Biomedical subjects

Matthew R Powell

Publications and source records attributed to Matthew R Powell.

5 recordsLinked to original sources

PubMed2006

Cognitive measures predict pathologic Alzheimer disease.

BACKGROUND: Neuropsychologic testing is often used to infer neuropathologic processes, but clinicopathologic correlations for individual cognitive measures are based on a small number of published studies. OBJECTIVE: To examine the usefulness of the age- and education-adjusted Mayo Cognitive Factor Scales (MCFS) obtained at participants' initial assessments for predicting the presence or absence of pathologic Alzheimer disease (AD). DESIGN: This was a longitudinal study of a cohort of elderly patients with and without cognitive complaints who were followed up until death. Mayo Cognitive Factor Scales age- and education-adjusted standard scores from the participants' initial evaluations were used to calculate classification accuracy statistics for neuropathologic AD diagnosis obtained approximately 6 years after testing. Subjects with non-AD diagnoses or substantial non-AD-related changes were excluded from the study. SETTING: Academic medical center. PARTICIPANTS: One hundred two participants were evaluated clinically and underwent neuropathologic examination at autopsy. All were part of the Mayo Clinic Alzheimer's Disease Patient Registry or Alzheimer Disease Research Center. RESULTS: All Mayo Cognitive Factor Scale scores were significantly correlated with AD criteria. Logistic regression modeling including Mayo Cognitive Factor Scales Verbal Comprehension and Retention indices revealed high positive predictive value with moderate sensitivity and specificity for pathologic AD. CONCLUSION: Neuropsychologic test scores at initial evaluations were predictive of pathologic AD.

Aged↗

PubMed2006

Negative incremental resistance induced by calcium in asymmetric nanopores.

Single polymer nanopores with permanent surface charges act as rectifiers of ionic current. The pores are tapered cones with narrow openings of several nanometers and wide openings of approximately 1 mum. The pores are cation-selective, and in symmetric solutions of potassium chloride they rectify the flow of potassium ions from the small opening toward the wide opening. Millimolar concentrations of calcium reverse the rectification, and a negative incremental resistance is observed. These observations can be interpreted by a model containing flashing ratchets.

Calcium↗

PubMed2006

Calcium-induced voltage gating in single conical nanopores.

We examine time signals of ion current through single conically shaped nanopores in the presence of sub-millimolar concentrations of calcium ions. We show that calcium induces voltage-dependent ion current fluctuations in time in addition to the previously reported negative incremental resistance (Nano Lett. 2006, 6, 473-477). These current fluctuations occur on the millisecond time scale at voltages at which the effect of negative incremental resistance was observed. We explain the fluctuations as results of transient binding of calcium ions to carboxyl groups on the pore walls that cause transient changes in electric potential inside a conical nanopore. We support this explanation by recordings of ion current in the presence of manganese ions that bind to carboxyl groups 3 orders of magnitude more tightly than calcium ions. The system of a single conical nanopore with calcium ions is compared to a semiconductor device of a unijunction transistor in electronic circuits. A unijunction transistor also exhibits negative incremental resistance and current instabilities.

Calcium↗

PubMed2004

Detecting symptom- and test-coached simulators with the test of memory malingering.

The ability of the Test of Memory Malingering (TOMM; Tombaugh, 1996) to detect feigned-memory impairment was explored. The TOMM was administered to three groups: (a) a control group instructed to perform optimally, (b) a symptom-coached group instructed to feign memory problems after being educated about traumatic brain injury symptomatology, and (c) a test-coached group instructed to feign memory problems after being educated about test-taking strategies to avoid detection. The recommended cutoff scores (Tombaugh, 1996) on Trial 2 and the Retention Trial produced overall classification accuracy rates of 96%, with high levels of sensitivity and specificity. Although the symptom-coached group performed more poorly on the TOMM relative to the test-coached group, the test was equally sensitive in detecting suboptimal effort across the different coaching paradigms.

Adult↗

PubMed2004

The Rey AVLT Serial Position Effect: a useful indicator of symptom exaggeration?

This investigation explored the usefulness of serial position patterns during word recall on the Rey Auditory Verbal Learning Test (RAVLT; Rey, 1964) as an indicator of poor effort. Significantly better recall for early (primacy) and recent (recency) material defines the serial position effect (SPE; Rundus, 1971). The SPE on the RAVLT was examined in four groups: normal controls (NC), symptom-coached simulators (SC), test-coached simulators (TC), and a group of moderate to severe subacute traumatic brain injury (TBI) patients. Normal control participants and TBI patients demonstrated the expected SPE. Only the SC simulators clearly suppressed the primacy effect. The SPE appears neither sensitive nor specific enough to be used independently of more sensitive symptom validity tests in the detection of suboptimal effort. It may be especially problematic when used with clients presenting with sophisticated styles of exaggeration and in settings with lower base rates of compromised effort.

Adult↗