Brain composition and olfactory learning in honey bees

Correlations between brain or brain component size and behavioral measures are frequently studied by comparing different animal species, which sometimes introduces variables that complicate interpretation in terms of brain function. Here, we have analyzed the brain composition of honey bees (Apis mellifera) that have been individually tested in an olfactory learning paradigm. We found that the total brain size correlated with the bees’ learning performance. Among different brain components, only the mushroom body, a structure known to be involved in learning and memory, showed a positive correlation with learning performance. In contrast, visual neuropils were relatively smaller in bees that performed better in the olfactory learning task, suggesting modality-specific behavioral specialization of individual bees. This idea is also supported by inter-individual differences in brain composition. Some slight yet statistically significant differences in the brain composition of European and Africanized honey bees are reported. Larger bees had larger brains, and by comparing brains of different sizes, we report isometric correlations for all brain components except for a small structure, the central body.     

Suppression of operant vs consummatory behavior

The magnitude and variability of conditioned suppression of bar pressing and dipper licking were compared. In two steady-state experiments, suppression of bar pressing was more profound and more stable from day to day. The two measures of suppression were uncorrelated as indexed by Pearson product-moment correlation coefficients computed for adjacent trials. Correlations within measures (internal consistency) were somewhat higher for the bar-press system except when a high proportion of rats completely suppressed on one of the correlated trials. In a transient state experiment in which possible adventitious punishment of both response systems was eliminated, suppression of bar pressing was again more profound and considerably slower to extinguish.     

Scaling relative incentive value in consummatory behavior

Surprising downshifts from more preferred (training incentive) to less preferred incentives (test incentive) are usually accompanied by emotional activation and suppression of conditioned behavior in rats. Two experiments were designed to determine whether consummatory behavior is similarly affected by downshifts of equal proportions. Within limits, the degree of consummatory responding during incentive downshift was similar with equal ratios of test concentration to training concentration. Thus, 32–4% and 16–2% downshifts (1:8 test/training ratios) caused similar levels of consummatory behavior, despite differences in the absolute concentrations of the solutions involved in the downshift. An interpretation based on sensory contrast was discarded because of the long intervals between training and test solutions (40 min and 24 h in Experiments 1 and 2, respectively). It is suggested that Weber’s law regulates behavioral suppression after reward downshifts. A theoretical framework for the interpretation of these data is presented.     

Automated discrete-trials techniques of appetitive conditioning in honey bees

Automated techniques of appetitive conditioning in honey bees are described. The subject is pretrained to come to the laboratory, where it is confined while the training trials are programmed and then is free to return to the hive. The responses recorded are approach to and entering a tube into which sucrose solution is pumped. Illustrative experiments on classical conditioning, simple instrumental conditioning, and choice are reported.     

Spontaneous recovery of consummatory behavior, but not of consummatory successive negative contrast

Five experiments were designed to study spontaneous recovery (SR) in two situations involving consummatory behavior: consummatory successive negative contrast (cSNC) and consummatory extinction (cE). SR of consummatory suppression should occur if incentive downshift induces an egocentric memory encoding information about the emotional reaction to the downshift that is counterconditioned or extinguished during exposure to the downshifted reward. SR of cSNC failed to occur after resting periods of 24, 96, or 336 h interpolated following complete (Experiment 1) and incomplete (Experiment 2) recuperation of consummatory behavior, and was not induced by the opioid-receptor antagonist naloxone (2 mg/kg), known to enhance cSNC (Experiment 3). However, SR of consummatory behavior occurred across sessions in cSNC (Experiment 3) and cE (Experiments 4-5). Furthermore, naloxone facilitated cE without affecting SR (Experiments 4-5). These results are discussed in relation to evidence for the development of an egocentric memory of the aversive downshift experience in consummatory situations.     

Continuous, fixed-ratio, and fixed-interval reinforcement in honey bees

Bees learned to enter a Plexiglas tube and to suck small portions of sugar solution; every entry or every fifth entry was reinforced. During an extinction phase, the bees on the fixed-ratio schedule emitted twice as many responses as did those given continuous reinforcement. Bees on a fixed-interval schedule of reinforcement emitted lower response rates than did those given fixed-ratio reinforcement. By extending the conditioning procedure for several days, it was possible to maintain responding with fixed-ratio schedules requiring 30 responses per reinforcement and with fixed-interval values up to 90 sec. Under fixed-interval schedules, response rates did not increase toward the end of the reinforcement intervals.     

Improved techniques for the measurement of consummatory behavior in fishes

Improvements on a technique for the study of consummatory behavior and appetitive conditioning in fishes are described: a target-strike detector module easily incorporated into conventional relay programming equipment, a liquid-food formula highly attractive to goldfish and carp, a reliable Teflon-headed syringe plunger capable of handling gritty foods, and a silent food-pumping system.     

Disrupted patterns of consummatory behavior in rats with fornix transections

The feeding and drinking behavior was examined in male rats with fornix transections and sham-operated control rats. Total food and water consumption was recorded but supplemented by a pattern analysis of feeding and drinking behavior. The behavior of the rats was continuously monitored during four hour morning and afternoon sessions under ad lib access and during a two hour session following adaptation to a restricted access feeding schedule. Rats with fornix transections were more active and exhibited increased frequencies of rearing, eating and drinking. The increased meal frequency in rats with fornix transections was accompanied by decreased meal durations and a reduction in the length of intermeal intervals. Total food and water consumption was unaffected by fornix transection as were the duration of sleep bouts and the frequencies of grooming, sleeping and carrying shavings. Fornix transections also reduced food carrying and food hoarding but only under conditions of restricted food access. The results suggest that fornix transection does not alter major homeostatic regulatory mechanisms nor does it alter the components of feeding and drinking behavior. Fornix transection alters, instead, the organization of microregulatory feeding and drinking patterns.     

