Brain Regions Responsive to Novelty in the Absence of Awareness

TLDR

The study mapped brain regions responding to novel, unperceived sequences using PET while participants performed a reaction‑time task with stimuli following an unknown complex pattern. Participants learned the hidden sequences, and a subtle, unperceived change in sequence elicited increased activity in left premotor, left anterior cingulate, and right ventral striatum while decreasing activity in right dorsolateral prefrontal and parietal areas, indicating that ventral striatum signals novelty and right prefrontal cortex maintains context without awareness.

Abstract

Brain regions responsive to novelty, without awareness, were mapped in humans by positron emission tomography. Participants performed a simple reaction-time task in which all stimuli were equally likely but, unknown to them, followed a complex sequence. Measures of behavioral performance indicated that participants learned the sequences even though they were unaware of the existence of any order. Once the participants were trained, a subtle and unperceived change in the nature of the sequence resulted in increased blood flow in a network comprising the left premotor area, left anterior cingulate, and right ventral striatum. Blood flow decreases were observed in the right dorsolateral prefrontal and parietal areas. The time course of these changes suggests that the ventral striatum is responsive to novel information, and the right prefrontal area is associated with the maintenance of contextual information, and both processes can occur without awareness.