Assessing dissolution in the tests of planktonic foraminifera using computed tomography (CT): potential for improving paleoceanographic reconstructions

An empirical dissolution index for planktonic foraminifera, XDX, was established based on the appearance of tests in computed tomography (CT) scans (Chapter 4). Calibrations between XDX and Delta[CO32-], Delta-mass (mass lost to dissolution) and Delta Mg/Ca (reduction in Mg/Ca due to dissolution) allow estimates of deep ocean Delta[CO32-] and also dissolution-corrected test mass and Mg/Ca (Chapter 5). Delta[CO32-] reconstructed for the deep (4,157 m) tropical western Indian Ocean (WIND28K) increased by ~25 µmol/kg over Termination I and ~15 µmol/kg over Termination II while dissolution maxima coincided with transitions to colder stages (Chapter 6). XDX-corrected Mg/Ca-derived SSTs were coolest during MIS 3. Minimum test mass in the corrected record coincided with the lowest temperatures. Comparison of two methods of cleaning foraminiferal tests from a depth transect (Chapter 7) found no offset in Mg/Ca between methods for G. sacculifer and P. obliquiloculata. Mg/Ca was decreased by reductive cleaning by ~4% for G. ruber and ~10% for N. dutertrei. Offset in Mg/Ca between the two methods was insensitive to preservation state

Distinct responses of planktonic foraminiferal B/Ca to dissolution on seafloor

We have measured B/Ca in four core-top planktonic foraminiferal species (Globigerinoides ruber (white), Globigerinoides sacculifer (without final sac-like chamber), Neogloboquadrina dutertrei, and Pulleniatina obliquiloculata) from three depth transects (the Caribbean Sea, the southwestern Indian Ocean, and the Ontong Java Plateau) to evaluate the effect of dissolution on planktonic foraminiferal B/Ca. At each transect, G. ruber (w) and G. sacculifer (w/o sac) show decreasing B/Ca with increasing water depth. This decrease in B/Ca is accompanied with decreases in shell weights, Mg/Ca, and bottom water calcite saturation state. This indicates a postdepositional dissolution effect on B/Ca in these two species. The strong correlation observed between changes in B/Ca and bottom water calcite saturation state offers an approach to correcting for the dissolution bias. By contrast, B/Ca in N. dutertrei and P. obliquiloculata remains unchanged along depth transects, although shell weights and Mg/Ca display significant declines. Overall, our core-top results suggest species-specific dissolution effects on B/Ca in different planktonic foraminiferal species

Failure to regulate: counterproductive recruitment of top-down prefrontal-subcortical circuitry in major depression

Although depressed mood is a normal occurrence in response to adversity in all individuals, what distinguishes those who are vulnerable to major depressive disorder (MDD) is their inability to effectively regulate negative mood when it arises. Investigating the neural underpinnings of adaptive emotion regulation and the extent to which such processes are compromised in MDD may be helpful in understanding the pathophysiology of depression. We report results from a functional magnetic resonance imaging study demonstrating left-lateralized activation in the prefrontal cortex (PFC) when downregulating negative affect in nondepressed individuals, whereas depressed individuals showed bilateral PFC activation. Furthermore, during an effortful affective reappraisal task, nondepressed individuals showed an inverse relationship between activation in left ventrolateral PFC and the amygdala that is mediated by the ventromedial PFC (VMPFC). No such relationship was found for depressed individuals, who instead show a positive association between VMPFC and amygdala. Pupil dilation data suggest that those depressed patients who expend more effort to reappraise negative stimuli are characterized by accentuated activation in the amygdala, insula, and thalamus, whereas nondepressed individuals exhibit the opposite pattern. These findings indicate that a key feature underlying the pathophysiology of major depression is the counterproductive engagement of right prefrontal cortex and the lack of engagement of left lateral-ventromedial prefrontal circuitry important for the downregulation of amygdala responses to negative stimuli

Calcite saturation, foraminiferal test mass, and Mg/Ca-based temperatures dissolution corrected using XDX—A 150 ka record from the western Indian Ocean

A record of deep-sea calcite saturation inline image, derived from X-ray computed tomography-based foraminifer dissolution index, XDX, was constructed for the past 150 ka for a core from the deep (4157 m) tropical western Indian Ocean. G. sacculifer and N. dutertrei recorded a similar dissolution history, consistent with the process of calcite compensation. Peaks in calcite saturation (∼15 µmol/kg higher than the present-day value) occurred during deglaciations and early in MIS 3. Dissolution maxima coincided with transitions to colder stages. The mass record of G. sacculifer better indicated preservation than did that of N. dutertrei or G. ruber. Dissolution-corrected Mg/Ca-derived SST records, like other SST records from marginal Indian Ocean sites, showed coolest temperatures of the last 150 ka in early MIS 3, when mixed layer temperatures were ∼4°C lower than present SST. Temperatures recorded by N. dutertrei showed the thermocline to be ∼4°C colder in MIS 3 compared to the Holocene (8 ka B.P.)

