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At least 865 records · Page 48Linked to original sources
PubMed2006

Characterizing exploration behavior in spatial neglect: omissions and repetitive search.

In search tasks, patients with spatial neglect typically fail to respond to stimuli on the contralesional side. Such behavior has been associated with hyperattention to the ipsilesional side and a deficit in disengaging from attended stimuli. The present study investigated whether such explanations can also account for a further kind of behavior frequently shown by neglect patients: repetitive returns to previously indicated stimuli, particularly on the ipsilesional side. A group of neglect patients was tested along with a group of healthy participants and a patient control group without neglect. Participants performed an exploration task in which they searched for targets defined by their shape or for all stimuli either with the aid of vision or blindfolded. The results showed differential effects of reducing the salience of visual stimuli by blindfolding. For a subgroup of patients, detection rate improved, while for others the percentage of omissions increased. However, contrary to the control groups, blindfolding had no effect on repetitive search in the neglect group, inconsistent with hyperattention, a disengage or impaired working memory deficits. The rate of repetitive returns to previously indicated locations did not seem to be associated with the percentage of omitted stimuli, suggesting that repetitive returns may be best explained by a disruption of systematic search and lack of volitional control in spatial neglect. The results further underline the importance of considering repetitive search behavior in addition to omissions in standard neglect assessments.

Aged↗
PubMed2005

Object recognition with severe spatial deficits in Williams syndrome: sparing and breakdown.

Williams syndrome (WS) is a rare genetic disorder that results in severe visual-spatial cognitive deficits coupled with relative sparing in language, face recognition, and certain aspects of motion processing. Here, we look for evidence for sparing or impairment in another cognitive system-object recognition. Children with WS, normal mental-age (MA) and chronological age-matched (CA) children, and normal adults viewed pictures of a large range of objects briefly presented under various conditions of degradation, including canonical and unusual orientations, and clear or blurred contours. Objects were shown as either full-color views (Experiment 1) or line drawings (Experiment 2). Across both experiments, WS and MA children performed similarly in all conditions while CA children performed better than both WS group and MA groups with unusual views. This advantage, however, was eliminated when images were also blurred. The error types and relative difficulty of different objects were similar across all participant groups. The results indicate selective sparing of basic mechanisms of object recognition in WS, together with developmental delay or arrest in recognition of objects from unusual viewpoints. These findings are consistent with the growing literature on brain abnormalities in WS which points to selective impairment in the parietal areas of the brain. As a whole, the results lend further support to the growing literature on the functional separability of object recognition mechanisms from other spatial functions, and raise intriguing questions about the link between genetic deficits and cognition.

Adolescent↗
PubMed2004

Neurological and cognitive impairment associated with leaded gasoline encephalopathy.

BACKGROUND: A toxic encephalopathy (or 'lead encephalopathy') may arise from leaded gasoline abuse that is characterised by tremor, hallucinations, nystagmus, ataxia, seizures and death. This syndrome requires emergency and intensive hospital treatment. METHODS: We compared neurological and cognitive function between chronic gasoline abusers with (n=15) and without (n=15) a history of leaded gasoline encephalopathy, and with controls who had never abused gasoline (n=15). RESULTS: Both groups of chronic gasoline abusers had abused gasoline for the same length of time and compared to controls, showed equivalently elevated blood lead levels and cognitive abnormalities in the areas of visuo-spatial attention, recognition memory and paired associate learning. However, where gasoline abusers with no history of leaded gasoline encephalopathy showed only mild movement abnormalities, gasoline abusers with a history of leaded gasoline encephalopathy showed severe neurological impairment that manifest as higher rates of gait ataxia, abnormal rapid finger tapping, finger to nose movements, dysdiadochokinesia and heel to knee movements, increased deep tendon reflexes and presence of a palmomental reflex. CONCLUSIONS: While neurological and cognitive functions are disrupted by chronic gasoline abuse, leaded gasoline encephalopathy is associated with additional and long-lasting damage to cortical and cerebellar functions.

Administration, Inhalation↗
PubMed2004

Spatial attention in individuals with pervasive developmental disorders using the gap overlap task.

