-scale hierarchical framework for time-consciousness and timing of cognition.

Temporality and the feeling of 'now' is a fundamental property of consciousness. Different conceptualizations of time-consciousness have argued that both the content of our experiences and the representations of those experiences evolve in time, or neither have temporal extension, or only content does. Accounting for these different positions, we propose a nested hierarchical model of multiple timescales that accounts for findings on timing of cognition and phenomenology of temporal experience. This framework hierarchically combines the three major philosophical positions on time-consciousness (i.e. cinematic, extensional and retentional) and presents a common basis for temporal experience. We detail the properties of these hierarchical levels and speculate how they could coexist mechanistically. We also place several findings on timing and temporal experience at different levels in this hierarchy and show how they can be brought together. Finally, the framework is used to derive novel predictions for both timing of our experiences and time perception. The theoretical framework offers a novel dynamic space that can bring together sub-fields of cognitive science like perception, attention, action and consciousness research in understanding and describing our experiences both in and of time.