2015 Undergraduate Awards

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Caffeine is widely considered to be a reinforcer in humans, but this effect is difficult to measure in non-human animals. This study extended the understanding of the effects of caffeine on reinforcement and locomotor activity by testing rat animal models. A group of 24 adult male Long Evans rats was split into three groups, caffeine (15mg/kg), Scopolamine (spatial learning inhibitor) or a NaCl control. Each drug was administered 15 min prior to behavioural testing. The rats were given one habituation session to familiarize with eating the reinforcing agent, one baseline session before testing and on test day were monitored for the number of bar presses, vertical movements, horizontal movement and latency to first reinforcement across six 2 minute time bins. It was hypothesized that rats injected with caffeine would experience an increase in motivation for food reward, presenting as a greater number of bar presses compared to the control groups. Caffeine injected rats are expected to exhibit greater locomotor activity than control groups. Rats injected with caffeine had greater locomotor movement but had no positive reinforcement on bar presses and experienced a lower number of bar presses than the control group. Thus, the results of this study suggest caffeine had a negative reinforcement effect on operant learning mechanisms. Future studies should explore what could have caused this negative reinforcement interaction between caffeine and learning of the bar pressing reinforcement task.


Image by Umer Shabib, licensed for reuse under CC BY 2.0.

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