Biomedical subjects

Howard Chertkow

Publications and source records attributed to Howard Chertkow.

10 recordsLinked to original sources

PubMed2003

Semantic category differences in cross-form priming.

Findings of category-specific impairments have suggested that human semantic memory may be organized around a living/nonliving dichotomy. In order to assess implicit memory performance for living and nonliving concepts, one group of neurologically intact individuals participated in a cross-form conceptual priming paradigm. In Block 1, pictures primed words while in Block 2 words were used to prime pictures. Across all phases of the experiment, subjects decided whether items represented something which was living or nonliving, and response times were recorded. Results revealed greater priming for living concepts across both blocks. Greater priming for living concepts may have occurred because of increased or prolonged conceptual activation of these concepts. Results are discussed in the context of theoretical accounts of the category-specific impairments observed in brain-damaged populations.

Adolescent↗

PubMed2002

Regional magnetization transfer ratio changes in mild cognitive impairment.

Reduction in temporal lobe volume is consistently found in dementia of Alzheimer's type (DAT). However, due to the lack of a consistent association between brain volume and cognitive decline in mild cognitive impairment (MCI), volumetric measures are not a reliable predictor for the progression of the disease. In our study, we hypothesized that changes in the magnetization transfer ratio (MTR) may reflect underlying brain pathology in the absence of quantifiable volumetric changes. Such a measure may be used as a predictor for abnormal cognitive decline in elderly subjects. The study was carried out on 15 normal elderly controls, 11 subjects with DAT, and 12 subjects with MCI. We used MTRs with magnetic resonance imaging (MRI) to detect tissue changes in the four lobes of each hemisphere, and compared that to the volumetric changes in the same regions. Our results indicate that the MTR of both temporal lobes is significantly reduced in subjects with MCI in the absence of significant volumetric changes. In comparison, DAT subjects have significantly reduced temporal lobe volumes and MTR. We conclude that changes in MTR have the potential to mark the progression of MCI to DAT, before volumetric changes are detected on conventional MRI scans.

Aged↗

PubMed2002

Magnetization transfer ratio in mild cognitive impairment and dementia of Alzheimer's type.

Almost half of the elderly subjects that are diagnosed with mild cognitive impairment (MCI) go on to develop dementia of Alzheimer's type (DAT) over a 5-year follow-up. MCI and DAT subjects show regional decreases in the volume of brain structures, which correlate with the cognitive decline among these groups. Volumetric changes are found more consistently in the DAT group than in the MCI group. Since not all MCI subjects demonstrate volumetric decline, we propose that the underlying changes in the structural integrity of the brain, measured using magnetization transfer ratio (MTR), may be used as an additional predictor for abnormal cognitive decline in the elderly. Magnetic resonance (MR) images were obtained in 15 DAT, MCI, and elderly control subjects. Using automatic tissue classification, the brain region of each MR volume was segmented into gray matter and white matter. Mean and standard error of the mean MTR measured within the gray matter was found to be significantly lower in the MCI (30.77 +/-0.29; P = 0.037) and the DAT (29.37 +/-0.41; P = 0.000) group compared to the control group (32.11 +/-0.20). The MTR of white matter was significantly lower only in the DAT group. The gray matter volume was significantly lower (P = 0.000) in the DAT (387.29 +/-26.04 cm(3)) group compared to controls (532.93 +/-20.53 cm(3)) and MCI (464.64 +/-16.93 cm(3)). No significant differences were found in the white matter volume between the three groups. We conclude that changes in MTR are measurable even in the absence of detectable volumetric changes in gray and white matter in the MCI group. Furthermore, MTR changes may present a novel MRI measure for the early diagnosis of dementia of Alzheimer's type.

Aged↗

PubMed2002

Semantic memory.

Our concepts about objects, states, and events are stored in a cognitive structure termed semantic memory. There are several types of neurologic disorders that may cause impairments of semantic memory. Clinical evaluations of these impairments are complex, because semantic memory is linked to other cognitive systems that, when damaged, may produce related syndromes or difficulties. In an attempt to gain further understanding of these breakdown patterns, we review data from both neuropsychologic and brain activity research that have been concerned with how object concepts are represented and localized in the brain. Although these data have spawned varying and controversial views regarding the content and organization of semantic knowledge, converging evidence suggests that semantic memory is mainly localized in the posterior region of the left temporal lobe, and that particular categories of knowledge may be represented in different but overlapping regions within this area.

Functional Laterality↗

PubMed2002

Increased variability accompanies frontal lobe damage in dementia.

Performance variability on neuropsychological measures is not a unitary phenomenon, and different measures (consistency, dispersion, diversity) evaluate separate elements of variability. It has been suggested that increased variability may be a specific attribute of frontal lobe pathology. This hypothesis was tested in 2 matched groups of demented subjects, 8 with dementia of the Alzheimer type (DAT), 5 with frontal lobe dementia (FLD), compared with 10 elderly normal controls (ENC). A Stroop test and Reaction Time measures were administered weekly for 5 weeks to all subjects. Both measures contained three subtests varying in degree of complexity. The results from the Stroop task indicated that the FLD group showed significantly greater variability on measures of consistency (fluctuations over time) and diversity (between participant variability) regardless of the complexity of the subtest. For the Reaction Time subtests, measures of consistency and diversity showed significantly greater variability in FLD, but were affected in a different pattern. Greater variability in terms of consistency of performance was manifested only in the more attentionally demanding of the Reaction Time subtests (Choice Reaction Time, CRT). On the measure of diversity, variable performance was found to be greater on the Simple Reaction Time (SRT) subtest than on the more effortful CRT. Dispersion (within participant variability) was only assessed on the reaction time subtests. The results indicate no significant evidence for an increase in dispersion for the FLD patients. The hypothesis that variability will be increased in frontal lobe dementia is thus confirmed, and the independence of the three forms of variability measurement is demonstrated in dementia subjects.

