Molecular characterization of Staphylococcus aureus in Lebanon.

Staphylococcus aureus is an important human pathogen and is a growing public health concern. In this study, 130 S. aureus, 93 methicillin-resistant S. aureus (MRSA) and 37 methicillin-sensitive S. aureus (MSSA), clinical isolates recovered from Lebanon were typed by protein A gene (spa) sequencing and multi-locus sequence typing (MLST). Forty-eight different spa types were identified and clustered into 30 different groups. MLST revealed 10 sequence types (STs) among the isolates. There were eight major MRSA clones defined as isolates with the same ST and the same SCCmec type. The majority of the PVL-positive isolates (53%) were ST80-MRSA-IVc. Systematic surveillance of both hospital and community isolates in Lebanon together with measures designed to limit the spread are required.

Antibiotic resistance patterns and sequencing of class I integron from uropathogenic Escherichia coli in Lebanon.

AIM: To study the prevalence and molecular basis of antimicrobial resistance in UPEC. METHODS AND RESULTS: PCR was used to detect the presence of the Class I integron variable region (VR). The VR amplicons were then characterized by partial sequencing and restriction digestion with AluI. VR negative isolates showed more antibiotic susceptibility than VR positive isolates. 30% of the isolates were positive for the VR and carried the genes dfrA7, dfrA17-aadA5, dfrA1-aadA1, dfrA12-orf5-aadA2 and bla(OXA-30)-aadA1. Five restriction patterns were detected and isolates with the same VR amplicon size had the same restriction pattern. CONCLUSIONS: Our data demonstrated that Class I integrons are widely disseminated in Lebanon and showed their importance for the occurrence and transmission of multidrug resistance. SIGNIFICANCE AND IMPACT OF THE STUDY: These findings will facilitate greater understanding of the factors that contribute to the presence and transfer of integron-associated antibiotic resistance genes in UPEC.

The neural basis of mental imagery.

Visual mental imagery, or 'seeing with the mind's eye', has been the subject of considerable controversy in cognitive science. At issue is whether images are fundamentally different from verbal thoughts, whether they share underlying mechanisms with visual perception, and whether information in images is represented in a spatial (i.e. map-like) format. Research on the neural systems underlying imagery brings a new source of evidence to bear on these cognitive science controversies, as well as on the cerebral localization of imagery processes. Emerging from this work is the view that mental imagery involves the efferent activation of visual areas in prestriate occipital cortex, parietal and temporal cortex, and that these areas represent the same kinds of specialized visual information in imagery as they do in perception. In addition, different components of imagery processing appear to be differentially lateralized, with the generation of mental images from memory depending primarily upon structures in the posterior left hemisphere, and the rotation of mental images depending primarily upon structures in the posterior right hemisphere.

Perception and awareness after brain damage.

Dissociations between perception and awareness of perception are of interest for what they can tell us about the neural correlates of awareness. Recent research in this field has focussed on perception-awareness dissociations in the syndromes of blindsight, covert recognition in two kinds of visual agnosia, and visual neglect.

Agnosia.

Object recognition can break down in a variety of ways after brain damage. The resulting different forms of agnosia provide us with useful constraints on theories of normal object recognition. Recent studies suggest a division of labor for the recognition of different types of stimuli (common objects, words, faces, direction of eye gaze, spatial relations among parts of the human body), a high degree of interactivity in the processes underlying object recognition, and the possibility that recognition and awareness of recognition may be neurally distinct.

Bimodal correlation between the circulating insulin level and the production rate of dehydroepiandrosterone: positive correlation in controls and negative correlation in the polycystic ovary syndrome with acanthosis nigricans.

The objective of this study was to define the relationship among the circulating insulin level (IRI), the MCR of dehydroepiandrosterone (MCR-D), and the production rate of DHEA (PR-D) in 10 women with the polycystic ovary syndrome and acanthosis nigricans (PCOS-AN). Seven normal weight and 10 obese women served as controls. Measurement of the MCR-D and PR-D was accomplished by iv saline infusion (0.9% NaCl solution) on day 1 as a control and a 4-h iv dehydroepiandrosterone (unlabeled) infusion (1 mg/h) was performed on day 2. Mean MCR-D was more than 2-fold higher in the obese controls compared to the normal weight controls. However, the plasma concentration of DHEA(PC-D) was not significantly different in the normal and obese control women, since the PR-D was increased proportionately to the MCR-D. The MCR-D and the PR-D were coupled through insulin in the control women, and their correlation coefficients with IRI were positive and identical (0.77 and 0.73, respectively). In contrast, IRI was negatively correlated with PR-D in the PCOS-AN women. Also, unlike the control women, there was minimal or no change in the MCR-D across a broad range of IRI in the PCOS-AN women. Thus, the MCR-D and PR-D were not coupled in these women.

Current issues in the neuropsychology of image generation.

Image generation is the process by which long-term memory knowledge of the visual appearance of objects or scenes is used to create a short-term, percept-like image. In this article I will review recent neuropsychological evidence relevant to two questions about image generation: First, is there a distinct component of the cognitive architecture dedicated to image generation? Second, what brain regions are directly involved with image generation?

