Contributions of the nucleus accumbens and its subregions to different aspects of risk-based decision making

The nucleus accumbens (NAc) has been implicated in mediating different forms of decision making in humans and animals. In the present study, we observed that inactivation of the rat NAc, via infusion of GABA agonists, reduced preference for a large/risky option and increased response latencies on a probabilistic discounting task. Discrete inactivations of the NAc shell and core revealed further differences between these regions in mediating choice and response latencies, respectively. The effect on choice was attributable to reduced win–stay performance (i.e., choosing risky after a being rewarded for a risky choice on a preceding trial). Moreover, NAc inactivation altered choice only when the large/risky option had greater long-term value, in terms of the amount of food that could be obtained over multiple trials relative to the small/certain option. Inactivation of the NAc or the shell subregion also slightly reduced preference for larger rewards on a reward magnitude discrimination. Thus, the NAc seems to play a small role in biasing choice toward larger rewards, but its contribution to behavior is amplified when delivery of these rewards is uncertain, helping to direct response selection toward more favorable outcomes.     

Cholinergic modulation of hippocampal CA1 basal-dendritic long-term potentiation

Extensive research suggests that long-term potentiation (LTP) may serve as a cellular mechanism for memory and that alterations in synaptic plasticity may underlie the gross memory impairments observed in patients with Alzheimer's disease. Cholinergic facilitation of hippocampal LTP in the behaving rat is a useful model for the study of the effects of anticholinesterase or other drugs on synaptic plasticity. Field excitatory postsynaptic potentials were recorded from the hippocampal CA1 region following excitation of the basal dendrites in behaving male Long-Evans rats. LTP was induced by a high-frequency train (200 Hz for 0.5s duration) following injection of the acetylcholinesterase inhibitor eserine sulfate (0.5 mg/kg, i.p.), specific muscarinic M1 receptor antagonist pirenzepine (21.2 microg/microl, i.c.v.), or saline (i.p. or i.c.v.). Pirenzepine was found to block basal-dendritic LTP when LTP was induced during walking, but not when LTP was induced during immobility. Eserine facilitated LTP when induction occurred during either immobility or walking. The present study demonstrates that an anticholinesterase enhances LTP in CA1 of the behaving rat, and that facilitation of basal-dendritic LTP during walking is mediated by muscarinic M1 receptors.     

The facilitation of important personal goals through exercise

In a sample of 1287 adolescents, it appeared that weekly exercise facilitates a variety of goals; particularly those related to being or remaining healthy, feeling relaxed, not being bored, feeling physically good, not being stressed, and attaining high achievements were endorsed. Sedentary and active adolescents reported a similar order of 10 specific goals with respect to the likelihood of being positively influenced by exercise. The frequency of reported facilitation for each of the goals, however, was higher among the active adolescernts. This suggests that the more exercise is incorporated in daily life, the more it can be regarded as an integral part of the personal goal structure.     

Spontaneous pointing by bottlenose dolphins (Tursiops truncatus)

Two bottlenose dolphins (Tursiops truncatus) participating in a symbolic communication project spontaneously developed behaviors that resembled pointing and gaze alternation. The dolphins' behavior demonstrated several features reminiscent of referential communicative behavior. It was triadic, involving a signaler, receiver, and referent. It was also indicative, specifying a focus of attention. The dolphins' points were distinct from the act of attending to or acting on objects. Spontaneous dolphin pointing was influenced by the presence of a potential receiver, and the distance between that receiver and the dolphin. These findings suggest that dolphins are capable of producing referential gestures. Accepted after revision: 14 August 2001 Electronic Publication     

Functional constraints on sentence processing: A cross-linguistic study

English and Italian provide some interesting contrasts that are relevant to a controversial problem in psycholinguistics: the boundary between grammatical and extra-grammatical knowledge in sentence processing. Although both are SVO word order languages without case inflections to indicate basic grammatical relations, Italian permits far more variation in word order for pragmatic purposes. Hence Italians must rely more than English listeners on factors other than word order. In this experiment, Italian and English adults were asked to interpret 81 simple sentences varying word order, animacy contrasts between the two nouns, topicalization and contrastive stress. Italians relied primarily on semantic strategies while the English listeners relied on word order—including a tendency to interpret the second noun as subject in non-canonical word orders (corresponding to word order variations in informal English production). Italians also made greater use of topic and stress information. Finally, Italians were much slower and less consistent in the application of word order strategies even for reversible NVN sentences where there was no conflict between order and semantics. This suggests that Italian is ‘less’ of an SVO language than English. Semantic strategies apparently stand at the ‘core’ of Italian to the same extent that word order stands at the ‘core’ of English. It is suggested that these results pose problems for claims about a ‘universal’ separation between semantics and syntax, and for theories that postulate a ‘universal’ priority of one type of information over another. Results are discussed in the light of the competition model, a functionalist approach to grammar that accounts in a principled way for probabilistic outcomes and differential ‘weights’ among competing and converging sources of information in sentence processing.