Suicide and Homicide Rates in Canada and the United States

Suicide and homicide rates by age were analyzed for Canada and the United States, indicating that suicide is higher in Canada and that homicide is higher in the United States. Results indicated a positive association between homicide and suicide rates in the United States but these two rates of death were not significantly associated in Canada. Holinger (1987) had associated the relative size of the cohort to the rates of suicide and homicide in young people in the United States. The more current data in both countries did not support Holinger's results. Using the measure devised by Easterlin (1980) and Ahlburg and Schapiro (1984) –that is, the proportion of youths aged 15–24 relative to adults aged 25–64–the correlation between the size of the youth cohort and the suicide rate of youths aged 15–24 was negative. It is concluded that the two patterns in these two countries may be explained from a historical perspective.     

Contextual conditional discriminations

Three experiments used a discriminated operant procedure to study conditional discrimination learning in rats. The first experiment showed that rats were capable of learning a biconditional discrimination in which two contexts served as conditional cues signalling the reinforcement contingencies associated with two discriminative stimuli. The discrimination was learned equally well when one discriminative stimulus signalled food, the other its absence, and when one stimulus signalled food, the other extinction plus mild footshock.

In Experiment 2 it was shown that prior training on such a conditional discrimination enhanced the subsequent context specificity of simple conditioning relative to control groups of animals for whom the prior training had not been conditional. Experiment 3 showed that a reversal of the significance of one pair of discriminative stimuli produced no spontaneous reversal in performance to a second, target, pair.

The pattern of results is best accounted for by an analysis of contextual conditional discrimination learning in terms of stimulus configurations and offers no support for the notion that rats may learn a general conditional rule or set.     

Stress, reactivity, and immune function in healthy men.

We examined the effects of acute psychological stress on lymphocyte proliferation and circulating levels of interleukin-1 and -2. Healthy men were exposed to two viewings of a gruesome surgery film and were asked to recall details of the film twice during a 30-min period. These subjects were compared to a nonstress control group. Lymphocyte proliferation to the mitogen concanavalin A (Con A; 5 micrograms/ml) was decreased during and after exposure to the stressor when compared to the control group. This decrease was more pronounced in subjects exhibiting greater blood pressure reactivity while viewing the film than in subjects showing smaller blood pressure responses. None of the other immunological measures was significantly affected by the stressor. Cortisol was not correlated with lymphocyte responsiveness. Possible explanations for these results and implications for further research are discussed.