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Biomedical subjects

R L Rogers

Publications and source records attributed to R L Rogers.

At least 19 recordsLinked to original sources
PubMed1992

Late magnetic fields and positive evoked potentials following infrequent and unpredictable omissions of visual stimuli.

Randomized and infrequent omissions during presentation of a steady train of visual stimulation produced distinctive wave forms of both the magnetic fields and electrical potentials. Electrical potentials at Pz showed a positive peak in response to the omitted stimuli which occurred on the average 445 msec after the time when a stimulus was anticipated. Analyses of the magnetic wave forms indicated that at least two separate sources appear to be active coincident with the electrical positive peak. One source localized in the occipital lobes in the vicinity of the visual cortex while the other source was located in the medial aspects of the temporal lobe or even deeper in the lateral thalamus. Judging from the calculated direction of current flow it appeared that the deep source would contribute greater potentials in the frontal areas of the scalp while the source in the occipital area would contribute to more posterior placement of electrodes, especially at Pz.

Brain↗
PubMed1991

Localization of the P3 sources using magnetoencephalography and magnetic resonance imaging.

In this study, two related issues were addressed: first, whether the P3 component of auditory evoked responses, obtained in the context of an oddball paradigm, and its magnetoencephalographically recorded counterpart (P3m) are generated by the same intracranial sources; and, second, whether these sources, modeled as equivalent current dipoles, can be localized in particular brain structures using magnetic resonance imaging. The study involving 8 normal adult subjects resulted in the following findings. (1) Both the similarities and differences in wave form characteristics of the simultaneously recorded P3 and P3m can be best accounted for by common intracranial sources. (2) Several successively activated single-dipolar sources, rather than a single source, account for the entire evolution of the P3m component. (3) Most of these sources were localized in the vicinity of the auditory cortex in all subjects, although some sources appeared to be in deeper structures, possibly the lateral thalamus. (4) The successive activation of sources followed an orderly medial-to-lateral course. These results suggest that activity responsible for the surface-recorded P3 (and P3m) component may be initiated in deep structures, but it quickly spreads over and is sustained in areas near the auditory cortex.

Adult↗
PubMed1991

Magnetoencephalographic localization of interictal spike sources. Case report.

The reliability of localization of interictal spike sources using magnetoencephalography (MEG) was examined by repeated measurements in a patient with temporal lobe epilepsy. During two preoperative recording sessions, the estimated sources, projected onto magnetic resonance images of the patient's brain, were found to lie less than 1 cm apart within the area subsequently resected. The MEG localization was in close agreement with intraoperative cortical recordings.

Adult↗
PubMed1990

Localization of auditory response sources using magnetoencephalography and magnetic resonance imaging.

Magnetoencephalography offers the possibility of localizing accurately and noninvasively the source of intracranial currents associated with normal and abnormal brain activity. The purpose of this study was to assess the validity and across-subject reliability of localization of cortical sources responding to ipsilateral and contralateral auditory stimulation. Magnetic evoked fields to both stimulation conditions were measured in eight consecutive normal subjects, and the cortical sources of these fields were estimated on the basis of these measurements. Subsequent projection of the source location coordinates onto magnetic resonance images showed that in all subjects the sources were accurately estimated to fall in the vicinity of the auditory cortex and that two separate sources may account for the response to ipsilateral and contralateral stimulation.

Acoustic Stimulation↗
PubMed1990

Source localization of two evoked magnetic field components using two alternative procedures.

The purpose of this study was to compare the relative efficacy of two methods in assessing the location of the sources of the N100 and P200 components of evoked magnetic fields (EMFs) to transient tone stimuli. EMFs to left ear stimulation, containing both components, were recorded over the right hemisphere of six normal subjects. The magnetic scalp distributions calculated at several adjacent time points, covering the duration of each component's peak, were used to estimate the source parameters of each component. Good estimates of the source of both components were obtained from all magnetic field distributions. The averaged spatial parameters derived from all distributions of each component as well as the parameters derived from the distribution that gave the best source estimate for each component were projected onto magnetic resonance images of subject's head. It was found that the source of each component is located on the superior surface of the temporal lobe and that the source of the P200 component is anterior to the N100 source in all subjects using both procedures.

Acoustic Stimulation↗
PubMed1990

Intersession replicability of dipole parameters from three components of the auditory evoked magnetic field.

