Abstract
People can conceptualize the same action (e.g. 'riding a bike') at different levels of abstraction (LOA), where higher LOAs specify the abstract motives that explain why the action is performed (e.g. 'getting exercise'), while lower LOAs specify the concrete steps that indicate how the action is performed (e.g. 'gripping handlebars'). Prior neuroimaging studies have shown that why and how questions about actions differentially activate two cortical networks associated with mental-state reasoning and action representation, respectively; however, it remains unknown whether this is due to the differential demands of the questions per se or to the shifts in LOA those questions produce. We conducted functional magnetic resonance imaging while participants judged pairs of action phrases that varied in LOA and that could be framed either as a why question (Why ride a bike? Get exercise.) or a how question (How to get exercise? Ride a bike.). Question framing (why vs how) had no effect on activity in regions of the two networks. Instead, these regions uniquely tracked parametric variation in LOA, both across and within trials. This suggests that the human capacity to understand actions at different LOA is based in the relative activity of two cortical networks.