Lateral line units in the amphibian brain could integrate wave curvatures

Aquatic predators like Xenopus laevis exploit mechano-sensory lateral lines to localise prey on the water surface by its wave emissions. In terms of distance, hypothetically, the source of a concentric wave could be centrally represented based on wave curvatures: for Xenopus, we present a first sample of 98 extracellularly recorded brainstem and midbrain responses to waves with curvatures ranging from 22.2-11.1 m(-1). At the frog, concurrently, wave amplitudes and their spectral composition were kept stable. Notably, 61% of 98 units displayed curvature-dependent spike rates, suggesting that wave curvatures could support an extraction of source distances in the amphibian brain.     

Food choice in the laboratory pigeon

Although food reward plays a large role in learning and behavioral experiments, there have been few studies examining the most motivating food reward for pigeons. Brown (1969) found that pigeons had a tendency to prefer peas, while Killeen et al. (1993) found pigeons to prefer peas and popcorn in Experiment 1A. We looked to further explore these options as well as expand upon the types of foods examined beyond mainly grains and seeds. Pigeons were presented with six novel foods (granulated peanuts, popping corn, freeze-dried mealworms, bread crumbs, split peas, and sunflower hearts) allocated into two sets of three food items. Once the most consumed food from each food set was determined, they were pooled together with sorghum seeds (a familiar food) to form a third set. Sunflower hearts were the most consumed of all the food items, followed by corn and granulated peanuts. We discuss the potential factors mediating consumption choice, including nutritional profile and food particle size.     

Toward an understanding of the brain substrates of reward in humans

A network of brain regions has been implicated in food-reward processing. now provide evidence that this network is differentially modulated by anticipation versus receipt of a food reward and suggest an additional effect of valence of the stimulus.     

Methylphenidate decreased the amount of glucose needed by the brain to perform a cognitive task

The use of stimulants (methylphenidate and amphetamine) as cognitive enhancers by the general public is increasing and is controversial. It is still unclear how they work or why they improve performance in some individuals but impair it in others. To test the hypothesis that stimulants enhance signal to noise ratio of neuronal activity and thereby reduce cerebral activity by increasing efficiency, we measured the effects of methylphenidate on brain glucose utilization in healthy adults. We measured brain glucose metabolism (using Positron Emission Tomography and 2-deoxy-2[18F]fluoro-D-glucose) in 23 healthy adults who were tested at baseline and while performing an accuracy-controlled cognitive task (numerical calculations) given with and without methylphenidate (20 mg, oral). Sixteen subjects underwent a fourth scan with methylphenidate but without cognitive stimulation. Compared to placebo methylphenidate significantly reduced the amount of glucose utilized by the brain when performing the cognitive task but methylphenidate did not affect brain metabolism when given without cognitive stimulation. Whole brain metabolism when the cognitive task was given with placebo increased 21% whereas with methylphenidate it increased 11% (50% less). This reflected both a decrease in magnitude of activation and in the regions activated by the task. Methylphenidate's reduction of the metabolic increases in regions from the default network (implicated in mind-wandering) was associated with improvement in performance only in subjects who activated these regions when the cognitive task was given with placebo. These results corroborate prior findings that stimulant medications reduced the magnitude of regional activation to a task and in addition document a "focusing" of the activation. This effect may be beneficial when neuronal resources are diverted (i.e., mind-wandering) or impaired (i.e., attention deficit hyperactivity disorder), but it could be detrimental when brain activity is already optimally focused. This would explain why methylphenidate has beneficial effects in some individuals and contexts and detrimental effects in others.     

Multiple reward signals in the brain

The fundamental biological importance of rewards has created an increasing interest in the neuronal processing of reward information. The suggestion that the mechanisms underlying drug addiction might involve natural reward systems has also stimulated interest. This article focuses on recent neurophysiological studies in primates that have revealed that neurons in a limited number of brain structures carry specific signals about past and future rewards. This research provides the first step towards an understanding of how rewards influence behaviour before they are received and how the brain might use reward information to control learning and goal-directed behaviour.     