The replicability of dipole localizations between sessions in an unselected group of subjects was studied. Auditory evoked magnetic fields (AEMFs) in response to contralaterally and ipsilaterally presented 1 kHz tone bursts were recorded from the right hemisphere of 12 subjects with normal hearing in two replicate sessions several days apart. Three long-latency components of the AEMF were studied, occurring at latencies near 50 msec (P1m), near 100 msec (N1m) and near 165 msec (P2m). A spherical model of the head was used to fit equivalent-current dipoles to the data. Statistical analysis of dipole parameters revealed virtually no differences between the two testing sessions. The variability between sessions had a mean absolute difference of 3 to 10 mm for the spatial parameters. Comparison of dipole parameters between components showed that there was a replicable, but nonsignificant, trend for a difference in the location of the N1m from contralateral vs. ipsilateral stimulation, and a statistically significant confirmation that the P2m is located anterior to the N1m for contralateral stimulation. Magnetic resonance images from each subject were used to locate the dipoles near the primary auditory cortex in the Sylvian fissure.

Acoustic Stimulation↗
PubMed1990

After reaching retirement age physical activity sustains cerebral perfusion and cognition.

Among neurologically normal volunteers approaching age 65 with an option for retirement, a four-year prospective longitudinal study was designed to examine effects of different levels of physical activity on cerebral perfusion by between-group comparisons. After the fourth year, cognitive performance was also tested. Three groups were compared, each composed of 30 elderly volunteers, assigned as follows: Group 1, who continued to work; Group 2, who retired but participated in regular physical activities; and Group 3, who retired but did not participate in regular, planned physical activities. Retirees who elected to become physically inactive exhibited significant declines in cerebral blood flow (CBF) throughout four years of follow-up. Those who continued to work or retirees who elected to participate in regular activities sustained more constant CBF levels. Active retirees and those who continued to work also scored better on cognitive testing after the fourth year of follow-up compared to inactive retirees.

Aged↗
PubMed1989

Randomized clinical trial of daily aspirin therapy in multi-infarct dementia. A pilot study.

Seventy multi-infarct dementia patients were randomized into an aspirin-treated group and an untreated control group for an exploratory investigation to determine any effects of 325 mg aspirin daily on cognitive performance. The control group did not receive placebo but evaluations were carried out in a blinded manner. The index group (N = 37, mean age 67.1 years) received 325 mg of aspirin by mouth once daily while the control group (N = 33, mean age 67.6 years) was followed and treated in a similar manner except that they received no aspirin. Both groups had comparable risk factors for stroke, which were treated similarly, as well as comparable initial cerebral blood flow values, as measured by the 133xenon inhalation method, and initial scores on Cognitive Capacity Screening Examination testing. Patients were evaluated at intervals of one year. Significant improvements were demonstrated for cerebral perfusion values (P less than .0001) and cognitive performance scores (P less than .0001) among aspirin-treated patients compared to untreated controls at each of three annual follow-up evaluations. Both men and women benefited from aspirin therapy and their quality of life and independence appeared to be improved, which was not apparent in the control group. Daily aspirin appears to improve or stabilize declines in cerebral perfusion and cognition among patients with multi-infarct dementia.

Aged↗
PubMed1989

Reducing hypertriglyceridemia in elderly patients with cerebrovascular disease stabilizes or improves cognition and cerebral perfusion.

Effects of lowering serum triglyceride levels were investigated among 44 elderly hypertriglyceridemic patients with risk factors for stroke, reduced cerebral perfusion, and a history compatible with symptomatic occlusive cerebrovascular disease. Patients were randomly assigned to either treatment with gemfibrozil, a lipid-lowering agent, or control conditions. Subjects in both groups were instructed to follow a diet recommended for lowering serum lipid levels, while the treatment group was additionally administered 600 mg daily of gemfibrozil. Subjects assigned to the treatment group (n = 22) showed significant reductions in serum triglyceride levels (p less than .0005). Control subjects (n = 22) did not show any significant changes in serum triglyceride levels. There were also no significant changes in total cholesterol levels in either group. Analyses of values for mean bihemispheric gray matter cerebral blood flow measured by the xenon 133 inhalation method and cognitive scores tested by the Cognitive Capacity Screening Examination indicated that gemfibrozil-treated patients maintained significantly higher levels of cerebral perfusion and cognitive performance than untreated controls did. Regression analyses for different treatment intervals indicated that both cerebral blood flow and cognition showed linear improvements that correlated directly with the duration of treatment. Lowering triglyceride levels in hyperlipidemic subjects appears to benefit cerebral perfusion and cognitive performance after four to six months.

