The Effect of the Brain Derived Neurotrophic Factor Val66Met Polymorphism on the Event-Related Potential Correlates of Object Recognition Memory

Abstract

Recognition memory involves the contribution of two distinct retrieval processes, recollection and familiarity. Recollection is generally assumed to reflect the retrieval of qualitative information associated with previously encountered stimuli, while familiarity reflects a measure of memory strength of an item. They have been shown to be functionally dissociable and to rely on distinct neural networks. Recent evidence has shown that recollection and familiarity are associated with different event-related potential (ERP) modulations: familiarity with an early-onset effect 400 – 600 ms after stimulus onset called the FN400, and recollection with a later positivity 600 – 800 ms after stimulus onset called the late positive component (LPC). A single nucleotide polymorphism in the brain-derived neurotrophic factor (BDNF) gene resulting in a Valine-to-Methionine substitution at codon 66 (Val66Met) reduces BDNF protein availability at the synapse and negatively impacts memory performance. In the present study we tested whether the presence of a BDNF-Met allele affected memory performance and recognition memory associated ERPs in two object recognition tasks. Both tasks involved ‘old/new’ recognition judgements of object images. In the Familiarity Task there was no time gap between the study and recall phases. In the Recollection Task the recall phase followed 24 hours after the study phase. It was hypothesised that the BDNF-Met allele would be associated with poorer object recognition performance in the Recollection Task but no genotype differences were expected in the Familiarity Task. The behavioural results showed no genotype difference in the memory performance in either task. As hypothesised no difference in FN400 amplitude was found between the genotype groups in the Familiarity Task. Only Met allele carriers exhibited a significant LPC effect in the Recollection Task which is contradictory to the hypothesis. The results can be interpreted in terms of compensatory mechanism, seen as an increase in activity (ERP amplitude), in Met allele carriers in the Recollection Task to achieve behavioural performance equal to that of Val/Val participants. The results suggest that the BDNF Val66Met polymorphism affects neural processes in recollection-based recognition more than in familiarity-based recognition. The results add further weight to the theory that the hippocampal networks involved in recollection-based recognition are more reliant on levels of BDNF for normal functioning than the perirhinal networks involved in familiarity-based recognition.