Gastrectomy mortality in Australia.

BACKGROUND: Despite advances in medical management and endoscopic therapy, gastrectomy remains an important yet high-risk procedure for a range of benign and malignant upper gastrointestinal pathologies. No study has previously analysed Australian gastrectomy perioperative mortality rate (POMR). This retrospective, population-based cohort study was conducted to determine the Australian national gastrectomy POMR, allowing state-based and regional trends and outcomes to be assessed. METHODS: Logistic regression models were compared using de-identified procedural data between 1 July 2005 and 30 June 2017 from the Australian Institute of Health and Welfare. Codes relating to total and subtotal gastrectomy contained in the Australian Classification of Health Interventions were used to extract patient data. Mortality rates were risk adjusted for age and gender. Temporal trends and differences between states/territories and regions were investigated. RESULTS: The national average POMR throughout the study period was 2.1%. For subtotal gastrectomy, the national mean POMR was 1.1%, decreasing from 2.7% (2005) to 1.3% (2017). For total gastrectomy, the national mean POMR was 2.8%, decreasing from 3.3% (2005) to 1.7% (2017). POMR significantly reduced over time without variation between states or regions. Procedure volume steadily reduced in rural centres with a concomitant increase in metropolitan centres over time. CONCLUSION: Pleasingly, the Australian gastrectomy POMR is favourable when compared to international cohorts. Improved outcomes were consistent between states and territories, and metropolitan and regional centres. Progressive metropolitan centralization of gastrectomy was demonstrated without evidence of improved outcomes.

Neuromodulation and Individuality.

Within populations, individuals show a variety of behavioral preferences, even in the absence of genetic or environmental variability. Neuromodulators affect these idiosyncratic preferences in a wide range of systems, however, the mechanism(s) by which they do so is unclear. I review the evidence supporting three broad mechanisms by which neuromodulators might affect variability in idiosyncratic behavioral preference: by being a source of variability directly upstream of behavior, by affecting the behavioral output of a circuit in a way that masks or accentuates underlying variability in that circuit, and by driving plasticity in circuits leading to either homeostatic convergence toward a given behavior or divergence from a developmental setpoint. I find evidence for each of these mechanisms and propose future directions to further understand the complex interplay between individual variability and neuromodulators.

The associations of factors with previous alcohol use in the Northern Territory compared to other states - an observational study.

BACKGROUND: Data on previous alcohol use in surgical patients who died in the Northern Territory (NT) are lacking and have important public health implications. METHODS: The prevalence of previous alcohol (ab)use among surgical patients who died (n=560) was assessed in patients within the Northern Territory and the remainder of Australia (n=28,245) over nine years. RESULTS: The likelihood of previous alcohol use (21.4%; 120 of 560), was the outcome measured and was higher in the Northern Territory than outside it (5.9%; 1,660 of 28,245). Factors associated with the outcome of previous alcohol use were: male gender (aOR 1.6); Aboriginal and Torres Strait Islander status (aOR 2.0); liver disease (aOR 7.8); comorbidities (aOR 2.5); and trauma (aOR 1.1), in both the Northern Territory (aOR 11.5) and all Australia (aOR 7.8). In the Northern Territory, alcohol use was high in both Aboriginal and Torres Strait Islander people (31%) and non-Aboriginal and Torres Strait Islander (16%) people (p=0.316). CONCLUSION: Of surgical patients who died, the likelihood of being a previous alcohol user was double in the Northern Territory as opposed to other states. Alcohol misuse is widespread across all groups in the Northern Territory. Implications for public health: Previous alcohol (ab)use is a negative factor for survival in any racial group.

Elective abdominal wall hernia repair surgical mortality-A systematic review of the literature and peer review of mortality in Australia.

