Ebbinghaus revisited: influences of the BDNF Val66Met polymorphism on backward serial recall are modulated by human aging

Brain oscillatory processes related to sequence memory in healthy older adults

Sequence memory is subject to age-related decline, but the underlying processes are not yet fully understood. We analyzed electroencephalography (EEG) in 21 healthy older (60-80 years) and 26 young participants (20-30 years) and compared time-frequency spectra and theta-gamma phase-amplitude-coupling (PAC) during encoding of the order of visually presented items. In older adults, desynchronization in theta (4-8 Hz) and synchronization in gamma (30-45 Hz) power did not distinguish between subsequently correctly and incorrectly remembered trials, while there was a subsequent memory effect for young adults. Theta-gamma PAC was modulated by item position within a sequence for older but not young adults. Specifically, position within a sequence was coded by higher gamma amplitude for successive theta phases for later correctly remembered trials. Thus, deficient differentiation in theta desynchronization and gamma oscillations during sequence encoding in older adults may reflect neurophysiological correlates of age-related memory decline. Furthermore, our results indicate that sequences are coded by theta-gamma PAC in older adults, but that this mechanism might lose precision in aging.

The emergence of all-or-none retrieval of chunks in verbal serial recall

People often subdivide a list into smaller pieces, called chunks. Some theories of serial recall assume memories are stored hierarchically, with all-or-none retrieval of chunks, but most mathematical models avoid hierarchical assumptions. Johnson (Journal of Verbal Learning and Verbal Behavior, 8(6), 725-731, 1969) found steep drops in errors following correct recalls (transitional-error probabilities) within putative chunks during multi-trial letter-list learning, and viewed this as evidence for all-or-none retrieval. Here we test whether all-or-none retrieval occurs in lists studied only once. In serial recall of six-word lists (Experiment 1), transitional-error probabilities were inconsistent with all-or-none retrieval, both when participants were instructed to subdivide and when temporal grouping induced subdivision. Curiously, the same analysis of previous temporally grouped nine-letter lists produced compelling evidence for all-or-none retrieval, which may result from recoding rather than the formation of chunks. In Experiment 2, participants were pre-trained on three-word chunks. For nine-word lists constructed from those trained chunks, transitional-error probabilities exhibited more pronounced evidence of all-or-none retrieval. Nearly all effects reversed with post-cued backward recall, suggesting mechanisms that play out over the course of recall rather than encoding of the list. In sum, subdivided lists do not result in hierarchical memories after a single study trial, although they may emerge in lists formed from chunks that are previously learned as such. This suggests a continuous transition from non-hierarchical subdivision of lists to all-or-none retrieval over the course of chunk formation.

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.

Heritability of cognitive abilities and regional brain structures in middle-aged to elderly East Asians

This study examined the single-nucleotide polymorphism heritability and genetic correlations of cognitive abilities and brain structural measures (regional subcortical volume and cortical thickness) in middle-aged and elderly East Asians (Korean) from the Gwangju Alzheimer's and Related Dementias cohort study. Significant heritability was found in memory function, caudate volume, thickness of the entorhinal cortices, pars opercularis, superior frontal gyri, and transverse temporal gyri. There were 3 significant genetic correlations between (i) the caudate volume and the thickness of the entorhinal cortices, (ii) the thickness of the superior frontal gyri and pars opercularis, and (iii) the thickness of the superior frontal and transverse temporal gyri. This is the first study to describe the heritability and genetic correlations of cognitive and neuroanatomical traits in middle-aged to elderly East Asians. Our results support the previous findings showing that genetic factors play a substantial role in the cognitive and neuroanatomical traits in middle to advanced age. Moreover, by demonstrating shared genetic effects on different brain regions, it gives us a genetic insight into understanding cognitive and brain changes with age, such as aging-related cognitive decline, cortical atrophy, and neural compensation.

Genetic and Neurophysiological Biomarkers of Neuroplasticity Inform Post-Stroke Language Recovery

BACKGROUND

There is high variability in post-stroke aphasia severity and predicting recovery remains imprecise. Standard prognostics do not include neurophysiological indicators or genetic biomarkers of neuroplasticity, which may be critical sources of variability.

