Perception of depth is a fundamental challenge for the visual system, particularly for observers moving through their environment. The brain makes use of multiple visual cues to reconstruct the three-dimensional structure of a scene. One potent cue, motion parallax, frequently arises during translation of the observer because the images of objects at different distances move across the retina with different velocities. Human psychophysical studies have demonstrated that motion parallax can be a powerful depth cue 1-5 , and motion parallax appears to be heavily exploited by animal species that lack highly developed binocular vision 6-8 . However, little is known about the neural mechanisms that underlie this capacity. We used a virtual-reality system to translate macaque monkeys while they viewed motion parallax displays that simulated objects at different depths. We show that many neurons in the middle temporal (MT) area signal the sign of depth (i.e., near vs. far) from motion parallax in the absence of other depth cues. To achieve this, neurons must combine visual motion with extra-retinal (non-visual) signals related to the animal's movement. Our findings suggest a new neural substrate for depth perception, and demonstrate a robust interaction of visual and non-visual cues in area MT. Combined with previous studies that implicate area MT in depth perception based on binocular disparities 9-12 , our results suggest that MT contains a more general representation of three dimensional space that leverages multiple cues.Humans can make precise judgments of depth based on motion parallax, the relative retinal image motion between objects at different distances 1-5 . However, motion parallax alone is not sufficient to specify the sign of depth, that is whether an object is near or far relative to the plane of fixation 13-15 . Rather, the direction of image motion relative to observer motion is crucial to specifying depth-sign (Fig. 1). Objects located nearer than the plane of fixation sweep across the visual field in a direction opposite to head translation (Fig. 1, black arrows). In contrast, objects located farther than the plane of fixation move in the same direction as the head (Fig 1, white arrows). Thus, image motion in a particular direction (e.g. leftward) can be associated with either a near (Fig. 1a) or far (Fig. 1b) object. Under some conditions, the brain could interpret such ambiguous visual motion by using other cues such as occlusion, size, or perspective. However, to compute depth-sign in the absence of these pictorial cues, the visual system needs access to extra-retinal signals related to observer movement. We exploited this fact to probe for a neural correlate of depth from motion parallax.We performed extracellular microelectrode recordings in area MT of two macaque monkeys that were trained to maintain visual fixation on a world-fixed target while being translated by

Ever since Bedford’s seminal Lancet case series in 1955, we have known that perioperative care is sometimes followed by significant cognitive dysfunction (1). Although the safety of perioperative care has improved dramatically since 1955, the descriptions of cognitive dysfunction in that case series are eerily similar to the complaints of current patients suffering from post-operative cognitive dysfunction (POCD). POCD remains a common post-operative complication associated with significant morbidity and even mortality, especially among elderly patients. There has been a great deal of interest in and controversy about POCD, from how it is measured, to how long it lasts, to its precise implications for patients. This interest and controversy is reflected partly in the increasing number of papers published on this subject recently (shown in Figure 1). Recent work has also suggested surgery may be associated with cognitive improvement in some patients (2–4), termed Post-Operative Cognitive Improvement (POCI). As the number of surgeries performed worldwide approaches 250 million per year (5) (with an increasing number elderly patients), optimizing postoperative cognitive function and preventing/treating POCD are major public health issues. In this article we review the literature on POCD and POCI, and discuss current research challenges in this area.

The capacity to perceive depth is critical for an observer to interact with their surroundings. During observer movement, information about depth can be extracted from the resulting patterns of image motion on the retina (motion parallax). Without extra-retinal signals related to observer movement, however, depth sign (near vs. far) from motion parallax can be ambiguous. We previously demonstrated that MT neurons combine visual motion with extra-retinal signals to code depth sign from motion parallax in the absence of other depth cues. In that study, head translations were always accompanied by compensatory tracking eye movements, allowing for at least two potential sources of extra-retinal input. We now show that smooth eye movement signals provide the critical extra-retinal input to MT neurons for computing depth sign from motion parallax. Our findings demonstrate a powerful modulation of MT activity by eye movements, as predicted by human studies of depth perception from motion parallax.

