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Biomedical subjects

David Q Beversdorf

Publications and source records attributed to David Q Beversdorf.

14 recordsLinked to original sources
PubMed2007

Network model of decreased context utilization in autism spectrum disorder.

Individuals with autism spectrum disorders (ASD) demonstrate impaired utilization of context, which allows for superior performance on the "false memory" task. We report the application of a simplified parallel distributed processing model of context utilization to the false memory task. For individuals without ASD, experiments support a model wherein presentation of one word, e.g., ''apple,'' strongly activates the neighboring nodes of closely related words such as ''fruit,'' ''tree,'' whereas in ASD these neighboring nodes are relatively less activated. We demonstrate this model to be consistent with the superior performance on recognition testing on the false memory test, but not on free recall. This may have an anatomic basis in diminished hippocampal neuronal arborization and the abnormal minicolumnar pathology in ASD.

Association Learning↗
PubMed2006

Blipped multi gradient-echo slice excitation profile imaging (bmGESEPI) for fast T2 * measurements with macroscopic B0 inhomogeneity compensation.

With the rapid development of human MRI at field strengths > or = 7 T, knowledge of T(2) (*) relaxation times at such field strengths is needed to optimize acquisition parameters and understand relaxation mechanisms in many applications. However, standard T(2) (*) measurements (e.g., using conventional multiecho gradient-echo (GE) sequences) are affected by macroscopic static magnetic field (B(0)) inhomogeneities, which are particularly severe at high field strength. The multi-GE slice excitation profile imaging (mGESEPI) method was developed for T(2) (*) measurements in the presence of macroscopic B(0) inhomogeneity, but it requires excessive acquisition times at field strengths > or = 7 T. In this paper a more efficient technique, named blipped mGESEPI (bmGESEPI), is proposed. To demonstrate its advantages, T(2) (*) maps were acquired using a conventional multiecho GE method, the mGESEPI method, and the bmGESEPI method in postmortem and in vivo human brains at 8 T.

Algorithms↗
PubMed2006

The effect of auditory stressors on cognitive flexibility.

Stress is known to activate the noradrenergic system which may have a modulatory influence on cognitive flexibility. We investigated whether an auditory stressor would thus affect performance on cognitive flexibility. A task utilizing cognitive flexibility and two memory tasks were presented in both stressful and non-stressful condition. In the stressful condition performance was impaired for the cognitive flexibility task but not for the memory tasks, arguing against the stressor serving as a general distracter. These findings suggest that stress caused by an auditory stressor may negatively impact performance on more complex tasks requiring a rapid search of the semantic and lexical associative networks.

Acoustic Stimulation↗
PubMed2006

Apparent transient effects of recent "ecstasy" use on cognitive performance and extrapyramidal signs in human subjects.

OBJECTIVES: Our purpose is to investigate cognitive performance and extrapyramidal function early after ecstasy use. BACKGROUND: Ecstasy, containing 3,4 methylenedioxymethamphetamine, has shown evidence of causing cognitive deficits and parkinsonian signs. Previous research has examined cognitive performance after a period of prolonged abstinence, but research assessing the early effects of ecstasy after recent use is limited despite temporal neurochemical differences demonstrated in nonhuman models. METHODS: This study compared task performance between 13 ecstasy users (10 to 15 h postdrug use) and a control group on a battery of neuropsychologic assessments while matching for education level, sleep deprivation, and premorbid IQ. The groups were also compared on measures relating to parkinsonian signs. RESULTS: The ecstasy subjects showed impairments on measures of executive function as evaluated by Raven's Standard Progressive Matrices (SPM) and the Wisconsin Card Sorting Task (WCST). Short-delay free recall memory was also impaired in ecstasy subjects on the California Verbal Learning Test (CVLT-II). No extrapyramidal motor impairments were detected. CONCLUSIONS: These deficits resemble deficits previously reported in chronic ecstasy use but also seem to reveal transient impairments in executive function. Future research is needed to better understand the neurologic and neuropsychologic implications of ecstasy use across time and extent of use.

Adult↗
PubMed2006

An fMRI study of semantic priming: modulation of brain activity by varying semantic distances.