OBJECTIVE

To evaluate whether a common polymorphism (Val⁶⁶Met) in the gene for brain-derived neurotrophic factor (BDNF) contributes to variability in post-stroke aphasia, and to assess whether BDNF polymorphism interacts with neurophysiological indicators of neuroplasticity (cortical excitability and stimulation-induced neuroplasticity) to improve estimates of aphasia severity.

METHODS

Saliva samples and motor-evoked potentials (MEPs) were collected from participants with chronic aphasia subsequent to left-hemisphere stroke. MEPs were collected prior to continuous theta burst stimulation (cTBS; index for cortical excitability) and 10 minutes following cTBS (index for stimulation-induced neuroplasticity) to the right primary motor cortex. Analyses assessed the extent to which BDNF polymorphism interacted with cortical excitability and stimulation-induced neuroplasticity to predict aphasia severity beyond established predictors.

RESULTS

Val⁶⁶Val carriers showed less aphasia severity than Val⁶⁶Met carriers, after controlling for lesion volume and time post-stroke. Furthermore, Val⁶⁶Val carriers showed expected effects of age on aphasia severity, and positive associations between severity and both cortical excitability and stimulation-induced neuroplasticity. In contrast, Val⁶⁶Met carriers showed weaker effects of age and negative associations between cortical excitability, stimulation-induced neuroplasticity and aphasia severity.

CONCLUSIONS

Neurophysiological indicators and genetic biomarkers of neuroplasticity improved aphasia severity predictions. Furthermore, BDNF polymorphism interacted with cortical excitability and stimulation-induced neuroplasticity to improve predictions. These findings provide novel insights into mechanisms of variability in stroke recovery and may improve aphasia prognostics.

Future time perspective: Dimensions of opportunities, life, and time are differentially associated with physical health, cognitive functioning, and well-being in old age

Objective: The present study investigated the multidimensional nature of the future time perspective scale and dimension-specific associations with measures of physical health, cognitive functioning, and well-being.Method: Using data from the Berlin Aging Study II (N = 1,038, M age = 71 years, range = 61-88 years, 52% women), different models of future time perspective were compared using confirmatory factor analyses, and the best-fitting model was then used to explore dimension-specific associations with physical health, cognitive functioning, and well-being measures.Results: A model of future time perspective composed of a focus on opportunities, a focus on life, and a focus on time was found to have the best fit. An extended focus on opportunities was associated with stronger grip strength, more accurate memory, as well as higher life satisfaction and positive affect. An extended focus on time was associated with less accurate memory, lower negative affect, and greater life satisfaction. A focus on life was unrelated to study measures.Discussion: Findings suggest that future time perspective is multidimensional and that these dimensions are differentially associated with physical health, cognitive functioning, and well-being in old age.

Non-Motor Symptoms after One Week of High Cadence Cycling in Parkinson's Disease

The objective was to investigate if high cadence cycling altered non-motor cognition and depression symptoms in individuals with Parkinson's disease (PD) and whether exercise responses were influenced by brain-derived neurotrophic factor (BDNF) Val66Met polymorphism. Individuals with idiopathic PD who were ≥50 years old and free of surgical procedures for PD were recruited. Participants were assigned to either a cycling (n = 20) or control (n = 15) group. The cycling group completed three sessions of high cadence cycling on a custom motorized stationary ergometer. The primary outcome was cognition (attention, executive function, and emotion recognition were assessed via WebNeuro® and global cognition via Montreal Cognitive Assessment). Depression symptoms were assessed via Beck Depression Inventory-II. There was a main effect of time for emotional recognition (p = 0.048), but there were no other changes in cognition or depression symptoms. Regardless of intervention or Val66Met polymorphism, high cadence cycling does not alter cognition or depression symptoms after three sessions in one week.

