BDNF Val⁶⁶Met polymorphism significantly affects d′ in verbal recognition memory at short and long delays

A functional polymorphism at the val66met locus in the BDNF gene has significant effects on the pro-form of the protein in intracellular trafficking and activity-dependent, but not constitutive, secretion. These differences are thought to underlie several findings in humans related to this polymorphism, including markers of neuronal viability, BOLD activation in medial temporal lob regions, and some aspects of behavior. However, many important questions remain about the impact of BDNF on various mnemonic subprocesses at the behavioral level. In this study, we examined the impact of the val/met polymorphism in a verbal recognition memory paradigm involving manipulation of depth of encoding and differential delays for recall and analyses of hits for previously presented target words and correct rejections of foils. Twenty-four human val homozygous individuals and 24 met carrier individuals comprised the sample. All were healthy controls. IQ between the groups was equivalent. In the encoding phase of the study, words were presented and encoded either by a decision as to whether they were living or nonliving ("deep") or if they contained the letter "A" (shallow). After this phase, recognition was tested immediately, half an hour, and 24 h later. BDNF genotype had significant effects on hits and discriminability (d′), accounting for at least 10% of the variance, but not on correct rejections or beta. BDNF did not interact with level of encoding, nor did it interact with delay. In sum, BDNF genotypes impacted "hits" in a recognition memory paradigm, findings consistent with the general notion that BDNF plays a prominent role in memory subprocesses thought to engage the medial temporal lobe.