Defensive properties of pyrrolizidine alkaloids against microorganisms

The understanding of the selection factors that drive chemical diversification of secondary metabolites of constitutive defence systems in plants, such as pyrrolizidine alkaloids (PAs), is still incomplete. Historically, plants always have been confronted with microorganisms. Long before herbivores existed on this planet, plants had to cope with microbial pathogens. Therefore, plant pathogenic microorganisms may have played an important role in the early evolution of the secondary metabolite diversity. In this review, we discuss the impact that plant-produced PAs have on plant-associated microorganisms. The objective of the review is to present the current knowledge on PAs with respect to anti-microbial activities, adaptation and detoxification by microorganisms, pathogenic fungi, root protection and PA induction. Many in vitro experiments showed effects of PAs on microorganisms. These results point to the potential of microorganisms to be important for the evolution of PAs. However, only a few in vivo studies have been published and support the results of the in vitro studies. In conclusion, the topics pointed out in this review need further exploration by carrying out ecological experiments and field studies

Picture or word superiority effects in implicit memory: levels of processing, attention and retrieval constraints

Previous research with implicit memory tests has shown that the typical picture superiority effect with explicit memory instructions can he reversed on verbal perceptual tests (e.g., word-stem completion task). Two experiments explored whether the picture superiority effect can be restored with a verbal conceptual test of implicit memory (i.e., category instance generation task). In the first experiment, participants received either a perceptual test or a conceptual test of implicit memory. Furthermore, in the study phase level of processing was varied. With a superficial orienting task, a word superiority effect was found on the perceptual test and a picture superiority effect was observed on the conceptual test. Only with a semantic orienting task, priming was found for pictures on the perceptual test and for words on the conceptual test. In the second experiment, this pattern of findings was replicated with a superficial orienting task in the study phase. Once again priming for pictures on the perceptual test and priming for words on the conceptual test was found to be at chance level. Dividing attention in the study phase did not influence these results

Selective amnesic effects of oxytocin on human memory

The neuropeptide oxytocin is essential for mammalian parturition and lactation. Recent animal studies suggest that oxytocin is also implicated in the central nervous control of behavior including learning and memory. There has been little investigation, however, of the impact of oxytocin on human memory. The purpose of this study was to investigate the effect of a single dose of intranasal oxytocin on implicit and explicit memory in humans. In a placebo-controlled, double-blind study, 38 healthy men were randomly assigned to receive intranasal oxytocin (24 IU) or placebo 50 min before the study phase (incidental learning). Memory was measured using three different memory tests: an implicit perceptual test (word stem completion), an implicit conceptual test (category-cued semantic association), and an explicit test (cued recall). Due to the reproductive-biological role of oxytocin and the impact of adequate environmental conditions for the stimulation of behavioral effects of oxytocin known from animal research, we used semantic word stimuli with reproduction-related vs. neutral meaning. Oxytocin significantly impaired recall performance as compared with placebo treatment irrespective of the meaning of words in the cued recall test. In the implicit conceptual test, characterized by a deepened information processing, compared with placebo, oxytocin significantly impaired only the overall generation of associated target words with reproduction relevant meaning, whereas no significant difference between oxytocin and placebo was obtained for neutral words. These findings concur with data from animal research suggesting that central oxytocin selectively influences memory performance depending on the kind of memory test used and, more importantly, the psychobiological relevance of stimuli

Stress modulates the use of spatial versus stimulus-response learning strategies in humans

Animal studies provided evidence that stress modulates multiple memory systems, favoring caudate nucleus-based “habit” memory over hippocampus-based “cognitive” memory. However, effects of stress on learning strategy and memory consolidation were not differentiated. We specifically address the effects of psychosocial stress on the applied learning strategy in humans. We designed a spatial learning task that allowed differentiating spatial from stimulus-response learning strategies during acquisition. In 13 subsequent trials, participants (88 male and female students) had to locate a “win” card out of four placed at a fixed location in a 3D model of a room. Relocating one cue in the last trial allowed inferring the applied learning strategy. Half of them participated first in the “Trier Social Stress Test.” Salivary cortisol and heart rate measurements were taken. Stressed participants used a stimulus-response strategy significantly more often than controls. Subsequent verbal report revealed that spatial learners had a more complete awareness of response options than stimulus-response learners. Importantly, learning performance was not affected by stress. Taken together, stress prior to learning facilitated simple stimulus-response learning strategies in humans—at the expense of a more cognitive learning strategy. Depending on the context, we consider this as an adaptive response

Explaining the enigmatic anchoring effect: Mechanisms of selective accessibility

Results of 3 studies support the notion that anchoring is a special case of semantic priming; specifically, information that is activated to solve a comparative anchoring task will subsequently be more accessible when participants make absolute judgments. By using the logic of priming research, in Study 1 the authors showed that the strength of the anchor effect depends on the applicability of activated information. Study 2 revealed a contrast effect when the activated information was not representative for the absolute judgment and the targets of the 2 judgment tasks were sufficiently different. Study 3 demonstrated that generating absolute judgments requires more time when comparative judgments include an implausible anchor and can therefore be made without relevant target information that would otherwise be accessible. In current psychological research, few phenomena are easier to demonstrate and harder to explain than the so-called anchoring effect, a biased estimate toward an arbitrary value considered by judges before making a numerical estimate This finding, that an absolute numerical judgment may be assimilated toward the standard of a preceding comparative The present research was supported by a grant from the Deutsche Forschungsgemeinschaft. We thank Rudiger Pohl for providing methodological advice and calibration data. We are grateful to Marti Hope Gonzales for valuable suggestions concerning this article and to Klau