Motivated by the link between play and learning, proposed in literature to have a neurobiological basis, we study the electroencephalogram and associated psychophysiology of "learning game" players. Forty-five players were tested for topic comprehension by a questionnaire administered before and after solo playing of the game Peacemaker (Impact Games 2007), during which electroencephalography and other physiological signals were measured. Play lasted for one hour, with a break at half time. We used the Bloom taxonomy to distinguish levels of difficulty in demonstrated learning--with the first five levels assigned to fixed questions--and "gain" scores to measure actual value of demonstrated learning. We present the analysis of the physiological signals recorded during game play and their relationship to learning scores. Main effects related to biomarkers of vigilance and motivation--including decreased delta power and relatively balanced fronto-hemispheric alpha power--predicted learning at the analysed Bloom levels. Results suggest multiple physiological dispositions that support on-task learning styles, and highlight the utility of the psychophysiological method for interpreting game-based learning evaluations.