Psychology

Recent studies indicate that decreased central dopamine is associated with diet-induced obesity in humans and in animal models. In the current study, we assessed the hypothesis that diet-induced obesity reduces mesolimbic dopamine function. Specifically, we compared dopamine turnover in this region between rats fed a high-fat diet and those consuming a standard low-fat diet. We also assessed behavioral consequences of diet-induced obesity by testing the response of these animals in a conditioned place paradigm using amphetamine as a reinforcer and in an operant conditioning paradigm using sucrose reinforcement. Results demonstrate that animals consuming a high-fat diet, independent of the development of obesity, exhibit decreased dopamine turnover in the mesolimbic system, reduced preference for an amphetamine cue, and attenuated operant responding for sucrose. We also observed that diet induced obesity with a high fat diet attenuated mesolimbic dopamine turnover in the nucleus accumbens. These data are consistent with recent hypotheses that the hormonal signals derived from adipose tissue regulate the activity of central nervous system structures involved in reward and motivation, which may have implications for the treatment of obesity and/or addiction.

The regulation of energy balance depends on the precise coordination of multiple peripheral and central systems. Much recent research has highlighted the importance of behavioral mechanisms is this control and suggested that the regulation of body weight shares CNS pathways in common with other complex behaviors, including learning and drug addiction. Here, we present a brief review of some of this work and highlight the novel functions for central orexigenic neuropeptides. We review evidence that organisms engage in critical regulatory behaviors both before an after ingestion has occurred. Additional evidence supports the idea that appetitive mechanisms are engaged that are critical for the regulation of intake during the act of ingestion. Finally, we briefly discuss the recent work on the potential role for CNS reward centers and how those might be critically linked to the central regulation of food intake, as well as how they may be disregulated by the abundance of highly palatable, energy-dense foods.

Nausea and aversive food responses are commonly reported following bariatric surgery, along with post-surgical reduction in meal size. This study investigates whether a meal size limit can be conditioned by associating large meals with aversive outcomes. In rats, the intake of meals exceeding a pre-defined size threshold was paired with lithium chloride-induced gastric illness, and the effects on self-determined food intakes and body weight were measured. Rats given LiCl contingent on the intake of a large meal learned to reliably reduce intake below this meal size threshold, while post-meal saline or LiCl before meals did not change meal size. It was further demonstrated that this is not a conditioned taste aversion and that this effect transferred to foods not explicitly trained. Finally, when rats received LiCl following all large meals, the number of small meals increased, but total food intake and body weight decreased. While further work is needed, this is the first demonstrat...

To develop and use a behavioral paradigm for assessments of what nutrient properties are detected by intestinal chemoreceptors, we combined features of the "electronic esophagus" preparation (Elizalde and Sclafani, 1990) and the conditioned taste aversion protocol (Garcia and Koelling, 1966). In four experiments, separate groups of food-deprived rats with gastric (Experiments 1-4) or duodenal (Experiment 4) catheters were infused with either carbohydrates (maltodextrin) or fats (corn oil) into their stomachs or small intestines, either while they consumed non-nutritive flavored solutions (Experiments 1 and 2) or in the absence of any intake (Experiments 3 and 4). For some animals, one of the macronutrient infusions was paired with lithium chloride injections shown to support conventional conditioned aversions. After training, in various oral preference test trials, animals were given opportunities to taste and consume the non-nutritive solutions that had served as orophary...

Visual clutter imposes significant challenges to older adults in everyday tasks and often calls on selective processing of relevant information. Previous research has shown that both visual search habits and task goals influence older adults' allocation of spatial attention, but has not examined the relative impact of these two sources of attention when they compete. To examine how aging affects the balance between goal-driven and habitual attention, and to inform our understanding of different attentional subsystems, we tested young and older adults in an adapted visual search task involving a display laid flat on a desk. To induce habitual attention , unbeknownst to participants, the target was more often placed in one quadrant than in the others. All participants rapidly acquired habitual attention toward the high-probability quadrant. We then informed participants where the high-probability quadrant was and instructed them to search that screen location first—but pitted their habit-based, viewer-centered search against this instruction by requiring participants to change their physical position relative to the desk. Both groups prioritized search in the instructed location, but this effect was stronger in young adults than in older adults. In contrast, age did not influence viewer-centered search habits: the two groups showed similar attentional preference for the visual field where the target was most often found before. Aging disrupted goal-guided but not habitual attention. Product, work, and home design for people of all ages––but especially for older individuals––should take into account the strong viewer-centered nature of habitual attention.

Age-related decline is pervasive in tasks that require explicit learning and memory, but such reduced function is not universally observed in tasks involving incidental learning. It is unknown if habitual attention, involving incidental probabilistic learning, is preserved in older adults. Previous research on habitual attention investigated contextual cuing in young and older adults, yet contextual cuing relies not only on spatial attention but also on context processing. Here we isolated habitual attention from context processing in young and older adults. Using a challenging visual search task in which the probability of finding targets was greater in 1 of 4 visual quadrants in all contexts, we examined the acquisition, persistence, and spatial-reference frame of habitual attention. Although older adults showed slower visual search times and steeper search slopes (more time per additional item in the search display), like young adults they rapidly acquired a strong, persistent search habit toward the high-probability quadrant. In addition, habitual attention was strongly viewer-centered in both young and older adults. The demonstration of preserved viewer-centered habitual attention in older adults suggests that it may be used to counter declines in controlled attention. This, in turn, suggests the importance, for older adults, of maintaining habit-related spatial arrangements.

Recent empirical studies confirm that the use of neuroscientific evidence is rising. This parallels a rapid increase in legal scholarship on neurolaw, and suggests a trend toward more brain evidence in courts in the coming years. As a consequence, admissibility decisions on brain science are now being made by courts, jury experts are debating the
use of brain science in the courtroom in practitioner journals, and brain evidence is being used across a variety of substantive areas of law. The admissibility of neuroscientific evidence is becoming an increasingly important issue for American courts.