Behavioral plasticity in aneural organisms.

Few contemporary psychologists would probably object to the notion that cognitive processes contribute to behavioral plasticity (learning) and are intimately linked to brain function. However, growing evidence suggests that behavioral plasticity is present in organisms lacking neurons (i.e., aneural organisms). This possibility would imply that at least some cognitive processes might have preceded the evolution of nervous systems. Evidence of learning in aneural organisms is reviewed within a mechanistic framework emphasizing four levels of analysis: psychological, neurobiological, neurochemical, and cell-molecular. Learning phenomena ranging from habituation to conditioning have been reported in some aneural organisms, and some key examples are reviewed with attention to evidence of underlying mechanisms. Species comparisons are framed in terms of the central evolutionary concepts of homology and homoplasy. This evidence raises the question of what new behavioral capacities were supported by the evolution of neurons that were not possible before. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Instrumental successive negative contrast in rats: Trial distribution, reward magnitude, and prefrontal cortex activation.

Successive negative contrast (SNC) has been used to study reward relativity, reward loss, and frustration for decades. In instrumental SNC (iSNC), the anticipatory performance of animals downshifted from a large reward to a small reward is compared to that of animals always reinforced with the small reward. iSNC involves a transient deterioration of anticipatory behavior in downshifted animals compared to unshifted controls. There is scattered information on the optimal parameters to produce this effect and even less information about its neural basis. Five experiments with rats trained in a runway to collect food pellets explored the effects of trial distribution (massed or spaced), amount of preshift training, reward disparity, and reward magnitude on the development of an iSNC effect. Start, run, and goal latencies were measured. Using spaced trials (one trial per day), evidence of the iSNC effect was observed with 24 preshift trials and a 32-to-4 pellet disparity. With massed trials (4 trials per session separated by 30-s intertrial intervals), evidence of iSNC was found with 12 preshift sessions (a total of 48 trials) and a 16-to-2 pellet disparity. The massed-training procedure was then used to assess neural activity in three prefrontal cortex areas using c-Fos expression in animals perfused after the first downshift session. There was evidence of increased activation in the anterior cingulate cortex and a trend toward increased activation in the infralimbic and prelimbic cortices. These procedures open a venue for studying the neural basis of the instrumental behavior of animals that experience reward loss.

Open field activity is linked to, but is not affected by, the rate of recovery from reward downshift in female Wistar rats.

Frustration is an aversive emotion triggered by unexpected reward downshifts. Using the consummatory successive negative contrast (cSNC) task, a 32-to-2% sucrose downshift was shown to initially suppress consummatory behavior. Such suppression was followed by behavioral recovery over subsequent sessions. Individual differences often emerge in the rate of recovery after the initial consummatory suppression. These experiments were designed to determine whether a stable trait of sensation/novelty seeking (SNS) is related to such individual differences in recovery from reward downshift. In Experiment 1, open field (OF) activity in the central area served as a measure of SNS. A week later, animals received training in the cSNC task involving ten 5-min sessions of access to 32% sucrose followed by four sessions of access to 2% sucrose. Higher OF activity predicted greater consummatory suppression after downshift, but a steeper recovery rate across downshifted sessions. Controls not exposed to the OF showed cSNC, but downshifted animals performed at equivalent levels whether they had OF exposure or not. In Experiment 2, after a 32-to-2% sucrose downshift, fast vs. slow recovery animals displayed similar levels of central activity in the OF. In Experiment 3, animals exhibited similar levels of central activity whether after a 32-to-2% or an 8-to-2% sucrose downshift. In both experiments, activity levels were similar whether immediately after session 12 (onset of recovery) or after session 15 (fully recovered). These results suggest that individual variations in recovery from reward downshift are correlated with levels of SNS as a stable trait.

Behavioral and neural correlates of licking for 66% alcohol in Wistar rats: Caloric balance or sensation/novelty seeking?

