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PubMed2005

The spatial representation of numerical and non-numerical sequences: evidence from neglect.

Psychophysical and neuropsychological studies have revealed that humans represent numbers along a continuous, left-to-right oriented mental line. However, it has been recently claimed that this format of representation is not special to numbers because non-numerical sequences would be spatially coded in the same way. To test this hypothesis, the present study investigated the effects of left neglect upon the bisection of numerical and non-numerical intervals. Eight patients with left neglect performed a visual line bisection task and three mental bisection tasks with number, letter, and month intervals. The error pattern in the number bisection task, indexed by the modulating effect of interval length, mirrored that of the visual task and confirmed the left-to-right spatial orientation of the mental number line. In contrast, the bisection of non-numerical intervals showed a very different pattern. The results suggest that the spatial layout characterizing numerical representations constitutes a specific property of numbers rather than a general characteristic of ordered sequences.

Aged↗
PubMed2005

Modulation of recognition and temporal order memory retrieval by dopamine D1 receptor in rats.

The present study examines the effects of SKF 81297, a selective D1 agonist, on information retrieval in recognition and temporal order memory for objects, using three different tasks. Separate groups of rats were trained in each task and then given an intraperitoneal injection of saline or the D1 agonist (0.03, 0.3 mg/kg), before the memory testing trial in an object recognition, object location, and object temporal order memory tasks. We show that SKF 81297, at high dose (0.3 mg/kg), facilitates information retrieval after a long delay (4 h) in the three memory tasks whereas both high and low doses of D1 agonist impair recognition memory after a short delay (15 min). These results indicate a significant role of dopamine D1 receptors in recognition memory for both familiarity and place of objects in addition to object temporal order memory.

Analysis of Variance↗
PubMed2006

Attentional performance of (C57BL/6Jx129Sv)F2 mice in the five-choice serial reaction time task.

Impaired attention is evident in several neurological and psychiatric disorders. In the present study, attentional capabilities were measured in the operant five-choice serial reaction time task (5-CSRTT) in male (C57BL/6Jx129Sv)F2 hybrid (B6129F2) mice. Main aims were to validate and standardize the test in these mice: to setup procedures, measure potential beneficial effects of sub-chronic nicotine in degraded versions of the 5-CSRTT (by decreasing stimulus duration, inducing white noise and making the stimuli unpredictable) and study disruptive effects of additional administration of the muscarinic antagonist scopolamine. During the baseline pre-nicotine sessions, the B6129F2 mice attained a very good performance in the test (95% accuracy). As stimulus duration was reduced from 2 s to 1 s, response accuracy of the mice decreased. Mice treated with nicotine (0.16 mg/kg) attained significantly higher response accuracy and had a lower percentage of incorrect responses in comparison with the solvent-treated animals. No further beneficial effects of nicotine were found. Reduced response accuracy was also obtained when stimulus duration was reduced from 1 s to 0.5 s and when a variable intertrial interval was introduced. Noise interpolation between trials did not impair performance. Finally, scopolamine (0.16 mg/kg) disrupted attentional functioning. Although most studies have been performed in rats, these results add to the existing evidence that the 5-CSRTT can also be used to assess attentional performance in mice. This offers the opportunity to test transgenic and knockout mice with similar background as the B6129F2 as animal models of psychiatric and neurological diseases.

Analysis of Variance↗
PubMed2006

Impairment of event schema in patients with schizophrenia: examination of script for shopping at supermarket.

The purpose of this study was to examine event schema, the conceptualization of past experience based on script theory, in Japanese patients with schizophrenia. Subjects comprised 25 patients meeting DSM-IV criteria for schizophrenia and 31 normal individuals who gave informed consent. This experiment used three script tasks measuring free recall, frequency judgment, and sequencing of events encountered when shopping at a supermarket. Patients with schizophrenia performed significantly worse than did control subjects on all tasks. In particular, patients committed more errors when judging the events that "occasionally happen" in the frequency judgment task. On the other hand, these patients judged "seldom occurring events" relatively well. Patients with schizophrenia made more errors than normal people in the free recall task. Specifically, patients made more intrusion errors and failed to close scripts. There was a negative correlation between scores the Scale for the Assessment of Positive Symptoms and performance on the free recall task. The results of the present study suggest that event schemas (semantic structure) in patients with schizophrenia are impaired which may be associated with positive symptoms and frontal lobe dysfunction.