Acoustic startle reflexes in the rat during consummatory behavior.

Auditory startle reflexes were elicited in thirsty rats when they were drinking water or were between drinking boutsmthe reaction was greater during drinking, this enhancement developing over the first few seconds after drinking onset. The startle reaction was lowest immediately after the termination of drinking. Reflex enhancement was reduced when thirsty rats drank milk rather than the more preferred water. The reflex was smaller with increased water deprivation, but enhancement produced by drinking was apparent at all levels of deprivation studied, satiety to 4-days deprivation. The inhibitory effect of a preliminary stimulus was not affected by consummatory behavior. Attention is drawn to suggestive parallels between these behavioral effects and other consequences of consummatory activity, primarily having to do with electrophysiological events and arousal processes     

Effect of varied taste experience on negative contrast in consummatory behavior

Rats shifted from 32% to 4% sucrose consume less 4% sucrose than animals that experience only the 4% solution. Previous experiments have suggested that a stress/emotional factor may be causally related to this negative contrast effect on the second postshift day, but not on the first postshift day. The present experiment was concerned with the possibility that contrast on the first postshift day is related to a neophobic response to the postshift solution. Results showed that giving animals experience with variously flavored (seven different flavors) 32% sucrose during the preshift period reduced degree of contrast when the animals were shifted to 4% sucrose. These data are considered in terms of solution novelty, specific loss of "sweetness", and caloric loss as contributors to negative contrast.     

Sampling and decision rules used by honey bees in a foraging arena

Animals must continuously choose among various available options to exploit the most profitable resource. They also need to keep themselves updated about the values of all available options, since their relative values can change quickly due to depletion or exploitation by competitors. While the sampling and decision rules by which foragers profitably exploit a flower patch have attracted a great deal of attention in theory and experiments with bumble bees, similar rules for honey bee foragers, which face similar foraging challenges, are not as well studied. By presenting foragers of the honey bee Apis cerana with choice tests in a foraging arena and recording their behavior, we investigate possible sampling and decision rules that the foragers use to choose one option over another and to track other options. We show that a large part of the sampling and decision-making process of a foraging honey bee can be explained by decomposing the choice behavior into dichotomous decision points and incorporating the cost of sampling. The results suggest that a honey bee forager, by using a few simple rules as part of a Bayesian inference process, is able to effectively deal with the complex task of successfully exploiting foraging patches that consist of dynamic and multiple options.     

Some conditions for the dissociation of consummatory and instrumental behavior in rats

To investigate whether consummatory and instrumental behavior depend upon different motivational factors, rats were trained to press a bar for saccharin solution, then given various treatments designed to reduce the palatability of saccharin, and finally tested for bar-pressing in extinction and for free intake of saccharin. Prefeeding with dextrose, prefeeding with saccharin, and association of saccharin with injections of lithium chloride all reduced intake of saccharin compared to control treatments, but only prefeeding with dextrose also reduced barpressing in extinction. Thus, performance of an instrumental response may depend upon need for food rather than appetite for it.     

Successive negative contrast after partial reinforcement in the consummatory behavior of rats

Rats given access to a 32% sucrose solution later reject a 4% solution significantly more than controls that have only received the 4% solution. In Experiment 1, this consummatory successive negative contrast (cSNC) effect was attenuated by previous exposure to 50% partial reinforcement. Furthermore, recovery from cSNC was also facilitated by partial reinforcement. In Experiment 2, the attenuating effects of partial reinforcement on cSNC were eliminated by administration of the benzodiazepine anxiolytic chlordiazepoxide (5 mg/kg) before nonreinforced trials. In Experiment 3, the attenuating effect of partial reinforcement was greater after a shift from 32 to 6% solution, than after a shift from 32 to 2% solution. The parallels between the effects of partial reinforcement on consummatory and instrumental behavior are discussed.     

Evidence for associative learning in newly emerged honey bees (Apis mellifera)

The honey bee is a model organism for studies on the neural substrates of learning and memory. Associative olfactory learning using sucrose rewards is fast and reliable in foragers and older hive bees. However, researchers have so far failed to show any significant learning in newly emerged bees. It is generally argued that in these bees only part of the brain structures important for learning are fully developed. Here we show for the first time that newly emerged honey bees are capable of associative learning, if they are sufficiently responsive to sucrose. Responsiveness to sucrose, which can be measured using the proboscis extension response (PER), increases with age. Newly emerged bees are on average very unresponsive to sucrose. We show that if newly emerged bees displaying a PER to 10% sucrose or lower sucrose concentrations are conditioned to an odour, they show significant associative learning and early long-term memory. Nevertheless, the level of acquisition is still lower than in foragers. The general assumption that newly emerged honey bees are incapable of associative learning must therefore be reconsidered. Further, our study suggests that an age-dependent increase in responsiveness to rewarding stimuli is directly related to the development of early learning abilities. The decisive influence of responsiveness to rewarding stimuli in associative learning of newly emerged bees has far reaching consequences for studies on the development of associative learning capabilities in insects and vertebrates.