Impact of ambiguity and risk on decision making in mild Alzheimer's disease.

Decisions under ambiguity and decisions under risk are crucial types of decision making in daily living at any age. This is the first study assessing these two types of decisions in patients with mild dementia of Alzheimer's type (DAT) by means of the Iowa Gambling Task (IGT) and a newly developed, Probability-Associated Gambling (PAG) task. While rules for gains and losses are implicit in the IGT, in the PAG task rules are explicit and winning probabilities, which change from trial to trial, can be estimated. Results of the IGT indicated that DAT patients made more disadvantageous decisions than healthy controls. Patients also shifted more frequently among decks, i.e. under ambiguity decisions were taken randomly and no advantageous strategy was established over time by DAT patients. Thus, not only actual choices but also development of advantageous strategies may be revealing about decision making in the IGT. Compared to controls, patients demonstrated less advantageous choices in the PAG task as well. They gambled more often in the low winning probabilities and less frequently in the high probabilities than healthy participants. Patients' performance on both tasks correlated with measures of executive functions. Findings of the present investigation are consistent with the early pathological cerebral changes and related (cognitive, emotional) deficits reported for DAT. As suggested by our study, decisions under ambiguity as well as decisions under risk are impaired in mild DAT. It may thus be expected that patients with mild DAT have difficulties in taking decisions in every-day life situations, both in cases of ambiguity (information on probability is missing or conflicting, and the expected utility of the different options is incalculable) and in cases of risk (outcomes can be predicted by well-defined or estimable probabilities).

Decision-making with explicit and stable rules in mild Alzheimer's disease.

Decision-making in mild dementia of Alzheimer's type (DAT) was assessed in a gambling task with stable and explicit rules [Game of Dice Task; Brand, M., Labudda, K., Kalbe, E., Hilker, R., Emmans, D., Fuchs, G., et al. (2004). Decision-making impairments in patients with Parkinson's disease. Behavioural Neurology, 15, 77-85]. DAT patients in an early stage of the disease chose safe alternatives as frequently as healthy elderly persons and did not show risky behaviour as has been reported for other neurological patient groups. However, a more detailed analysis disclosed important differences between DAT and healthy elderly. Compared to healthy controls, DAT patients shifted more frequently between safe and risky alternatives and showed less consistent response patterns. Frequent changes between strategies indicate that decisions were taken randomly, that no advantageous strategy was established and that no consistent response pattern was developed over time. As regards performance changes over the task, healthy participants had a stronger tendency towards safe and advantageous responses than DAT patients. While healthy controls showed learning as the task proceeded, DAT patients did not adapt their strategies. The proportion of "consistently safe responders" was significantly higher in the control group than in the DAT group. Analysis of reaction times indicated that differences in response behaviour were not due to fast and impulsive decision taking in the DAT group. DAT patients' response pattern may be attributed to deficits in learning and in executive functions. The frequency of changes between safe and risky choices proved to be a fair predictor for the distinction between mild DAT and healthy aging.

Decision making under risk and under ambiguity in Parkinson's disease.

In the present study we investigate decision making under ambiguity and decision making under risk in Parkinson's disease (PD) patients without cognitive impairment and in patients affected by Parkinson's disease dementia (PDD). In decisions under ambiguity, participants are not aware of the rules for gains and losses and have to learn about the utility of their selections through feedback. The two patient groups showed significant deficits and did not differ in the frequency of advantageous choices, though they had a markedly different cognitive profile. In decisions under risk, explicit information on the options' probabilities as well as on the associated gains and losses is given. PD patients and healthy controls performed at the same level, whereas PDD patients made significantly more risky and disadvantageous decisions. Results of the study suggest that both patient groups are impaired in decision making when learning by feedback and emotional processing is required, while only the PDD group shows difficulties when decision making is based on cognitive reasoning strategies.