An Exploration of a Possible Physiological Explanation for Stressor Aftereffects1

The present study examined the relationship between performance deficits that occur following exposure to uncontrollable stressors and activation of the endogenous opioid system. Subjects were given an injection of saline or naloxone, an opioid antagonist, prior to exposure to 23 min of unpredictable intermittent bursts of noise or silence. Changes in mood were assessed following the injection and the stressor. Performance was measured during and after stressor exposure. Measures of performance following the stressor included a proofreading, an encoding, and a puzzle task. Results replicated previous work on the effects of noise on performance; exposure to noise was associated with performance deficits during and after the stressor. Although naloxone had no effect on performance following the noise, it was associated with greater performance deficits during exposure to the stressor. Further, although all subjects became more hostile, anxious, and depressed following exposure to noise or silence, naloxone improved mood before the stressor began.     

Acute Stressors and Chronic Response: The Case of Traumatic Stress1

The nature of acute and chronic stress is explored, including analysis of three different ways of categorizing the duration of a stressful episode: the duration of the physical stressor, the duration of threat perception or demand, and the persistence of response. Of particular interest here are situations characterized by brief stressor exposure but long-term threat perception and/ or stress response. Traumatic events are ordinarily very brief but frequently give rise to chronic threat and stubborn response patterns. In many of these cases, distress clearly outlives the event and the “normal” postevent recovery period. Possible mechanisms for such situations are discussed, as are implications for the study of traumatic stress.     

Approach-withdrawal and cerebral asymmetry: emotional expression and brain physiology. I

In this experiment, we combined the measurement of observable facial behavior with simultaneous measures of brain electrical activity to assess patterns of hemispheric activation in different regions during the experience of happiness and disgust. Disgust was found to be associated with right-sided activation in the frontal and anterior temporal regions compared with the happy condition. Happiness was accompanied by left-sided activation in the anterior temporal region compared with disgust. No differences in asymmetry were found between emotions in the central and parietal regions. When data aggregated across positive films were compared to aggregate negative film data, no reliable differences in brain activity were found. These findings illustrate the utility of using facial behavior to verify the presence of emotion, are consistent with the notion of emotion-specific physiological patterning, and underscore the importance of anterior cerebral asymmetries for emotions associated with approach and withdrawal.     

Shock preexposure and the reduced effectiveness of shock

In three experiments experience with shock was shown to reduce the effectiveness of shock as a reinforcer or motivator. In Experiment 1 rats were given signaled shock in a box separate from the runway where they were subsequently punished. These rats were less suppressed by shock punishment than rats that had no previous shock experience. In Experiment 2 preshocked rats were less suppressed by punishment and were slower to learn an escape-avoidance response than nonpreshocked rats, whether the preshock was signaled or unsignaled. In Experiment 3 as number of CS-shock pairings increased, fear of the CS decreased as did fear of the context. These results suggest that some central adaptation process produced by experience with shock reduces the effectiveness of shock as a reinforcer whenever shock is used repeatedly. This is independent of other effects, such as context blocking, that can affect responding after shock preexposure.