Both anteromedial and anteroventral thalamic lesions impair radial-maze learning in rats

Disruption to the anterior thalamus (AT) may be an important factor in diencephalic amnesia. Rats with small lesions of the anteromedial (AM) or anteroventral (AV) nucleus showed persistent working-memory and reference-memory deficits in a 12-arm radial maze, although they were comparable to controls during the early part of training. The only activity difference in the maze was that lesioned rats failed to run more slowly when revisiting a baited arm. For all groups, both working and reference memory were impaired after extramaze cues were removed; removal of intramaze cues further impaired performance relative to the original conditions. These findings suggest the AT makes a distinct contribution to mnemonic functions, probably as part of an integrated system involving limbic cortex and the hippocampal formation, and that AT lesions produce a general rather than a specific deficit in spatial or working memory.

Caricature effects, distinctiveness, and identification: testing the face-space framework

According to the multidimensional space framework, faces are represented as locations in a psychological face-space. Our aim was to test whether the locations of veridical, caricatured, and anticaricatured face stimuli in face-space, derived from multidimensional scaling analyses, could account for identification accuracy and distinctiveness ratings for these stimuli. Caricatures were identified more accurately and rated as more distinctive than veridical images, whereas anticaricatures were identified less accurately but were not significantly less distinctive than veridical images. In the face-space derived from multidimensional scaling, caricatures were further from the origin and less densely clustered than veridical images, whereas anticaricatures were closer to the origin and located in denser regions of the space. A quantitative model successfully predicted identification performance from the spatial locations of the stimuli. In general, the physically transformed faces were systematically mapped in the psychological space.

Recognition of own-race and other-race caricatures: implications for models of face recognition

Valentine's (Valentine T. Q J Exp Psychol 1991;43A:161-204) face recognition framework supports both a norm-based coding (NBC) and an exemplar-only, absolute coding, model (ABC). According to NBC; (1) faces are represented in terms of deviations from a prototype or norm; (2) caricatures are effective because they exaggerate this norm deviation information; and (3) other-race faces are coded relative to the (only available) own-race norm. Therefore NBC predicts that, for European subjects, caricatures of Chinese faces made by distorting differences from the European norm would be more effective than caricatures made relative to the Chinese norm. According to ABC; (1) faces are encoded as absolute values on a set of shared dimensions with the norm playing no role in recognition; (2) caricatures are effective because they minimise exemplar density and (3) the dimensions of face-space are inappropriate for other-race faces leaving them relatively densely clustered. ABC predicts that all faces would be recognised more accurately when caricatured against their own-race norm. We tested European subjects' identification of European and Chinese faces, caricatured against both race norms. The ABC model's prediction was supported. European faces were also rated as more distinctive and recognised more easily than Chinese faces. However, the own-race recognition bias held even when the races were equated for distinctiveness which suggests that the ABC model may not provide a complete account of race effects in recognition.

Both anteromedial and anteroventral thalamic lesions impair radial-maze learning in rats

Disruption to the anterior thalamus (AT) may be an important factor in diencephalic amnesia. Rats with small lesions of the anteromedial (AM) or anteroventral (AV) nucleus showed persistent working-memory and reference-memory deficits in a 12-arm radial maze, although they were comparable to controls during the early part of training. The only activity difference in the maze was that lesioned rats failed to run more slowly when revisiting a baited arm. For all groups, both working and reference memory were impaired after extramaze cues were removed; removal of intramaze cues further impaired performance relative to the original conditions. These findings suggest the AT makes a distinct contribution to mnemonic functions, probably as part of an integrated system involving limbic cortex and the hippocampal formation, and that AT lesions produce a general rather than a specific deficit in spatial or working memory.