BDNF Val66Met Polymorphism and Gamma Band Disruption in Resting State Brain Functional Connectivity: A Magnetoencephalography Study in Cognitively Intact Older Females

The pathophysiological processes undermining brain functioning decades before the onset of the clinical symptoms associated with dementia are still not well understood. Several heritability studies have reported that the Brain Derived Neurotrophic Factor (BDNF) Val66Met genetic polymorphism could contribute to the acceleration of cognitive decline in aging. This mutation may affect brain functional connectivity (FC), especially in those who are carriers of the BDNF Met allele. The aim of this work was to explore the influence of the BDNF Val66Met polymorphism in whole brain eyes-closed, resting-state magnetoencephalography (MEG) FC in a sample of 36 cognitively intact (CI) older females. All of them were ε3ε3 homozygotes for the apolipoprotein E (APOE) gene and were divided into two subgroups according to the presence of the Met allele: Val/Met group (n = 16) and Val/Val group (n = 20). They did not differ in age, years of education, Mini-Mental State Examination scores, or normalized hippocampal volumes. Our results showed reduced antero-posterior gamma band FC within the Val/Met genetic risk group, which may be caused by a GABAergic network impairment. Despite the lack of cognitive decline, these results might suggest a selective brain network vulnerability due to the carriage of the BDNF Met allele, which is linked to a potential progression to dementia. This neurophysiological signature, as tracked with MEG FC, indicates that age-related brain functioning changes could be mediated by the influence of particular genetic risk factors.

Genetics of stroke recovery: BDNF val66met polymorphism in stroke recovery and its interaction with aging

Stroke leads to long term sensory, motor and cognitive impairments. Most patients experience some degree of spontaneous recovery which is mostly incomplete and varying greatly among individuals. The variation in recovery outcomes has been attributed to numerous factors including lesion size, corticospinal tract integrity, age, gender and race. It is well accepted that genetics play a crucial role in stroke incidence and accumulating evidence suggests that it is also a significant determinant in recovery. Among the number of genes and variations implicated in stroke recovery the val66met single nucleotide polymorphism (SNP) in the BDNF gene influences post-stroke plasticity in the most significant ways. Val66met is the most well characterized BDNF SNP and is common (40-50 % in Asian and 25-32% in Caucasian populations) in humans. It reduces activity-dependent BDNF release, dampens cortical plasticity and is implicated in numerous diseases. Earlier studies on the effects of val66met on stroke outcome and recovery presented primarily a maladaptive role. Novel findings however indicate a much more intricate interaction between val66met and stroke recovery which appears to be influenced by lesion location, post-stroke stage and age. This review will focus on the role of BDNF and val66met SNP in relation to stroke recovery and try to identify potential pathophysiologic mechanisms involved. The effects of age on val66met associated alterations in plasticity and potential consequences in terms of stroke are also discussed.

Genetic markers of dopaminergic transmission predict performance for older males but not females

Mobility and memory declines with aging can limit independence. Several single-nucleotide polymorphisms have been associated with cognitive performance, but studies investigating motor function are scant. We examined 4 single-nucleotide polymorphisms involved in dopaminergic metabolism: BDNF (Val66Met), DRD3 (Ser9Gly), DBH (C>T), and COMT (Val158Met) for their relationship to motor and cognitive function in healthy older adults (n = 4605 and n = 7331) who participated in the U.S. Health and Retirement Study. Individuals with genotypes associated with reduced dopamine metabolism exhibited poorer balance and memory. We found the most pronounced effects in the oldest participants (aged 85+ years), supporting the notion that age-related declines in dopamine availability contribute to magnified genotype effects with advancing age. Moreover, males demonstrated stronger associations than did females between a number of beneficial dopamine alleles and cognitive scores, suggesting that sex differences in dopaminergic transmission interact with genotype to influence performance. These findings point to common genetic variants related to dopaminergic metabolism that characterizes individual differences in motor and cognitive function in older adults.

Sex Differences in the Impact of BDNF Genotype on the Longitudinal Relationship between Physical Activity and Cognitive Performance

BACKGROUND

Physical activity may preserve cognitive function in older adults, but benefits vary by sex and genetic factors.