Activities of Daily Living↗
PubMed2004

Cognitive changes in short-term hypothyroidism assessed with event-related brain potentials.

Hypothyroidism is a common clinical problem during (131)Iodine-therapy of thyroid cancer. In the present investigation, possible cognitive dysfunction during hypothyroid state was assessed by means of neuropsychological tests and the recording of event-related brain potentials (ERPs). Fifteen patients undergoing therapy for thyroid cancer were examined twice: (1) substituted with thyroid hormones, (2) during hypothyroid state immediately prior to treatment. Standard neuropsychological tests were applied during both sessions and subjects showed a mild-to-moderate impairment in their hypothyroid state. In addition, ERPs were recorded from 19 scalp sites while subjects performed two visual search tasks. The serial task required the effortful one-by-one scanning of several items within a visual array, while the parallel task allowed processing of all stimulus items in parallel and automatically. ERPs showed a marked amplitude decrement and delay of the P3 component known to index the speed of stimulus evaluation and the amount of available processing resources. This effect was present only for the serial search task, while no changes were seen in the parallel search task. These data show that hypothyroidism during (131)Iodine-therapy is associated with clinically relevant cognitive dysfunctions, especially with effortful attention demanding tasks.

Acute Disease↗
PubMed2006

Neural correlates of working memory dysfunction in first-episode schizophrenia patients: an fMRI multi-center study.

Working memory dysfunction is a prominent impairment in patients with schizophrenia. Our aim was to determine cerebral dysfunctions by means of functional magnetic resonance imaging (fMRI) in a large sample of first-episode schizophrenia patients during a working memory task. 75 first-episode schizophrenia patients and 81 control subjects, recruited within a multi-center study, performed 2- and 0-back tasks while brain activation was measured with fMRI. In order to guarantee comparability between data quality from different scanners, we developed and adopted a standardized, fully automated quality assurance of scanner hard- and software as well as a measure for in vivo data quality. After these quality-control measures had been implemented, 48 patients and 57 controls were included in the final analysis. During attention-related processes, even when the performance between patients and controls was comparable, there was a recognizable emergence of cerebral dysfunctions with hypoactivations in the ventrolateral prefrontal cortex (VLPFC), in the superior temporal cortex and in the thalamus. During working memory performance, parietal hypoactivations, especially in the precuneus, were prominent and were accompanied by poorer performance in patients. A hyperfrontality emerged in the ventrolateral prefrontal cortex. Hence, results point to a dysfunctional ventrolateral prefrontal-parietal network during working memory in patients, suggesting impairments in basic functions such as retrieval, storage and maintenance. The brain activation pattern of this large and significant sample of first-episode schizophrenia patients indicates an imbalanced system failing to adjust the amount of brain activity required in the cerebral network involved in attention and working memory.

Adolescent↗
PubMed2006

White matter abnormalities and brain activation in schizophrenia: a combined DTI and fMRI study.

Diffusion tensor imaging (DTI) studies of schizophrenia have revealed white matter abnormalities in several areas of the brain. The functional impact on either psychopathology or cognition remains, however, poorly understood. Here we analysed both functional MRI (during a working memory task) and DTI data sets in 18 patients with schizophrenia and 18 controls. Firstly, DTI analyses revealed reductions of fractional anisotropy (FA) in the right medial temporal lobe adjacent to the right parahippocampal gyrus, likely to contain fibres of the inferior cingulum bundle, and in the right frontal lobe. Secondly, functional MRI revealed prefrontal, superior parietal and occipital relative hypoactivation in patients with the main effect of task. This was accounted for by reduced prefrontal activation during the encoding phase of the task, but not during maintenance or retrieval phases. Thirdly, we found a direct correlation in patients between the frontal FA reduction (but not medial temporal reductions) and fMRI activation in regions in the prefrontal and occipital cortex. Our study combining fMRI and DTI thus demonstrates altered structure-function relationships in schizophrenia. It highlights a potential relationship between anatomical changes in a frontal-temporal anatomical circuit and functional alterations in the prefrontal cortex.

Adult↗
PubMed2006

DRD2 C957T polymorphism interacts with the COMT Val158Met polymorphism in human working memory ability.

