Program Comprehension Does Not Primarily Rely On the Language Centers of the Human Brain

Our goal is to identify brain regions involved in comprehending computer programs. We use functional magnetic resonance imaging (fMRI) to investigate two candidate systems of brain regions which may support this -- the Multiple Demand (MD) system, known to respond to a range of cognitively demanding tasks, and the Language system (LS), known to primarily respond to language stimuli. We devise experiment conditions to isolate the act of code comprehension, and employ a state-of-the-art method to locate brain systems of interest. We administer these experiments in Python (24 participants) and Scratch Jr. (19 participants) - which provides a visual interface to programming, thus eliminating the effect of text in code comprehension. From this robust experiment setup, we find that the Language system is not consistently involved in code comprehension, while the MD is. Further, we find no other brain regions beyond those in the MD to be responsive to code. We also find that variable names, the control flow used in the program, and the types of operations performed do not affect brain responses. We discuss the implications of our findings on the software engineering and CS education communities.