OBJECTIVE

We tested the longitudinal association between physical activity and cognitive performance to de termine whether a common genetic polymorphism for brain-derived neurotrophic factor (BDNF Val66Met) moderated this effect.

METHODS

In a 12-year longitudinal population-based sample of older adults (n = 2,218), we used growth curve modeling to investigate whether the benefits of physical activity on cognitive preservation differed by BDNF genotype and sex across multiple cognitive domains including processing speed, attention, working memory, and episodic verbal memory.

RESULTS

The relationship between physical activity and cognitive performance was dependent on BDNF carrier status in males (Δχ2 [Δdf] = 12.94 [4], p = 0.01), but not in females (Δχ2 [Δdf] = 4.38 [4], p = 0.36). Cognition benefited from physical activity in male BDNF met noncarriers, but not met carriers, whereas cognition was not statistically significantly related to physical activity in females regardless of genotype.

CONCLUSION

We observed longitudinal, but not cross-sectional, effects of physical activity on cognitive performance. Our study highlights the importance of longitudinal follow-up and consideration of sex differences in the relationships between physical activity, BDNF genotype, and cognitive decline. The findings contribute to understanding gene-lifestyle interactions in promoting cognitive health.

Aging and a genetic KIBRA polymorphism interactively affect feedback- and observation-based probabilistic classification learning

Probabilistic category learning involves complex interactions between the hippocampus and striatum that may depend on whether acquisition occurs via feedback or observation. Little is known about how healthy aging affects these processes. We tested whether age-related behavioral differences in probabilistic category learning from feedback or observation depend on a genetic factor known to influence individual differences in hippocampal function, the KIBRA gene (single nucleotide polymorphism rs17070145). Results showed comparable age-related performance impairments in observational as well as feedback-based learning. Moreover, genetic analyses indicated an age-related interactive effect of KIBRA on learning: among older adults, the beneficial T-allele was positively associated with learning from feedback, but negatively with learning from observation. In younger adults, no effects of KIBRA were found. Our results add behavioral genetic evidence to emerging data showing age-related differences in how neural resources relate to memory functions, namely that hippocampal and striatal contributions to probabilistic category learning may vary with age. Our findings highlight the effects genetic factors can have on differential age-related decline of different memory functions.

The impact of physical activity and sex differences on intraindividual variability in inhibitory performance in older adults

It is well-known that processing speed and executive functions decline with advancing age. However, physical activity (PA) has a positive impact on cognitive performances in aging, specifically for inhibition. Less is known concerning intraindividual variability (iiV) in reaction times. This study aims to investigate the influence of PA and sex differences on iiV in inhibitory performance during aging. Healthy adults were divided into active and sedentary groups according to PA level. To analyse iiV in reaction times, individual mean, standard deviation and the ex-Gaussian parameters were considered. An interaction between activity level and sex was revealed, sedentary females being slower and more variable than sedentary men. No sex differences were found in the active groups. These results indicate that the negative impact of sedentariness on cognitive performance in older age is stronger for females. The present findings underline the need to consider sex differences in active aging approaches.

Non-invasive brain stimulation of the aging brain: State of the art and future perspectives

Favored by increased life expectancy and reduced birth rate, worldwide demography is rapidly shifting to older ages. The golden age of aging is not only an achievement but also a big challenge because of the load of the elderly on social and medical health care systems. Moreover, the impact of age-related decline of attention, memory, reasoning and executive functions on self-sufficiency emphasizes the need of interventions to maintain cognitive abilities at a useful degree in old age. Recently, neuroscientific research explored the chance to apply Non-Invasive Brain Stimulation (NiBS) techniques (as transcranial electrical and magnetic stimulation) to healthy aging population to preserve or enhance physiologically-declining cognitive functions. The present review will update and address the current state of the art on NiBS in healthy aging. Feasibility of NiBS techniques will be discussed in light of recent neuroimaging (either structural or functional) and neurophysiological models proposed to explain neural substrates of the physiologically aging brain. Further, the chance to design multidisciplinary interventions to maximize the efficacy of NiBS techniques will be introduced as a necessary future direction.

