Neural differentiation is moderated by age in scene- but not face-selective cortical regions

The aging brain is characterized by neural dedifferentiation, an apparent decrease in the functional selectivity of category-selective cortical regions. Age-related reductions in neural differentiation have been proposed to play a causal role in cognitive aging. Recent findings suggest, however, that age-related dedifferentiation is not equally evident for all stimulus categories and, additionally, that the relationship between neural differentiation and cognitive performance is not moderated by age. In light of these findings, in the present experiment, younger and older human adults (males and females) underwent fMRI as they studied words paired with images of scenes or faces before a subsequent memory task. Neural selectivity was measured in two scene-selective (parahippocampal place area (PPA) and retrosplenial cortex (RSC)] and two face-selective [fusiform face area (FFA) and occipital face area (OFA)] regions using both a univariate differentiation index and multivoxel pattern similarity analysis. Both methods provided highly convergent results, which revealed evidence of age-related reductions in neural dedifferentiation in scene-selective but not face-selective cortical regions. Additionally, neural differentiation in the PPA demonstrated a positive, age-invariant relationship with subsequent source memory performance (recall of the image category paired with each recognized test word). These findings extend prior findings suggesting that age-related neural dedifferentiation is not a ubiquitous phenomenon, and that the specificity of neural responses to scenes is predictive of subsequent memory performance independently of age

The relationship between age, neural differentiation, and memory performance

Healthy aging is associated with decreased neural selectivity (dedifferentiation) in category-selective cortical regions. This finding has prompted the suggestion that dedifferentiation contributes to age-related cognitive decline. Consistent with this possibility, dedifferentiation has been reported to negatively correlate with fluid intelligence in older adults. Here, we examined whether dedifferentiation is associated with performance in another cognitive domain—episodic memory—that is also highly vulnerable to aging. Given the proposed role of dedifferentiation in age-related cognitive decline, we predicted there would be a stronger link between dedifferentiation and episodic memory performance in older than in younger adults. Young (18–30 years) and older (64–75 years) male and female humans underwent fMRI scanning while viewing images of objects and scenes before a subsequent recognition memory test. We computed a differentiation index in two regions of interest (ROIs): parahippocampal place area (PPA) and lateral occipital complex (LOC). This index quantified the selectivity of the BOLD response to preferred versus nonpreferred category of an ROI (scenes for PPA, objects for LOC). The differentiation index in the PPA, but not the LOC, was lower in older than in younger adults. Additionally, the PPA differentiation index predicted recognition memory performance for the studied items. This relationship was independent of and not moderated by age. The PPA differentiation index also predicted performance on a latent “fluency” factor derived from a neuropsychological test battery; this relationship was also age invariant. These findings suggest that two independent factors, one associated with age, and the other with cognitive performance, influence neural differentiation

Very high strain rate deformation twinning behaviour of Ti–6Al–4V

Equiaxed fine-grained and coarse-grained samples of h.c.p. α phase Ti–6Al–4V with trace amounts of retained b.c.c. β phase were ballistically tested at room temperature. The deformed microstructures were characterised by electron back scattered diffraction. The extensive deformation twinning observed in the α phase in both samples was limited to the {1 0 -1 2} and {1 1 -2 1} tensile twinning modes. These two deformation twinning types have very different morphologies: thin {1 1 -2 1} deformation twins span multiple α phase grain boundaries, while the wider {1 0 -1 2} deformation twins are usually limited to individual grains, reorienting almost entire grains to a twinned orientation. Both {1 0 -1 2} and {1 1 -2 1} deformation twins are able to propagate across low angle α lath boundaries, but only the {1 1 -2 1} deformation twinning types can propagate across high angle α grain boundaries.This work was supported by the Rolls-Royce plc/EPSRC strategic partnership under EP/H022309/1

Modulation of Oscillatory Power and Connectivity in the Human Posterior Cingulate Cortex Supports the Encoding and Retrieval of Episodic Memories