The present study examined spatial attention in individuals with pervasive developmental disorders (PDD) using the gap overlap task and analyzed the express saccade, which is defined by its extremely short reaction time, as a measure of the state of attention. Participants were required to move their eyes to the target stimulus appearing on the left or right side of a fixation point. In this task, participants had to disengage their attention from the central fixation point and shift it to the peripheral target stimulus. In the gap condition, the fixation point disappeared 200 ms before the target stimulus was presented, and in the overlap condition, the fixation point remained while the target stimulus was presented. Saccade latencies were not different between the groups. However, the express saccade was more frequent in the PDD group than in the normal group in the overlap condition. We conclude that individuals with PDD have deficiencies in attentional engagement. Moreover, our study suggests that analysis of the express saccade will be useful in further examinations of attentional processes in PDD.

Adult↗
PubMed2006

Bipolar and schizophrenic patients differ in patterns of visual motion discrimination.

BACKGROUND: Since Kraepelin's early distinction between bipolar disorder and schizophrenia, it has been assumed that these disorders represent two different pathophysiological processes, although they share many clinical symptoms. Previous studies showed that velocity discrimination, a sensitive psychophysiological measure of the visual motion system, is deficient in schizophrenia. Here we examined whether the motion processing impairment found in schizophrenia also occurs in bipolar disorder. METHODS: We compared 16 bipolar patients, 25 schizophrenic patients, and 25 normal controls on a velocity discrimination task. We measured the psychophysical threshold for velocity discrimination and contrast detection (as a control task) in all subjects. RESULTS: Bipolar patients showed normal velocity discrimination thresholds at intermediate velocities, the range in which velocity cues dominate velocity discrimination, and at low velocities. Schizophrenic patients, however, showed elevated velocity discrimination thresholds at intermediate and low velocities. At higher velocities, both bipolar and schizophrenic patients showed elevated thresholds. All subjects showed normal contrast detection thresholds. CONCLUSIONS: Normal velocity discrimination in the intermediate range of velocity indicates unimpaired motion processing in bipolar disorder. The abnormal velocity discrimination of both schizophrenic and bipolar patients at higher velocities may reflect impaired temporal processing rather than impaired motion processing per se. These results suggest that the pathophysiological processes of bipolar disorder and schizophrenia diverge at the stage of visual motion processing, a sensory component mediated primarily in the extrastriate cortex.

Adolescent↗
PubMed1999

Hypermnesia in unilateral neglect.

Thirteen right brain-damaged patients who were found to neglect pictures presented on the left of a display were presented the same stimuli, intermixed with foils, in a yes-no recognition test. Fifty per cent of patients claimed to have already seen one or more of the previously neglected pictures. This demonstrates that visual information that fails to access consciousness in neglect patients does retain the ability to surface as explicit memory at a later stage.

Adult↗
PubMed1977

Constructional apraxia in left brain-damaged patients: a planning disorder?

The aim of the present study was to verify the hypothesis advanced by Hécaen and Assal (1970), that the presence of landmarks can improve the copying performance of left brain-damaged patients, while leaving unchanged that of right brain-damaged patients. Sixty-two control subjects and 196 brain-damaged patients with lesions restricted to the right (N = 84) or to the left (N = 112) cerebral hemisphere were given two tests of copying drawings. In the first task the patients were asked to directly copy a drawing; to perform the second test they were given guiding landmarks. On both tests no difference was found between the performance of the two hemispheric groups. Right-sided patients used a lower number of guiding landmarks, but this occurred only on the half of the drawings contralateral to the side of the lesion and was apparently due to unilateral spatial neglect.

Apraxias↗
PubMed1997

The relationship between naming and semantic knowledge for different categories in dementia of Alzheimer's type.

