Biomedical subjects

Matthew Menear

Publications and source records attributed to Matthew Menear.

5 recordsLinked to original sources

PubMed2006

Associative memory encoding and recognition in schizophrenia: an event-related fMRI study.

BACKGROUND: We used an event-related functional Magnetic Resonance Imaging (fMRI) approach to examine the neural basis of the selective associative memory deficit in schizophrenia. METHODS: Fifteen people with schizophrenia and 18 controls were scanned during a pair and item memory encoding and recognition task. During encoding, subjects studied items and pairs of visual objects. In a subsequent retrieval task, participants performed an item recognition memory test (old/new decisions) and an associative recognition test (intact/rearranged decisions). The fMRI analysis of the recognition data was restricted to correct items only and a random effects model was used. RESULTS: At the behavioral level, both groups performed equally well on item recognition, whereas people with schizophrenia demonstrated lower performance on associative recognition relative to the control group. At the brain level, the comparison between associative and item encoding revealed greater activity in the control group in the left prefrontal cortex and cingulate gyrus relative to the schizophrenia group. During recognition, greater left dorsolateral prefrontal and right inferior prefrontal activations were observed in the control group relative to the schizophrenia group. CONCLUSION: This fMRI study implicates the prefrontal cortex among other brain regions as the basis for the selective associative memory encoding and recognition deficit seen in schizophrenia.

Adult↗

PubMed2006

Episodic memory impairment in Huntington's disease: a meta-analysis.

Memory dysfunction is an important feature in the clinical presentation of Huntington's disease (HD) and may precede the onset of motor symptoms. Although several studies have contributed to the quantitative and qualitative description of memory impairments in HD, the characterization of episodic memory impairments has varied considerably. Whereas most studies report significant impairments on free recall tests, performance on recognition tests has been considerably more variable, ranging from normal to markedly deficient. This absence of a well-established recognition memory deficit has led some investigators to attribute the memory deficits in HD to a retrieval-based episodic memory impairment. We felt that a quantitative review of the literature was needed to better characterize these episodic memory impairments. We conducted a meta-analysis to assess the magnitude of the recognition memory deficit in HD and to examine it in relation to the known deficit in recall. Memory data were provided by 544 symptomatic HD patients, 224 presymptomatic gene-carriers, and 963 control subjects. The overall group comparison between symptomatic patients and controls yielded effect sizes of d=1.95 for free recall and d=1.73 for recognition. We split the symptomatic group into two subgroups based on their mental status (mild and moderate/severe dementia) and both showed significant deficits in recall and recognition memory, though recall was more impaired than recognition in the mild dementia subgroup. Only slight memory impairment was observed in the presymptomatic subjects. The results show that deficits in recognition memory must be accounted for in future models of memory impairment in HD.

Adult↗

PubMed2006

Brain imaging and cognitive dysfunctions in Huntington's disease.

Recent decades have seen tremendous growth in our understanding of the cognitive dysfunctions observed in Huntington's disease (HD). Advances in neuroimaging have contributed greatly to this growth. We reviewed the role that structural and functional neuroimaging techniques have played in elucidating the cerebral bases of the cognitive deficits associated with HD. We conducted a computer-based search using PubMed and PsycINFO databases to retrieve studies of patients with HD published between 1965 and December 2004 that reported measures on cognitive tasks and used neuroimaging techniques. Structural neuroimaging has provided important evidence of morphological brain changes in HD. Striatal and cortical atrophy are the most common findings, and they correlate with cognitive deficits in attention, working memory and executive functions. Functional studies have also demonstrated correlations between striatal dysfunction and cognitive performance. Striatal hypoperfusion and decreased glucose utilization correlate with executive dysfunction. Hypometabolism also occurs throughout the cerebral cortex and correlates with performance on recognition memory, language and perceptual tests. Measures of presynaptic and postsynaptic dopamine biochemistry have also correlated with measurements of episodic memory, speed of processing and executive functioning. Aided by the results of numerous neuroimaging studies, it is becoming increasingly clear that cognitive deficits in HD involve abnormal connectivity between the basal ganglia and cortical areas. In the future, neuroimaging techniques may shed the most light on the pathophysiology of HD by defining neurodegenerative disease phenotypes as a valuable tool for knowing when patients become "symptomatic," having been in a gene-positive presymptomatic state, and as a biomarker in following the disease, thereby providing a prospect for improved patient care.

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PubMed2005

Associative interference does not affect recognition memory in schizophrenia.

Studies of schizophrenia suggest a specific impairment in binding different parts of a memory event into a cohesive whole, a finding that may account for the reported preferential deficits in associative recognition memory relative to item recognition. As a further test of this hypothesis and to exert greater control over task differences, we used a recognition memory interference test in which participants encoded landscape pictures that had each been divided into three segments. During encoding, subjects were presented with one segment from each of the landscapes. Then, an interference generating task followed consisting of the presentation of the second segment from half of the landscapes. Finally, a forced-choice recognition memory test consisted of the presentation of each encoding picture stimulus concurrently with the related third segment that had never been presented before. Thus, for half of the stimuli, additional related information was encoded and this is known to interfere with recognition memory. However, an impaired ability to bind this related information should reduce the interfering effect of associated stimuli. Thirty-five schizophrenia patients and 37 healthy controls were administered this memory interference task. A significant interaction between groups and recognition conditions was found with a significant interference effect observed for controls (performance dropping from 76% to 62%) but not for patients (performance remaining unchanged from 66% to 68%). These results provide further support for faulty associative memory processing in schizophrenia.

Adult↗

PubMed2004

The interfering effect of related events on recognition memory discriminability: a functional magnetic resonance imaging study.

Retrieval of information from memory often involves the selection of an event among competing related events, a process that frequently gives rise to interference effects. The present study used a forced-choice recognition test to identify neural correlates of the interfering effect of related events on recognition memory discriminability. Participants encoded landscape pictures divided into three segments. One segment was presented during encoding, and a forced-choice recognition task contrasted a studied and a nonstudied segment for each landscape. For half of the landscapes, the third segment was presented between encoding and recognition tasks to induce associative interference by reducing recognition discriminability. A behavioral study with 40 subjects yielded a significant difference in the correct recognition rate between control and interference trials (76% and 64%, respectively, p<0.001). A subsequent event-related fMRI study with 16 subjects yielded significant activations for correct interference recognition trials relative to control trials in left superior parietal regions, which suggests that these regions play a role in the representation of stimuli and associated information. The opposite contrast yielded significant activations in inferior prefrontal regions bilaterally, right dorsolateral prefrontal cortex and right parahippocampal cortex. Since this contrast was conducted using only correctly recognized trials, these findings could reflect an index of memory discriminability or saliency which could influence conscious recollection.

Adult↗