The Effect of BDNF polymorphism on the Neural Substrates of Recognition Memory

Abstract

Recognition memory involves the conscious identification of previously encountered event or stimuli. Recognition memory is categorized into two distinct processes, which are known as Familiarity and Recollection. The Familiarity process is defined as ‘knowing’ that a stimulus was previously encountered, however, Recollection involves ‘remembering’ contextual details regarding the stimulus that was previously presented. These processes have been shown to be functionally dissociable and to rely on distinct neural networks. Prior studies have shown that brain oscillations are activated in the perirhinal and prefrontal cortex during Familiarity, whereas during Recollection areas of the hippocampus and frontal cortex are activated. Furthermore, there have been ERP studies, which shows that Familiarity processing generates an FN400 effect where there is an early onset after stimulus presentation at 300-500ms, whereas Recollection has a later positivity around 500-800ms after stimulus onset called the late parietal 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 synapses and negatively impacts memory performance. In the present study, object-recognition memory tasks were conducted to investigate the effects of BDNF polymorphism in memory performance. It was seen that there were no significant differences in memory performance between the genotypic groups. Source localisation results showed that there are distinct areas of activation during memory tasks within genes and these results correlates with previous studies. However, there were no significant between genotypic group differences that were generated in the source localisation results. The results illustrated that in the Familiarity-related task, there was higher activity in the Met carriers compared to the Val homozygotes, which is contradictory to previous studies. A Recollection-related task showed that there was higher activity in the Val homozygotes compared to the Met carriers. It was postulated that the Met carriers during the Familiarity related task have some compensatory mechanism that would allow them to achieve memory performance equal to the Val homozygotes. However, in the Recollection-related task, the results obtained correlates with previous studies. The results suggest that the discrepancy in results could be due to the differences in sensitivity of the techniques that were used to analyse the data.