BACKGROUND: This study systematically reviewed the literature regarding perioperative mortality in human adults undergoing elective surgical abdominal wall hernia repair, including an audit of the Royal Australasian College of Surgeons (RACS) Australian and New Zealand Audit of Surgical Mortality (ANZASM) database. METHODS: A systematic review was conducted in accordance with PRISMA guidelines for the reporting of systematic reviews and meta-analysis of observational studies. Cochrane Library, PubMed, MEDLINE and Embase database searches and data extraction were conducted from June 1979 to October 2019. Statistical analysis was undertaken utilising denominator values for elective hernia procedures derived from the Australian Institute of Health and Welfare (AIHW) data. Risk-adjusted perioperative mortality rates for the relevant procedures were also produced, using a binary logistic regression for the risk adjustment. RESULTS: Through systematic review of the literature, it was established that the overall reported perioperative mortality in human adults undergoing elective surgical abdominal wall hernia repair was low (0.1%-0.5%). Using ANZASM and AIHW data, the calculated risk-adjusted mortality rate for Australian patients was found to be significantly lower (0.04%-0.06%, p < 0.001). CONCLUSION: The risk-adjusted mortality rate for elective abdominal wall hernia surgery in Australia is very low and compares favourably to international cohorts. Despite low absolute numbers, the factors which were most significantly associated with increased perioperative mortality in patients undergoing elective surgical abdominal wall hernia repair were increased age, cardiorespiratory co-morbidity and incisional hernia repair.

Decoding Neural Responses to Motion-in-Depth Using EEG.

Two stereoscopic cues that underlie the perception of motion-in-depth (MID) are changes in retinal disparity over time (CD) and interocular velocity differences (IOVD). These cues have independent spatiotemporal sensitivity profiles, depend upon different low-level stimulus properties, and are potentially processed along separate cortical pathways. Here, we ask whether these MID cues code for different motion directions: do they give rise to discriminable patterns of neural signals, and is there evidence for their convergence onto a single "motion-in-depth" pathway? To answer this, we use a decoding algorithm to test whether, and when, patterns of electroencephalogram (EEG) signals measured from across the full scalp, generated in response to CD- and IOVD-isolating stimuli moving toward or away in depth can be distinguished. We find that both MID cue type and 3D-motion direction can be decoded at different points in the EEG timecourse and that direction decoding cannot be accounted for by static disparity information. Remarkably, we find evidence for late processing convergence: IOVD motion direction can be decoded relatively late in the timecourse based on a decoder trained on CD stimuli, and vice versa. We conclude that early CD and IOVD direction decoding performance is dependent upon fundamentally different low-level stimulus features, but that later stages of decoding performance may be driven by a central, shared pathway that is agnostic to these features. Overall, these data are the first to show that neural responses to CD and IOVD cues that move toward and away in depth can be decoded from EEG signals, and that different aspects of MID-cues contribute to decoding performance at different points along the EEG timecourse.

Monetary feedback modulates performance and electrophysiological indices of belief updating in reward learning.

Belief updating entails the incorporation of new information about the environment into internal models of the world. Bayesian inference is the statistically optimal strategy for performing belief updating in the presence of uncertainty. An important open question is whether the use of cognitive strategies that implement Bayesian inference is dependent upon motivational state and, if so, how this is reflected in electrophysiological signatures of belief updating in the brain. Here, we recorded the EEG of participants performing a simple reward learning task with both monetary and nonmonetary instructive feedback conditions. Our aim was to distinguish the influence of the rewarding properties of feedback on belief updating from the information content of the feedback itself. A Bayesian updating model allowed us to quantify different aspects of belief updating across trials, including the size of belief updates and the uncertainty of beliefs. Faster learning rates were observed in the monetary feedback condition compared to the instructive feedback condition, while belief updates were generally larger, and belief uncertainty smaller, with monetary compared to instructive feedback. Larger amplitudes in the monetary feedback condition were found for three ERP components: the P3a, the feedback-related negativity, and the late positive potential. These findings suggest that motivational state influences inference strategies in reward learning, and this is reflected in the electrophysiological correlates of belief updating.

Asymmetries between achromatic and chromatic extraction of 3D motion signals.