Coding spatial variations in faces and simple shapes: a test of two models

Faces all have the same basic elements in the same overall arrangement, and must be discriminated using variations in this shared configuration. An efficient way to represent these variations would be to code how each configuration differs from an average face (norm-based coding model). Alternatively, configurations could be represented simply by coding their absolute values in some coordinate system (absolute coding model). The two models differ in the variables they predict will influence an image's recognizability. Absolute coding predicts that recognizability will depend on an image's distinctiveness and degree of distortion from its veridical target. Norm-based coding predicts that recognizability will also depend on the way the image differs from a norm or average face, namely its distance from the norm and/or its degree of displacement from the norm-deviation vector for the target. We determined the effects of these four critical variables on recognition of undistorted (veridical) images, caricatures, anticaricatures and 'lateral' distortions of famous faces (Experiment 1), newly learned faces (Experiment 2), and simple shapes that also share a configuration (Experiment 2). The results favored absolute coding of both faces and shapes, and indicate that caricatures derive their power from their distinctiveness.

Facial distinctiveness and the power of caricatures

Caricatures, which increase the distinctiveness of faces, are generally recognised at least as well as undistorted images of those faces. However, caricatures seem to facilitate recognition more for some faces than others. An investigation was made into whether the effectiveness of caricaturing depends on a face's initial distinctiveness. In experiments 1-3, subjects learned names for unfamiliar faces (photographs) that varied in distinctiveness, and were tested on recognition of caricatures, anticaricatures, and undistorted images of those faces. The test images were line drawing in experiment 1 and 2 photographic images in experiment 3. Experiments 1 and 2 were identical except that subjects had more exposure to the study photographs in experiment 1. In all three experiments, distinctive faces were recognised (named) more accurately than less-distinctive faces, and caricatures were recognised at least as accurately as undistorted images and better than anticaricatures. However, distinctiveness and caricature level did not interact. Nor did a face's initial distinctiveness correlate with the degree of recognition facilitation produced by caricaturing (experiments 1-3) or with the caricature level chosen as the best likeness (experiment 4). The effectiveness of caricatures varied across faces and experimental conditions, but these differences did not relate to differences in initial distinctiveness. These results prompted a more careful analysis of the expected relationship between initial distinctiveness and the power of caricatures, which indicated that the relationship may be curvilinear rather than linear. In addition, it was found that line-drawing caricatures functioned as superportraits (recognised better than undistorted images--experiment 1) but photographic caricatures did not (experiment 3) suggesting that the forensic potential of caricatures may be limited.

Zebrafish: a big fish in the study of the gut microbiota

The importance of the gut microbiota in host health is now well established, but the underlying mechanisms remain poorly understood. Among the animal models used to investigate microbiota-host interactions, the zebrafish (Danio renio) is gaining attention. Several factors contribute to the recent interest in this model, including its low cost, the ability to assess large cohorts, the possibility to obtain germ-free larvae from non-axenic parents, and the availability of optical methodologies to probe the transparent larvae and adults from various genetic lines. We review recent findings on the zebrafish gut microbiota and its modulation by exogenous microbes, nutrition, and environmental factors. We also highlight the potential of this model for assessing the impact of the gut microbiota on brain development.

Systematic Analysis of the Stress-Induced Genomic Instability of Type Three Secretion System in Aeromonas salmonicida subsp. salmonicida

The type three secretion system (TTSS) locus of Aeromonas salmonicida subsp. salmonicida, located on the plasmid pAsa5, is known to be lost when the bacterium is grown at temperatures of 25 °C. The loss of the locus is due to the recombination of the insertion sequences flanking the TTSS region. However, the mechanism involved in this recombination is still elusive. Here, we analyzed 22 A. salmonicida subsp. salmonicida strains that had already lost their TTSS locus, and we systematically explored another 47 strains for their susceptibility to lose the same locus when grown at 25 °C. It appeared that strains from Europe were more prone to lose their TTSS locus compared to Canadian strains. More specifically, it was not possible to induce TTSS loss in Canadian strains that have AsaGEI2a, a genomic island, and prophage 3, or in Canadian strains without a genomic island. A comparative genomic approach revealed an almost perfect correlation between the presence of a cluster of genes, not yet characterized, and the susceptibility of various groups of strains to lose their locus. This cluster of genes encodes putative proteins with DNA binding capacity and phage proteins. This discovery creates new opportunities in the study of pAsa5 thermosensitivity.