Cerebrovascular Circulation↗
PubMed1988

Computerized history and self-assessment questionnaire for diagnostic screening among patients with dementia.

In order to standardize and quantify diagnostic information derived from medical histories and case reports given by demented patients, their families or care-providers, a questionnaire has been developed containing 94 questions. The output is categorized by computer into graphic clinical scales which correlate and weigh information relating to seven of the most common causes of dementia. The present investigation assesses the validity of predictive diagnostic classifications derived from the clinical scales tested on admission by correlating them later with final diagnoses determined independently by thorough clinical evaluation including standard diagnostic tests, computed tomography and nuclear magnetic resonance scans. Results of 101 healthy, neurologically normal, age-matched volunteers and 140 patients representative of the more common forms of dementia indicate that correct diagnostic identification was: 75% for dementia secondary to Parkinson's disease, 100% for Huntington's disease, 90.2% for Alzheimer's disease, 82.4% for multi-infarct dementia, 90.0% for posttraumatic dementia, 77.8% for normal-pressure hydrocephalus and 85.7% for Wernicke-Korsakoff dementia. Correct diagnostic assignment was highly significant (P less than .0005). The screening questionnaire may prove to be a useful and standard diagnostic tool for clinicians and investigators concerned with epidemiology, prevention and treatment of dementia.

Adult↗
PubMed1988

Aetiological considerations and risk factors for multi-infarct dementia.

One hundred and seventy five multi-infarct dementia (MID) patients were evaluated for risk factors for stroke as well as for the types of cerebrovascular lesions that were present. The incidence of associated risk factors for stroke were as follows: hypertension (66%), heart disease (47%), cigarette smoking (37%), diabetes mellitus (20%), moderate alcohol consumption (19%) and hyperlipidaemia (21%). The most frequently occurring type of lesions were multiple lacunar infarctions of the brain (43%). These were combined with other types of stroke in an additional 21%. Atherosclerotic occlusive disease of the carotid and vertebrobasilar arteries occurred alone in 18% and was associated with other types of stroke in another 25%. Embolic cerebral infarctions were present alone in 8% and were combined with other types of stroke in 15%. MID was more frequent in men (62%) than women (p less than 0.002). Mean bihemispheric gray matter cerebral blood flow (CBF) values showed a fluctuating course and when results were pooled and compared between different types of MID, extracranial occlusive disease and/or multiple lacunar infarctions resulted in lowest CBF values. The location of cerebral infarctions was more importantly related to cognitive impairments than was the total volume of infarcted brain. Mortality rates among 125 MID patients followed for 31 months has been 5%. Correct clinical classification of the types of cerebrovascular lesions was confirmed in three necropsied cases.

Aged↗
PubMed1988

Cognition and cerebral blood flow fluctuate together in multi-infarct dementia.

Longitudinal measurements of cognitive ability measured by serial testing using the Cognitive Capacity Screening Examination (CCSE) were correlated with cerebral blood flow (CBF) throughout (mean +/- SD) 19.9 +/- 12.6 months among 57 patients with multi-infarct dementia, 17 with dementia of the Alzheimer's type, 10 with both, and among 32 age-matched elderly normal controls. Longitudinal CCSE and CBF measurements among controls yielded stable normative values. Reduced mean CCSE scores correlated directly with CBF reductions in patients with multi-infarct dementia (p less than 0.0005) and dementia of the Alzheimer's type (p less than 0.028). Patients with multi-infarct dementia had CCSE scores with retest variability exceeding those of controls (p less than 0.001) and of patients with dementia of the Alzheimer's type (p less than 0.003). CCSE scores and CBF changed together 78.6% (p less than 0.001) of the time in patients with multi-infarct dementia compared with 66.2% of the time (p less than 0.01) in those with both, 62.9% of the time (p less than 0.05) in those with dementia of the Alzheimer's type, and 47.7% of the time (NS) in controls. Further analyses indicated that changes in CCSE scores and CBF were predominantly progressive declines in patients with dementia of the Alzheimer's type, whereas the changes were more bidirectional (both increases and decreases) in patients with multi-infarct dementia; these differences were also significant. Results support the diagnostic usefulness of the Hachinski ischemic scale and confirm that both cognition and CBF fluctuate together among patients with multi-infarct dementia, whereas patients with dementia of the Alzheimer's type exhibit a more stable course, with progressive declines in cognition and CBF.