Motion in depth (MID) can be cued by high-resolution changes in binocular disparity over time (CD), and low-resolution interocular velocity differences (IOVD). Computational differences between these two mechanisms suggest that they may be implemented in visual pathways with different spatial and temporal resolutions. Here, we used fMRI to examine how achromatic and S-cone signals contribute to human MID perception. Both CD and IOVD stimuli evoked responses in a widespread network that included early visual areas, parts of the dorsal and ventral streams, and motion-selective area hMT+. Crucially, however, we measured an interaction between MID type and chromaticity. fMRI CD responses were largely driven by achromatic stimuli, but IOVD responses were better driven by isoluminant S-cone inputs. In our psychophysical experiments, when S-cone and achromatic stimuli were matched for perceived contrast, participants were equally sensitive to the MID in achromatic and S-cone IOVD stimuli. In comparison, they were relatively insensitive to S-cone CD. These findings provide evidence that MID mechanisms asymmetrically draw on information in precortical pathways. An early opponent motion signal optimally conveyed by the S-cone pathway may provide a substantial contribution to the IOVD mechanism.

Sensitivity to Velocity- and Disparity-Based Cues to Motion-In-Depth With and Without Spared Stereopsis in Binocular Visual Impairment.

Purpose: Two binocular sources of information serve motion-in-depth (MID) perception: changes in disparity over time (CD), and interocular velocity differences (IOVD). While CD requires the computation of small spatial disparities, IOVD could be computed from a much lower-resolution signal. IOVD signals therefore might still be available under conditions of binocular vision impairment (BVI) with limited or no stereopsis, for example, amblyopia. Methods: Sensitivity to CD and IOVD was measured in adults who had undergone therapy to correct optical misalignment or amblyopia in childhood (n = 16), as well as normal vision controls with good stereoacuity (n = 8). Observers discriminated the interval containing a smoothly oscillating MID "test" stimulus from a "control" stimulus in a two-interval forced choice paradigm. Results: Of the BVI observers with no static stereoacuity (n = 9), one displayed evidence for sensitivity to IOVD only, while there was otherwise no sensitivity for either CD or IOVD in the group. Generally, BVI observers with measurable stereoacuity (n = 7) displayed a pattern resembling the control group: showing a similar sensitivity for both cues. A neutral density filter placed in front of the fixing eye in a subset of BVI observers did not improve performance. Conclusions: In one BVI observer there was preserved sensitivity to IOVD but not CD, though overall only those BVI observers with at least gross stereopsis were able to detect disparity- or velocity-based cues to MID. The results imply that these logically distinct information sources are somehow coupled, and in some cases BVI observers with no stereopsis may still retain sensitivity to IOVD.

Directional Limits on Motion Transparency Assessed Through Colour-Motion Binding.

Motion-defined transparency is the perception of two or more distinct moving surfaces at the same retinal location. We explored the limits of motion transparency using superimposed surfaces of randomly positioned dots defined by differences in motion direction and colour. In one experiment, dots were red or green and we varied the proportion of dots of a single colour that moved in a single direction ('colour-motion coherence') and measured the threshold direction difference for discriminating between two directions. When colour-motion coherences were high (e.g., 90% of red dots moving in one direction), a smaller direction difference was required to correctly bind colour with direction than at low coherences. In another experiment, we varied the direction difference between the surfaces and measured the threshold colour-motion coherence required to discriminate between them. Generally, colour-motion coherence thresholds decreased with increasing direction differences, stabilising at direction differences around 45°. Different stimulus durations were compared, and thresholds were higher at the shortest (150 ms) compared with the longest (1,000 ms) duration. These results highlight different yet interrelated aspects of the task and the fundamental limits of the mechanisms involved: the resolution of narrowly separated directions in motion processing and the local sampling of dot colours from each surface.

Probing the Characteristics of Colour-Motion Binding and Its Dependence on Persistent Surface Segregation.

Identifying the spatial and temporal characteristics of visual feature binding is a remaining challenge in the science of perception. Within the feature-binding literature, disparate findings have suggested the existence of more than one feature-binding mechanism with differing temporal resolutions. For example, one surprising result is that temporal alternations between two different feature pairings of colour and motion (e.g., orange dots moving left with blue dots moving right) support accurate conjunction discrimination at alternation frequencies of around 10 Hz and greater. However, at lower alternation frequencies around 5 Hz, conjunction discrimination falls to chance. To further investigate this effect, we present two experiments that probe the stimulus characteristics that facilitate or impede feature binding. Using novel manipulations of random dot kinematograms, we identify that facilitating surface representations through temporal integration can enable accurate conjunction discrimination at both intermediate and high alternation frequencies. We also offer a neurally plausible evidence accumulator model to describe these results, removing the need to suggest multiple binding mechanisms acting at different timescales. In effect, we propose a single, flexible binding process, whereby the relatively low temporal resolution for binding features can be circumvented by extracting them from rapidly formed and persistent surface representations.