Minimal cross-trial generalization in learning the representation of an odor-guided choice task

There is no single way to represent a task. Indeed, despite experiencing the same task events and contingencies, different subjects may form distinct task representations. As experimenters, we often assume that subjects represent the task as we envision it. However, such a representation cannot be taken for granted, especially in animal experiments where we cannot deliver explicit instruction regarding the structure of the task. Here, we tested how rats represent an odor-guided choice task in which two odor cues indicated which of two responses would lead to reward, whereas a third odor indicated free choice among the two responses. A parsimonious task representation would allow animals to learn from the forced trials what is the better option to choose in the free-choice trials. However, animals may not necessarily generalize across odors in this way. We fit reinforcement-learning models that use different task representations to trial-by-trial choice behavior of individual rats performing this task, and quantified the degree to which each animal used the more parsimonious representation, generalizing across trial types. Model comparison revealed that most rats did not acquire this representation despite extensive experience. Our results demonstrate the importance of formally testing possible task representations that can afford the observed behavior, rather than assuming that animals’ task representations abide by the generative task structure that governs the experimental design.     

Be quick about it. Endogenous estradiol level,menstrual cycle phase and trait impulsiveness predict impulsive choice in the context of reward acquisition

This article is part of a Special Issue “Estradiol and Cognition”.Variations in the steroid hormone 17ß-estradiol (E2) may promote intra-individual differences in reward seeking behavior and temporal decision-making (Reimers et al., 2014; Front. Neurosci. 8: 401). Yet, in humans the exact role of E2 in impulsive choice still needs to be determined. The present study assessed the effect of a cycle-dependent rise in endogenous E2 on temporal response adaptation across the follicular phase (FP). For this purpose a reward acquisition paradigm was employed that is sensitive to hormone-induced changes in central dopamine (DA) level. The present data show that women acted more impulsively in the early as opposed to the late FP. Early follicular E2 further correlated with an increased capacity to speed up for reward maximization, while simultaneously the ability to wait for higher reward was compromised. This correlation was most pronounced in women with low trait impulsiveness. In contrast, E2 and optimized response speed failed to correlate in women with high trait impulsiveness and in the late FP, despite a generally higher E2 level. Collectively, these findings support the theory that E2 may act as an endogenous DA agonist. The fact that the hormone–behavior relationship was restricted to women with low trait impulsiveness and thus supposedly lower central DA level provides indirect support for this idea. Yet, choices became relatively less impulsive in the state of heightened E2 (i.e., in the late FP), suggesting that the relationship between E2 and impulsive choice may not be linear, but might resemble an inverted U-function.     

Motivation dependence of brain self-stimulation in the pigeon

Several brain sites in the pigeon were identified as maintaining electrical brain self-stimulation. Depending on the site, stimulus currents yielding maximal responding varied from 20 to 160 μA. A high proportion of the sites only yielded self-stimulation behaviour if the subjects were deprived of food; when the birds were at full weight there was only one site at which the stimulation continued to be rewarding. Some, but weak, evidence of stimulus satiation was found. Overt behaviour elicited by non-contingent stimulation did not correlate with the reinforcing or neutral nature of the sites tested. While some positive sites were associated with structures known to be involved in the control of feeding, others were not. The hypothesis that stimulation at the hunger-dependent sites might have elicited temporary satiation signals is considered.     

Cortisol alters reward processing in the human brain

Dysfunctional reward processing is known to play a central role for the development of psychiatric disorders. Glucocorticoids that are secreted in response to stress have been shown to attenuate reward sensitivity and thereby might promote the onset of psychopathology. However, the underlying neurobiological mechanisms mediating stress hormone effects on reward processing as well as potential sex differences remain elusive. In this neuroimaging study, we administered 30 mg cortisol or a placebo to 30 men and 30 women and subsequently tested them in the Monetary Incentive Delay Task. Cortisol attenuated anticipatory neural responses to a verbal and a monetary reward in the left pallidum and the right anterior parahippocampal gyrus. Furthermore, in men, activation in the amygdala, the precuneus, the anterior cingulate, and in hippocampal regions was reduced under cortisol, whereas in cortisol-treated women a signal increase was observed in these regions. Behavioral performance also indicated that reward learning in men is impaired under high cortisol concentrations, while it is augmented in women. These findings illustrate that the stress hormone cortisol substantially diminishes reward anticipation and provide first evidence that cortisol effects on the neural reward system are sensitive to sex differences, which might translate into different vulnerabilities for psychiatric disorders.     

