Purpose of review
Novel events tend to attract attention and become more effectively encoded in memory than predictable events. The hippocampus and medial-temporal cortical regions, along with regions of the prefrontal cortex, have been associated with enhanced memory for novel events. This review provides an update on recent studies of hippocampal novelty responses in relation to memory.
Several different types of novelty have been studied. Stimulus novelty effects have been observed as reduced neural activity in the medial-temporal and prefrontal regions when the same stimulus is repeatedly presented. Contextual novelty effects, the detection of a stimulus or event in an unexpected context, is impaired in patients with hippocampal damage. Single-trial analyses of brain activity show that the hippocampus rapidly habituates to contextually novel situations. Associative novelty, the detection of new arrangements of familiar stimuli, has also been related to the medial-temporal regions. A division of labour among the medial-temporal regions has been proposed such that associative novelty selectively engages the hippocampus, whereas stimulus novelty is mediated by the perirhinal cortex. However, a simple account of when the hippocampus versus other medial-temporal cortical regions is recruited awaits further studies. Increased dopaminergic and cholinergic neurotransmission may account for enhanced memory encoding of novel events, and relate to structural neuronal changes.
Interindividual variability in the responsiveness of the hippocampal-novelty system may be genetically mediated, and personality factors can also play a role. A better understanding of such variability can have implications for interventions aimed at supporting memory and for the treatment of drug abuse.