Lack of neural compensatory mechanisms of BDNF val66met met carriers and APOE E4 carriers in healthy aging, mild cognitive impairment, and Alzheimer's disease

Compromises in compensatory neurobiologic mechanisms due to aging and/or genetic factors (i.e., APOE gene) may influence brain-derived neurotrophic factor (BDNF) val66met polymorphism effects on temporal lobe morphometry and memory performance. We studied 2 cohorts from Alzheimer's Disease Neuroimaging Initiative: 175 healthy subjects and 222 with prodromal and established Alzheimer's disease. Yearly structural magnetic resonance imaging and cognitive performance assessments were carried out over 3 years of follow-up. Both cohorts had similar BDNF Val/Val and Met allele carriers' (including both Val/Met and Met/Met individuals) distribution. In healthy subjects, a significant trend for thinner posterior cingulate and precuneus cortices was detected in Met carriers compared to Val homozygotes in APOE E4 carriers, with large and medium effect sizes, respectively. The mild cognitive impairment/Alzheimer's disease cohort showed a longitudinal decline in entorhinal thickness in BDNF Met carriers compared to Val/Val in APOE E4 carriers, with effect sizes ranging from medium to large. In addition, an effect of BDNF genotype was found in APOE E4 carriers for episodic memory (logical memory and ADAS-Cog) and semantic fluency measures, with Met carriers performing worse in all cases. These findings suggest a lack of compensatory mechanisms in BDNF Met carriers and APOE E4 carriers in healthy and pathological aging.

Interactive effects of age and multi-gene profile on motor learning and sensorimotor adaptation

The interactive association of age and dopaminergic polymorphisms on cognitive function has been studied extensively. However, there is limited research on whether age interacts with the association between genetic polymorphisms and motor learning. We examined a group of young and older adults' performance in three motor tasks: explicit sequence learning, visuomotor adaptation, and grooved pegboard. We assessed whether individuals' motor learning and performance were associated with their age and genotypes. We selected three genetic polymorphisms: Catechol-O-Methyl Transferase (COMT val158met) and Dopamine D2 Receptor (DRD2 G>T), which are involved with dopaminergic regulation, and Brain Derived Neurotrophic Factor (BDNF val66met) that modulates neuroplasticity and has been shown to interact with dopaminergic genes. Although the underlying mechanisms of the function of these three genotypes are different, the high performance alleles of each have been linked to better learning and performance. We created a composite polygene score based on the Number of High Performance Alleles (NHPA) that each individual carried. We found several associations between genetic profile, motor performance, and sensorimotor adaptation. More importantly, we found that this association varies with age, task type, and engagement of implicit versus explicit learning processes.

The BDNF gene Val66Met polymorphism as a modifier of psychiatric disorder susceptibility: progress and controversy

Brain-derived neurotrophic factor (BDNF) has a primary role in neuronal development, differentiation and plasticity in both the developing and adult brain. A single-nucleotide polymorphism in the proregion of BDNF, termed the Val66Met polymorphism, results in deficient subcellular translocation and activity-dependent secretion of BDNF, and has been associated with impaired neurocognitive function in healthy adults and in the incidence and clinical features of several psychiatric disorders. Research investigating the Val66Met polymorphism has increased markedly in the past decade, and a gap in integration exists between and within academic subfields interested in the effects of this variant. Here we comprehensively review the role and relevance of the Val66Met polymorphism in psychiatric disorders, with emphasis on suicidal behavior and anxiety, eating, mood and psychotic disorders. The cognitive and molecular neuroscience of the Val66Met polymorphism is also concisely reviewed to illustrate the effects of this genetic variant in healthy controls, and is complemented by a commentary on the behavioral neuroscience of BDNF and the Val66Met polymorphism where relevant to specific disorders. Lastly, a number of controversies and unresolved issues, including small effect sizes, sampling of allele inheritance but not genotype and putative ethnicity-specific effects of the Val66Met polymorphism, are also discussed to direct future research.

