Distinct neural mechanisms mediate olfactory memory formation at different timescales

Habituation is one of the oldest forms of learning, broadly expressed across sensory systems and taxa. Here, we demonstrate that olfactory habituation induced at different timescales (comprising different odor exposure and intertrial interval durations) is mediated by different neural mechanisms. First, the persistence of habituation memory is greater when mice are habituated on longer timescales. Second, the specificity of the memory (degree of cross-habituation to similar stimuli) also depends on induction timescale. Third, we demonstrate a pharmacological double dissociation between the glutamatergic mechanisms underlying short- and long-timescale odor habituation. LY341495, a class II/III metabotropic glutamate receptor antagonist, blocked habituation only when the induction timescale was short. Conversely, MK-801, an N-methyl-D-aspartate (NMDA) receptor antagonist, prevented habituation only when the timescale was long. Finally, whereas short-timescale odor habituation is mediated within the anterior piriform cortex, infusion of MK-801 into the olfactory bulbs prevented odor habituation only at longer timescales. Thus, we demonstrate two neural mechanisms underlying simple olfactory learning, distinguished by their persistence and specificity, mediated by different olfactory structures and pharmacological effectors, and differentially utilized based solely on the timescale of odor presentation.     

Hypothalamo-Pituitary-Adrenocortical Regulation Following Lesions of the Central Nucleus of the Amygdala

Previous reports indicate that the central nucleus of the amygdala (CeA) stimulates adrenocorticotropin and corticosterone secretion, suggesting a role for this region in central hypothalamo-pituitary-adrenocortical (HPA) stress regulation. To evaluate this hypothesis, this study assessed the impact of CeA lesion on the response of hypophysiotrophic paraventricular nucleus (PVN) neurons to acute restraint and chronic unpredictable stress exposure. In contrast to previous reports, CeA lesions did not affect corticosterone or ACTH secretion induced by acute stress. Acute restraint increased PVN corticotropin releasing hormone (CRH) mRNA expression, increased the number of parvocellular PVN neurons expressing the co-secretagogue arginine vasopressin (AVP), and induced cFOS mRNA expression in the parvocellular PVN. However, there was no additional effect of CeA lesion on any measure of PVN activation. Chronic unpredictable stress exposure induced long-term activation of the HPA axis, noted by thymic involution, adrenal hypertrophy and increased PVN CRH mRNA expression. Stress-induced changes in thymus and adrenal weights were not affected by CeA lesion. Further, CeA lesion rats did not differ from controls in post-stress CRH mRNA expression. However, basal CRH mRNA expression was increased in the PVN of CeA rats, suggesting that the CeA plays a role in long-term inhibition of the PVN. The results of these studies are not consistent with the hypothesis that the CeA is necessary for stress-induced pituitary-adrenocortical activation. Rather, this region may play a stressor-specific modulatory role in regulation of HPA function.     

Topography of signal-centered behavior in the rat: Effects of deprivation state and reinforcer type

In a series of three experiments, groups of food-deprived and water-deprived rats were given pairings of a retractable lever (CS⁺) with response-independent deliveries of either solid or liquid reinforcers. In Experiment 1 food-deprived rats given a solid-pellet reinforcer differentially tended to sniff, paw, mouth, and bite the CS⁺ lever more often than a lever that was not paired with food (CS⁻), whereas food-deprived rats given a liquid reinforcer tended to differentially sniff, paw, and lick the CS⁺ lever. 23½-hour water-deprived rats given liquid reinforcers showed very little CS⁺ contact. In Experiment 2 increasing the severity of water deprivation from 23½ to 47½ hours significantly increased CS⁺ contact. In Experiment 3, subjects that were simultaneously food and water deprived and given a water reinforcer failed to exhibit differential CS⁺ contact, but subjects that were simultaneously food and water deprived and given a food reinforcer did acquire differential CS⁺-contact behavior. These results suggest that (a) even under a single motivational state the nature of signal-centered behavior can be determined by type of reinforcer, (b) although water reinforcement produces less signal contact than food reinforcement, this can be facilitated with more severe water-deprivation levels, and (c) high CS-contact rates using food reinforcement are not simply a product of reductions in body weight with food deprivation.     

Existential measurement: A factor analytic study of some current psychometric instruments

The foray of quantification research into the arena of existentialism and ontology has given rise to several psychometric instruments pertinent to the area. Both exploratory and Confirmatory principal-factor analyses were used to study the relationships among 16 existential scales currently in use in the research literature. Participants were 133 individuals comprised of 74 females and 59 males with a median age of approximately 30.5 years. Approximately one half of the sample was in attendance at the University of Regina and Saskatchewan during the 1976–1977 fall term, while the remainder was drawn from the respective communities. Confirmatory factor analysis supported both the prediction of substantial condensation of existential scales and the presence of an avoidance of ontological confrontation factor. Exploratory factor analysis provided some support of the theory that the avoidance of existential confrontation is a central function of neurosis. Extracted factors were interpreted and examined with respect to implications for existential-ontological theory and research.     

Frequency effects in spoken and visual word recognition: evidence from dual-task methodologies

The authors report 3 dual-task experiments concerning the locus of frequency effects in word recognition. In all experiments, Task 1 entailed a simple perceptual choice and Task 2 involved lexical decision. In Experiment 1, an underadditive effect of word frequency arose for spoken words. Experiment 2 also showed underadditivity for visual lexical decision. It was concluded that word frequency exerts an influence prior to any dual-task bottleneck. A related finding in similar dual-task experiments is Task 2 response postponement at short stimulus onset asynchronies. This was explored in Experiment 3, and it was shown that response postponement was equivalent for both spoken and visual word recognition. These results imply that frequency-sensitive processes operate early and automatically.