While cognition was long thought to be an exclusive property of nervous systems, in recent years research has unearthed memory and learning in various aneural and even single celled organisms. This allows for comparative studies to find universal traits of cognition, differentiate them from those that originate from a nervous system and find the evolutionary roots of learning in neurons. In this regard, slime molds are an interesting model as complex amoeboid organisms with a transition from a single-celled stage to a complex plasmodial stage. Here, we investigate memory and induced behavioral change in the slime mold Physarum polycephalum, an interesting model for both its complex behavior und memristive abilities. Despite their lack of specialized anatomy as a macroscopic amoeboid cell, they are known to habituate to aversive stimuli and change their decision making processes, although the mechanisms behind this behavioral change are still unknown. In this study, we examined associative learning in slime molds to investigate their learning capabilities. First, we examined their reaction to various wavelengths of light, finding positive phototaxis for red light and negative phototaxis for blue light. Then, using oat flakes and valerian as positive reinforcement during training sessions, we were able to change their phototactic behavior over time, both showing negative phototaxis to red light as well as positive phototaxis to weak blue light, both of which would fade over time without further reinforcement. This shows the capability for flexible behavioral change and memory in a single-celled organism.