Whereas rodents generally reject high alcohol concentrations, access to 66% alcohol can reinforce operant licking in a progressive ratio situation. Three experiments were conducted to identify a potential mechanism underlying this effect. In Experiment 1, food-restricted male and female Wistar rats received access to either 66% alcohol or water in their home cage for one hour over four sessions. Consumption of alcohol and water was similar, showing that rats neither preferred nor rejected 66% alcohol. Peripheral (but not central) activity in an open field (OF) was higher after access to 66% alcohol than water, a result inconsistent with motor impairment. Blood alcohol concentration was higher after 66% alcohol than water and was positively correlated with fluid displacement and peripheral distance in the OF. c-Fos immunoreactivity after exposure to 66% alcohol vs. water showed increased activation in the nucleus accumbens shell, anterior cingulate cortex, and insular cortex. In Experiment 2, whether access to food was restricted (to an 81-84% of the ad libitum weight) or free (ad libitum), female Wistar rats licked at similar frequency from a sipper tube delivering 66% alcohol. This result is inconsistent with an account based on the caloric content of 66% alcohol. In Experiment 3, food-restricted male and female Wistar rats exhibited a positive correlation between activity in the central area of an OF (an index of sensation/novelty seeking) and licking for 66% alcohol. These results are consistent with the hypothesis that the reinforcing value of 66% alcohol is related to sensation/novelty seeking.

Frustrative nonreward and the basal ganglia: Chemogenetic inhibition and excitation of the nucleus accumbens and globus pallidus externus during reward downshift.

Frustrative nonreward contributes to anxiety disorders and addiction, and is included in the Research Domain Criteria initiative as a relevant endophenotype. These experiments explored the role of the basal ganglia in consummatory reward downshift (cRD) using inhibitory and excitatory DREADDs (designer receptors exclusively activated by designer drugs) infused in either the nucleus accumbens (NAc) or one of its downstream targets, the globus pallidus externus (GPe). NAc inhibition did not disrupt consummatory suppression during a 32-to-2% (Experiment 1) or 8-to-2% sucrose downshift (Experiment 2). However, NAc excitation enhanced consummatory suppression during a 32-to-2% sucrose downshift (Experiment 1). GPe inhibition caused a trend toward increased consummatory suppression after a 32-to-2% sucrose downshift, whereas GPe excitation eliminated consummatory suppression after an 8-to-2% sucrose downshift (Experiment 3). Chemogenetic manipulations of NAc and GPe had no detectable effects on open field activity. The effects of DREADD activation via clozapine N-oxide (CNO) administration were compared to controls that carried the DREADDs, but received vehicle injections. There was no evidence that CNO or vehicle injections in virus vector control (VVC) animals affected cRD or OF activity after either CNO or vehicle injections. NAc and GPe excitation led to opposite results in the cRD task, providing evidence that the basal ganglia circuit has a function in frustrative nonreward in the absence of detectable motor effects.

Evidence of successive negative contrast in terrestrial toads (Rhinella arenarum): central or peripheral effect?

Prior research with terrestrial toads (Rhinella arenarum) in a water-reinforced instrumental situation indicated a direct relationship between acquisition rate and reward magnitude. However, a reward downshift produced a gradual adjustment of instrumental performance and a rapid adjustment of consummatory performance, rather than the abrupt and transient deterioration of behavior typical of a successive negative contrast effect. In Experiment 1, using a two-chamber box, a downshift from deionized water (which supports maximal rehydration) to 250-mM sodium chloride solution (which supports a lower rehydration), also yielded a gradual adjustment of instrumental behavior. In this experiment, animals received one trial per day and were allowed 300 s of access to the reward in the goal box. Experiment 2 used the same procedure, except that animals were allowed access to the solution in the goal box for 600 s. Under these conditions, reward downshift led to longer latencies (instrumental) and lower rehydration levels (consummatory) than those of unshifted controls, providing evidence for successive negative contrast. Unlike in similar experiments with mammals, the effect was not transient, but persisted relatively unmodified over twelve daily postshift trials. In this case, the possibility of adaptation of the peripheral mechanisms for water uptake is considered. The comparative relevance of these results is discussed in terms of habit formation versus expectancy-guided behavior in vertebrate learning.

Psychological pain and opioid receptors: Reward downshift is disrupted when tested in a context signaling morphine.

A sucrose downshift causes a temporary suppression of consumption accompanied by psychological pain, a negative emotion triggered by reward loss. When administered systemically before downshift sessions, opioid agonists reduce and opioid antagonists enhance such behavioral suppression. However, little is known about the effects of signals of opioid drugs on behavior during a reward downshift episode. Research showed that morphine administration can induce a direct effect (e.g., hypoalgesia) followed by a compensatory effect (e.g., hyperalgesia). Therefore, a signal for morphine could elicit either a direct or a compensatory effect. Male Wistar rats were exposed to ten 5-min sessions of access to 32% sucrose in context A, followed by three sessions of access to 4% sucrose in context B. In parallel, animals received pairings between context B and morphine (5 mg/kg, sc) occurring each day immediately after sucrose sessions (contexts were counterbalanced). Control conditions included a saline control (no morphine injected), an unpaired control (morphine injected after exposure to B) tested in A (Experiment 1), and an unpaired control tested in B (Experiment 2). In both experiments, behavioral suppression induced by the 32-to-4% sucrose downshift was attenuated when the downshift occurred in a context previously paired with morphine. These data are consistent with the hypothesis that reward downshift is accompanied by an emotion of negative valence that can be counteracted by the conditioned release of endogenous opioids triggered by signals of morphine, much like it is attenuated by systemic morphine administration. Alternative hypotheses are also discussed.