Aged↗

PubMed2002

A case study of pure word deafness: modularity in auditory processing?

AL, a woman with an acquired disturbance of auditory processing beginning in the second decade, was originally diagnosed as having pure word deafness. Recent analysis with a wide range of stimuli suggests that her comprehension deficit also extends to a subset of musical and non-verbal environmental sounds. The perceptual demands of the different auditory stimuli appear to account for part of the apparent material specificity. Additionally, over the years, the presumed temporal lobe cortical pathology has been supplemented by a mild to moderate, peripheral low-frequency hearing loss and evidence of dysfunction in lower level auditory processing pathways. The current peripheral dysfunction closely resembles cases recently labeled as auditory neuropathy. The diagnosis of pure word deafness should not be based on a limited set of auditory stimuli; additionally, a careful assessment using modern audiological techniques should be performed to evaluate peripheral auditory functions.

Achievement↗

PubMed2002

Mild cognitive impairment.

Mild cognitive impairment is an emerging term that encompasses the clinical state between elderly normal cognition and dementia. Controversy surrounds its characterization, implementation, and definition. Mild cognitive impairment is now the focus of natural history studies, biomarker studies, along with Alzheimer's disease prevention studies. The mild cognitive impairment stage may be the optimum stage at which to intervene with preventive therapies. Depending on the cohort source and definition, between 19 and 50% of mild cognitive impairment individuals progress to dementia (usually Alzheimer's disease) over 3 years. Despite controversy, progress has been achieved in defining risk factors for progression from mild cognitive impairment to dementia. New treatments to prevent development of Alzheimer's disease are targeting mild cognitive impairment as a treatment group and neurologists will increasingly be called upon to make this diagnosis.

Brain Diseases↗

PubMedDate not supplied

Word-reading thresholds in Alzheimer disease and mild memory loss: a pilot study.

PURPOSE: To determine whether subjects with early Alzheimer Disease (AD) or Mild Cognitive Impairment (MCI) would demonstrate significant abnormalities on tests of word reading threshold (WRT), spatial contrast sensitivity (SCS), and color discrimination (CD). METHODS: Prospective cohort study of 13 AD subjects, 13 subjects with Mild Cognitive Impairment (MCI), and 12 healthy elderly normal controls (ENC). CD was determined using the Farnsworth D-15 method. SCS was tested using a Vistech photographic chart. For WRT determination, pattern-masked words were presented successively at increasing target durations. The threshold was determined as the target duration at which 50% of the words were read. RESULTS: The mean number of errors in Color Discrimination and Spatial Contrast Sensitivity did not differ significantly among the three groups. WRT was significantly longer in the AD group (122.6 +/- 70.8 ms) in comparison with ENC group (53.8 +/- 15.9 ms) (p < 0.001). A WRT threshold limit of 85 msec correctly classified 11/12 ENC subjects and 10/13 AD subjects. Four of the 13 MCI subjects also exceeded this threshold and all four progressed to AD within 2 year follow-up. CONCLUSION: Word Reading Threshold determination discriminates mild AD subjects from ENC, and correlates with severity of cognitive impairment. It may have diagnostic and prognostic utility in early AD and MCI subjects.

Aged↗

PubMedDate not supplied

Visual retinocortical function in dementia of the Alzheimer type.

BACKGROUND: Some histological investigations have reported anomalies in the primary visual pathways of individuals with dementia of the Alzheimer type (DAT), while others have suggested that these visual structures are spared by the disease process. OBJECTIVES: This study was conducted to address this issue of substantial controversy. We determined in vivo whether DAT alters the functioning of the primary visual pathways by evaluating pattern-reversal electroretinograms (ERGs) and cortical visual evoked potentials (VEPs). METHODS: Twenty-seven individuals with mild to moderate DAT and 27 age- and sex-matched control subjects were included in the investigation. ERG and VEP recordings were obtained from all participants with the use of a clinical electrodiagnostic system. Stimulus conditions were biased towards a preferential response from the magnocellular and parvocellular subdivisions of the visual system. RESULTS: Amplitude and latency of the ERG were not affected by DAT. The VEP amplitude was not attenuated in DAT individuals, but there was a delay in the latency of the VEPs arising from both magnocellular and parvocellular streams of visual processing. CONCLUSION: Our results indicate that while the inner retina appears to be spared by the disease process, the visual function is altered upstream in the retinocortical visual pathways of individuals with DAT.

Aged↗

PubMedDate not supplied

Behavioral and electrical brain measures of semantic priming in patients with Alzheimer's disease: implications for access failure versus deterioration hypotheses.

This study investigated the nature of anomia and semantic memory deficits in patients with Alzheimer's disease (DAT). We measured reaction time (RT) and the N400 event-related brain potential (ERP) in a word-picture semantic priming paradigm for DAT patients and elderly controls. For patients, pictures were classified as a function of the individual's naming ability to determine whether naming deficits reflected a failure to access a picture's name or reflected a deterioration of its semantic representation. As expected, DAT patients had significantly poorer naming performance than controls. For successfully named pictures, robust RT and ERP priming effects were obtained in both groups. In DAT patients, priming for unnamed pictures was heterogeneous. The results are discussed in terms of current hypotheses of semantic memory deficits in DAT.

Aged↗