Curiosity, the drive to seek knowledge and learn, has been a topic of debate in cognitive and neuroscientific research. This review explores traditional and emerging theories of curiosity, emphasizing its role in optimal exploration. The authors propose a model-based approach that considers factors like uncertainty, information gain, and learning progress to understand curiosity's temporal dynamics. They argue that traditional theories, which focus on resolving uncertainty, are insufficient and that a unified account of curiosity as a 'common currency' for exploration, balanced with other drives like safety and hunger, is more comprehensive. The review highlights that curiosity is not solely driven by the resolution of uncertainty but also by the learning process itself. Recent studies show that curiosity is sustained when individuals perceive improvements in their performance and actively engage in learning. This learning progress framework provides insights into the temporal dynamics of curiosity, explaining how it fluctuates based on learning progress. The authors integrate the classic view of curiosity as a desire to obtain information with the new view of curiosity as a drive for learning progress. They use predictive processing, a framework for understanding perception and action, to analyze these aspects. Predictive processing suggests that curiosity arises from prediction errors, which are mismatches between expected and actual outcomes. The precision of predictions and evidence is crucial in determining curiosity. The review also discusses the role of dopamine in reward processing and how it relates to learning progress. It challenges the traditional view that curiosity is driven by uncertainty, suggesting instead that the opportunity to gain information is the key factor. The authors propose that curiosity is driven by the learning process, which leads to improved internal models of the world. The review concludes that a unified account of curiosity, integrating information gain and learning progress, offers a more comprehensive understanding of curiosity as a tool for optimal exploration. This account allows for a better understanding of how curiosity drives exploration and learning, and how it can be harnessed to enhance cognitive abilities and promote well-being. The authors emphasize the importance of considering individual differences in curiosity and the need for further research into the biological substrates of curiosity.Curiosity, the drive to seek knowledge and learn, has been a topic of debate in cognitive and neuroscientific research. This review explores traditional and emerging theories of curiosity, emphasizing its role in optimal exploration. The authors propose a model-based approach that considers factors like uncertainty, information gain, and learning progress to understand curiosity's temporal dynamics. They argue that traditional theories, which focus on resolving uncertainty, are insufficient and that a unified account of curiosity as a 'common currency' for exploration, balanced with other drives like safety and hunger, is more comprehensive. The review highlights that curiosity is not solely driven by the resolution of uncertainty but also by the learning process itself. Recent studies show that curiosity is sustained when individuals perceive improvements in their performance and actively engage in learning. This learning progress framework provides insights into the temporal dynamics of curiosity, explaining how it fluctuates based on learning progress. The authors integrate the classic view of curiosity as a desire to obtain information with the new view of curiosity as a drive for learning progress. They use predictive processing, a framework for understanding perception and action, to analyze these aspects. Predictive processing suggests that curiosity arises from prediction errors, which are mismatches between expected and actual outcomes. The precision of predictions and evidence is crucial in determining curiosity. The review also discusses the role of dopamine in reward processing and how it relates to learning progress. It challenges the traditional view that curiosity is driven by uncertainty, suggesting instead that the opportunity to gain information is the key factor. The authors propose that curiosity is driven by the learning process, which leads to improved internal models of the world. The review concludes that a unified account of curiosity, integrating information gain and learning progress, offers a more comprehensive understanding of curiosity as a tool for optimal exploration. This account allows for a better understanding of how curiosity drives exploration and learning, and how it can be harnessed to enhance cognitive abilities and promote well-being. The authors emphasize the importance of considering individual differences in curiosity and the need for further research into the biological substrates of curiosity.