The C957T polymorphism in the dopamine D2 receptor (DRD2) gene and the Val158Met polymorphism in the Catechol-O-Methyl-Transferase (COMT) gene affect dopamine transmission and have been found to be associated with schizophrenia. Since DRD2 in mice and the COMT gene in humans modulate working memory, we examined the relationship and possible interaction of both polymorphisms to working memory performance in 188 healthy adults. Subjects having the DRD2 C/C allele showed the poorest performance in a word serial position test. Moreover, the effect of the C957T genotype was strengthened when interaction with the COMT Val158Met polymorphism was included in the analysis. We propose that an interaction of the DRD2 C957T and COMT Val158Met may be involved in the generation of some working memory deficits in schizophrenia.

Adolescent↗
PubMed2004

Emergence of rhythm during motor learning.

Complex motor skill often consists of a fixed sequence of movements. Recent studies show that a stereotyped temporal pattern or rhythm emerges as we learn to perform a motor sequence. This is because the sequence is reorganized during learning as serial chunks of movements in both a sequence-specific and subject-specific manner. On the basis of human imaging studies we propose that the formation of chunk patterns is controlled by the cerebellum, its posterior and anterior lobes contributing, respectively, to the temporal patterns before and after chunk formation. The motor rhythm can assist the motor networks in the cerebral cortex to control automatic movements within chunks and the cognitive networks to control non-automatic movements between chunks, respectively. In this way, organized motor skill can be performed automatically and flexibly.

Cerebellum↗
PubMed2006

Computational principles of working memory in sentence comprehension.

Understanding a sentence requires a working memory of the partial products of comprehension, so that linguistic relations between temporally distal parts of the sentence can be rapidly computed. We describe an emerging theoretical framework for this working memory system that incorporates several independently motivated principles of memory: a sharply limited attentional focus, rapid retrieval of item (but not order) information subject to interference from similar items, and activation decay (forgetting over time). A computational model embodying these principles provides an explanation of the functional capacities and severe limitations of human processing, as well as accounts of reading times. The broad implication is that the detailed nature of cross-linguistic sentence processing emerges from the interaction of general principles of human memory with the specialized task of language comprehension.

Attention↗
PubMed2006

What is the relationship between phonological short-term memory and speech processing?

Traditionally, models of speech comprehension and production do not depend on concepts and processes from the phonological short-term memory (pSTM) literature. Likewise, in working memory research, pSTM is considered to be a language-independent system that facilitates language acquisition rather than speech processing per se. We discuss couplings between pSTM, speech perception and speech production, and we propose that pSTM arises from the cycling of information between two phonological buffers, one involved in speech perception and one in speech production. We discuss the specific role of these processes in speech processing, and argue that models of speech perception and production, and our understanding of their neural bases, will benefit from incorporating them.

Attention↗
PubMed2001

Temporal-spatial memory: retrieval of spatial information does not reduce recency.

Factors influencing the shape of serial position curves in non-verbal serial short-term memory were examined, using a task testing memory for the position of dots. Similar recency slopes were found when both position and order were recalled (Experiment 1A) and when order only was required (Experiment 1B). This observation was confirmed and tested further in conditions requiring the same encoding but different amounts of spatial information at retrieval (Experiment 2). However, Experiment 2 also revealed an effect of spatial information retrieval on the overall level of memory for recency items. Overall, the results indicate that spatial items produce bow-shaped serial positions curves in tasks requiring the maintenance of order information and that recency is affected by the demand on spatial information retrieval in terms of the overall level of performance but not in terms of the recency slope. These findings are contrary to what is found in the literature on serial verbal recall when both item and order information are required.

Adult↗
PubMed1998

On the independence of modality effects and end-term and distance effects in episodic comparative judgement: dissociations of errors and reaction times.

The experiments reported in this paper explore the effect of modality variations on end-term and distance effects in an episodic comparative judgement task. In each experiment, subjects were to store serial orders of objects on a size dimension. Memory was tested after a brief retention interval by a comparative judgement task, in which subjects were presented with two elements of an order and had to point to the formerly larger one. Regarding the response times, we hypothesized that modality variations affect speed of stimulus identification and code access processes. We further hypothesized that distance variations and end-term variations affect processing components that are independent of the component affected by the modality variation. Finally, we assumed that end-term and distance effects interact in a predictable way, because they mirror competing response selection strategies. The latency data clearly support these hypotheses. As regards the accuracy data, we argued that modality and end-term effects, if they show up within the accuracy data, very likely have a different basis than the effects within the latency data. Again, the data support this assumption showing clear dissociations of accuracy and latency data. With respect to the stimulus modality variation, the whole data pattern shows that explanations which rely on modality-specific codings are not justifiable.

