A sleep physiologist's view of the drowsy driver

Drowsy driving is dangerous because of the impairment of driving skills that it causes. Unfortunately, the conceptual basis that underlies much of the multi-disciplinary research on this topic is muddled. The same poorly defined terms, such as fatigue and sleepiness, are used differently by different disciplines and researchers. Some new definitions and concepts are proposed here which may be helpful, as least as a stimulus for discussion by others. Drowsiness, sleepiness and fatigue are distinguished. A new conceptual model of sleepiness is outlined, based on a mutually inhibitory interaction between a putative sleep drive and a wake drive. Sleepiness, defined as sleep propensity, is a function of the relative strengths, not the absolute strengths, of the sleep and wake drives. The measurement of sleepiness requires some new variables such as instantaneous sleep propensity, to be distinguished from either the situational or the average sleep propensity. A subject's instantaneous sleep propensity depends on many variables including his average sleep propensity in daily life, the time of day, the duration of prior wakefulness, the subject's posture, physical and mental activity at the time, and individual differences based on psychophysiological traits. The relationship between dozing at the wheel while driving and crashing the vehicle may not be as straightforward as it appears at first.     

Latent inhibition of US signal value.

Three experiments with rats examined the effects of preexposure to an unconditioned stimulus (US; a single food pellet) on the subsequent ability of that US to effectively signal the delivery of three food pellets during a US-US conditioning procedure. In Experiment 1, latent inhibition (LI) rats showed attenuated conditioning, compared to control (C) rats, when a single food pellet, delivered 10 minutes into a session, was followed by three additional pellets. In preexposure, one pellet had been delivered 10 minutes into each session (in group LI), or placed into the magazine at the beginning of each session (in group C). Experiment 2 showed that this effect was evident when the conditions of preexposure matched those of conditioning for group C, and Experiment 3 showed that the difference between groups LI and C was not a product of context conditioning, or latent inhibition to the noise of the feeder in group LI. Implications of these results for theories of latent inhibition are considered.     

Prediction of Suicide Intent in Aboriginal and Non-Aboriginal Adolescent Inpatients: A Research Note

The relationship among depressive symptoms, anxiety, hopelessness, and suicidal intent was explored in a group of 77 adolescents who had been hospitalized after attempting suicide. Regression analyses indicated that hopelessness was the only significant predictor of suicide intent in Caucasian patients, and depressed mood was the only significant predictor in the Aboriginal group. Clinicians should be aware that measures of hopelessness may be of limited value in assessing suicidal risk in Aboriginal adolescents.