Tri-axial recording of event-related potentials during passive cognitive tasks in patients with Alzheimer's disease

Sedation modulates recognition of novel stimuli and adaptation to regular stimuli in critically ill adults

BACKGROUND

Responsiveness of critically ill patients is affected by disease and by therapy. Subjective tests of responsiveness (e.g., modified Ramsay score) reflect global integrity of a response arc that includes transduction, perception, classification, and an overt response. The performance of individual components is usually not assessed.

OBJECTIVE

To determine whether an association exists among sedative medications and the brain's component information processing and adaptive abilities.

DESIGN

Initial observational study of a convenience sample.

SETTING

A surgical intensive care unit of a university hospital.

PATIENTS

A total of 22 endotracheally intubated, mechanically ventilated patients chemically sedated with narcotics and a benzodiazepine (n = 12), or narcotics and propofol (n = 10) using sedation protocols.

INTERVENTIONS

None.

MEASUREMENTS AND FINDINGS

Patients were presented flashes of light and pulses of sound at fixed or random intervals. Patients receiving low doses of fentanyl and propofol adapted to stimuli presented at fixed intervals and retained the response to novelty. Patients receiving higher doses of those medications did not respond to novelty and responded to stimuli presented at fixed intervals as if they were novel. Patients receiving fentanyl and benzodiazepines had generally weaker responses to all stimuli. Moreover, their responses to fixed and random stimuli were similar. At low doses, the patients retained responses to novelty and adapted to fixed, whereas at higher doses the opposite was observed: the response to novelty was lost and the patients responded to fixed stimuli as if they were novel. These observations suggest that the sedative medications generally accelerate the physiologic decay of stimuli as they engage the brain's information processing and adaptive abilities and further suggest that different sedative medications may have different effects on the brain.

CONCLUSIONS

Commonly administered sedative medications may alter the brain's biophysical state and thereby modulate specific aspects of the brain's information processing and adaptive functions. These functions can be interrogated even when the patient is seemingly unresponsive. If this observation is confirmed in subsequent prospective controlled randomized trials, electrophysiologic interrogation of the brain's information processing and adaptive capacities could serve as an adjunct to clinical assessment of responsiveness and management of sedative medications.

Attention: neuropsychological predictor of competency in Alzheimer's disease

This study was undertaken to examine the relationship between two different competencies, financial and medical decision making, and explore whether neuropsychological testing can identify a common underlying cognitive operation impaired in patients with AD. The objective was to examine the neuropsychological predictors of financial and medical decision-making competencies in patients with Alzheimer's disease (AD). Twenty individuals with mild to moderate AD and 20 control subjects matched for age and education were evaluated at a university medical center. All participants were administered a financial competency questionnaire, a competency test for medical decision making, and a set of standardized neuropsychological tests selected to reflect cognitive processes theoretically related to competency. In addition, an informant provided information regarding banking history for each participant. AD patients performed more poorly on all measures, including both measures of competency, which were highly related (R = .718, P < .001). Two tests, Trails A and Word List Recall, were significantly correlated with both competency measures, with Trails A predicting over 85% of the variance in competency scores. Trails A discriminated competent from not competent participants with an accuracy ranging from 77% to 82%. Measures of financial and medical decision-making competency were significantly correlated among patients with AD. One brief neuropsychological test of attention, Trails A, proved to be highly predictive of performance on both competency measures and useful in the discrimination of competent performance on these measures and by informant report.