Christopher C. Stewart

Mental fatigue influence on effort-related cardiovascular response: Extension across the regulatory (inhibitory)/non-regulatory performance dimension ☆

Participants first performed a scanning task that was weak (fatigue low) or strong (fatigue high) in self-regulatory (inhibitory) demand. They then were presented a cognitive challenge that had a strong regulatory component (the Stroop color-word conflict task) or a weak regulatory component (single-digit mental multiplication) with instructions that they would avoid noise if they attained a moderate performance standard. Analysis of cardiovascular data collected during the two work periods revealed fatigue main effects for systolic blood pressure, diastolic blood pressure, and mean arterial blood pressure. The effects reflected stronger blood pressure responses for High Fatigue participants across work periods and regardless of the character of the challenge presented in work period 2. Results conceptually replicate previous mental fatigue findings, which have shown extension of fatigue influence across cognitive performance domains. At least as importantly, they also extend those findings by showing extension across a fresh and theoretically significant cognitive performance dimension.

Structural and functional neuroimaging correlates of depression in temporal lobe epilepsy.

Depression is commonly experienced among persons with temporal lobe epilepsy (TLE). Although evidence exists implicating dysfunction of distributed neural structure and circuitry among depressed persons without epilepsy, little is known regarding the neural correlates of depression in TLE. We examined the relationship between self-reported depression severity and both structural MRI volumetry and [(18)F]fluorodeoxyglucose positron emission tomography (PET)-measured resting metabolism of the amygdala and hippocampus of 18 patients with TLE. Significant positive relationships were noted between right and left amygdala volumes and depression. No other significant relationships were observed between amygdala PET measures, hippocampal volumes, or hippocampal PET measures and degree of depressive symptomatology. These findings indicate that both right and left amygdala volumes are associated with depression severity among persons with TLE. Future studies examining the potential role of extended neural regions may clarify the observed structural relationship between depressive symptoms and the amygdala.

Outcome expectancy as a moderator of mental fatigue influence on cardiovascular response

Female undergraduates performed an easy (fatigue low) or difficult (fatigue high) scanning task and then were presented mental arithmetic problems with instructions that they would earn a high or low chance of winning a prize if they did as well as or better than 50% of those who had performed previously. As expected, blood pressure responses in the second work period rose or tended to rise with fatigue where the chance of winning was high. By contrast, the responses tended weakly to decline with fatigue where the chance of winning was low. The pressure findings support the suggestion of a recent fatigue analysis that success importance should moderate fatigue influence on CV responses to a challenge so long as fatigued performers view success as possible. They also conceptually replicate previous fatigue results and provide a special class of evidence that fatigue influence on CV response is mediated by effort.

Magnetic Resonance Imaging Volume of the Angular Gyri Predicts Financial Skill Deficits in People with Amnestic Mild Cognitive Impairment

OBJECTIVES: To better understand how brain atrophy in amnestic mild cognitive impairment (MCI) as measured using magnetic resonance imaging (MRI) volumetrics could affect instrumental activities of daily living (IADLs) such as financial abilities.

Chapter 6 Proton Magnetic Resonance Spectroscopy In Dementias And Mild Cognitive Impairment

With the anticipated increase in dementias due to the aging demographic of industrialized nations, biomarkers for neurodegenerative diseases are increasingly important as new therapies are being developed for clinical trials. Proton MR spectroscopy ((1)H MRS) appears poised to be a viable means of tracking brain metabolic changes due to neurodegenerative diseases and potentially as a biomarker for treatment effects in clinical therapeutic trials. This review highlights the body of literature investigating brain metabolic abnormalities in Alzheimers disease, amnestic mild cognitive impairment, frontotemporal dementia, vascular dementia, Lewy body dementia, and Parkinsons disease dementia. In particular, the review addresses the viability of (1)H MRS to discriminate among dementias, to measure disease progression, and to measure the effects of pharmacological treatments. While findings to date are encouraging, more study is needed in longitudinal patterns of brain metabolic changes, correspondence with changes in clinical markers of disease progression, and sensitivity of (1)H MRS measures to treatment effects. Such developments will hopefully benefit the search for effective treatments of dementias in the twenty-first century.

Contributions of Volumetrics of the Hippocampus and Thalamus to Verbal Memory in Temporal Lobe Epilepsy Patients.

Recent theories have posited that the hippocampus and thalamus serve distinct, yet related, roles in episodic memory. Whereas the hippocampus has been implicated in long-term memory encoding and storage, the thalamus, as a whole, has been implicated in the selection of items for subsequent encoding and the use of retrieval strategies. However, dissociating the memory impairment that occurs following thalamic injury as distinguished from that following hippocampal injury has proven difficult. This study examined relationships between MRI volumetric measures of the hippocampus and thalamus and their contributions to prose and rote verbal memory functioning in 18 patients with intractable temporal lobe epilepsy (TLE). Results revealed that bilateral hippocampal and thalamic volume independently predicted delayed prose verbal memory functioning. However, bilateral hippocampal, but not thalamic, volume predicted delayed rote verbal memory functioning. Follow-up analyses indicated that bilateral thalamic volume independently predicted immediate prose, but not immediate rote, verbal recall, whereas bilateral hippocampal volume was not associated with any of these immediate memory measures. These findings underscore the cognitive significance of thalamic atrophy in chronic TLE, demonstrating that hippocampal and thalamic volume make quantitatively, and perhaps qualitatively, distinct contributions to episodic memory functioning in TLE patients. They are also consistent with theories proposing that the hippocampus supports long-term memory encoding and storage, whereas the thalamus is implicated in the executive aspects of episodic memory.

