Spontaneous thought as play: the value of fictional goals in the default mode network

Given its prevalence in our wakeful mental activity, spontaneous thought (ST) has been attributed several roles in cognition, most of which engage the brain's default mode network. Among the benefits of ST is its ability to support the proactive simulation of possible future scenarios, including situations that, prima facie, may seem frivolous, futile, or simply unlikely. By drawing an analogy between ST and children's play, we propose a substantial role for what might otherwise seem like useless mental activity. In children's play, ‘fictional’ activities have been argued to hold inherent value, as they hone the capacity to generate new plans and ideas — even if never pursued — and the ability to generate increasingly accurate simulations. We suggest that ST similarly provides a platform for the simulation of goals and scenarios outside the boundaries of what is likely or even feasible in the given context, facilitating learning and innovation. In this capacity, ST supports human intelligence and mental well-being. We discuss the implications of our proposal for the understanding of ST and its underlying neural circuitry.