Adult↗
PubMed1999

Obsessive compulsive disorder, checking, and non-verbal memory: a neuropsychological investigation.

There is considerable evidence in the literature for the presence of non-verbal and praxic memory deficits in OCD. Such deficits may represent the cognitive substrate of doubt-related phenomenon such as checking. Neuropsychological tests of non-verbal memory functioning and memory for actions were administered to patients with OCD (whose predominant symptom was checking) and a group of matched healthy controls. Significant differences were found between the experimental and control groups, suggesting some memory impairment in the OCD group; however, no significant relationship was found linking neuropsychological test indices with checking. Significant relationships were found linking recognition memory problems and immediate memory for actions with general symptom severity.

Adult↗
PubMed2001

Patterns of cortical activity and memory performance in Alzheimer's disease.

BACKGROUND: Declarative memory changes are the hallmark of Alzheimer's disease, although their functional neuroanatomy is not restricted to a single structure. Factor analysis provides statistical methods for evaluating patterns of cerebral changes in regional glucose uptake. METHODS: Thirty-three Alzheimer's patients and 33 age- and gender-matched control subjects were studied with magnetic resonance imaging and positron emission tomography with [(18)F] deoxyglucose. During the tracer-uptake period, subjects performed a serial verbal learning task. Cortical activity was measured in 32 regions of interest, four in each lobe on both hemispheres. RESULTS: Factor analysis with varimax rotation identified seven factors explaining 80% of the variance ("parietal cortex," "occipital cortex," "right temporo-prefrontal areas," "frontal cortex," "motor strip," "left temporal cortex," and "posterior temporal cortex"). Relative to control subjects, Alzheimer's patients showed significantly reduced values on the factors occipital cortex, right temporo-prefrontal areas, frontal cortex, and left temporal cortex. The factor temporo-prefrontal areas showed large differences between patients with good and poor performance, but little difference when control subjects were similarly divided. CONCLUSIONS: Findings suggest that Alzheimer's disease is characterized by altered patterns of cortical activity, rather than deficits in a single location, and emphasize the importance of right temporo-prefrontal circuitry for understanding memory deficits.

Aged↗
PubMed2000

The separate but related origins of the recency effect and the modality effect in free recall.

The recency effect found in free recall can be accounted for almost entirely in terms of the recall of ordered sequences of items. It is such sequences, presented at the end of the stimulus list but recalled at the very beginning of the response protocol, which produce a recency effect. Such sequences are recalled at the beginning of the response protocol equally often following auditory and visual presentation. These same stimulus sequences are also frequently recalled other than initially in the response protocol following auditory presentation. However, such responses are rarely found following visual presentation. The modality effect in free recall, the advantage of auditory over visual presentation, can be substantially accounted for in these terms. Theoretical and procedural implications of these data are discussed.

Adult↗
PubMed2002

Motor sequencing in Parkinson's disease: relationship to executive function and motor rigidity.

Parkinson's disease (PD) is a movement disorder that also affects central cognitive processing; however, the extent to which high-order cognitive processes disrupted by PD affect complex motor function is incompletely explicated. The present analysis provides an examination of the relative contributions of simple motor versus complex cognitive functions involving sequencing, problem solving, and overall cognitive status to complex motor movements involving sequencing and temporal ordering in PD. Motor sequencing performance was videotaped for quantitative scoring. Compared with an age-matched control group, the PD group was impaired on motor agility and motor sequencing tasks in addition to cognitive sequencing and set shifting tasks. Neither current cognitive functioning, age, disease duration, nor overall intellectual abilities accounted for the relationships between motor sequencing and cognitive sequencing abilities in PD. By contrast, both sequencing and nonsequencing executive functions predicted motor sequencing performance as well as or better than motor rigidity or overall cognitive status. These relationships were strongest for the most challenging motor sequencing task, fist-edge-palm, and did not apply to the least challenging task, which required simple alternations of hand movements. Unlike PD, controls showed correlations between motor sequencing tests and executive functioning only tapping nonsequencing abilities. Thus, despite the predominant motor feature of PD, executive functions, as assessed by sequencing and set formation, predicted motor sequencing performance as well as or better than simple motor performance. The results further suggest that the more complex the motor sequencing task, the more susceptible it is to influence from generalized cognitive sequencing ability.

Adult↗