The Role of the BDNF Val66Met Polymorphism in Individual Differences in Long-Term Memory Capacity

Physical Exercise and Serum BDNF Levels: Accounting for the Val66Met Polymorphism in Older Adults

BACKGROUND

Brain-derived neurotrophic factor (BDNF) expression, which can be measured in blood serum, has been found to increase with aerobic exercise. The link between BDNF level, physical exercise, and genetic status (Val66Met polymorphism) has not been well researched in older adults.

OBJECTIVE

To investigate the possible link between BDNF expression, acute aerobic exercise, and the Val66Met polymorphism in older adults.

METHOD

Twenty-three healthy older adults participated in one session of acute aerobic exercise. Their serum BDNF levels were measured both at baseline and post exercise. Saliva samples were collected to identify each individual's genetic status.

RESULTS

At baseline, the individuals' mean serum BDNF level was 16.03 ng/mL (Val66Val = 15.89 ng/mL; Val66Met = 16.34 ng/mL); post exercise, the individuals' mean serum BDNF level was 16.81 ng/mL (Val66Val = 16.14 ng/mL; Val66Met = 18.34 ng/mL).

CONCLUSION

One session of acute aerobic exercise significantly increased the individuals' mean serum BDNF level. Males had higher BDNF levels than females. There was a significant interaction between gender and BDNF expression post exercise and a significant between-group effect of gender. The Val66Met carriers had a more positive response to the acute aerobic exercise compared with the Val66Val carriers, although without a significant difference between the two groups.

BDNF Val66Met polymorphism is associated with consolidation of episodic memory during sleep

The brain-derived neurotrophic factor (BDNF) is an essential regulator of synaptic plasticity, a candidate neurobiological mechanism underlying learning and memory. A functional polymorphism in the BDNF gene, Val66Met (rs6265), has been linked to memory and cognition in healthy individuals and clinical populations. Sleep contributes to memory consolidation, yet information about the possible role of BDNF in this process is scarce. To address this question, we investigated the relationship between the BDNF Val66Met genotype and consolidation of episodic declarative and procedural (motor) non-declarative memories in healthy adults. The carriers of Met66 allele, as compared with Val66 homozygotes, showed stronger forgetting overnight (24hours after encoding), but not over shorter time (immediately or 20minutes after word list presentation). There was no effect of Val66Met genotype on motor learning. These data suggest that BDNF plays a role in neuroplasticity underlying episodic memory consolidation during sleep.

The BDNF val66met polymorphism is associated with decreased use of landmarks and decreased fMRI activity in the hippocampus during virtual navigation

People can navigate in a new environment using multiple strategies dependent on different memory systems. A series of studies have dissociated between hippocampus-dependent 'spatial' navigation and habit-based 'response' learning mediated by the caudate nucleus. The val66met polymorphism of the brain-derived neurotrophic factor (BDNF) gene leads to decreased secretion of BDNF in the brain, including the hippocampus. Here, we aim to investigate the role of the BDNF val66met polymorphism on virtual navigation behaviour and brain activity in healthy older adults. A total of 139 healthy older adult participants (mean age = 65.8 ± 4.4 years) were tested in this study. Blood samples were collected, and BDNF val66met genotyping was performed. Participants were divided into two genotype groups: val homozygotes and met carriers. Participants were tested on virtual dual-solution navigation tasks in which they could use either a hippocampus-dependent spatial strategy or a caudate nucleus-dependent response strategy to solve the task. A subset of the participants (n = 66) were then scanned in a 3T functional magnetic resonance imaging (fMRI) scanner while engaging in another dual-solution navigation task. BDNF val/val individuals and met carriers did not differ in learning performance. However, the two BDNF groups differed in learning strategy. BDNF val/val individuals relied more on landmarks to remember target locations (i.e., increased use of flexible spatial learning), while met carriers relied more on sequences and patterns to remember target locations (i.e., increased use of inflexible response learning). Additionally, BDNF val/val individuals had more fMRI activity in the hippocampus compared with BDNF met carriers during performance on the navigation task. This is the first study to show in older adults that BDNF met carriers use alternate learning strategies from val/val individuals and to identify differential brain activation of this behavioural difference between the two groups.