Incentive disengagement and the adaptive significance of frustrative nonreward.

Mammals respond to an unexpected reward omission or reduction with a variety of behavioral and physiological responses consistent with an aversive emotion traditionally called frustrative nonreward. This review focuses on two aspects of frustrative nonreward, namely (1) the evidence for an aversive emotional state activated by the surprising omission or reduction of a rewarding outcome, and (2) the adaptive value of frustration. Frustrative nonreward has been mainly studied in terms of its mechanisms, across development in rats and across vertebrate species in comparative research. However, its adaptive function remains obscure. Following Domjan's approach to animal learning, this article explores a specific adaptive function hypothesis of frustrative nonreward called the incentive disengagement hypothesis. According to this hypothesis, the adaptive function of frustrative nonreward is to break an attachment to a site, situation, or stimulus that no longer yields appetitive resources (especially food and fluids) to promote the search for rewards in alternative locations. This function is of particular relevance given that mammals are especially vulnerable to reward loss due to their high metabolic rate and the energy demands of their relatively large brain.

Frustrative nonreward and cannabinoid receptors: Chronic (but not acute) WIN 55,212-2 treatment increased resistance to change in two reward downshift tasks.

Assessing the role of cannabinoid (CB) receptors in behavior is relevant given the trend toward the legalization of medicinal and recreational marijuana. The present research aims at bridging a gap in our understanding of CB-receptor function in animal models of frustrative nonreward. These experiments were designed to (1) determine the effects of chronic administration of the nonselective CB1-receptor agonist WIN 55,212-2 (WIN) on reward downshift in rats and (2) determine whether the effects of chronic WIN were reducible to acute effects. In Experiment 1, chronic WIN (7 daily injections, 10 mg/kg, ip) accelerated the recovery of consummatory behavior after a 32-to-4% sucrose downshift relative to vehicle controls. In addition, chronic WIN eliminated the preference for an unshifted lever when the other lever was subject to a 12-to-2 pellet downshift in free-choice trials, but only in animals with previous experience with a sucrose downshift. In Experiment 2, acute WIN (1 mg/kg, ip) reduced consummatory behavior, but did not affect recovery from a 32-to-4% sucrose downshift. The antagonist SR 141716A (3 mg/kg, ip) also failed to interfere with recovery after the sucrose downshift. In Experiment 3, acute WIN administration (1 mg/kg, ip) did not affect free-choice behavior after a pellet downshift, although it reduced lever pressing and increased magazine entries relative to vehicle controls. The effects of chronic WIN on frustrative nonreward were not reducible to acute effects of the drug. Chronic WIN treatment in rats, like chronic marijuana use in humans, seems to increase resistance to the effects of frustrative nonreward.

Frustrative nonreward and emotional self-medication:Factors modulating alcohol consumption following reward downshift in rats.

Life experience involving unexpected incentive loss (e.g., loss of job or a significant other) may result in negative emotional reactions (frustration) and promote alcohol drinking. Similarly, animals exposed to a frustrative 32-to-4% sucrose downshift increase their preference for alcohol (2%) vs. water. This result was interpreted as reflecting emotional self-medication-the consumption of substances that reduce negative emotions. We conducted three experiments examining parametric manipulations of the animal model: (1) effects of a severe reward downshift (32-to-4% sucrose) on consumption of various alcohol concentrations (Experiment 1); (2) effects of different magnitudes of reward downshifts on consumption of 32% alcohol (Experiment 2); and (3) effects of partial reinforcement (an intervention that increases resistance to frustration) on 2% alcohol intake induced by a 32-to-4% sucrose downshift (Experiment 3). The results show that (1) a 32-to-4% sucrose downshift leads to an increase in alcohol intake over a wide range of alcohol concentrations; (2) the greater the reward downshift, the higher the relative increase in alcohol consumption; and (3) a treatment that increases resistance to frustration (partial reinforcement) also attenuates alcohol consumption after a sucrose downshift. These data are discussed in relation to the role of frustrative nonreward in alcohol consumption.