We studied the relationship between naming and semantic memory in a group of 10 patients with dementia of Alzheimer's type. In an extension to a previous cross-sectional study (Hodges, J. R. et al., Brain and Language, 1996, 54, 302-325), this relationship was investigated at two longitudinal points within each patient's cognitive decline. Two types of naming performance were compared: items that each patient named correctly at the first stage but failed to name at the second stage, as contrasted with items named correctly at both stages (thereby providing a control for cognitive decline in general). Semantic knowledge of the concepts represented by the pictures in the naming test was investigated at each stage using definitions to the spoken object name, scored particularly for the number of sensory and associative/functional features provided by the patient. At stage 2, an analysis of the definitions for named-->unnamed items as contrasted with named-->named objects revealed a significant loss of both sensory and associative information. A comparison between natural kinds (animals and birds) and artefacts (household objects, vehicles, etc.), however, demonstrated a striking interaction between category and type of information contained in the definitions. Specifically, stage 2 definitions of artefacts in the named-->unnamed set showed a disproportionate loss of associative/functional information, while definitions of animal names that patients failed to produce in response to the pictures were notably lacking in sensory features. This pattern supports the notion that successful naming relies on a subset of critical semantic features which vary somewhat across different categories of semantic knowledge. We suggest that these findings are best encompassed by a conception of semantic organization, Weighted Overlappingly Organized Features (WOOF), in which (i) knowledge about all objects is represented by a central, distributed network of features activated by both words and pictures, but (ii) natural kinds and artefacts are differentially weighted in favour of those features that are involved in learning about and experiencing different kinds of objects.

Aged↗
PubMed1999

Spatial influences on motor and language function.

In subjects with parietal lobe lesions, performance on motor and language tasks differed as a function of the side of space to which subjects directed their attention or acted. Subjects with left parietal lesions performed better when attention was directed to stimuli in left hemispace (that is, the left side of their environment), and those with right parietal lesions showed a similar effect when attending to stimuli in right hemispace. Hemispace effects were not observed in subjects with lesions located elsewhere in the cerebral hemispheres, or in subjects with subcortical lesions. These data are consistent with the view that not only motor but also cognitive operations such as language, which do not appear to have any intrinsic spatial organization, are maintained in registration with spatial systems, and that this attention-requiring linkage confers a processing advantage.

Aged↗
PubMed2000

A category-specific deficit of spatial representation: the case of autotopagnosia.

Following a vascular lesion in the parietal cortex of the language dominant hemisphere (right in one case), two patients showed a striking dissociation between spared naming, recognition and use of their body parts and an inability in localising on verbal command the same body parts on themselves and on a mannequin (Autotopagnosia, AT). The patients were submitted to a modified version of Reed and Farah Test (1995), a test that taps the ability to encode changes of body position as opposed to changes of position of objects. Their performance differed from normal controls, showing a specific deficit in encoding body position. It is suggested that AT could be the consequence of a lesion in a specific neural circuit, located in the language dominant hemisphere, whose function is to encode the body position for both oneself and others.

Aged↗
PubMed2001

Educational level and age influence spatial working memory and Wisconsin Card Sorting Test performance differently: a controlled study in schizophrenic patients.

The influence of educational level and age on executive function, as evaluated by the Wisconsin Card Sorting Test (WCST), and 'working memory,' as evaluated by means of a visual-manual delayed-response task, has been investigated in 25 schizophrenic patients and 35 healthy controls matched for age. Different patterns of correlations between educational level, age and cognitive variables were seen for the 'working memory' task but not for the WCST. No significant correlations between the WCST and the 'working memory' task indexes have been observed. Based on multivariate analyses, poor performance of schizophrenic patients on working memory and executive function tasks was observed; after covarying for the educational level, group differences were no longer significant for executive functions, but the difference in 'working memory' performance persisted. The implications of sociodemographic variables as well as the role of statistical manipulation are evaluated and their differential impact on 'working memory' and executive functions is proposed in further support of these neurocognitive constructs that may be dissociable.

Adolescent↗
PubMed2003

The cognitive and anatomo-functional basis of reality distortion in schizophrenia: a view from memory event-related potentials.

