Episodic memory in normal aging and Alzheimer disease: Insights from imaging and behavioral studies

Age-related cognitive changes often include difficulties in retrieving memories, particularly those that rely on personal experiences within their temporal and spatial contexts (i.e., episodic memories). This decline may vary depending on the studied phase (i.e., encoding, storage or retrieval), according to inter-individual differences, and whether we are talking about normal or pathological (e.g., Alzheimer disease; AD) aging. Such cognitive changes are associated with different structural and functional alterations in the human neural network that underpins episodic memory. The prefrontal cortex is the first structure to be affected by age, followed by the medial temporal lobe (MTL), the parietal cortex and the cerebellum. In AD, however, the modifications occur mainly in the MTL (hippocampus and adjacent structures) before spreading to the neocortex. In this review, we will present results that attempt to characterize normal and pathological cognitive aging at multiple levels by integrating structural, behavioral, inter-individual and neuroimaging measures of episodic memory.

Are OSAS patients impaired in their driving ability on a circuit with medium traffic density?

OBJECTIVES

Many studies have demonstrated that patients with Obstructive Sleep Apnea Syndrome (OSAS), a very common sleep-related breathing disorder, are usually impaired in their driving ability because of decreased sleep quality. However, most of the simulation procedures in laboratories are designed to create monotonic conditions with low traffic density, if any, thereby leading to a dramatic decrease in performance in OSAS patients because of the lack of stimulation. The aim of this study was therefore to evaluate driving abilities in OSAS patients involved in a driving simulation task with medium traffic density, in order to replicate as far as possible real world conditions. The behavioral and physiological attributes likely to predict driving performance in these patients were also investigated.

METHODS

After a normal night of sleep, 12 OSAS patients and 8 healthy controls performed 6 driving sessions during a 24-h period of sustained wakefulness. Driving performances (speed, lateral position, distances...) were measured and correlated to sleep parameters and to a waking EEG recorded during the task.

RESULTS

Compared to controls, patients showed difficulties in speed adjustment. However, they maintained longer inter-vehicle distances, including during overtaking. Their waking EEG, while driving, showed increased spectral power in theta (3.9-7.8Hz) but also in beta (12.7-29.2Hz) activity, alpha power (7.9-12.6Hz) being increased in both groups due to sustained wakefulness. Poor sleep indices were correlated to increased theta and beta activities, as well as to more cautious behavior.

DISCUSSION

In medium traffic density conditions, driving performance in OSAS patients remained at near normal levels, but with more cautious behavior than controls. This could be the result of a bigger effort to stay awake, as suggested by an increased beta activity in these patients.

Oculomotor changes due to road events during prolonged monotonous simulated driving

The possible influence of occuring external events on driver attention and vigilance level was assessed during a prolonged simulated driving task. Special attention was given to the duration of the task, as well as to the influence of time of day and of individual factors. Thirty six subjects drove for two hours. Blinking activity and eye movements associated with glances to the speedometer were recorded during the entire driving task and particularly during specific road events. During significant events, blinking and ocular activity decreased, attesting a higher attention of the driver. With increased duration of driving, the reduction in blinking and ocular activity was progressively smaller for the less significant events, indicating a reduction in attention. During driving, women blinked more frequently than men. With increased duration of driving, drivers adopted different behavioural strategies depending on their age and sex to reach a safe and adapted method of driving.

Variations of the level of vigilance and of behavioural activities during simulated automobile driving

During a monotonous activity, certain behaviours occur that are not necessary to the performance of the task. These are subsidiary or collateral activities. Our purpose was to find out if the number of these behaviours tends to increase during a monotonous and prolonged activity. A study was carried out with 17 subjects performing a 2-h car drive on the Vigilance Analysis Driving Simulator. An analysis of the drivers' behaviour and of their state of vigilance allowed us to confirm the existence of a relation between the occurrence of these behaviours and the variations of the level of arousal. In addition, we determined for all produced behaviours, those that preceded, those that coincided with, and those that followed low vigilance phenomena. These results were interpreted in terms of behavioural signs, precursory of low vigilance, indicative of low vigilance, or reactivating the driver.