Transparent surface segregation enables visual feature binding in rapidly alternating displays.

Visual feature binding-the mechanism by which our typically coherent and unified perceptual experience arises from distributed neural representations-is the source of much intrigue in the neuroscience of perception. Surprisingly, feature binding can occur in rapidly alternating displays of color-orientation combinations (e.g., rightward-orange, leftward-blue). However, we found that when the angular separation between orientations is reduced, binding is selectively impaired at temporal alternation frequencies around 5 Hz. To isolate the mechanisms involved, we devised a novel display in which color-orientation conjunction information was distributed temporally over two checkered stimuli and was perceptually discriminable only within an intermediate range of temporal frequencies (7.5-15 Hz). We propose that accurate color-orientation judgments at frequencies exceeding 5 Hz depend on the rapid formation of persistent surface representations that can be accessed by binding mechanisms, circumventing the latter's relatively low temporal resolution.

Orientation anisotropies in human primary visual cortex depend on contrast.

Orientation processing in visual cortex appears matched to the environment, such that larger neural populations are tuned to cardinal (horizontal/vertical) than oblique orientations. This may be manifested perceptually as a cardinal bias: poorer sensitivity to oblique compared to cardinal orientations (the "oblique effect"). However, a growing body of psychophysical data reveals the opposite pattern of anisotropy: a bias towards the oblique over the cardinal orientations (the "horizontal effect"), something matched by recent functional magnetic resonance imaging (fMRI) studies that have found an increased response to the oblique over the cardinal orientations in early visual cortex. This may reveal the operation of an efficient coding strategy optimised to the diet of orientations encountered during natural viewing. From consideration of coding efficiency, it might be expected that the anisotropies would change as the quality/strength of the oriented stimulus changes. In two experiments, fMRI response modulations were measured in retinotopically-defined human early visual cortex as a function of the contrast and orientation of sinusoidal gratings. Both experiments revealed a marked change in the V1 response from a cardinal (vertical) bias at low contrast to an oblique bias at high contrast. In Experiment 2, this was also apparent in areas V2 and V3. On average, there was no systematic "radial bias" (a preference for orientations aligned with the visual field meridian) in V1, although it was present in some individual subjects. The change in orientation anisotropies with contrast is consistent with an adaptive stimulus coding strategy in cortex that shifts according to the strength of the sensory inputs.

The basis of orientation decoding in human primary visual cortex: fine- or coarse-scale biases?

Orientation signals in human primary visual cortex (V1) can be reliably decoded from the multivariate pattern of activity as measured with functional magnetic resonance imaging (fMRI). The precise underlying source of these decoded signals (whether by orientation biases at a fine or coarse scale in cortex) remains a matter of some controversy, however. Freeman and colleagues (J Neurosci 33: 19695-19703, 2013) recently showed that the accuracy of decoding of spiral patterns in V1 can be predicted by a voxel's preferred spatial position (the population receptive field) and its coarse orientation preference, suggesting that coarse-scale biases are sufficient for orientation decoding. Whether they are also necessary for decoding remains an open question, and one with implications for the broader interpretation of multivariate decoding results in fMRI studies.

Determinants of motion response anisotropies in human early visual cortex: the role of configuration and eccentricity.

