Behavioral rebound following stereotype suppression

Attempts to suppress stereotypes have often been found to result in an increased accessibility of these stereotypes. According to thought suppression literature together with research on prime‐to‐behavior effects, we hypothesized that suppression of stereotype can lead people to subsequently behave in accordance with its content and that these effects are stronger after suppression (rebound) than after a classical priming condition (i.e., no‐suppression condition). Experiment 1 showed that suppression of the stereotype of sportsmen (associated with poor math performance) but not of Italian men (not related to math performance) led participants to subsequently perform worse on a calculus task in comparison to non‐suppressors. These effects were replicated in a second experiment with another stereotype (elderly) and another behavior that does not require self‐regulation (walking speed): Suppressors walked slower than non‐suppressors. These findings are considered in the context of mental control and social stereotyping. Copyright © 2009 John Wiley & Sons, Ltd.     

Behavioral economics and within-session changes in responding

Pigeons and rats responded on fixed-ratio schedules with requirements ranging from 5 to 120 responses. Consistent with past results from several schedules and procedures, responding usually changed systematically within experimental sessions. The within-session changes were usually larger and were less symmetrical around the middle of the session for schedules that provided higher, rather than lower, rates of reinforcement. These results suggest that similar variables contribute to within-session changes in responding under different schedules. When an economic demand function was fit to the data, the intensity and elasticity of demand for food and the percentage of the variance accounted for decreased within sessions, although the trend for elasticity did not reach statistical significance for pigeons. These results suggest that relatively short sessions should be used to study economic demand in open economies and that demand may differ at different times in a session and in sessions of different lengths. Within-session changes in intensity, but not necessarily elasticity, of demand are consistent with behavioral economic theories.     

Amygdaloid function in the central cholinergic mediation of shock-induced aggression in the rat

A series of experiments was designed to examine the role of central cholinergic mechanisms in shock-induced aggression. Cholinergic blockade in the basolateral amygdala, ventral hippocampus, or dorsal hippocampus resulted in greatly reduced levels of fighting in response to footshock. However, while pain sensitivity remained unaltered in the amygdala group, both of the hippocampal groups exhibited decreased shock sensitivity. Further investigation of the amygdala revealed (1) increased fighting in response to increased cholinergic levels, (2) neuroanatomical specificity to the basolateral division of this complex, (3) that an intact basolateral amygdala is essential to the normal manifestation of shock-induced aggression, and (4) that social attraction remains unaltered by cholinergic blockade of the basolateral amygdala. Motor coordination and motor activity were not significantly affected in any treatment condition.     

Behavioral effects of neurotoxic lesions of the ascending monoamine pathways in the rat brain

Intracranial microinjections of 6-hydroxydopamine or 5,6-dihydroxytryptamine into six ascending monoamine pathways produced the expected patterns of depletion of telencephalic serotonin, dopamine, and norepinephrine. Serotonin level was specifically lowered after dorsal or median raphe lesions but not after mesolimbic or nigrostriatal system lesions which lowered both norepinephrine and dopamine. Lesions in the locus coeruleus or ventral nor-adrenergic bundle lowered only norepinephrine, and locus coeruleus lesions elevated serotonin level. Behavior was examined in an open field, one-way active avoidance, and two passive avoidance tasks, and measures were taken of water consumption and body weight. Dorsal raphe lesions had no effect on any of the measures; the other five lesion groups exhibited deficient acquisition of the one-way active avoidance task. In the appetitive passive avoidance task, only the substantia nigra lesion group exhibited a deficiency. In the step-through passive avoidance task, both the substantia nigra and the median raphe groups exhibited a deficit, with the median raphe group exhibiting hyperactivity in the start box during testing. Water consumption was decreased by lesions in the ventral noradrenergic bundle during the first postoperative week and was increased in the median raphe group by the fourth postoperative week. Lastly, lesions in the locus coeruleus dramatically decreased activity in the open field. The results are discussed in regard to the search for specificity of behavioral functions of the distinct ascending monoamine pathways.     

Behavioral effects following rehabilitation from postnatal exposure to lead acetate

At 21 days of age three groups of male hooded rats of the Sprague-Dawley strain were exposed to either untreated water or lead acetate at concentrations of 25 or 50 ppm provided ad lib. in the drinking water for 40 days. When tested for spontaneous alternation, the subjects receiving both 50 ppm and 25 ppm lead acetate exhibited significantly reduced rates of alternation below those of untreated control subjects. Immediately subsequent to testing, lead was removed from the diet of the experimental groups and water substituted which was provided ad lib. for the duration of the experiment. This regimen of rehabilitation was continued for 70 days at which time all subjects were tested on the problems of the Hebb-Williams closed-field maze-learning task. No significant differences were found in the time taken to traverse the maze enclosure, the number of squares traversed, or in the total number of error zones entered over the 12 test problems, although significantly increased latencies to leave the start box were noted for subjects previously exposed to lead acetate. These data indicate that some deficits produced by postweaning lead acetate exposure may be reversible and not persist beyond a period of rehabilitation.