Biomedical subjects

Robert N Davis

Publications and source records attributed to Robert N Davis.

11 recordsLinked to original sources

PubMed2006

Is basic memory structure invariant across epilepsy patient subgroups?

It is well known that epilepsy patients often exhibit material-specific deficits in memory for verbal versus nonverbal material. However, it is also apparent that such deficits are not always discernible, and that numerous factors may potentially moderate the degree to which fractionation between verbal and nonverbal material is evident. Using confirmatory factor analysis, we compared the relative fit of one-factor (general) and two-factor (material-specific) models of memory in data from 330 patients with intractable seizure disorder. Data from verbal and nonverbal selective reminding tests, as well as Logical Memory and Visual Reproduction (immediate and delayed recall indices), were used in analyses. The one-factor model fit the data poorly in the full sample, whereas the two-factor model fit the data significantly better. We then assessed the invariance of these two models using multiple-group modeling across subsamples of patients with left versus right sided seizure focus, earlier versus later age of seizure onset, lower versus higher Full Scale IQ, fewer versus more years of education, younger versus older patients, and male versus female patients. In all cases, the two-factor model comprised of verbal and nonverbal memory factors fit the data better than a one-factor (general) model. These findings indicate robust consistency of verbal and nonverbal memory constructs in the epilepsy population, which remain viable in this patient group despite considerable heterogeneity in other respects.

Adult↗

PubMed2004

The cognitive sequelae of standard-dose adjuvant chemotherapy in women with breast carcinoma: results of a prospective, randomized, longitudinal trial.

BACKGROUND: Retrospective trials have reported that chemotherapy-induced cognitive dysfunction was experienced by a subset of patients with breast carcinoma. However, recent evidence indicated that a subset also exhibited impaired cognitive function at baseline, before the start of chemotherapy. A prospective, longitudinal trial that incorporates baseline neuropsychologic evaluations is necessary to determine to what extent cognitive dysfunction is attributable to chemotherapy in this population. METHODS: Eighteen women with breast carcinoma underwent a comprehensive neuropsychologic evaluation before treatment and at short-term and long-term intervals after chemotherapy. The incidence, nature, severity, and chronicity of cognitive dysfunction developing in patients with breast carcinoma treated with a standard dose of adjuvant chemotherapy were assessed. RESULTS: Before the start of systemic therapy, 33% of women in the current cohort exhibited cognitive impairment. At the short-term postchemotherapy time point, 61% of the cohort exhibited a decline relative to baseline in 1 or more domains of cognitive functioning and reported greater difficulty in maintaining their ability to work. The most common domains of cognitive dysfunction were related to attention, learning, and processing speed. At the long-term postchemotherapy time point, approximately 50% of patients who experienced declines in cognitive function demonstrated improvement, whereas 50% remained stable. Self-reported ability to perform work-related activities also improved over this interval. Neither impairment at baseline nor subsequent treatment-related cognitive decline exhibited any statistically significant correlation with affective well-being or with demographic or clinical characteristics. CONCLUSIONS: The current study is the first longitudinal trial to report evidence of an association between cognitive dysfunction and chemotherapy in a subgroup of women with nonmetastatic breast carcinoma. The importance of using prospective research designs, appropriate cognitive measures, and statistical methods to evaluate subgroup effects was discussed. Identification of mechanisms associated with cognitive dysfunction and of risk factors contributing to subgroup vulnerability is necessary.

Adult↗

PubMed2004

No more chances for supply-chain savings? Look again!

To optimize supply-chain performance, hospitals must: Take into account all elements of the supply chain; Decide who will lead the supply-chain improvement effort; Decide where to focus improvement initiatives; Assess the savings potential; Overcome barriers to success; Set appropriate targets and measure performance.

Cost Control↗

PubMed2003

Differential brain activation patterns during perception of voice and tone onset time series: a MEG study.