OBJECTIVE: Our purpose was to study the effect of semantic priming at varying semantic distances on brain activation during a lexical decision experiment, using functional magnetic resonance imaging (fMRI). BACKGROUND: Neuroimaging studies have demonstrated decreased brain activation for primed versus unprimed stimuli in language areas due to semantic priming, suggesting facilitated semantic retrieval. However, the effect of varying semantic distances on brain activation has not been studied. Therefore we examined direct and indirect priming effects on cerebral activation to provide information regarding spread of activation in the semantic network. METHODS: Participants were presented with closely, distantly, and unrelated word pairs during fMRI, and asked to make a lexical decision on the second word. RESULTS: Behavioral measurements demonstrated significant priming effects for all semantic distances. Imaging results showed modulation of brain activation due to different semantic relationships in the left inferior frontal gyrus, bilateral middle frontal gyrus and anterior temporal lobe, and consisted of decreased magnitude of activation when primed stimuli were processed compared with unprimed stimuli, with the greatest effect observed for closely related words. CONCLUSIONS: This study demonstrates graduated effects of semantic priming on fMRI in semantic but not attentional brain regions, contributing to explain how semantic knowledge is organized and retrieved. These findings support the network model for organization of the semantic lexicon.

Adult↗
PubMed2006

The effect of alpha-2 adrenergic agonists on memory and cognitive flexibility.

BACKGROUND: The noradrenergic system modulates cognitive flexibility for insight-based problem solving in studies using beta-adrenergic antagonists, which block noradrenergic neurotransmission postsynaptically. However, it is not known whether alpha2-adrenergic agonists, that decrease noradrenergic neurotransmission by presynaptic inhibition, have the same effect. OBJECTIVES: Therefore, we wished to test whether alpha2-adrenergic agonists would have a similar effect on cognitive flexibility. METHODS: Eighteen normal adults were tested on cognitive flexibility, problem solving, verbal and spatial memory tasks after receiving clonidine (0.1 mg), an alpha2-agonist, placebo, or ephedrine (25 mg), a noradrenergic stimulant. RESULTS: Three-way analysis of variance revealed no significant drug effect on cognitive flexibility or problem solving. There was also no significant effect of clonidine on memory. CONCLUSIONS: Therefore, alpha2-agonists do not influence cognitive flexibility in the same manner as beta-antagonists. Better performance on memory with clonidine might be expected based on primate studies demonstrating benefits in working memory using clonidine. This benefit was not observed for the commonly used clinical memory tasks in our study. This may have implications for why clonidine has not demonstrated efficacy for cognitive disorders such as Alzheimer disease, despite its known benefit for working memory in animal models.

Adolescent↗
PubMed2005

Effects of static and radiofrequency magnetic field inhomogeneity in ultra-high field magnetic resonance imaging.

To characterize the severe static (B(0)) and radiofrequency (B(1)) magnetic field inhomogeneity in ultra-high field (> or =7 T) magnetic resonance imaging, gradient echo (GE) and spin echo (SE) images of in vivo and postmortem human brains were acquired. The B(0) and B(1) inhomogeneity were experimentally mapped and/or numerically simulated, and correlated with the image artifacts. Whereas B(0) inhomogeneity affects predominantly GE images near air/tissue interfaces, B(1) inhomogeneity affects SE images more severely and shows non-intuitive patterns. Mapping of the B(0) and B(1) inhomogeneity is important in characterizing image artifacts. This will help develop better B(0) and B(1) inhomogeneity correction methods.

Adult↗
PubMed2005

High-resolution 8 Tesla imaging of the formalin-fixed normal human hippocampus.

The purpose of this study was to evaluate the capacity of high-resolution magnetic resonance imaging (MRI) to visualize the normal anatomic features of the human hippocampus in vitro, using high field imaging equipment, parameters, and acquisition times appropriate for imaging human subjects in vivo. This research compared high field, high-resolution MRI of formalin-fixed normal human hippocampus specimens to histologic sectioning of the same hippocampus samples. Four specimens were evaluated using an 8 Tesla (T), 80 cm bore whole-body MRI scanner equipped with a 12.7 cm single strut transverse electromagnetic resonator (TEM) coil. Hahn spin echo images were acquired with a repetition time (TR) of 800 msec, echo times (TE) of 20, 50, 90, and 134 msec, and an acquisition time (TA) of 3.25 min. The image quality was superb with demonstration of most of the features of the hippocampus. High field, high-resolution MRI can be used to depict multiple layers of the formalin-fixed human hippocampus in vitro using an 8 T whole-body scanner, a TEM coil, and short acquisition times compatible with human imaging in vivo.

Aged↗
PubMed2005

Cognitive impairment in acute cocaine withdrawal.