Anisotropies in the cortical representation of various stimulus parameters can reveal the fundamental mechanisms by which sensory properties are analysed and coded by the brain. One example is the preference for motion radial to the point of fixation (i.e. centripetal or centrifugal) exhibited in mammalian visual cortex. In two experiments, this study used functional magnetic resonance imaging (fMRI) to explore the determinants of these radial biases for motion in functionally-defined areas of human early visual cortex, and in particular their dependence upon eccentricity which has been indicated in recent reports. In one experiment, the cortical response to wide-field random dot kinematograms forming 16 different complex motion patterns (including centrifugal, centripetal, rotational and spiral motion) was measured. The response was analysed according to preferred eccentricity within four different eccentricity ranges. Response anisotropies were characterised by enhanced activity for centripetal or centrifugal patterns that changed systematically with eccentricity in visual areas V1-V3 and hV4 (but not V3A/B or V5/MT+). Responses evolved from a preference for centrifugal over centripetal patterns close to the fovea, to a preference for centripetal over centrifugal at the most peripheral region stimulated, in agreement with previous work. These effects were strongest in V2 and V3. In a second experiment, the stimuli were restricted to within narrow annuli either close to the fovea (0.75-1.88°) or further in the periphery (4.82-6.28°), in a way that preserved the local motion information available in the first experiment. In this configuration a preference for radial motion (centripetal or centrifugal) persisted but the dependence upon eccentricity disappeared. Again this was clearest in V2 and V3. A novel interpretation of the dependence upon eccentricity of motion anisotropies in early visual cortex is offered that takes into account the spatiotemporal "predictability" of the moving pattern. Such stimulus predictability, and its relationship to models of predictive coding, has found considerable support in recent years in accounting for a number of other perceptual and neural phenomena.

Determinants of the direction illusion: motion speed and dichoptic presentation interact to reveal systematic individual differences in sign.

When two fields of dots with different directions of movement are presented in tandem, the perceived direction of one is biased by the presence of the other. Although this ''direction illusion'' typically involves repulsion, with an exaggeration of the perceived angular difference in direction between the dot fields, attraction effects, where the perceived difference is reduced, have also been found under certain presentation conditions. Earlier literature has been inconsistent, and there is debate surrounding the nature of the interactions that facilitate the direction illusion, as well as whether they occur at a local or global stage of the motion processing hierarchy. Here we measured the operating characteristics of the direction illusion by parametrically varying inducer contrast and coherence while examining the effects of stimulus speed and dichoptic presentation. It was found that the magnitude and sign of the direction illusion differed substantially from earlier research. Furthermore, there appeared to be significant interindividual variability, with dichoptic presentation producing an attractive rather than repulsive direction illusion in some participants.

Motion-defined surface segregation in human visual cortex.

Surface segregation provides an efficient way to parse the visual scene for perceptual analysis. Here, we investigated the segregation of a bivectorial motion display into transparent surfaces through a psychophysical task and fMRI. We found that perceptual transparency correlated with neural activity in the early areas of the visual cortex, suggesting these areas may be involved in the segregation of motion-defined surfaces. Two oppositely rotating, uniquely colored random dot kinematograms (RDKs) were presented either sequentially or in a spatially interleaved manner, displayed at varying alternation frequencies. Participants reported the color and rotation direction pairing of the RDKs in the psychophysical task. The spatially interleaved display generated the percept of motion transparency across the range of frequencies tested, yielding ceiling task performance. At high alternation frequencies, performance on the sequential display also approached ceiling, indicative of perceived transparency. However, transparency broke down in lower alternation frequency sequential displays, producing performance close to chance. A corresponding pattern mirroring the psychophysical data was also evident in univariate and multivariate analyses of the fMRI BOLD activity in visual cortical areas V1, V2, V3, V3AB, hV4, and V5/MT+. Using gray RDKs, we found significant presentation by frequency interactions in most areas; differences in BOLD signal between presentation types were significant only at the lower alternation frequency. Multivariate pattern classification was similarly unable to discriminate between presentation types at the higher frequency. This study provides evidence that early visual cortex may code for motion-defined surface segregation, which in turn may enable perceptual transparency.

Human cortical and behavioral sensitivity to patterns of complex motion at eccentricity.