Aging-related magnification of genetic effects on cognitive and brain integrity

Heritability studies document substantial genetic influences on cognitive performance and decline in old age. Increasing evidence shows that effects of genetic variations on cognition, brain structure, and brain function become stronger as people age. Disproportionate impairments are typically observed for older individuals carrying disadvantageous genotypes of different candidate genes. These data support the resource-modulation hypothesis, which states that genetic effects are magnified in persons with constrained neural resources, such as older adults. However, given that findings are not unequivocal, we discuss the need to address several factors that may resolve inconsistencies in the extant literature (gene-gene and gene-environment interactions, study populations, gene-environment correlations, and epigenetic mechanisms).

No association between CTNNBL1 and episodic memory performance

Polymorphisms in the gene encoding catenin-β-like 1 (CTNNBL1) were recently reported to be associated with verbal episodic memory performance--in particular, delayed verbal free recall assessed between 5 and 30 min after encoding--in a genome-wide association study on healthy young adults. To further examine the genetic effects of CTNNBL1, we tested for association between 455 single-nucleotide polymorphisms (SNPs) in or near CTNNBL1 and 14 measures of episodic memory performance from three different tasks in 1743 individuals. Probands were part of a population-based study of mentally healthy adult men and women, who were between 20 and 70 years old and were recruited as participants for the Berlin Aging Study II. Associations were assessed using linear regression analysis. Despite having sufficient power to detect the previously reported effect sizes, we found no evidence for statistically significant associations between the tested CTNNBL1 SNPs and any of the 14 measures of episodic memory. The previously reported effects of genetic polymorphisms in CTNNBL1 on episodic memory performance do not generalize to the broad range of tasks assessed in our cohort. If not altogether spurious, the effects may be limited to a very narrow phenotypic domain (that is, verbal delayed free recall between 5 and 30 min). More studies are needed to further clarify the role of CTNNBL1 in human memory.

BDNF polymorphisms are linked to poorer working memory performance, reduced cerebellar and hippocampal volumes and differences in prefrontal cortex in a Swedish elderly population

Background

Brain-derived neurotrophic factor (BDNF) links learning, memory and cognitive decline in elderly, but evidence linking BDNF allele variation, cognition and brain structural differences is lacking.

Methods

367 elderly Swedish men (n = 181) and women (n = 186) from Prospective Investigation of the Vasculature in Uppsala seniors (PIVUS) were genotyped and the BDNF functional rs6265 SNP was further examined in subjects who completed the Trail Making Task (TMT), verbal fluency task, and had a magnetic resonance imaging (MRI) scan. Voxel-based morphometry (VBM) examined brain structure, cognition and links with BDNF.

Results

The functional BDNF SNP (rs6265,) predicted better working memory performance on the TMT with positive association of the Met rs6265, and was linked with greater cerebellar, precuneus, left superior frontal gyrus and bilateral hippocampal volume, and reduced brainstem and bilateral posterior cingulate volumes.

Conclusions

The functional BDNF polymorphism influences brain volume in regions associated with memory and regulation of sensorimotor control, with the Met rs6265 allele potentially being more beneficial to these functions in the elderly.

Dopamine and glutamate receptor genes interactively influence episodic memory in old age

Both the dopaminergic and glutamatergic systems modulate episodic memory consolidation. Evidence from animal studies suggests that these two neurotransmitters may interact in influencing memory performance. Given that individual differences in episodic memory are heritable, we investigated whether variations of the dopamine D2 receptor gene (rs6277, C957T) and the N-methyl-D-aspartate 3A (NR3A) gene, coding for the N-methyl-D-aspartate 3A subunit of the glutamate N-methyl-D-aspartate receptor (rs10989591, Val362Met), interactively modulate episodic memory in large samples of younger (20-31 years; n = 670) and older (59-71 years; n = 832) adults. We found a reliable gene-gene interaction, which was observed in older adults only: older individuals carrying genotypes associated with greater D2 and N-methyl-D-aspartate receptor efficacy showed better episodic performance. These results are in line with findings showing magnification of genetic effects on memory in old age, presumably as a consequence of reduced brain resources. Our findings underscore the need for investigating interactive effects of multiple genes to understand individual difference in episodic memory.

