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1.  Differential effects of COMT on gait and executive control in aging 
Neurobiology of aging  2008;31(3):523.
Walking speed is associated with attention and executive control processes subserved by the prefrontal cortex. Because polymorphisms in COMT influence these cognitive processes we hypothesized that the same polymorphisms may influence gait velocity. We examined the associations between the Val 158 Met polymorphism in COMT and gait velocity as well as attention and executive function. Participants were 278 non-demented older adults. The results revealed that Met/Val was associated with faster gait velocity. This association can be explained by the putative role of the Val allele in regulating tonic dopamine release in the striatum. In contrast, Met/Met was associated with better attention and executive function. Stratification by gender revealed that the association between COMT genotype and gait was significant only in men. Conversely, the association between COMT genotype and attention and executive function was significant only in women. These findings suggest a differential effect in relating the Val158 Met polymorphism to gait and to cognitive function while supporting the previously described sexual dimorphism in the phenotypic expressions of COMT.
PMCID: PMC2821742  PMID: 18547681
Gait velocity; COMT; Cognition; Aging; Attention; Executive Function
2.  Extending the Administration Time of the Letter Fluency Test Increases Sensitivity to Cognitive Status in Aging 
Experimental aging research  2009;35(3):317-326.
We examined whether extending the administration time of letter fluency from one minute per letter trial (standard administration) to two minutes increased the sensitivity of this test to cognitive status in aging. Participants (mean age = 84.6) were assigned to cognitive impairment (n=20) and control (n=40) groups. Pearson correlations and scatter plot analyses showed that associations between the Dementia Rating Scale scores and letter fluency were higher and less variable when performance on the latter was extended to two minutes. ANOVA showed that the cognitive impairment group generated fewer words in the second minute of the letter fluency task compared to the control group. Finally, discriminant function analyses revealed that extending the letter fluency trials to two minutes increased discrimination between the control and cognitive impairment groups.
PMCID: PMC2832286  PMID: 19449244
letter fluency; aging; cognitive impairment
3.  The relationship between subjective reports of fatigue and executive control in Multiple Sclerosis 
Previous studies failed to show a relationship between fatigue and cognitive performance. We used a theory-based Delayed Item Recognition (DIR) paradigm to examine the hypothesis that subjective reports of fatigue and executive control processes were related in MS. Participants were 20 individuals diagnosed with definite diagnosis of MS with Relapsing-Remitting course and 20 controls case matched for age, sex, education and IQ. The DIR paradigm manipulated executive demands in three conditions: Alone, Partial Interference (PI), and Complete Interference (CI). Fatigue was assessed using the Fatigue Severity Scale (FSS). Results: ANOVA Repeated measures analyses showed that DIR performance was slower and less accurate as a function of MS and increased executive demands across the three task conditions. Separate linear regressions revealed that fatigue was related to DIR reaction time and accuracy performance only in the CI condition where executive demands are maximized, and only in the MS group. The present study provided first behavioral evidence that fatigue and executive control are uniquely related in MS.
PMCID: PMC2734416  PMID: 19303081
Multiple Sclerosis; Executive Control; Fatigue; Cognitive Function

Results 1-3 (3)