Existing data from noninvasive studies have led researchers to posit that the posterior cingulate cortex (PCC) supports mnemonic processes: It exhibits degeneration in memory disorders, and fMRI investigations have demonstrated memory-related activation principally during the retrieval of memory items. Despite these data, the role of the PCC in episodic memory has received only limited treatment using the spatial and temporal precision of intracranial EEG, with previous analyses focused on item retrieval. Using data gathered from 21 human participants who underwent stereo-EEG for seizure localization, we characterized oscillatory patterns in the PCC during the encoding and retrieval of episodic memories. We identified a subsequent memory effect during item encoding characterized by increased gamma band oscillatory power and a low-frequency power desynchronization. Fourteen participants had stereotactic electrodes located simultaneously in the hippocampus and PCC, and with these unique data, we describe connectivity changes between these structures that predict successful item encoding and that precede item retrieval. Oscillatory power during retrieval matched the pattern we observed during encoding, with low-frequency (below 15 Hz) desynchronization and a gamma band (especially high gamma, 70–180 Hz) power increase. Encoding is characterized by synchrony between the hippocampus and PCC, centered at 3 Hz, consistent with other observations of properties of this oscillation akin to those for rodent theta activity. We discuss our findings in light of existing theories of episodic memory processing, including the information via desynchronization hypothesis and retrieved context theory, and examine how our data fit with existing theories for the functional role of the PCC. These include a postulated role for the PCC in modulating internally directed attention and for representing or integrating contextual information for memory items

The stability of food intake between adolescence and adulthood: a 21-year follow-up

Studies of the diet of adolescents in the UK demonstrate that dietary habits known to be detrimental to health in adulthood are evident at an early age. For example, Gregory et al (2000) found 4-18 year olds in the UK to have a frequent consumption of fatty and sugary foods and low consumption of fruit and vegetables. Concerns have therefore been expressed regarding the diet of children and adolescents and the continuation of these dietary habits into adulthood (HEA, 1995; Gaziano, 1998). This study aimed to investigate the extent to which these concerns may be justified by determining the stability of food intake of a group of adolescents followed up 21 years later in adulthood. The investigation involved 202 individuals from whom dietary data were collected in 1979-80 (mean age 11.6 years) (Hackett et al. 1984) and again in 2000-1 (mean age 32.5 years). Dietary data were collected at both time-points using two 3 d estimated food diaries followed by an interview to determine portion sizes using the method considered most appropriate at the time, i.e. calibrated food models in 1979-80 and a photographic food atlas (Nelson et al. 1997) in 2000-1. Foods consumed were allocated to one, or a combination of, the five food groups of the ‘Balance of Good Health’ food selection guide (HEA, 1994) according to Gatenby et al. (1995). The weight of food eaten from each of the five food groups was calculated (percentage of total weight of food consumed) and Pearson correlation coefficients generated to provide an estimate of the stability of food intake. The HEA guide advises that a balanced diet should consist of around 33% fruit and vegetables, 33% bread, other cereals and potatoes, 8% foods containing fat and/or sugar, 12% meat, fish and alternatives and 15% milk and dairy products (Gatenby et al. 1995). A shift in the group’s food intake towards the recommendations had occurred with age, most notably with a decrease in foods containing fat and/or sugar and an increase in fruit and vegetables. Nevertheless, at both ages, intakes of foods containing fat and/or sugar, meat, fish and alternatives were higher, and fruit, vegetables, bread, other cereals and potatoes lower than currently recommended. In addition, although there was significant evidence of tracking of relative intake of bread, cereals and potatoes (P<0.01), fruit and vegetables (P<0.01), and meat, fish and alternatives (P=0.02) between 11.6 and 32.5 years, the correlations were not strong. In conclusion, food intake patterns had changed considerably from early adolescence through to adulthood in a direction more in line with the current recommendations. The predictive value of an adolescent’s food intake of their intake in adulthood was found to be significant, but not strong. Further investigations will consider the extent to which this is influenced by factors such as social class, gender and educational level, as well as assessing tracking in terms of relative nutrient intakes