Effects of the BDNF Val66Met polymorphism and met allele load on declarative memory related neural networks

It has been suggested that the BDNF Val66Met polymorphism modulates episodic memory performance via effects on hippocampal neural circuitry. However, fMRI studies have yielded inconsistent results in this respect. Moreover, very few studies have examined the effect of met allele load on activation of memory circuitry. In the present study, we carried out a comprehensive analysis of the effects of the BDNF polymorphism on brain responses during episodic memory encoding and retrieval, including an investigation of the effect of met allele load on memory related activation in the medial temporal lobe. In contrast to previous studies, we found no evidence for an effect of BDNF genotype or met load during episodic memory encoding. Met allele carriers showed increased activation during successful retrieval in right hippocampus but this was contrast-specific and unaffected by met allele load. These results suggest that the BDNF Val66Met polymorphism does not, as previously claimed, exert an observable effect on neural systems underlying encoding of new information into episodic memory but may exert a subtle effect on the efficiency with which such information can be retrieved.

Toward a unified biological hypothesis for the BDNF Val66Met-associated memory deficits in humans: a model of impaired dendritic mRNA trafficking

Brain-derived neurotrophic factor (BDNF) represents promotesa key molecule for the survival and differentiation of specific populations of neurons in the central nervous system. BDNF also regulates plasticity-related processes underlying memory and learning. A common single nucleotide polymorphism (SNP) rs6265 has been identified on the coding sequence of human BDNF located at 11p13. The SNP rs6265 is a single base mutation with an adenine instead of a guanine at position 196 (G196A), resulting in the amino acid substitution Val66Met. This polymorphism only exists in humans and has been associated with a plethora of effects ranging from molecular, cellular and brain structural modifications in association with deficits in social and cognitive functions. To date, the literature on Val66Met polymorphism describes a complex and often conflicting pattern of effects. In this review, we attempt to provide a unifying model of the Val66Met effects. We discuss the clinical evidence of the association between Val66Met and memory deficits, as well as the molecular mechanisms involved including the reduced transport of BDNF mRNA to the dendrites as well as the reduced processing and secretion of BDNF protein through the regulated secretory pathway.

Synergy effects of HbA1c and variants of APOE and BDNFVal66Met explains individual differences in memory performance

We aimed at exploring if synergy effects of Brain-Derived Neurotrophic Factor (BDNF) Val(66)Met, Apolipoprotein E (APOE) and HbA1c (glycated haemoglobin) could explain individual differences in memory performance over 10 years in a population based sample of nondemented adults (N=888, 35-85 years at baseline). Episodic memory was affected by such agents, wheras semantic memory was spared. Both age and HbA1c were associated with episodic memory decline. BDNF(66)Met carriers with higher HbA1c levels evidenced slope decline in episodic recall. We found support for joint effects of BDNFVal(66)Met×APOE×HbA1c and BDNFVal(66)Met×APOE×age on rates of episodic memory change over ten years, after controlling for age, sex, education and cardiovascular diseases. We conclude that variants of genetic polymorphisms act in synergy with long-term blood glucose control in shaping patterns of cognitive aging.

Dopaminergic Gene Polymorphisms Affect Long-term Forgetting in Old Age: Further Support for the Magnification Hypothesis

Emerging evidence from animal studies suggests that suboptimal dopamine (DA) modulation may be associated with increased forgetting of episodic information. Extending these observations, we investigated the influence of DA-relevant genes on forgetting in samples of younger (n = 433, 20–31 years) and older (n = 690, 59–71 years) adults. The effects of single nucleotide polymorphisms of the DA D2 (DRD2) and D3 (DRD3) receptor genes as well as the DA transporter gene (DAT1; SLC6A3) were examined. Over the course of one week, older adults carrying two or three genotypes associated with higher DA signaling (i.e., higher availability of DA and DA receptors) forgot less pictorial information than older individuals carrying only one or no beneficial genotype. No such genetic effects were found in younger adults. The results are consistent with the view that genetic effects on cognition are magnified in old age. To the best of our knowledge, this is the first report to relate genotypes associated with suboptimal DA modulation to more long-term forgetting in humans. Independent replication studies in other populations are needed to confirm the observed association.