The laterality of mental image generation: a test with normal subjects.

Recent evidence supporting the hypothesis that mental image generation is lateralized to the left hemisphere is summarized, and a new test of this hypothesis, using a tachistoscopic, lateralized visual discrimination task with normal subjects, is presented. When mental images of the stimuli were used as templates to facilitate the visual discrimination, the effect of imagery was greater for the right visual field (left hemisphere) stimulus presentations. This result is discussed in relation to earlier findings on the hemisphericity of imagery and of visual expectancy.

Semantically-bounded anomia: implications for the neural implementation of naming.

We describe a patient whose anomia is disproportionately severe for fruits and vegetables when familiarity and name frequency are taken into account. His fruit and vegetable naming impairment was evident in a variety of different tasks. In contrast, he retained good general knowledge of fruits and vegetables, and he could access their names when given a phonemic cue. We discuss the phenomenon of semantically-bounded anomia in relation to the issues of local vs distributed representation, the existence of semantic "maps" in the brain, and the implementation of arbitrary associations in neural networks.

A category-specific naming impairment after temporal lobectomy.

Unilateral temporal lobectomy patients and normal control subjects were tested in a speeded naming task with pictures of living and nonliving things that were equated for name frequency, familiarity, and visual complexity. Although right temporal lobectomy patients and normal subjects performed equally well with the living relative to nonliving things, left temporal lobectomy patients were disproportionately impaired at naming nonliving things. This result has several implications: First, it supports the existence of category-specific naming impairments. In particular, it undermines the proposal that living-nonliving dissociations are artifactual, resulting from the greater difficulty of living things. Second, it demonstrates an asymmetry in the neural representation of nonliving things, in favor of the left hemisphere. Third, it casts doubt on the hypothesis that the anterior temporal cortices are convergence zones that are particularly necessary for the naming of living things.

Can recognition of living things be selectively impaired?

Brain damage sometimes seems to impair recognition of living things, despite relatively preserved recognition of nonliving things. The most straightforward interpretation of this dissociation is that the recognition of living things depends on some specialized mechanisms that are not needed for the recognition of nonliving things. However, there are alternative interpretations of the dissociation in terms of the greater complexity or inter-item similarity of living things, or the more specific, within-category identifications that are usually required for living things. Surprisingly, the relevant tests to discriminate among these rival hypotheses have never been performed. We took the factors of visual complexity, inter-item similarity, specificity of identification, as well as others, into account in analyzing the visual recognition performance of two head-injured visual agnosic patients. In each case we found that recognition of living things was still disproportionately impaired when the effects of the other factors were accounted for.

Face perception and within-category discrimination in prosopagnosia.

Prosopagnosics are impaired at face recognition, but unimpaired, or relatively less impaired, at common object recognition. It has been suggested that this dissociation results simply from the greater difficulty of face recognition compared to object recognition, or from the greater need to discriminate visually similar members of a single category in face recognition compared to object recognition. We tested these hypotheses using the performance of normal subjects in an 'old/new' recognition paradigm to establish the true relative difficulty of face and object recognition, and required both normal subjects and a prosopagnosic subject to discriminate both faces and visually similar exemplars of nonface object categories. In two different experiments, the prosopagnosic patient performed disproportionately poorly with faces. These results disconfirm the hypotheses described above, and imply that prosopagnosia is an impairment of a specialized form of visual recognition that is necessary for face recognition and is not necessary, or less necessary, for the recognition of common objects.

Unconscious perception of "extinguished" visual stimuli: reassessing the evidence.

When parietal-damaged patients fail to report a contralesional stimulus because of extinction, is this because the stimulus is not perceived, or because it is perceived but cannot reach conscious awareness? VOLPE et al. [10] reported an intriguing study that seemed to locate the problem at least partly in the transfer of information to conscious awareness. They showed patients with extinction pairs of stimuli, one in each hemifield. Although patients were predictably poor at reporting the identity of the contralesional stimulus, they were able to make accurate same/different judgements comparing the two stimuli. This was interpreted as evidence that both stimuli were perceived. In the present paper, we point out that the dissociation between identification and same/different matching could also be due to the possibility that less visual information about the contralesional stimulus is necessary to make a same/different judgement than to identify the stimulus, and that chance performance is considerably higher in the first than in the second type of task. In Experiment 1, we verified this by degrading one side of a stimulus display and "replicating" the dissociation with normal subjects. We also equated the amount of visual information needed for the two tasks by yoking the stimulus pairs on "different" trials of the same/different matching task with the choice pairs on a forced choice identification task. Under these conditions, the dissociation vanished. In Experiment 2, we administered these tasks to three parietal-damaged patients with extinction. When the original method was used, same/different matching was better than identification of the contralesional stimulus. With the forced choice identification method, the dissociation again vanished.

Category-specificity and modality-specificity in semantic memory.