Revised masses of dust and gas of SLUGS FIR bright galaxies based on a recent CO survey

Recent CO measurements of an essentially complete sub-sample of galaxies from the SCUBA Local Universe Survey (SLUGS) are used to examine their implications for dust and gas masses in this sample. Estimates of dust masses are affected by a contribution to the SCUBA brightness measurements by CO(3-2) emission, and molecular gas masses by the use of a modified value of the CO-to-H_2 conversion factor X. The average dust mass is reduced by 25-38 per cent, which has no bearing on earlier conclusions concering the shapes of the dust mass luminosity function derived from the SLUGS. The value of X found from the CO survey, when applied together with the reduction in dust masses, leads to lower estimates for the mean gas-to-dust mass ratios, where the gas includes both H_2 and HI. For the CO sample, the mean global ratio is reduced from approximately 430 to about 320-360, but is further reduced to values near 50 when applied to the nuclear regions relevant to the CO observations. We discuss these results and suggest that the differences between the nuclear and outer regions may simply reflect differences in metallicity or the existence of considerable amounts of unobserved cold dust in the outer regions of these galaxiies.Comment: 18 pages, 2 tables, 4 figures, accepted for publication in MNRA

Individual Differences in Amygdala and Ventromedial Prefrontal Cortex Activity are Associated with Evaluation Speed and Psychological Well-being

Using functional magnetic resonance imaging, we examined whether individual differences in amygdala activation in response to negative relative to neutral information are related to differences in the speed with which such information is evaluated, the extent to which such differences are associated with medial prefrontal cortex function, and their relationship with measures of trait anxiety and psychological well-being (PWB). Results indicated that faster judgments of negative relative to neutral information were associated with increased left and right amygdala activation. In the prefrontal cortex, faster judgment time was associated with relative decreased activation in a cluster in the ventral anterior cingulate cortex (ACC, BA 24). Furthermore, people who were slower to evaluate negative versus neutral information reported higher PWB. Importantly, higher PWB was strongly associated with increased activation in the ventral ACC for negative relative to neutral information. Individual differences in trait anxiety did not predict variation in judgment time or in amygdala or ventral ACC activity. These findings suggest that people high in PWB effectively recruit the ventral ACC when confronted with potentially aversive stimuli, manifest reduced activity in subcortical regions such as the amygdala, and appraise such information as less salient as reflected in slower evaluative speed

Amygdala and ventromedial prefrontal cortex are inversely coupled during regulation of negative affect and predict the diurnal pattern of cortisol secretion among older adults

Among younger adults, the ability to willfully regulate negative affect, enabling effective responses to stressful experiences, engages regions of prefrontal cortex (PFC) and the amygdala. Because regions of PFC and the amygdala are known to influence the hypothalamic-pituitary-adrenal axis, here we test whether PFC and amygdala responses during emotion regulation predict the diurnal pattern of salivary cortisol secretion. We also test whether PFC and amygdala regions are engaged during emotion regulation in older (62- to 64-year-old) rather than younger individuals. We measured brain activity using functional magnetic resonance imaging as participants regulated (increased or decreased) their affective responses or attended to negative picture stimuli. We also collected saliva samples for 1 week at home for cortisol assay. Consistent with previous work in younger samples, increasing negative affect resulted in ventral lateral, dorsolateral, and dorsomedial regions of PFC and amygdala activation. In contrast to previous work, decreasing negative affect did not produce the predicted robust pattern of higher PFC and lower amygdala activation. Individuals demonstrating the predicted effect (decrease s attend in the amygdala), however, exhibited higher signal in ventromedial prefrontal cortex (VMPFC) for the same contrast. Furthermore, participants displaying higher VMPFC and lower amygdala signal when decreasing compared with the attention control condition evidenced steeper, more normative declines in cortisol over the course of the day. Individual differences yielded the predicted link between brain function while reducing negative affect in the laboratory and diurnal regulation of endocrine activity in the home environment

Grey matter changes can improve the prediction of schizophrenia in subjects at high risk

BACKGROUND: We hypothesised that subjects at familial high risk of developing schizophrenia would have a reduction over time in grey matter, particularly in the temporal lobes, and that this reduction may predict schizophrenia better than clinical measurements. METHODS: We analysed magnetic resonance images of 65 high-risk subjects from the Edinburgh High Risk Study sample who had two scans a mean of 1.52 years apart. Eight of these 65 subjects went on to develop schizophrenia an average of 2.3 years after their first scan. RESULTS: Changes over time in the inferior temporal gyrus gave a 60% positive predictive value (likelihood ratio >10) of developing schizophrenia compared to the overall 13% risk in the cohort as a whole. CONCLUSION: Changes in grey matter could be used as part of a predictive test for schizophrenia in people at enhanced risk for familial reasons, particularly for positive predictive power, in combination with other clinical and cognitive predictive measures, several of which are strong negative predictors. However, because of the limited number of subjects, this test requires independent replication to confirm its validity

Skin conductance responses indicate children are physiologically aroused by their favourite branded food and drink products

Children’s favourite food and beverage brands use various tactics to foster positive associations and loyalty. This brand-consumer dynamic is frequently influenced by the use of implicit techniques and emotional appeals. Few studies have used physiological methods to examine the connections that brands build with children and the influence this has on their automatic responses. These techniques are potentially less prone to bias than behavioural or cognitive methods. This is the first study to explore the implicit response that children have to images of their favourite food and beverage brands using skin conductance responses as a marker of arousal. Australian children aged 8–11 years (n = 48) were recruited. Images of the participants’ favourite branded food and beverage products, alongside images of the same products unpackaged, their family and friends, and neutral objects were presented in a randomised order with a standard timed interval between images. Children were significantly more aroused by branded images of their favourite food and beverage products than by their unpackaged counterparts (p < 0.042, d = 0.4). The physiological response to the branded products was similar to the response to the children’s family and friends (p = 0.900, d = −0.02). These findings suggest that children may have an implicit connection to their favourite branded products