Sex differences in cognitive impairment in Alzheimer's disease

Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/Sex differences in neurocognitive abilities have been extensively explored both in the healthy population and in many disorders. Until recently, however, little work has examined such differences in people with Alzheimer's disease (AD). This is despite clear evidence that AD is more prevalent in women, and converging lines of evidence from brain imaging, post-mortem analyses, hormone therapy and genetics suggesting that AD affects men and women differently. We provide an overview of evidence attesting to the poorer cognitive profiles in women than in men at the same stage of AD. Indeed, men significantly outperform women in several cognitive domains, including: Language and semantic abilities, visuospatial abilities and episodic memory. These differences do not appear to be attributable to any differences in age, education, or dementia severity. Reasons posited for this female disadvantage include a reduction of estrogen in postmenopausal women, greater cognitive reserve in men, and the influence of the apolipoprotein E ε4 allele. Assessment of cognitive abilities contributes to the diagnosis of the condition and thus, it is crucial to identify the role of sex differences if potentially more accurate diagnoses and treatments are to emerge.Peer reviewedFinal Published versio

Genetic loci influencing kidney function and chronic kidney disease

Using genome-wide association, we identify common variants at 2p12-p13, 6q26, 17q23 and 19q13 associated with serum creatinine, a marker of kidney function (P = 10 10 to 10 15). Of these, rs10206899 (near NAT8, 2p12-p13) and rs4805834 (near SLC7A9, 19q13) were also associated with chronic kidney disease (P = 5.0 × 10 5 and P = 3.6 × 10 4, respectively). Our findings provide insight into metabolic, solute and drug-transport pathways underlying susceptibility to chronic kidney disease

Category-specificity can emerge from bottom-up visual characteristics: evidence from a modular neural network

Original article can be found at: http://www.sciencedirect.com/science/journal/02782626 Copyright Elsevier Inc.The role of bottom-up visual processes in category-speciWc object recognition has been largely unexplored. We examined the role of low-level visual characteristics in category speciWc recognition using a modular neural network comprising both unsupervised and supervised components. One hundred standardised pictures from ten diVerent categories (Wve living and Wve nonliving, including body parts and musical instruments) were presented to a Kohonen self-organising map (SOM) which re-represents the visual stimuli by clustering them within a smaller number of dimensions. The SOM representations were then used to train an attractor network to learn the superordinate category of each item. The ease with which the model acquired the category mappings was investigated with respect to emerging category eVects. We found that the superordinates could be separated by very low-level visual factors (as extracted by the SOM). The model also accounted for the well documented atypicality of body parts and musical instrument superordinates. The model has clear relevance to human object recognition since the model was quicker to learn more typical category exemplars and Wnally the model also accounted for more than 20% of the naming variance in a sample of 57 brain injured subjects. We conclude that purely bottom-up visual characteristics can explain some important features of category-speciWc phenomena.Peer reviewe

Category specific naming the visual properties of line drawn stimuli

Original article can be found at: http://www.cortex-online.org/ Copyright Masson S.p.A.It has been argued that greater intra-category structural similarity for living things may make them more difficult to recognize and name (e.g. Humphreys et al., 1988). Nevertheless, the precise meaning and quantification of ‘structural similarity’ remain unclear. We developed three new visual measures derived from the Snodgrass and Vanderwart (1980) corpus and examined their relationship with picture naming in a speeded presentation paradigm. The three measures were: the proportion of black pixels (PB); the degree of pixel overlap within subcategories using Euclidean Overlap (EO); and the degree of consistency in inter-pixel distribution across each picture (IPC). Within-category EO was greater for nonliving than living things, indicating less within-category visual overlap for living things. Finally, EO correlated significantly with error rates (PB and IPC did not). These findings contradict existing notions that line drawings of living things have greater visual similarity than nonliving things.Peer reviewe

Why are our similarities so different A reply to Humphreys and Riddoch

Original article can be found at: http://www.cortex-online.org/ Copyright Masson S.p.A.Humphreys and Riddoch (2002: hereafter, H&R) entitle their commentary on Laws and Gale (2002) with the following question: “Do pixel level analyses describe psychological perceptual similarity”? (We will use the term perceptual similarity to refer also to structural similarity as used by Humphreys and colleagues). This perhaps betrays some misunderstanding of our intention. Throughout our paper, we specifically refer to visual overlap – which we take to mean retinotopic similarity at the pixel level. This differs from notions of psychological or perceptual similarity and certainly differs from the position advanced by Humphreys and colleagues. Although we do not view the two approaches as mutually exclusive, we have some reservations about the utility of perceptual similarity as measured by Contour Overlap (CO) and partonomic features (Humphreys et al., 1988). Moreover, on grounds of parsimony, it is important to examine the role of low-level variables in object recognition and category specificity before turning to high-level variables i.e. psychological/perceptual variables. In response to the commentary by H&R (2002), we would like to draw attention to some issues that relate to: (a) the points they raise about Euclidean Overlap (EO); and (b) difficulties with their conception of perceptual similarity.Peer reviewe

The effect of 'masking' on picture naming

Original article can be found at: http://www.cortex-online.org/ Copyright Masson S.p.A.It is frequently assumed that because compared to nonliving things, living things are less familiar, have lower name frequency, and are more visually complex, this makes them more difficult to name by patients and normal subjects. This has also been implicitly accepted as an explanation for the greater incidence of living thing disorders. Patient studies do not, however, typically contain any premorbid data and so, we do not know that the same variables would have necessarily predicted their ‘normal’ performance. To examine this issue, we measured picture-naming latencies in normal subjects presented with unmasked and masked versions of the same line drawings. In accord with other recent studies, living things were named faster than nonliving things. Furthermore, contrary to some theories of category naming, the living thing advantage persisted regardless of whether stimuli were undegraded, degraded or the density of degradation. Finally, multiple simultaneous regression analyses showed that one visual variable (Euclidean Overlap) and one linguistic variable (Age of Acquisition) predicted naming latencies across all masked and unmasked conditions. Other variables either had no predictive value (Contour Overlap; Name Frequency; Category); predicted only high masking (Visual Complexity; Familiarity), or normal and low masking (Number of Phonemes). These findings imply that the more commonly documented deficits for living things do not reflect an exaggeration of the normal profile (be it with masked or unmasked stimuli) or the influence of the same variables that affect normal naming.Peer reviewe

A domain specific deficit for foodstuffs in patients with Alzheimer's disease

Original article can be found at: http://journals.cambridge.org/--Copyright Cambridge University PressAlthough some studies have reported a category specific naming deficit in Alzheimer’s patients (invariably for living things), others have failed to replicate this finding (Laws et al., in press). Inconsistencies may partly stem from the fact that category effects are hidden in group analyses because individual Alzheimer’s patients show category deficits in opposing directions, namely, some living and some nonliving (Gonnerman et al., 1997). Additionally, category effects may depend upon the specific composition of living things, such as the ratio of animals to fruits and vegetables, though this has never been explicitly examined. To examine this, we conducted a more detailed fractionation of living and nonliving categories for individual patients.Peer reviewe