Reinforcing properties of alcohol in rats: Progressive ratio licking performance reinforced with 66% alcohol.

Rodents are generally reluctant to consume high concentrations of alcohol. However, few experiments have reported the behavior of rats when they are given access to high alcohol concentrations. Four experiments with food-deprived Wistar rats were designed to determine whether 66% alcohol could be used as a positive reinforcer for operant responses. In Experiment 1, animals learned to lick an empty sipper to gain access to 66% alcohol in a second tube; licking extinguished after it if provided a only access to water (operant licking task, OL). Experiment 2 used the OL task combined with a progressive ratio (PR) schedule in a within-subject design with the order of alcohol concentrations counterbalanced across subjects. The breakpoint (the last completed ratio in the PR schedule) was higher for 10% and 66% alcohol concentrations than for water. In Experiment 3, animals trained in the same PR task gained access to water, 10%, or 66% alcohol in a between-subject design. Breakpoints were higher for 66% alcohol than for water, but not for 10% alcohol relative to water. Experiment 4 tested the effects of the orexin-1 receptor antagonist SB-334,867 on licking reinforced with access to 66% alcohol in the PR task. The antagonist reduced the breakpoint at 1- and 5-mg/kg doses, but not at 10 mg/kg. These results suggest that 66% alcohol can be used to reinforce operant behavior. Although the effects were modest, they were reliable. The estimated amount of alcohol consumed in the OL task suggests that these reinforcing effects were not dependent on the pharmacological effects of 66% alcohol, but could perhaps reflect a sensation-seeking effect.

Recovery profiles from reward downshift are correlated with operant licking maintained by alcohol, but not with genetic variation in the mu opioid receptor.

After ten 5-min sessions of access to 32% sucrose, a reward downshift (RD) to 2% sucrose induces a transient rejection of the reward. Animals were segregated according to the speed of recovery from RD into Fast-recovery and Slow-recovery subgroups. Animals were subsequently trained in an operant licking (OL) task in which licking at an empty tube provided 10 s of access to a second tube containing 66% alcohol. Licking on the first tube was subjected to a progressive ratio (PR) schedule with a step of 4 licks. Fast-recovery animals (both males and females) licked to a higher ratio than Slow-recovery animals. Animals were also exposed to a well-lit open field (OF) for 20 min. Fast- and Slow-recovery males and females exhibited equal levels of activity in the OF. Tissue samples from tails were assessed for two well-known allelic variations of the human opioid receptor gene, OPRM1, known to affect mu opioid sensitivity: The C17T and A118G single nucleotide polymorphisms. There was no evidence of a relationship between genotype and behavior, suggesting that these genetic mechanisms in humans do not account for the individual differences in recovery from RD and OL for alcohol in rats.

Effects of partial reinforcement on autoshaping in inbred Roman high- and low-avoidance rats.

Individuals trained under partial reinforcement (PR) typically show a greater resistance to extinction than individuals exposed to continuous reinforcement (CR). This phenomenon is referred to as the PR extinction effect (PREE) and is interpreted as a consequence of uncertainty-induced frustration counterconditioning. In this study, we assessed the effects of PR and CR in acquisition and extinction in two strains of rats, the inbred Roman high- and low-avoidance (RHA and RLA, respectively) rats. These two strains mainly differ in the expression of anxiety, the RLA rats showing more anxiety-related behaviors (hence, more sensitive to frustration) than the RHA rats. At a neurobiological level, mild stress is known to elevate corticosterone in RLA rats and dopamine in RHA rats. We tested four groups of rats (RHA/CR, RHA/PR, RLA/CR, and RLA/PR) in two successive acquisition-extinction phases to try to consolidate the behavioral effects. Animals received training in a Pavlovian autoshaping procedure with retractable levers as the conditioned stimulus, food pellets as the unconditioned stimulus, and lever presses as the conditioned response. In Phase 1, we observed a PREE in lever pressing in both strains, but this effect was larger and longer lasting in RHA/PR than in RLA/PR rats. In Phase 2, reacquisition was fast and the PREE persisted in both strains, although the two PR groups no longer differed in lever pressing. The results are discussed in terms of frustration theory and of uncertainty-induced sensitization of dopaminergic neurons.

