Neural activity differs between explicit and implicit learning of artificial grammar strings: An fMRI study

Functional magnetic resonance imaging was used to investigate the neural areas underlying retrieval of implicit and explicit knowledge about letter strings. Participants studied strings formed according to an artificial grammar, then performed implicit-learning-based judgments (judging the grammatical status of the string) or explicit-learning-based judgments (recognition) on novel grammatical strings. In comparison with a baseline task, recognition and grammatical judgments led to different patterns of neural activation: Recognition activated the right frontal cortex, whereas grammatical judgment activated the left frontal cortex. Recognition led to higher activity in the precuneus and medial occipital cortex, whereas grammatical judgments led to suppression of activity in the precuneus and activation in the lateral occipital cortex. When the surface structure of the strings was changed, grammatical judgments led to bilateral frontal activity and bilateral but left-lateralized activity in the occipital and parietal lobes. These results provide further evidence for a dissociation between the neural bases of implicit and explicit learning.