Biomedical subjects

Vincent P Clark

Publications and source records attributed to Vincent P Clark.

4 recordsLinked to original sources

PubMed2006

Differentiation of speech and nonspeech processing within primary auditory cortex.

Primary auditory cortex (PAC), located in Heschl's gyrus (HG), is the earliest cortical level at which sounds are processed. Standard theories of speech perception assume that signal components are given a representation in PAC which are then matched to speech templates in auditory association cortex. An alternative holds that speech activates a specialized system in cortex that does not use the primitives of PAC. Functional magnetic resonance imaging revealed different brain activation patterns in listening to speech and nonspeech sounds across different levels of complexity. Sensitivity to speech was observed in association cortex, as expected. Further, activation in HG increased with increasing levels of complexity with added fundamentals for both nonspeech and speech stimuli, but only for nonspeech when separate sources (release bursts/fricative noises or their nonspeech analogs) were added. These results are consistent with the existence of a specialized speech system which bypasses more typical processes at the earliest cortical level.

Acoustic Stimulation↗

PubMed2005

Low-dose estradiol alters brain activity.

Although several studies have examined the effects of estrogen replacement therapy (ERT) on neural activity associated with tasks of learning and memory, no study has examined such effects on a sustained attention task. This study examined the effect of low-dose estrogen replacement therapy on hemodynamic activity elicited by a visual three-stimulus oddball task recorded using event-related functional magnetic resonance imaging (fMRI). Participants included 16 women between the ages of 73 and 84 who were part of a randomized controlled double-blind study to evaluate the effect of an ultralow dose micronized estradiol on bone. No significant differences in behavioral performance were found with ERT. However, there was evidence that ERT group participants had both reductions and increases in the amplitude of hemodynamic response in a variety of subcortical and cortical brain regions. These included regions involved in perception and attention such as the occipital and parietal lobes, motor cortex, anterior cingulate and prefrontal cortex. These findings suggest that estrogen may facilitate the efficiency of brain function during the performance of sustained attention tasks in post-menopausal elderly women.

Aged↗

PubMed2002

Altered functional MRI responses in Huntington's disease.

This study examined the effects of Huntington's disease (HD) on neural activity during performance of the Porteus maze task. fMRI data were acquired from three HD patients and three controls. Reduced fMRI signal was observed in the patients relative to the controls in occipital, parietal and somato-motor cortex and in the caudate, while increased signal was found in HD in the left postcentral and right middle frontal gyri. The altered fMRI responses in HD patients may result from neural, metabolic, neurovascular coupling and/or hemodynamic differences associated with this disorder.

Adult↗

PubMed2002

Orthogonal polynomial regression for the detection of response variability in event-related fMRI.

Previous studies using event-related potentials (ERPs) have identified a variety of brain regions that respond to rare nontarget distractor stimuli presented in the visual oddball task. By contrast, event-related functional magnetic resonance imaging (ER-fMRI) studies using similar stimuli have found little or no response in these same regions, suggesting that ER-fMRI may be less sensitive than ERPs for detecting stimulus-evoked activity. It was hypothesized here that variations in ER-fMRI response amplitude evoked by successive stimuli may have reduced detection sensitivity in these previous studies. Multiple regression with orthogonal polynomials (OPR) was used to increase detection sensitivity by employing orthogonal polynomial equations to model such variations in response amplitude. ER-fMRI data was collected from 17 subjects during performance of the visual oddball task, which included frequent nontarget, rare nontarget distractor, and rare target block letter stimuli, to which subjects made a speeded button press response. When compared with multiple regression using main effect regressors alone, OPR identified an increased volume of significant target and distractor evoked main effect response due to reduced error variance. In addition, distractor-evoked activity was found to correlate with orthogonal polynomial regressors but not main effect regressors across a large volume of prefrontal and paralimbic brain regions including dorsal-lateral prefrontal, inferior-lateral prefrontal, and cingulate cortex. These results illustrate that considerable variability is present in ER-fMRI responses evoked by rare distractor stimuli in the oddball task. Such variability can be modeled using OPR, leading to increased detection sensitivity and better anatomical correspondence between the findings of ER-fMRI and ERP studies.

Adult↗