Effects of alcohol consumption induced by reward loss on behavior in the hole-board test.

Rats exposed to reward downshift (from 32 to 4% sucrose) increase 2% alcohol intake in a 2-h, free-choice preference test which also offered water. This effect was accompanied by augmented general activity in the elevated plus maze (Donaire et al., 2018, Behav Proc, 150, 59-65). In the present study we analyzed the effect of alcohol consumption induced by reward downshift on anxiety behaviors registered in the hole-board (HB) test. Sixteen food-deprived female Wistar rats received 32% sucrose for ten 5-min daily sessions and were then downshifted to 4% sucrose for two 5-min daily sessions (postshift). Sessions also involved testing animals in a 2-h, 2-bottle preference task with 2% alcohol vs. water (Group A), or water vs. water (Group W). On postshift sessions, animals were exposed to a 6-min HB test after the preference task. Reward devaluation significantly reduced sucrose intake in Groups A and W, and increased alcohol consumption in Group A, but had no effect on water consumption in Group W. Increased alcohol consumption was followed by higher head-dipping frequency in the HB test compared with Group W. The results are discussed in terms of the impact of reward loss on anxiety behaviors in the HB test and the anxiolytic effects of alcohol in situations involving negative affect.

Frustrative nonreward: Chemogenetic inactivation of the central amygdala abolishes the effect of reward downshift without affecting alcohol intake.

The role of the central amygdala (CeA) in the adjustment to a 32-to-2% sucrose downshift in the consummatory successive negative contrast (cSNC) task and in a free-choice 10% alcohol-water preference task (PT) was studied using chemogenetic inactivation. cSNC is a model of frustrative nonreward that enhances alcohol consumption. In Experiment 1, sessions 1-10 involved 5-min access to 32% sucrose and sessions 11-12 involved access to 2% sucrose. Vehicle or clozapine N-oxide (CNO; 1 or 3 mg/kg, ip), used later to activate the inhibitory designer receptor, was administered 30 min before sessions 11-12. There was no evidence that CNO affected consummatory behavior after the sucrose downshift. In Experiment 2, all animals received an infusion of the inhibitory designer receptor hM4D(Gi) into the CeA. After recovery, animals received access to either 32% or 2% sucrose on sessions 1-10, followed by 2% sucrose on sessions 11-12. Immediately after each 5-min sucrose session, animals received a 2-bottle, 1-h PT with 10% alcohol and water. CNO (3 mg/kg, ip) or vehicle was administered 30 min before sessions 11-12. CeA inactivation prior to sucrose downshift eliminated the cSNC effect, which was observed in vehicle controls. However, there was no evidence that CeA inactivation affected preference for 10% alcohol over water. These results support the hypothesis that CeA activity is critical for cSNC effect, an outcome consistent with the view that the amygdala plays a central role in frustrative nonreward.

Lateral habenula lesions disrupt appetitive extinction, but do not affect voluntary alcohol consumption.

This study analyzed the effects of LHb lesions on appetitive extinction and alcohol consumption. Eighteen male Wistar rats received neurochemical lesions of the LHb (quinolinic acid) and 12 received a vehicle infusion (PBS). In a runway instrumental task, rats received acquisition (12 pellets/trial, 6 trials/session, 10 sessions) and extinction training (5 sessions). In a consummatory task, rats had daily access to 32% sucrose (5 min, 10 sessions) followed by access to water (5 sessions). Then, animals received 2 h preference tests with escalating alcohol concentrations (2%-24%), followed by two 24 h preference tests with 24% alcohol. Relative to Shams, LHb lesions delayed extinction, as indicated by lower response latencies (instrumental task) and higher fluid consumption (consummatory task). LHb lesions did not affect alcohol consumption regardless of alcohol concentration or test duration. The LHb modulates appetitive extinction and needs to be considered as part of the brain circuit underlying reward loss.

Consummatory Successive Negative Contrast in Rats.

Using animal models in addiction and pain research is pivotal to unravel new pathways and mechanisms for the treatment of these disorders. Reward devaluation through a consummatory successive negative contrast (cSNC) task has shown the ability to reduce physical pain sensitivity (hypoalgesia) and increase oral ethanol consumption in rats. The procedure is based on exposing the experimental animals to a 32% sucrose solution during several sessions (preshift sessions) followed by a devaluation to 4% sucrose during the next few sessions (postshift sessions). The cSNC effect can be monitored by comparing the experimental group to an unshifted control that had access to 4% sucrose throughout the entire experiment (preshift and postshift sessions). The cSNC phenomenon is defined by lower consumption of sucrose in the downshifted group than in the unshifted group during postshfit sessions.