Studies of agnosia have revealed two apparently orthogonal dimensions along which knowledge may break down. In some cases, knowledge of specific categories (such as living things) seems lost, regardless of the modality being tested. In other cases, knowledge in specific modalities (such as vision) seems lost, regardless of the category of stimuli being tested. These different sets of phenomena suggest different organizations for knowledge in the brain, the first by category and the second by modality. Unfortunately, possible confoundings between category, modality, and difficulty level in the previous studies prevent us from drawing strong conclusions from these data. The present study was aimed at assessing the nature of the breakdown in the semantic memory of a prosopagnosic patient, by orthogonally varying category and modality, while assessing difficulty level. The findings do not implicate a simple categorical or modality-dependent organization of his knowledge, but rather an organization in which both category and modality play a role.

Mental rotation may underlie apparent object-based neglect.

Previous investigations have suggested that object-based neglect may reflect an impairment in attentional allocation that occurs relative to the intrinsic left and right of objects. We report a patient with apparent "object-based" neglect of 90 degrees rotated stimuli for whom the pattern of neglect was a function of task strategy. When the patient was instructed to visualize the rotated stimuli as if they were upright, i.e. mentally rotate them, he showed apparent "object-based" neglect to the left of the principal axes of the stimuli. In contrast, when instructed to refrain from mental rotation, neglect was apparent only with respect to his left, but not the left of the stimuli. Thus, the apparent "object-based" neglect of this patient may be attributed to a process of mental rotation of objects to upright, and subsequent neglect in viewer-centered or environment-centered coordinates. These data suggest a mechanism whereby object-based and viewer/environment-centered reference frames may be aligned, thereby causing viewer/environment-centered neglect to appear as if object-based.

A neural basis for category and modality specificity of semantic knowledge.

Prevalent theories hold that semantic memory is organized by sensorimotor modality (e.g., visual knowledge, motor knowledge). While some neuroimaging studies support this idea, it cannot account for the category specific (e.g., living things) knowledge impairments seen in some brain damaged patients that cut across modalities. In this article we test an alternative model of how damage to interactive, modality-specific neural regions might give rise to these categorical impairments. Functional MRI was used to examine a cortical area with a known modality-specific function during the retrieval of visual and non-visual knowledge about living and non-living things. The specific predictions of our model regarding the signal observed in this area were confirmed, supporting the notion that semantic memory is functionally segregated into anatomically discrete, but highly interactive, modality-specific regions.

A left hemisphere basis for visual mental imagery?

The lateralization of visual mental imagery was investigated by presenting each hemisphere of a commissurotomy patient with a letter classification task known to require imagery and with a pair of control tasks designed to require all of the same processes as the imagery task except for the imagery processing itself. Whereas both hemispheres performed well on the control tasks, only the left hemisphere performed the imagery task.

Parietal lobe mechanisms of spatial attention: modality-specific or supramodal?

Is the spatial attention system divided into separate, modality-specific subsystems, or is there a supramodal spatial attention system? More specifically, does the role of the parietal lobe in spatial attention involve modality-specific or supramodal mechanisms? We addressed this question using a variant of Posner's spatial cuing task. Parietal-lesioned patients performed a simple reaction time task to lateralized visual target stimuli, preceded on each trial by either non-predictive lateralized visual cue stimuli or non-predictive lateralized auditory cue stimuli. With both types of cues, we found disproportionate slowness in responding to invalidly cued contralesional targets, indicative of an impairment in disengaging attention from the ipsilesional to the contralesional side of space. The finding of an attentional disengagement impairment for visual targets with auditory cues implies that the parietal lobe's attentional mechanism operates on a representation of space in which both visual and auditory stimuli are represented, in other words, a supramodal representation of space.

Frames of reference for allocating attention to space: evidence from the neglect syndrome.

With respect to what frames of reference, or spatial coordinate systems, is attention allocated to locations in space? We posed this question about the spatial attention system that has been damaged in neglect patients, distinguishing among three possible types of spatial reference frame: viewer-centered, according to which locations are coded with respect to the viewer, environment-centered, according to which locations or coded with respect to the environment, and object-centered, according to which locations are coded with respect to an object. The three candidate frames of reference were decoupled from one another by rotating either the viewer or the stimulus object. Visual search performance suggested that the neglected hemifield was defined with respect to both viewer-centered and environment-centered frames of reference, but not with respect to an object-centered frame of reference. The role of objects in the allocation of attention to space, and the relation between our findings and the "two cortical visual systems" hypothesis, are discussed.

A functional MRI study of mental image generation.

The neural substrates of mental image generation were investigated with functional MRI. Subjects listened to words under two different instructional conditions: to generate visual mental images of the words' referents, or to simply listen to each word and wait for the next word. Analyses were performed which directly compared the regional brain activity during each condition, with the goal of discovering whether mental image generation engages modality-specific visual areas, whether it engages primary visual cortex, and whether it recruits the left hemisphere to a greater extent than the right. Results revealed that visual association cortex, and not primary visual cortex, was engaged during the mental image generation condition. Left inferior temporal lobe (Brodmann's area 37) was the most reliably and robustly activated area across subjects, had activity which extended superiorly into occipital association cortex (area 19). The results of this experiment support the hypothesis that visual mental imagery is a function of visual association cortex, and that image generation is asymmetrically localized to the left.