Evoked magnetic fields were recorded from 18 adult volunteers using magnetoencephalography (MEG) during perception of speech stimuli (the endpoints of a voice onset time (VOT) series ranging from /ga/ to /ka/), analogous nonspeech stimuli (the endpoints of a two-tone series varying in relative tone onset time (TOT), and a set of harmonically complex tones varying in pitch. During the early time window (approximately 60 to approximately 130 ms post-stimulus onset), activation of the primary auditory cortex was bilaterally equal in strength for all three tasks. During the middle (approximately 130 to 800 ms) and late (800 to 1400 ms) time windows of the VOT task, activation of the posterior portion of the superior temporal gyrus (STGp) was greater in the left hemisphere than in the right hemisphere, in both group and individual data. These asymmetries were not evident in response to the nonspeech stimuli. Hemispheric asymmetries in a measure of neurophysiological activity in STGp, which includes the supratemporal plane and cortex inside the superior temporal sulcus, may reflect a specialization of association auditory cortex in the left hemisphere for processing speech sounds. Differences in late activation patterns potentially reflect the operation of a postperceptual process (e.g., rehearsal in working memory) that is restricted to speech stimuli.

Adult↗

PubMed2003

WAIS-R factor structure in Alzheimer's disease patients: a comparison of alternative models and an assessment of their generalizability.

The WAIS-R is often used in neuropsychological evaluations of individuals with probable Alzheimer's disease (AD), but its factor structure in this population is unknown. Moreover, theories and past research findings make competing predictions concerning its structure. Using confirmatory factor analysis, the authors compared 5 alternative WAIS-R factor models among 516 AD patients: 1-factor (Spearman's g) and 2-factor (Verbal IQ and Performance IQ) models; a 3-factor model including Verbal Comprehension (VC), Perceptual Organization (PO), and Freedom From Distractibility (FD) factors; a 3-factor model in which Digit Symbol loads on PO rather than FD; and a 3-factor model in which Digit Symbol loads on both PO and FD. Results favored the 3-factor model in which Digit Symbol loads on PO rather than FD. Moreover, this model fit the data best among subsamples of patients defined by age, dementia severity, years of education, and gender.

Aged↗

PubMed2003

Brain mechanisms for reading in children with and without dyslexia: a review of studies of normal development and plasticity.

In this article we review our experience with the application of magnetic source imaging (MSI), the newest of the functional imaging methods, to the study of brain mechanisms for reading among children who read normally and among those with dyslexia. After giving a general description of MSI, we present evidence for reliable and valid maps of the brain mechanism for aural language comprehension as well as for reading. Next, we present data from 39 normal readers, 40 children with dyslexia, and 30 younger children at risk for developing a reading disability. These data show different brain activation maps for individual children with dyslexia and children at risk for dyslexia than for those of normal readers. Such differences most likely reflect aberrant brain organization underlying phonological decoding, rather than variables such as degree of effort. Finally, we present preliminary data demonstrating that the aberrant activation profiles of children with dyslexia may return to normative patterns as a result of a successful reading intervention that enables children to improve phonological decoding skills.

Adolescent↗

PubMed2003

Effects of blood pressure on neuropsychological functioning in Alzheimer's disease.

Blood pressure is often lower among patients with Alzheimer's disease (AD) compared to nondemented older adults. Lower blood pressure in AD correlates with reduced cerebral blood flow and cortical atrophy, but its effect on neuropsychological functioning is unclear. We assessed the effects of blood pressure on tests of dementia severity, attention, memory, language, verbal and nonverbal reasoning, motor/psychomotor functioning, and activities of daily living (ADL) among probable AD patients (n=609). As hypothesized, lower systolic blood pressure (SBP) predicted reduced attention (Digits Forward and Backward), memory (Visual Reproduction I), and ADLs. Unexpectedly, lower pulse pressure (SBP-DBP) predicted greater dementia severity (Mini-Mental State Examination, MMSE), attention (Digits Forward and Backward), memory (Logical Memory I and Visual Reproduction I), and ADLs. These findings may reflect a tendency for less severely demented patients to exhibit normal age-related changes in blood pressure, whereas abnormal patterns may develop with increased dementia severity.

Aged↗

PubMed2002

Multimodality functional imaging evaluation in a patient with Rasmussen's encephalitis.

Rasmussen's encephalitis (RE) is a cryptogenic progressive inflammatory disorder of the brain that causes severe neurological problems, including intractable focal epilepsy. In select patients, aggressive treatment using cerebral hemispherectomy may ameliorate the devastating cognitive decline that accompanies this disease, even if the epileptic focus appears broadly distributed. We present a case of histopathologically-confirmed RE evaluated using a multimodal process that explored the physical and functional aspects of the associated epilepsy. This process included magnetic resonance imaging, single photo emission computed tomography, electroencephalography, and magnetoencephalography (MEG). The findings indicate that functional brain imaging data may greatly assist the surgical treatment decision-making process in RE, especially when structural imaging fails to reveal definitive localizing information. In addition, MEG may provide insights about the cortical reorganization of somatosensory cortex following hemispherectomy.