MRI volume of the medial frontal cortex predicts financial capacity in patients with mild Alzheimer’s disease

Persons with mild Alzheimer’s disease (AD) have significant deficits in financial abilities. This study examined the relationship between brain structure volumes, cognition, and financial capacity in patients with mild AD. Sixteen mild AD patients and 16 older adult comparisons completed the Financial Capacity Instrument (FCI), a psychometric measure of financial abilities, and also underwent magnetic resonance imaging (MRI) to obtain volumes of the bilateral hippocampi, angular gyri, precunei, and medial and dorsolateral frontal cortices. Mild AD patients performed significantly below comparisons on the FCI and had significantly smaller hippocampi. Among mild AD patients, FCI performance was moderately correlated with frontal (medial and dorsolateral frontal cortex) and posterior (angular gyri and precunei) cortical volumes. Stepwise regression demonstrated that medial frontal cortex volume predicted FCI score. The relationship between medial frontal cortex volume and overall FCI score was partially mediated by two measures of simple attention (DRS Attention, DRS Construction). The findings suggest that medial frontal cortex atrophy and associated declines in simple attention play an increasingly important role in declining financial skills in patients with mild AD.

Lower hippocampal volume predicts decrements in lane control among drivers with amnestic mild cognitive impairment

Objectives: There are few methods to discern driving risks in patients with early dementia and mild cognitive impairment (MCI). We aimed to determine whether structural magnetic resonance imaging (MRI) of the hippocampus—a biomarker of probable Alzheimer pathology and a measure of disease severity in those affected—is linked to objective ratings of on-road driving performance in older adults with and without amnestic MCI. Methods: In all, 49 consensus-diagnosed participants from an Alzheimer’s Disease Research Center (15 diagnosed with amnestic MCI and 34 demographically similar controls) underwent structural MRI and on-road driving assessments. Results: Mild atrophy of the left hippocampus was associated with less-than-optimal ratings in lane control but not with other discrete driving skills. Decrements in left hippocampal volume conferred higher risk for less-than-optimal lane control ratings in the patients with MCI (B = −1.63, standard error [SE] = .74, Wald = 4.85, P = .028), but not in controls (B = 0.13, SE = .415, Wald = 0.10, P = .752). The odds ratio and 95% confidence interval for below-optimal lane control in the MCI group was 4.41 (1.18-16.36), which was attenuated to 3.46 (0.88-13.60) after accounting for the contribution of left hippocampal volume. Conclusion: These findings suggest that there may be a link between hippocampal atrophy and difficulties with lane control in persons with amnestic MCI. Further study appears warranted to better discern patterns of brain atrophy in MCI and Alzheimer disease and whether these could be early markers of clinically meaningful driving risk.

Effects of Nicotine on Spinal Cord Injury Pain: A Randomized, Double-Blind, Placebo Controlled Crossover Trial

BACKGROUND One factor affecting spinal cord injury (SCI)-related pain may be nicotine. Case reports have described a worsening of neuropathic pain from smoking and relief from abstinence. Neurobiological correlates also implicate the potential effect of nicotine on SCI-related pain. METHOD The current study employed a randomized, placebo-controlled crossover design to examine the effect of nicotine exposure on subtypes of SCI-related pain among smokers and nonsmokers. RESULTS Whereas nonsmokers with SCI showed a reduction in mixed forms of pain following nicotine exposure, smokers with SCI showed a converse increase in pain with regard to both mixed and neuropathic forms of pain. The exacerbation of pain in chronic nicotine or tobacco users may not only elucidate possible pain mechanisms but may also be of use in smoking cessation counseling among those with SCI.

Difficulty, effort and cardiovascular response to a working memory challenge: Older adults with and without mild cognitive impairment ☆

We presented cognitively healthy older adults and patients with mild cognitive impairment (MCI) three versions of a modified Sternberg memory task designed to range in difficulty from low to high. Among cognitively healthy older adults, blood pressure responses assessed during the work periods rose with difficulty. By contrast, among MCI patients, blood pressure responses assessed during the work periods were low irrespective of difficulty. Findings are discussed primarily in relation to a conceptual analysis concerned with ability determinants of effort (task engagement) and associated cardiovascular responses. They also are discussed in the context of other recent cardiovascular studies involving older adults and with regard to the potential for exaggerated cardiovascular responses to accelerate cognitive decline in advanced age.