Cannabinoid CB1 receptor activation mediates the opposing effects of amphetamine on impulsive action and impulsive choice

It is well known that acute challenges with psychostimulants such as amphetamine affect impulsive behavior. We here studied the pharmacology underlying the effects of amphetamine in two rat models of impulsivity, the 5-choice serial reaction time task (5-CSRTT) and the delayed reward task (DRT), providing measures of inhibitory control, an aspect of impulsive action, and impulsive choice, respectively. We focused on the role of cannabinoid CB1 receptor activation in amphetamine-induced impulsivity as there is evidence that acute challenges with psychostimulants activate the endogenous cannabinoid system, and CB1 receptor activity modulates impulsivity in both rodents and humans. Results showed that pretreatment with either the CB1 receptor antagonist/inverse agonist SR141716A or the neutral CB1 receptor antagonist O-2050 dose-dependently improved baseline inhibitory control in the 5-CSRTT. Moreover, both compounds similarly attenuated amphetamine-induced inhibitory control deficits, suggesting that CB1 receptor activation by endogenously released cannabinoids mediates this aspect of impulsive action. Direct CB1 receptor activation by Δ9-Tetrahydrocannabinol (Δ9-THC) did, however, not affect inhibitory control. Although neither SR141716A nor O-2050 affected baseline impulsive choice in the DRT, both ligands completely prevented amphetamine-induced reductions in impulsive decision making, indicating that CB1 receptor activity may decrease this form of impulsivity. Indeed, acute Δ9-THC was found to reduce impulsive choice in a CB1 receptor-dependent way. Together, these results indicate an important, though complex role for cannabinoid CB1 receptor activity in the regulation of impulsive action and impulsive choice as well as the opposite effects amphetamine has on both forms of impulsive behavior.     

Topographical distribution of CRF immunoreactivity in the pigeon brain

The distribution of corticotropin-releasing factor (CRF) immunoreactivity was demonstrated by immunocytochemistry in intact and colchicine-treated pigeons. Colchicine injections were administered at different times related to the circadian activity of the CRF-adrenocorticotropin (ACTH)-corticosterone axis. Three CRF antisera were used, two directed against synthetic rat CRF and one directed against synthetic ovine CRF. No fundamental differences appeared in the pigeon brain with respect to the specific CRF antiserum used. The most effective colchicine injection times corresponded to hypersecretion in the corticotropic axis. CRF-immunopositive neurons were scattered throughout the pigeon brain. In addition to the paraventricular hypothalamic system, which is involved in adenohypophysial ACTH regulation, several other hypothalamic and extrahypothalamic areas showed CRF neurons. The distribution suggests that CRF may also act as a modulator and a neurotransmitter. Two hypothalamic paraventricular nucleus-median eminence CRF pathways are described here. Moreover, CRF-immunopositive reactions were observed in specific areas of cerebral ventricle walls, suggesting that CRF may be released into the cerebral fluid.     

Partner's behavior, not reward distribution, determines success in an unequal cooperative task in capuchin monkeys

It was recently demonstrated that capuchin monkeys notice and respond to distributional inequity, a trait that has been proposed to support the evolution of cooperation in the human species. However, it is unknown how capuchins react to inequitable rewards in an unrestricted cooperative paradigm in which they may freely choose both whether to participate and, within the bounds of their partner's behavior, which reward they will receive for their participation. We tested capuchin monkeys with such a design, using a cooperative barpull, which has been used with great success in the past. Contrary to our expectations, the equity of the reward distribution did not affect success or pulling behavior. However, the behavior of the partner in an unequal situation did affect overall success rates: pairs that had a tendency to alternate which individual received the higher-value food in unequal reward situations were more than twice as successful in obtaining rewards than pairs in which one individual dominated the higher-value food. This ability to equitably distribute rewards in inherently biased cooperative situations has profound implications for activities such as group hunts, in which multiple individuals work together for a single, monopolizable reward.     

Vascular reactivity of the brain in the pigeon Columba livia

In experiments on awake relatively unrestrained pigeons, studies have been made on the reactions of the cerebrovascular bed to fixed functional loads of physical (orthostasis) and chemical (inhalation of hypoxic and hypercapnic gas mixtures) nature. Using hydrogen clearance method, the increase in the intensity of local cerebral blood flow in different structures of the telencephalon during inhalation of the mentioned gas mixtures was demonstrated. Bilateral vagotomy resulted in inversed reactions. Influence of functional loads was accompanied by changes in rheoencephalographic parameters. The data obtained suggest the existence of an evident reactivity of cerebral vessels in birds which is controlled by neurogenic mechanism of regulation of vascular tone.     