Complex patterns of image motion (contracting, expanding, rotating, and spiraling fields) are important in the coordination of visually guided behaviors. Whereas specialized detectors in monkey visual cortex show selectivity for particular patterns of complex motion, their representation in human visual cortex remains unclear. In the present study, functional magnetic resonance imaging (fMRI) was used to investigate the sensitivity of functionally defined regions of human visual cortex to parametrically modulated complex motion trajectories, coupled with complementary psychophysical testing. A unique stimulus design made it possible to disambiguate the neural responses and psychophysical sensitivity to complex motions per se from the distribution of local motions relative to the fovea, which are known to enhance cortical activity when presented radial to fixation. This involved presenting several small, separate motion fields in the periphery in a manner that distinguished them from global optic flow patterns. The patterns were morphed through complex motion space in a systematic time-locked fashion when presented in the scanner. Anisotropies were observed in the fMRI signal, marked by an enhanced response to expanding vs. contracting fields, even in early visual cortex. Anisotropies in the psychophysical sensitivity measures followed a similar pattern that was correlated with activity in areas hV4, V5/MT, and MST. This represents the first systematic examination of complex motion perception at both a behavioral and neural level in human observers. The characteristic processing anisotropy revealed in both data sets can inform models of complex motion processing, particularly with respect to computations performed in early visual cortex.

Information processing bottlenecks in macaque posterior parietal cortex: an attentional blink?

When two brief stimuli are presented in rapid succession, our ability to attend and recognize the second stimulus is impaired if our attentional resources are devoted to processing the first. Such inability (termed the "attentional blink" in human studies) arises around 200-500 ms following the onset of the first stimulus. We trained two monkeys on a delayed-match-to-sample task where both the location and orientation of two successively presented grating patches had to be matched. When the delay between the two gratings was varied, monkey's behavioral performance (d') was affected in a way that was analogous to the attentional blink in humans. Furthermore, a subset of neurons in the monkey's lateral intraparietal area, known to be crucial in the control of attention, closely followed the variation in d', even on occasions when d' followed an atypical pattern. Our results provide the first behavioral demonstration of an attentional bottleneck in the macaque of a type similar to the human attentional blink as well as a possible single-neuron correlate of the phenomenon.

Colour misbinding during motion rivalry.

When two dissimilar colours are displayed to the two eyes at overlapping retinal locations, binocular rivalry typically results: a fluctuating struggle for perceptual dominance of each eye's stimulus. We found instead that isoluminant counter-rotating patterns consisting of coloured and achromatic portions can promote an illusory colour 'misbinding', where the colours from both eyes were perceived within a single rotating pattern. The achromatic portion of one rotating pattern thus appeared to take on the colour of the other, oppositely rotating pattern. The results suggest that the neural mechanisms of colour binding can operate even while representations of the same patterns' motions are undergoing rivalry, and support the idea that rivalry can occur in isolation within the motion system.

Distribution and physiological effects of B-type allatostatins (myoinhibitory peptides, MIPs) in the stomatogastric nervous system of the crab Cancer borealis.

The crustacean stomatogastric ganglion (STG) is modulated by a large number of amines and neuropeptides that are found in descending pathways from anterior ganglia or reach the STG via the hemolymph. Among these are the allatostatin (AST) B types, also known as myoinhibitory peptides (MIPs). We used mass spectrometry to determine the sequences of nine members of the AST-B family of peptides that were found in the stomatogastric nervous system of the crab Cancer borealis. We raised an antibody against Cancer borealis allatostatin-B1 (CbAST-B1; VPNDWAHFRGSWa) and used it to map the distribution of CbAST-B1-like immunoreactivity (-LI) in the stomatogastric nervous system. CbAST-B1-LI was found in neurons and neuropil in the commissural ganglia (CoGs), in somata in the esophageal ganglion (OG), in fibers in the stomatogastric nerve (stn), and in neuropilar processes in the STG. CbAST-B1-LI was blocked by preincubation with 10(-6) M CbAST-B1 and was partially blocked by lower concentrations. Electrophysiological recordings of the effects of CbAST-B1, CbAST-B2, and CbAST-B3 on the pyloric rhythm of the STG showed that all three peptides inhibited the pyloric rhythm in a state-dependent manner. Specifically, all three peptides at 10(-8) M significantly decreased the frequency of the pyloric rhythm when the initial frequency of the pyloric rhythm was below 0.6 Hz. These data suggest important neuromodulatory roles for the CbAST-B family in the stomatogastric nervous system.