Background Preclinical studies have found differential effects of isoflurane and propofol on the Alzheimer’s disease (AD)-associated markers tau, phosphorylated tau (p-tau)and amyloid-β (Aβ). Objective We asked whether isoflurane and propofol have differential effects on the tau/Aβ ratio (the primary outcome), and individual AD biomarkers. We also examined whether genetic/intraoperative factors influenced perioperative changes in AD biomarkers. Methods Patients undergoing neurosurgical/otolaryngology procedures requiring lumbar cerebrospinal fluid (CSF) drain placement were prospectively randomized to receive isoflurane (n = 21) or propofol (n = 18) for anesthetic maintenance. We measured perioperative CSF sample AD markers, performed genotyping assays, and examined intraoperative data from the electronic anesthesia record. A repeated measures ANOVA was used to examine changes in AD markers by anesthetic type over time. Results The CSF tau/Aβ ratio did not differ between isoflurane- versus propofol-treated patients (p = 1.000). CSF tau/Aβ ratio and tau levels increased 10 and 24h after drain placement (p = 2.002 × 10−6 and p = 1.985 × 10−6, respectively), mean CSF p-tau levels decreased (p = 0.005), and Aβ levels did not change (p = 0.152). There was no interaction between anesthetic treatment and time for any of these biomarkers. None of the examined genetic polymorphisms, including ApoE4, were associated with tau increase (n = 9 polymorphisms, p > 0.05 for all associations). Conclusion Neurosurgery/otolaryngology procedures are associated with an increase in the CSF tau/Aβ ratio, and this increase was not influenced by anesthetic type. The increased CSF tau/Aβ ratio was largely driven by increases in tau levels. Futurework should determine the functional/prognostic significance of these perioperative CSF tau elevations.

Evidence-based standardization of the perioperative management of patients undergoing complex spine surgery can improve outcomes such as enhanced patient satisfaction, reduced intensive care and hospital length of stay, and reduced costs. The Society for Neuroscience in Anesthesiology and Critical Care (SNACC) tasked an expert group to review existing evidence and generate recommendations for the perioperative management of patients undergoing complex spine surgery, defined as surgery on 2 or more thoracic and/or lumbar spine levels. Institutional clinical management protocols can be constructed based on the elements included in these clinical practice guidelines, and the evidence presented.

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Perception of depth is based on a variety of cues, with binocular disparity and motion parallax generally providing more precise depth information than pictorial cues. Much is known about how neurons in visual cortex represent depth from binocular disparity or motion parallax, but little is known about the joint neural representation of these depth cues. We recently described neurons in the middle temporal (MT) area that signal depth sign (near vs far) from motion parallax; here, we examine whether and how these neurons also signal depth from binocular disparity. We find that most MT neurons in rhesus monkeys (Macaca Mulatta) are selective for depth sign based on both disparity and motion parallax cues. However, the depth-sign preferences (near or far) are not always aligned: 56% of MT neurons have matched depth-sign preferences ("congruent" cells) whereas the remaining 44% of neurons prefer near depth from motion parallax and far depth from disparity, or vice versa ("opposite" cells). For congruent cells, depth-sign selectivity increases when disparity cues are added to motion parallax, but this enhancement does not occur for opposite cells. This suggests that congruent cells might contribute to perceptual integration of depth cues. We also found that neurons are clustered in MT according to their depth tuning based on motion parallax, similar to the known clustering of MT neurons for binocular disparity. Together, these findings suggest that area MT is involved in constructing a representation of 3D scene structure that takes advantage of multiple depth cues available to mobile observers.

IntroductionAside from direct effects on neurotransmission, inhaled and intravenous anesthetics have immunomodulatory properties. In vitro and mouse model studies suggest that propofol inhibits, while isoflurane increases, neuroinflammation. If these findings translate to humans, they could be clinically important since neuroinflammation has detrimental effects on neurocognitive function in numerous disease states.Materials and methodsTo examine whether propofol and isoflurane differentially modulate neuroinflammation in humans, cytokines were measured in a secondary analysis of cerebrospinal fluid (CSF) samples from patients prospectively randomized to receive anesthetic maintenance with propofol vs. isoflurane (registered with , identifier NCT01640275). We measured CSF levels of EGF, eotaxin, G-CSF, GM-CSF, IFN-α2, IL-1RA, IL-6, IL-7, IL-8, IL-10, IP-10, MCP-1, MIP-1α, MIP-1β, and TNF-α before and 24 h after intracranial surgery in these study patients.ResultsAfter Bonferroni correction for multiple comparisons, we found significant increases from before to 24 h after surgery in G-CSF, IL-10, IL-1RA, IL-6, IL-8, IP-10, MCP-1, MIP-1α, MIP-1β, and TNF-α. However, we found no difference in cytokine levels at baseline or 24 h after surgery between propofol- (n = 19) and isoflurane-treated (n = 21) patients (p > 0.05 for all comparisons). Increases in CSF IL-6, IL-8, IP-10, and MCP-1 levels directly correlated with each other and with postoperative CSF elevations in tau, a neural injury biomarker. We observed CSF cytokine increases up to 10-fold higher after intracranial surgery than previously reported after other types of surgery.DiscussionThese data clarify the magnitude of neuroinflammation after intracranial surgery, and raise the possibility that a coordinated neuroinflammatory response may play a role in neural injury after surgery.