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Biomedical subjects

David Wilkins

Publications and source records attributed to David Wilkins.

9 recordsLinked to original sources
PubMed2006

Clinical and anatomical correlates of apraxia of speech.

In a previous study (Dronkers, 1996), stroke patients identified as having apraxia of speech (AOS), an articulatory disorder, were found to have damage to the left superior precentral gyrus of the insula (SPGI). The present study sought (1) to characterize the performance of patients with AOS on a classic motor speech evaluation, and (2) to examine whether severity of AOS was influenced by the extent of the lesion. Videotaped speech evaluations of stroke patients with and without AOS were reviewed by two speech-language pathologists and independently scored. Results indicated that patients with AOS made the most errors on tasks requiring the coordination of complex, but not simple, articulatory movements. Patients scored lowest on the repetition of multisyllabic words and sentences that required immediate shifting between place and manner of articulation and rapid coordination of the lips, tongue, velum, and larynx. Last, all patients with AOS had lesions in the SPGI, whereas patients without apraxia of speech did not. Additional involvement of neighboring brain areas was associated with more severe forms of both AOS as well as language deficits, such as aphasia.

Adult↗
PubMed2006

Role of frontal versus temporal cortex in verbal fluency as revealed by voxel-based lesion symptom mapping.

Category and letter fluency tasks have been used to demonstrate psychological and neurological dissociations between semantic and phonological aspects of word retrieval. Some previous neuroimaging and lesion studies have suggested that category fluency (semantic-based word retrieval) is mediated primarily by temporal cortex, while letter fluency (letter-based word retrieval) is mediated primarily by frontal cortex. Other studies have suggested that both letter and category fluency are mediated by frontal cortex. We tested these hypotheses using voxel-based lesion symptom mapping (VLSM) in a group of 48 left-hemisphere stroke patients. VLSM maps revealed that category and letter fluency deficits correlate with lesions in temporal and frontal cortices, respectively. Other regions, including parietal cortex, were significantly implicated in both tasks. Our findings are therefore consistent with the hypothesis that temporal cortex subserves word retrieval constrained by semantics, whereas frontal regions are more critical for strategic word retrieval constrained by phonology.

Adult↗
PubMed2005

Is problem solving dependent on language?

There has been a long-standing debate in the fields of philosophy and cognitive science surrounding the relationship of language to cognition, but the exact nature of this relationship is still unclear (Sokolov, 1968/1972). In the current study, we explored the role of language in one aspect of cognition, namely problem solving, by administering the Wisconsin Card Sorting Test (WCST) to stroke patients with varying degrees of language impairment (Experiment 1) and to normal participants under conditions of articulatory suppression (Experiment 2). In Experiment 1, there was a significant correlation between performance on the WCST and language measures such as comprehension and naming. Demonstrating the specificity of this result, we also found a significant relationship between language performance and another test of problem solving, the Raven's Colored Progressive Matrices, but no relationship between language and a test of visuospatial functioning. In Experiment 2, normal participants were significantly impaired on the WCST under conditions of articulatory suppression, relative to a baseline condition. Together, these findings suggest that language plays a role in complex problem solving, possibly through covert language processes.

Adult↗
PubMed2004

Correlating the degree of needle trauma during prostate brachytherapy and the development of acute urinary toxicity.

PURPOSE: To determine if there is an association between the degree of prostate trauma during prostate brachytherapy and development of acute urinary toxicity. METHODS AND MATERIALS: In a consecutive prospective cohort of permanent (125)I prostate brachytherapy patients, the number of times each needle was repositioned was tracked, and the dosimetry plans were used to determine the number of times needles within 1 cm of the urethra were manipulated. Additionally, prostate volume, total number of needles, number of needles/prostate volume, and the number of periurethral needle manipulations/prostate volume were determined. The need for catheterization beyond 24 hours and the Radiation Therapy Oncology Group (RTOG) urinary toxicity score at 4 weeks were recorded. The independent samples t test was used to search for a correlation between these parameters and the recorded toxicity scores. RESULTS: Twenty-eight consecutive implant patients were evaluated in the study. Median (range) values were as follows: prostate volume 35 cc ( range, 15-51 cc), number of needles per patient 32 (range, 21-41), number of needle manipulations per patient 94.5 ( range, 55-147), and number of periurethral needle manipulations 42 (range, 17-65). The only significant association between urinary toxicity and these variables was for the number of periurethral needle manipulations (p = 0.025). CONCLUSIONS: These data provide evidence that needle prostate trauma during brachytherapy contributes to acute urinary toxicity.

Acute Disease↗
PubMed2004

TCP isoeffect analysis using a heterogeneous distribution of radiosensitivity.

A formula for the alpha/beta ratio is derived using the heterogeneous (population averaged) tumor control model. This formula is nearly identical to the formula obtained using the homogeneous (individual) tumor control model, but the new formula includes extra terms showing that the alpha/beta ratio, the ratio of the mean value of a divided by the mean value of beta that would be observed in a patient population, explicitly depends on the survival level and heterogeneity. The magnitude of this correction is estimated for prostate cancer, and this appears to raise the mean value of the ratio estimate by about 20%. The method also allows investigation of confidence limits for alpha/beta based on a population distribution of radiosensitivity. For a widely heterogeneous population, the upper 95% confidence interval for the alpha/beta ratio can be as high as 7.3 Gy, even though the population mean is between 2.3 and 2.6 Gy.

Cell Survival↗
PubMed2003

Comparison of alpha/beta estimates from homogeneous (individual) and heterogeneous (population) tumor control models for early stage prostate cancer.

Radiobiological parameter estimates for prostate cancer are obtained from both a homogeneous (individual) and heterogeneous (population) tumor control model based on Poisson statistics and the linear quadratic model of cell survival. Parameter estimates for both models are highly correlated: statistically equivalent fits are achievable using either (1) linear quadratic (LQ) parameters with low numbers of radioresistant tumor stem cells, or (2) LQ parameters with corresponding larger number of radiosensitive tumor stem cells. A theoretical framework is developed to explain this correlation. A Monte Carlo error analysis based on binomial statistics is used to estimate confidence intervals for all parameter estimates. It was found that both the homogeneous and heterogeneous models produce approximately equivalent estimates of radiobiological parameters, including the alpha/beta ratio. However, the 95% confidence interval for the alpha/beta ratio derived from the heterogeneous model are considerably larger than those derived from the homogeneous model, which indicate the homogeneous model overestimates the statistical significance of the alpha/beta estimate.

Cell Survival↗