A concept of welfare based on reward evaluating mechanisms in the brain: anticipatory behaviour as an indicator for the state of reward systems

In this review we attempt to link the efficiency by which animals behave (economy of animal behaviour) to a neuronal substrate and subjective states to arrive at a definition of animal welfare which broadens the scope of its study. Welfare is defined as the balance between positive (reward, satisfaction) and negative (stress) experiences or affective states. The state of this balance may range from positive (good welfare) to negative (poor welfare). These affective states are momentary or transient states which occur against the background of and are integrated with the state of this balancing system. As will be argued the efficiency in behaviour requires that, for instance, satisfaction is like a moving target: reward provides the necessary feedback to guide behaviour; it is a not steady-state which can be maintained for long. This balancing system is reflected in the brain by the concerted action of opioid and mesolimbic dopaminergic systems. The state of this system reflects the coping capacity of the animal and is determined by previous events. In other words, this integrative approach of behavioural biology and neurobiology aims at understanding how the coping capacity of animals may be affected and measured. We argue that this balancing system underlies the economy of behaviour. Furthermore we argue that among other techniques anticipation in Pavlovian conditioning is an easy and useful tool to assess the state of this balancing system: for estimating the state of an animal in terms of welfare we focus on the conditions when an animal is facing a challenge.     

Contributions of the amygdala to reward expectancy and choice signals in human prefrontal cortex

The prefrontal cortex (PFC) receives substantial anatomical input from the amygdala, and these two structures have long been implicated in reward-related learning and decision making. Yet little is known about how these regions interact, especially in humans. We investigated the contribution of the amygdala to reward-related signals in PFC by scanning two rare subjects with focal bilateral amygdala lesions using fMRI. The subjects performed a reversal learning task in which they first had to learn which of two choices was the more rewarding, and then flexibly switch their choices when contingencies changed. Compared with healthy controls, both amygdala lesion subjects showed a profound change in ventromedial prefrontal cortex (vmPFC) activity associated with reward expectation and behavioral choice. These findings support a critical role for the human amygdala in establishing expected reward representations in PFC, which in turn may be used to guide behavioral choice.     

Leveraging related health phenotypes for polygenic prediction of impulsive choice,impulsive action,and impulsive personality traits in 1534 European ancestry community adults

Impulsivity refers to a number of conceptually related phenotypes reflecting self-regulatory capacity that are considered promising endophenotypes for mental and physical health. Measures of impulsivity can be broadly grouped into three domains, namely, impulsive choice, impulsive action, and impulsive personality traits. In a community-based sample of ancestral Europeans (n = 1534), we conducted genome-wide association studies (GWASs) of impulsive choice (delay discounting), impulsive action (behavioral inhibition), and impulsive personality traits (UPPS-P), and evaluated 11 polygenic risk scores (PRSs) of phenotypes previously linked to self-regulation. Although there were no individual genome-wide significant hits, the neuroticism PRS was positively associated with negative urgency (adjusted R² = 1.61%, p = 3.6 × 10⁻⁷) and the educational attainment PRS was inversely associated with delay discounting (adjusted R² = 1.68%, p = 2.2 × 10⁻⁷). There was also evidence implicating PRSs of attention-deficit/hyperactivity disorder, externalizing, risk-taking, smoking cessation, smoking initiation, and body mass index with one or more impulsivity phenotypes (adjusted R²s: 0.35%–1.07%; FDR adjusted ps = 0.05–0.0006). These significant associations between PRSs and impulsivity phenotypes are consistent with established genetic correlations. The combined PRS explained 0.91%–2.46% of the phenotypic variance for individual impulsivity measures, corresponding to 8.7%–32.5% of their reported single-nucleotide polymorphism (SNP)-based heritability, suggesting a non-negligible portion of the SNP-based heritability can be recovered by PRSs. These results support the predictive validity and utility of PRSs, even derived from related phenotypes, to inform the genetics of impulsivity phenotypes.