Reward shifts in forced-choice and free-choice autoshaping with rats.

Successive negative contrast (SNC) involves a disruption of behavior when the paired reward is unexpectedly reduced from a large to a small amount, relative to a control always receiving the small amount. Five experiments with rats explored SNC in the Pavlovian autoshaping procedure in which a retractable lever is paired with the delivery of food pellets. In Experiment 1, a 12-to-2 pellet downshift either early in training (after 3 sessions) or late in training (after 20 sessions) yielded no significant evidence of SNC either in terms of lever pressing or goal entries. Experiment 2 showed that presession feeding (another form of reward devaluation) suppressed lever pressing in nonreinforced tests early in training. However, no statistical evidence of lever pressing suppression was found late in training. Presession feeding also suppressed lever pressing late in training if the test session included reinforcements. Experiment 3, using reward downshift, showed that adding a nontarget lever produced no statistical evidence of response suppression to the target lever during the downshift. Lever pressing to the target lever increased and goal entries tended to decrease after a 12-to-2 pellet downshift. Using a within-subject design and two target levers with distinct reward values (Experiment 4), reward downshift produced evidence of lever pressing enhancement in single-lever trials, but lever pressing suppression and a switch in preference to the unshifted lever in nonreinforced free-choice trials. Experiment 5 replicated these within-subject SNC effects, but found only modest evidence for a successive positive contrast effect in free-choice behavior. These results suggest that autoshaping in rats may induce response invigoration in forced-choice situations, but response suppression in free-choice situations. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Augmented voluntary consumption of ethanol induced by reward downshift increases locomotor activity of male Wistar rats in the elevated plus maze.

Rats exposed to unexpected reward loss increase voluntary oral consumption of ethanol. Such consumption has been assumed to attenuate loss-induced negative affect (called emotional self-medication). To test this assumption, food-deprived male Wistar rats were exposed to 10 sessions of access to 32% sucrose followed by 5 sessions of access to 4% sucrose (reward downshift). A two-bottle preference test was initiated immediately after each consummatory session to assess ethanol intake. The experimental group received access to 2% ethanol and water, whereas the control group received access to two water bottles. On sessions 11, 12, and 15, immediately after the preference test, animals were tested in the elevated plus maze (EPM) for signs of anxiety. Sucrose consumption was reduced after the 32-to-4% sucrose downshift on sessions 11 and 12, but behavior recovered by session 15. Consummatory suppression was followed by increased ethanol intake in the preference test after sessions 11 and 12, but intake was reduced to preshift levels by session 15; no changes were observed in water controls. Finally, general activity (closed-arm entries and total arm entries) in the EPM increased in the ethanol group on session 12, but not on session 15, relative to water controls. The increase in ethanol consumption induced by reward downshift had measurable effects on activity as assessed in the EPM. These results show that voluntary oral 2% ethanol consumption after reward downshift can affect subsequent behavior, but fall short of providing unambiguous evidence that such ethanol consumption reduces negative affect.

Avian Emotions: Comparative Perspectives on Fear and Frustration.

Emotions are complex reactions that allow individuals to cope with significant positive and negative events. Research on emotion was pioneered by Darwin's work on emotional expressions in humans and animals. But Darwin was concerned mainly with facial and bodily expressions of significance for humans, citing mainly examples from mammals (e.g., apes, dogs, and cats). In birds, emotional expressions are less evident for a human observer, so a different approach is needed. Understanding avian emotions will provide key evolutionary information on the evolution of related behaviors and brain circuitry. Birds and mammals are thought to have evolved from different groups of Mesozoic reptiles, theropod dinosaurs and therapsids, respectively, and therefore, their common ancestor is likely to be a basal reptile living about 300 million years ago, during the Carboniferous or Permian period. Yet, birds and mammals exhibit extensive convergence in terms of relative brain size, high levels of activity, sleep/wakefulness cycles, endothermy, and social behavior, among others. This article focuses on two basic emotions with negative valence: fear and frustration. Fear is related to the anticipation of dangerous or threatening stimuli (e.g., predators or aggressive conspecifics). Frustration is related to unexpected reward omissions or devaluations (e.g., loss of food or sexual resources). These results have implications for an understanding of the conditions that promote fear and frustration and for the evolution of supporting brain circuitry.