On the effect of hydrogen on the elastic moduli and acoustic loss behaviour of Ti-6Al-4V

The elastic moduli and acoustic loss behaviour of Ti-6Al-4V (wt.%) in the temperature range 5–298 K have been studied using Resonant Ultrasound Spectroscopy. A peak in the acoustic dissipation was observed at 160 K within the frequency range 250–1000 kHz. Analysis of the data acquired in this study, coupled with complementary data from the literature, showed that this was consistent with a Snoek-like relaxation process with an associated activation energy of 23 3 kJ mol$^{−1}$. However, the loss peak was broader than would be expected for a Snoek-like relaxation, and the underlying process was shown to have a spread of relaxation times. It is suggested that this effect arises as a result of variations in the strain experienced by the β phase due to different local microstructural constraint by the bounding secondary α phase.The authors would like to acknowledge Dr M Thomas of TIMET UK for providing compositional analysis, and the EPSRC / Rolls-Royce Strategic Partnership for funding (SLD under EP/H022309/1, NGJ and HJS under EP/H500375/1 and EP/M005607/1). RUS facilities were established in Cambridge through grants from the Natural Environment Research Council of Great Britain (NE/B505738/1 and NE/F017081/1).This is the final version of the article. It first appeared from Taylor & Francis via https://doi.org/10.1080/14786435.2016.119805

Recollection, Familiarity, and Cortical Reinstatement: A Multivoxel Pattern Analysis

SummaryEpisodic memory retrieval is thought to involve reinstatement of the neurocognitive processes engaged when an episode was encoded. Prior fMRI studies and computational models have suggested that reinstatement is limited to instances in which specific episodic details are recollected. We used multivoxel pattern-classification analyses of fMRI data to investigate how reinstatement is associated with different memory judgments, particularly those accompanied by recollection versus a feeling of familiarity (when recollection is absent). Classifiers were trained to distinguish between brain activity patterns associated with different encoding tasks and were subsequently applied to recognition-related fMRI data to determine the degree to which patterns were reinstated. Reinstatement was evident during both recollection- and familiarity-based judgments, providing clear evidence that reinstatement is not sufficient for eliciting a recollective experience. The findings are interpreted as support for a continuous, recollection-related neural signal that has been central to recent debate over the nature of recognition memory processes

Microstructural characterisation of metallic shot peened and laser shock peened Ti–6Al–4V

A detailed analysis has been conducted of Ti–6Al–4V processed by metallic shot peening and laser shock peening. Analysis by incremental hole drilling, electron backscattered diffraction microscopy, transmission electron microscopy and transmission Kikuchi diffraction microscopy is evaluated and discussed. The results of this analysis highlight the very different dislocation structures in surfaces processed by these two techniques. Transmission Kikuchi diffraction also has been used to evaluate sub-grains generated by laser shock peening. A notable feature of material processed by laser shock peening is the almost complete absence of deformation twinning, contrasting with the frequent observation of extensive deformation twinning observed in the material processed by metallic shot peening.This work was supported by the Rolls-Royce plc/EPSRC strategic partnership under EP/H022309/1

Mind over memory: cueing the aging brain

A decline in recollection is a hallmark of even healthy aging and is associated with wider impairments in mental control. Older adults have difficulty internally directing thought and action in line with their goals, and often rely more on external cues. To assess the impact this has on memory, emerging brain-imaging and behavioral approaches investigate the operation and effectiveness of goal-directed control before information is retrieved. Current data point to effects of aging at more than one stage in this process, particularly in the face of competing goals. These effects may reflect wider changes in the proactive, self-initiated regulation of thought and action. Understanding them is essential for establishing whether internal “self-cuing” of memory can be improved, and whether—and when—it is best to use environmental support from external cues to maximize memory performance