This study investigated the neural and cognitive correlates of reality distortion in schizophrenia by using event-related potentials (ERPs) recorded in a recognition memory task for face. This task has been chosen because previous studies have shown that it provides distinct indices related to specific cognitive processes and to the functioning of specific brain regions. ERPs have been recorded in controls and schizophrenia patients separated into high scorers (RD+) and low-scorers (RD-) according to their Reality Distortion score (hallucination and delusion SAPS subscales). The results indicate that RD+ presents abnormalities on various cognitive processes. First, RD+ are deficient at interference inhibition and knowledge integration (reduced P2a and N400 effect). The similar impairments found in RD- suggest that they represent basic traits of the illness. Second, RD+ showed inappropriate stimulus categorization and contextual integration (larger N300 and fronto-central effect). Third, RD+ showed a late index (P600 effect) not different from controls, but larger than in RD-. This result is consistent with a qualitative, rather than quantitative, impairment of mnemonic binding processes (inappropriate binding) in RD+. Since each of the ERP abnormalities observed represents associated with distinct brain dysfunction, the results are further discussed in regard of the respective contribution of the parietal, frontal and hippocampal structures to reality distortion symptoms.

Adult↗
PubMed2002

Processing of temporal duration information in working memory after frontodorsal tumour excisions.

This study aimed to test the hypothesis that impairments of temporal duration processing after frontal lobe lesions reflect deficits in executive monitoring functions rather than a domain-specific deficit in the maintenance of duration information in working memory. Patients with frontodorsal lesions, clinical controls with post-central lesions, and healthy controls performed recognition and classification tasks, which should allow for testing maintenance and monitoring functions, respectively. Results showed mild non-selective impairments of the frontal patients on both temporal and spatial recognition tasks, but a marked selective degradation on temporal classification while performance on spatial classification was unimpaired. This suggests that maintenance of duration information in working memory after frontal lesions is basically preserved but that, depending on executive task characteristics, there is a specific deficit in the strategic organization of this type of information.

Adult↗
PubMed1998

Neuropsychological correlates of negative, disorganized and psychotic symptoms in schizophrenia.

Recent studies suggest that three dimensions (negative, disorganized and psychotic) categorize schizophrenic symptoms. A developing literature indicates distinct cerebral correlates of each symptom cluster, but few investigations have determined their neuropsychological correlates. In the present study, the Schedules of Negative and Positive Symptoms measured symptom severity in 62 schizophrenics, and a subsequent principal components analysis revealed three symptom dimensions. Factor scores, age and parental socio-economic status were simultaneously entered into regression equations to explain variance across a broad neuropsychological test battery. Negative symptoms were associated with deficits involving intelligence, executive function, memory, sustained-attention and sensory-motor function, whereas disorganized symptoms correlated with decreased intelligence, attention-span and sensory-motor function. Psychotic symptoms were unrelated to deficits. These data are consistent with hypotheses that these three symptom dimensions have distinct neurobehavioral correlates.

Adolescent↗
PubMed2000

Addiction and its reward process through polymorphisms of the D2 dopamine receptor gene: a review.

Since 1990, association studies have amassed strong evidence implicating the D(2) dopamine receptor (DRD2) gene in alcoholism. Specifically, the TaqI A minor (A1) allele of the DRD2 gene has been associated with alcoholism. The DRD2 gene has also been found to be involved in other substance use disorders including cocaine, nicotine and opioid dependence, and obesity. Beyond association studies, pharmacologic studies have shown reduced brain D(2) dopamine receptor numbers in A1(+) allele carriers (A1A1 and A1A2 genotypes) compared to A1(-) allele carriers (A2A2 genotype). Through a number of other approaches, different phenotypes have also been identified in subjects with the A1(+) and A1(-) alleles. These include metabolic, neurophysiological, neuropsychological, personality, stress and treatment studies. It is hypothesized that in an effort to compensate for deficiencies in the dopaminergic system, substance abusers may seek to stimulate the mesocorticolimbic circuits of the brain, long thought to be important in behavioral reward and reinforcement. In effect, one form of the DRD2 gene, the A1 allele, renders the dopaminergic system inefficient and rewards substance abuse that increases brain dopamine levels.

Alcoholism↗