<p>Exploratory decisions could be motivated by multiple reasons, such as to reduce uncertainty of existing options (i.e. internal exploration) or to identify new alternatives (i.e. external exploration). Exploratory behaviours are related to a wide range of brain regions including the intraparietal cortex (IPS), anterior cingulate cortex (ACC), and medial prefrontal cortex (mPFC). However, whether these regions play unique roles signalling different aspects of exploration remain unclear. Here, we identified unique internal and external exploratory signals in the IPS and ACC, respectively. Crucially, these signals were invariant to the impending decisions. In contrast, the mPFC flexibly encoded the value of internal exploration, external exploration or collecting a reward based on the type of impending decision. This is consistent with the neural common currency hypothesis suggesting the mPFC’s role in signalling general decision value. Our findings contribute to the understanding of the unique roles of IPS, ACC and mPFC during exploratory decision-making.</p>