Depressive Emotionality Moderates the Influence of the BDNF Val66Met Polymorphism on Executive Functions and on Unconscious Semantic Priming

Automatic semantic processing can be assessed using semantic priming paradigms. Individual differences in semantic priming have been associated with differences in executive functions. The brain-derived neurotrophic factor (BDNF) Val66Met (substitution of valine (Val) to methionine (Met) at codon 66) polymorphism has been shown to be associated with executive functions as well as depression. Depression-associated variables such as depressed mood also moderated the relationship between BDNF Val66Met and executive functions in previous work. In this study, we therefore aimed at investigating whether BDNF Val66Met genotype modulates masked and unmasked semantic priming as well as executive functions and whether sadness is a moderator of these associations. We collected data of N = 155 participants measuring reaction times (RTs) as well as error rates (ERs) in masked and unmasked semantic priming paradigms using a lexical decision task. We assessed the primary emotion of SADNESS using the Affective Neuroscience Personality Scale (ANPS) and working memory using digit span forward and backward tasks. Met+ carriers showed reduced RT priming and increased ER priming in the masked priming paradigm. Even though there was no direct association between BDNF Val66Met and executive functions, SADNESS significantly moderated the association between BDNF Val66Met and executive functions as well as masked RT priming. We suggest that Met+ individuals with low depressive tendencies have not only superior EF, but also a faster and more superficial processing style, compared with Val/Val homozygotes. However, in Met+ individuals, cognitive functioning exhibits a greater vulnerability to depressed emotionality compared with Val/Val homozygotes. Our study thus demonstrates how emotional and molecular genetic factors exert an interacting influence on higher-level cognition.

Impact of brain-derived neurotrophic factor genetic polymorphism on cognition: A systematic review

INTRODUCTION

Brain-derived neurotrophic factor (BDNF) has an important role in the neurogenesis and neuroplasticity of the brain. This systematic review was designed to examine the association between BDNF Val66Met (rs6265) polymorphism and four cognitive domains-attention and concentration, executive function, verbal fluency, and memory, respectively.

METHODOLOGY

Primary literature search was performed using search engines such as PubMed and Scopus. Observational studies that evaluated the neurocognitive performances in relation to BDNF polymorphism within human subjects were included in this review, while animal studies, overlapping studies, and meta-analysis were excluded.

RESULTS

Forty of 82 reviewed studies (48.8%) reported an association between Val66Met polymorphism and neurocognitive domains. The proportion of the studies showing positive findings in cognitive performances between Val/Val homozygotes and Met carriers was comparable, at 30.5% and 18.3%, respectively. The highest percentage of positive association between Val66Met polymorphism and neurocognition was reported under the memory domain, with 26 of 63 studies (41.3%), followed by 18 of 47 studies (38.3%) under the executive function domain and four of 23 studies (17.4%) under the attention and concentration domain. There were no studies showing an association between Val66Met polymorphism and verbal fluency. In particular, Val/Val homozygotes performed better in tasks related to the memory domain, while Met carriers performed better in terms of executive function, in both healthy individuals and clinical populations.

CONCLUSION

While numerous studies report an association between Val66Met polymorphism and neurocognitive changes in executive function and memory domains, the effect of Met allele has not been clearly established.

The role of KIBRA in reconstructive episodic memory

BACKGROUND

In order to retrieve episodic past events, the missing information needs to be reconstructed using information stored in semantic memory. Failures in these reconstructive processes are expressed as false memories. KIBRA single nucleotide polymorphism (rs17070145) has been linked to episodic memory performance as well as an increased risk of Alzheimer's disease and post-traumatic stress disorder (PTSD).

METHODS

Here, the role of KIBRA rs17070145 polymorphism (male and female CC vs. CT/TT carriers) in reconstructive episodic memory in the Deese-Roediger-McDermott (DRM) paradigm was investigated in N = 219 healthy individuals.

RESULTS

Female participants outperformed males in the free recall condition. Furthermore, a trend towards a gender x genotype interaction was found for false recognition rates. Female CT/TT carriers exhibited a lower proportion of false recognition rates for associated critical lures as compared to male CT/TT. Additionally, an association between KIBRA rs17070145 genotype, familiarity and recollection based recognition performance was found. In trials with correct recognition of listed items CT/TT carriers showed more "remember", but fewer "know" responses as compared to CC carriers.

DISCUSSION AND CONCLUSION

Our findings suggest that the T-allele of KIBRA rs17070145 supports recollection based episodic memory retrieval and contributes to memory accuracy in a gender dependent manner. Findings are discussed in the context of the specific contribution of KIBRA related SNPs to reconstructive episodic memory and its implications for cognitive and emotional symptoms in dementia and PTSD.