UNLABELLED: To perform a pilot study to examine a range of cognitive flexibility tasks early in cocaine withdrawal. BACKGROUND: Previous neuropsychological investigations of cocaine withdrawal have conflicted regarding whether impaired cognitive flexibility occurs. However, most studies have examined patients later in withdrawal. Anxiety and yohimbine-induced panic are greatest early in withdrawal, and both anxiety and increased noradrenergic tone can impair cognitive flexibility. METHOD: Twelve patients acutely withdrawing from cocaine were compared with gender-, age-, and estimated premorbid intelligence-matched control subjects on tests of cognitive flexibility as well as verbal fluency, verbal memory, spatial memory, and attention. RESULTS: As predicted, impairments were found on the cognitive flexibility tasks. Impairments also were present in verbal fluency and verbal memory but not spatial memory or attention. CONCLUSIONS: We propose that the cognitive flexibility impairment may relate to the increased noradrenergic activation recently described in cocaine withdrawal. Impairments on verbal tasks may also relate to an impaired flexibility in the search of semantic networks. Further research will explore the effects of pharmacologic manipulation of the noradrenergic system on cognition in acute withdrawal. Recently, propranolol has been shown to benefit patients in cocaine withdrawal. Further research will explore whether impaired cognitive flexibility related to altered noradrenergic tone could serve as a mechanism for this treatment response.

Acute Disease↗
PubMed2004

Effect of anxiolytics on cognitive flexibility in problem solving.

OBJECTIVE: Our purpose is to examine the effect of different classes of anxiolytics on cognitive flexibility. BACKGROUND: Situational stressors and anxiety impede performance on "creativity" tests requiring cognitive flexibility. Noradrenergic agents have been shown to modulate cognitive flexibility as assessed by performance on anagrams. To determine whether these findings on noradrenergic modulation of cognitive flexibility are specific to the noradrenergic system or are a nonspecific anxiety effect, we compared the effects of propranolol, lorazepam, and placebo on the anagram task. METHODS: Subjects attended 3 test sessions. Prior to each session, subjects were given 1 of the 3 drugs. As in previous research, the natural log of the solution latency of each test item was summed for each test session and compared across drug conditions. RESULTS: For subjects able to solve the anagrams, solution times after propranolol, but not lorazepam, were significantly lower than after placebo. CONCLUSIONS: Therefore, this suggests that the phenomenon of noradrenergic modulation of cognitive flexibility does not result from a nonspecific anxiolytic effect, but rather is specific to the noradrenergic system.

Administration, Oral↗
PubMed2002

Central beta-adrenergic modulation of cognitive flexibility.

Situational stressors and anxiety impede performance on creativity tests requiring cognitive flexibility. Preliminary research revealed better performance on a task requiring cognitive flexibility, the anagram task, after propranolol (beta-adrenergic antagonist) than after ephedrine (beta-adrenergic agonist). However, propranolol and ephedrine have both peripheral and central beta-adrenergic effects. In order to determine whether noradrenergic modulation of cognitive flexibility is a centrally or peripherally mediated phenomenon, we compared the effects of propranolol (peripheral and central beta-blocker), nadolol (peripheral beta-blocker), and placebo on anagram task performance. Solution latency scores for each subject were compared across the drug conditions. Anagram solution latency scores after propranolol were significantly lower than after nadolol. This suggests a centrally mediated modulatory influence of the noradrenergic system on cognitive flexibility.

Adrenergic beta-Agonists↗
PubMedDate not supplied

Combination therapy of donepezil and vitamin E in Alzheimer disease.

A retrospective chart review was performed on 130 patients from the Ohio State University Memory Disorders Clinic to examine the long-term effects of combination therapy with donepezil and vitamin E on patients with Alzheimer disease. Subjects were included if they met National Institute of Neurological and Communicative Disorders and Stroke and Alzheimer's Disease and Related Disorders Association criteria for probable Alzheimer disease, had taken at least 5 mg donepezil and at least 1000 U vitamin E daily, had at least a 1-year follow-up while continuing these medications, and had a Mini-Mental State Examination score of 10-24. The Mini-Mental State Examination was then recorded annually thereafter. These data were compared with the Consortium to Establish a Registry for Alzheimer's Disease database for patients collected prior to the availability of these treatment options. Patients declined at a significantly lower rate as compared with the Consortium to Establish a Registry for Alzheimer's Disease data. The long-term combination therapy of donepezil and vitamin E appears beneficial for patients with Alzheimer disease. Future prospective studies would be needed to compare combination treatment to vitamin E and donepezil alone.

Aged↗
PubMedDate not supplied

A pilot open-label trial of citalopram for restless activity and aberrant motor behaviors in Alzheimer disease.

OBJECTIVE: In a prospective, open-label pilot study in probable-Alzheimer disease (AD) outpatients, the authors investigated the efficacy of citalopram to reduce restless activity and aberrant motor behaviors. METHODS: Nineteen subjects were evaluated with Neuropsychiatric Inventory subscale and total scores. RESULTS: There was a significant decline in aberrant motor behaviors and overall behavior problems at 4, 8, and 12 weeks. CONCLUSION: This study provides initial evidence that citalopram may be effective in reducing aberrant motor behaviors in AD. However, because of the potential biases of an open-label study, these findings need to be confirmed in a larger, controlled trial.

Aged↗