Not only because I am working with honey bees but because I myself consume an ‘acute’ dose of caffeine every day, I was particularly interested in this new article published in Behavioural brain research this spring having a look on the impact caffeine consumption has on learning and memory in Honey bees. The experiments follow a nice line of arguments answering upcoming questions right away with the next experiment and leave you at the end with almost no questions.
So far studies supporting the influence of caffeine on learning and memory are inconsistent: some show memory improvement after caffeine consumption whereas others report that caffeine ingestion has little or no effect on learning and memory in invertebrates. In particular in Honey bees caffeine had no effect on acquisition, but increased long term memory retention in an appetitive visual learning task whereas in experiments using Drosophila caffeine decreased acquisition. The authors argue that the differences may be a result of the different treatment: Flies consumed the caffeine while in bees the caffeine was delivered through the cuticle or via injection. Also in Drosophila an aversive stimulus was used during conditioning, whereas the bees were conditioned using an appetitive reward. Consequentially the authors investigate the effects of caffeine ingestion in Honey bees on acquisition and memory recall using olfactory appetitive learning.
In their first set of experiments they test whether ingesting caffeine during conditioning influences the rate of acquisition and memory recall and demonstrate that caffeine reduces the level of response to the conditioned odor. However a memory recall 24 hours later revealed that “the reduction in response observed during acquisition was not due to a failure of the bees to acquire the odor-reward association, as the majority of bees in each treatment responded to the odor as if it predicted reward.” Raising the question, if the reduction in the expression of the conditioned response during acquisition may be due to the bitter taste of caffeine? The authors rule out this possibility by feeding caffeine prior to conditioning with the same experimental outcome as before. Bringing the authors to the next question: Is the reduction in response levels during acquisition due to caffeine reducing motivation? Consumption of caffeine could possibly reduce the motivation for consumption of the sugar-reward either by producing malaise or by making the bees feel satiated. To examine this possibility, in a following experiment bees were given a dose of sucrose containing different caffeine concentrations but no differences in the amount of subsequent taken sucrose solution were observed.
In the last experiment the effect of caffeine on recall fed after acquisition is examined showing that caffeine does not influence post-acquisition consolidation processes. In summary the data suggest an effect of caffeine on acquisition without an effect on the one day later recall.
As an explanation for their results the authors suggest an increased calcium level as previous studies showed that injection of caffeine into the hemolymph increases calcium levels in the honey bee brain. They argue that ’in Drosophila, inhibition of protein kinase C (PKC) activity was shown to reduce the expression of the learned behavior (a reduction in courting of a mated female by a male fly) during the acquisition phase’. Similar to the present experiments the males with reduced PKC activity performed the same as control flies during memory tests indicating that they had learned. The authors suggest a following experiment to provide insight into the role of calcium signaling in the effects of caffeine on learning by mimicking the consequences of caffeine ingestion by increasing calcium levels during acquisition.
Finally after reading this article I am no more concerned about the coffee I was drinking during the preparation of my talk. I may not remember everything in 5 minutes but tomorrow I will be as good as any non coffee drinking talk-giver. That holds true obviously at least for bees!
Mustard JA, Dews L, Brugato A, Dey K, & Wright GA (2012). Consumption of an acute dose of caffeine reduces acquisition but not memory in the honey bee. Behavioural brain research, 232 (1), 217-224 PMID: 22521838
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