Child↗

PubMed2002

Brain activation profiles during the early stages of reading acquisition.

In the present study, we demonstrate for the first time the presence of an aberrant brain mechanism for reading in children who have just started acquiring reading skills. Children who, at the end of kindergarten, are found to be at risk for developing reading problems display markedly different activation profiles than children who have, at this stage, already mastered important prereading skills. This aberrant profile is characterized by the lack of engagement of the left-hemisphere superior temporal region, an area normally involved in converting print into sound, and an increase in activation in the corresponding right-hemisphere region. This finding is consistent with current cognitive models of reading acquisition and dyslexia, pointing to the critical role of phonologic awareness skills in learning to read.

Brain↗

PubMed2002

Localization of ictal and interictal bursting epileptogenic activity in focal cortical dysplasia: agreement of magnetoencephalography and electrocorticography.

Focal cortical dysplasia (FCD) is often associated with severe partial epilepsy. In such cases, interictal frequent rhythmic bursting epileptiform activity (FBREA) on both scalp electroencephalography (EEG) and electrocorticography (ECoG) is generally accepted to be identical to the ictal epileptiform activity. We used magnetoencephalography (or Magnetic Source Imaging (MSI)) to determine the epileptogenic zone in a 6-year-old patient with histopathologically proven FCD and normal magnetic resonance imaging (MRI). MSI was used to localize the sources of both ictal activity and FRBEA, which was then compared with ECoG findings. The intracranial sources of both types of activity co-localized in the left inferior frontal and superior temporal gyri. The location and extent of the epileptogenic area determined by MSI was essentially identical to that determined directly through extra-operative ECoG. In the absence of structural abnormalities detectable on MRI, the noninvasive method of MSI provided valuable information regarding the location and extent of the primary epileptogenic area. This was critical for pre-surgical planning regarding placement of intracranial electrodes and for risk-benefit evaluation.

Cerebral Cortex↗

PubMed2002

Detection and significance of focal, interictal, slow-wave activity visualized by magnetoencephalography for localization of a primary epileptogenic region.

OBJECT: Magnetoencephalography (MEG) is a novel noninvasive diagnostic tool used to determine preoperatively the location of the epileptogenic zone in patients with epilepsy. The presence of focal slowing of activity recorded by electroencephalography (EEG) is an additional indicator of an underlying pathological condition in cases of intractable mesial temporal lobe epilepsy (MTLE). In the present study the authors examined the significance of focal, slow-wave and interictal spike activity detected using MEG in 29 patients who suffered from MTLE that was not associated with structural brain lesions. METHODS: All patients underwent resective surgery after MEG and EEG monitoring. Equivalent single-dipole modeling was applied to focal low-frequency magnetic activity (LFMA) and interictal paroxysmal activity. Lateralized LFMA was defined as trains of rhythmic activity over the temporal area, with frequencies lower than 7 Hz, which were easily distinguished from background activity. Lateralized LFMA was found in 17 patients (58.6%); it always occurred on the side ipsilateral to the side of resection and displayed a maximum amplitude over the temporal area. Dipolar sources of magnetic flux computed during slow-wave trains were found in the majority of cases in the posterior superior temporal region and, occasionally, in mesial temporal structures that were subsequently resected. With respect to lateralization there was never disagreement between LFMA and MEG interictal spike sources. Thus, in patients with MTLE that is not associated with a mass lesion LFMA is topographically related to the epileptogenic area and, therefore, has value for reliable determination of the side and, possibly, the location of this area. CONCLUSIONS: Although focal slowing of EEG background activity is generally considered to be a nonspecific sign of functional disturbance, interictal LFMA in patients with MTLE should be conceptualized as a distinct electrographic phenomenon that is directly related to the epileptogenic abnormality. Analyzing the interictal MEG distribution of LFMA and sharp activity improves the diagnostic utility of MEG in patients with suspected TLE who are undergoing surgical evaluation.

Adolescent↗