Aged↗
PubMed1987

Hyperlipidemia is a risk factor for decreased cerebral perfusion and stroke.

Possible effects of chronically elevated serum cholesterol and triglyceride levels on measurements of cerebral blood flow were investigated by between-group comparisons of individuals, with and without hyperlipidemia, among 56 neurologically normal elderly volunteers and among 102 age-matched patients with symptoms of transient ischemic attacks (TIAs). Results demonstrated significantly higher levels of serum cholesterol and triglyceride among the TIA patients compared with randomly selected age-matched normal controls of similar educational and environmental backgrounds. Cerebral blood flow levels were reduced among groups of TIA patients with elevated levels of either cholesterol or triglycerides compared with the TIA patients with normal lipid levels. Similar trends were seen among normal volunteers, but these did not reach levels of statistical significance because of the limited numbers available. Analysis of frequency distributions for risk factors other than hyperlipidemia indicated that hypertension, atherosclerotic heart disease, diabetes mellitus, and cigarette smoking were also more prevalent among TIA patients than among age-matched normal controls.

Aged↗
PubMed1986

Abstinence improves cerebral perfusion and brain volume in alcoholic neurotoxicity without Wernicke-Korsakoff syndrome.

Twenty severe chronic alcoholic patients with signs of neurotoxicity but without Wernicke-Korsakoff syndrome were treated by abstinence from alcohol and examined prospectively at intervals thereafter. Serial examinations included detailed medical histories, neurological examinations, cognitive capacity screening examinations, computed tomography scans with measurements of sulcal and ventricular volume, and measurements of regional CBF. All sedatives were withdrawn before CBF measurements were made. Before treatment, gray matter blood flow values were significantly reduced compared with those of age-matched normal volunteers, but white matter blood flow values were normal and the ventricles were enlarged. After abstinence from alcohol, mean gray matter blood flow values and brain volume both increased significantly.

Adult↗
PubMed1986

Cognitive performance correlates with cerebrovascular impairments in multi-infarct dementia.

Cerebral blood flow (CBF) was measured by the 133Xe inhalation method in patients with multi-infarct dementia (MID, N = 26), Alzheimer's dementia (AD, N = 19), and among age-matched, neurologically normal, healthy volunteers (N = 26). Cognitive performance was assessed in all subjects using the Cognitive Capacity Screening Examination (CCSE). Cerebral vasomotor responses were calculated from differences in values of mean hemispheric gray matter blood flow (Delta CBF) measured during inhalation of 100% oxygen (hyperoxia) compared with CBF measured while breathing room air. Significant correlations were found between CCSE performance and vasomotor responsiveness in patients with MID (P less than .01), but not in patients with AD or in neurologically normal volunteers. Loss of vasomotor responsiveness is an indicator of cerebrovascular disease with rigidity and/or loss of reactivity of cerebral vessels, which impairs cerebrovascular responses to situational demands and predisposes to cerebral ischemia. Loss of cerebral vasomotor responsiveness among MID patients, which is a biologic marker of cerebrovascular disease, provides confirmatory evidence of the vascular etiology of MID and assists in separating MID from AD patients.

Aged↗
PubMed1986

Decreased cerebral blood flow precedes multi-infarct dementia, but follows senile dementia of Alzheimer type.

A 7-year prospective study among 181 neurologically normal elderly volunteers (mean age, 70.6 years) revealed an incidence of 3.3%, or 0.47% new cases per year, for Alzheimer's disease (SDAT) and 5.5%, or 0.78% new cases per year, for multi-infarct dementia (MID). The unusually high incidence of MID is considered to reflect preselection of a large percentage of volunteers (48.6%) with risk factors for (but without symptoms of) atherothrombotic stroke. Of 88 volunteers at risk of stroke, 11.4% developed MID within 7 years. In MID patients, cerebral blood flow (CBF) values began to decline around 2 years before onset of symptoms, while in SDAT patients, CBF levels remained normal until symptoms of dementia appeared; thereafter, CBF declined rapidly.

Aged↗