Estrogens and the cognitive symptoms of schizophrenia: Possible neuroprotective mechanisms

Schizophrenia is a complex neuropsychiatric illness with marked sex differences. Women have later onset and lesser symptoms, which has led to the hypothesis that estrogens are protective in schizophrenia. Cognitive dysfunction is a hallmark of the disease and the symptom most correlated with functional outcome. Here we describe a number of mechanisms by which estrogens may be therapeutic in schizophrenia, with a focus on cognitive symptoms. We review the relationship between estrogens and brain derived neurotrophic factor, neuroinflammation, NMDA receptors, GABA receptors, and luteinizing hormone. Exploring these pathways may enable novel treatments for schizophrenia and a greater understanding of this devastating disease.

Brain-Derived Neurotrophic Factor (Val66Met) and Serotonin Transporter (5-HTTLPR) Polymorphisms Modulate Plasticity in Inhibitory Control Performance Over Time but Independent of Inhibitory Control Training

Several studies reported training-induced improvements in executive function tasks and also observed transfer to untrained tasks. However, the results are mixed and there is a large interindividual variability within and across studies. Given that training-related performance changes would require modification, growth or differentiation at the cellular and synaptic level in the brain, research on critical moderators of brain plasticity potentially explaining such changes is needed. In the present study, a pre-post-follow-up design (N = 122) and a 3-weeks training of two response inhibition tasks (Go/NoGo and Stop-Signal) was employed and genetic variation (Val66Met) in the brain-derived neurotrophic factor (BDNF) promoting differentiation and activity-dependent synaptic plasticity was examined. Because Serotonin (5-HT) signaling and the interplay of BDNF and 5-HT are known to critically mediate brain plasticity, genetic variation in the 5-HTT gene-linked polymorphic region (5-HTTLPR) was also addressed. The overall results show that the kind of training (i.e., adaptive vs. non-adaptive) did not evoke genotype-dependent differences. However, in the Go/NoGo task, better inhibition performance (lower commission errors) were observed for BDNF Val/Val genotype carriers compared to Met-allele ones supporting similar findings from other cognitive tasks. Additionally, a gene-gene interaction suggests a more impulsive response pattern (faster responses accompanied by higher commission error rates) in homozygous l-allele carriers relative to those with the s-allele of 5-HTTLPR. This, however, is true only in the presence of the Met-allele of BDNF, while the Val/Val genotype seems to compensate for such non-adaptive responding. Intriguingly, similar results were obtained for the Stop-Signal task. Here, differences emerged at post-testing, while no differences were observed at T1. In sum, although no genotype-dependent differences between the relevant training groups emerged suggesting no changes in the trained inhibition function, the observed genotype-dependent performance changes from pre- to post measurement may reflect rapid learning or memory effects linked to BDNF and 5-HTTLPR. In line with ample evidence on BDNF and BDNF-5-HT system interactions to induce (rapid) plasticity especially in hippocampal regions and in response to environmental demands, the findings may reflect genotype-dependent differences in the acquisition and consolidation of task-relevant information, thereby facilitating a more adaptive responding to task-specific requirements.

Central monoaminergic systems are a site of convergence of signals conveying the experience of exercise to brain circuits involved in cognition and emotional behavior

Physical activity can enhance cognitive function and increase resistance against deleterious effects of stress on mental health. Enhanced cognitive function and stress resistance produced by exercise are conserved among vertebrates, suggesting that ubiquitous mechanisms may underlie beneficial effects of exercise. In the current review, we summarize the beneficial effects of exercise on cognitive function and stress resistance and discuss central and peripheral signaling factors that may be critical for conferring the effects of physical activity to brain circuits involved in cognitive function and stress. Additionally, it is suggested that norepinephrine and serotonin, highly conserved monoamines that are sensitive to exercise and able to modulate behavior in multiple species, could represent a convergence between peripheral and central exercise signals that mediate the beneficial effects of exercise. Finally, we offer the novel hypothesis that thermoregulation during exercise could contribute to the emotional effects of exercise by activating a subset of temperature-sensitive serotonergic neurons in the dorsal raphe nucleus that convey anxiolytic and stress-protective signals to forebrain regions. Throughout the review, we discuss limitations to current approaches and offer strategies for future research in exercise neuroscience.