Cohort profile: The Berlin Aging Study II (BASE-II)

Similar to other industrialized countries, Germany's population is ageing. Whereas some people enjoy good physical and cognitive health into old age, others suffer from a multitude of age-related disorders and impairments which reduce life expectancy and affect quality of life. To identify and characterize the factors associated with 'healthy' vs. 'unhealthy' ageing, we have launched the Berlin Aging Study II (BASE-II), a multidisciplinary and multi-institutional project that ascertains a large number of ageing-related variables from a wide range of different functional domains. Phenotypic assessments include factors related to geriatrics and internal medicine, immunology, genetics, psychology, sociology and economics. Baseline recruitment of the BASE-II cohort was recently completed and has led to the sampling of 1600 older adults (age range 60-80 years), as well as 600 younger adults (20-35 years) serving as the basic population for in-depth analyses. BASE-II data are linked to the German Socio-Economic Panel Study (SOEP), a long-running panel survey representative of the German population, to estimate sample selectivity. A major goal of BASE-II is to facilitate collaboration with other research groups by freely sharing relevant phenotypic and genotypic data with qualified outside investigators.

Dopamine and training-related working-memory improvement

Converging evidence indicates that the neurotransmitter dopamine (DA) is implicated in working-memory (WM) functioning and that WM is trainable. We review recent work suggesting that DA is critically involved in the ability to benefit from WM interventions. Functional MRI studies reveal increased striatal BOLD activity following certain forms of WM interventions, such as updating training. Increased striatal BOLD activity has also been linked to transfer of learning to non-trained WM tasks, suggesting a neural signature of transfer. The striatal BOLD signal is partly determined by DA activity. Consistent with this assertion, PET research demonstrates increased striatal DA release during updating of information in WM after training. Genetic studies indicate larger increases in WM performance post training for those who carry advantageous alleles of DA-relevant genes. These patterns of results corroborate the role of DA in WM improvement. Future research avenues include: (a) neuromodulatory correlates of transfer; (b) the potential of WM training to enhance DA release in older adults; (c) comparisons among different WM processes (i.e., updating, switching, inhibition) regarding regional patterns of training-related DA release; and (d) gene-gene interactions in relation to training-related WM gains.

The Met-genotype of the BDNF Val66Met polymorphism is associated with reduced Stroop interference in elderly

Aging is accompanied by impairments of executive functions that rely on the functional integrity of fronto-striatal networks. This integrity is modulated by the release of neurotrophins like the brain-derived-neurotrophic factor (BDNF). Here, we investigate effects of the functional BDNF Val66Met polymorphism on interference processing in 131 healthy elderly subjects using event-related potentials (ERPs). In a Stroop task, participants had to indicate the name or the colour of colour-words while colour was either compatible or incompatible with the name. We show that susceptibility to Stroop-interference is affected by the BDNF Val66Met polymorphism: the Met-allele carriers showed better performance and enhanced N450 in interference trials. Other processes necessary to prepare and allocate cognitive resources to a particular task were not affected by BDNF Val66Met polymorphism, underlining the specificity of the observed effects. The observed performance and ERP difference is possibly due to dopamine related effects of BDNF in fronto-striatal networks, where it putatively mediates a shift in the balance of the direct and indirect pathway involved in inhibitory functions.

Memory aging and brain maintenance

Episodic memory and working memory decline with advancing age. Nevertheless, large-scale population-based studies document well-preserved memory functioning in some older individuals. The influential ‘reserve’ notion holds that individual differences in brain characteristics or in the manner people process tasks allow some individuals to cope better than others with brain pathology and hence show preserved memory performance. Here, we discuss a complementary concept, that of brain maintenance (or relative lack of brain pathology), and argue that it constitutes the primary determinant of successful memory aging. We discuss evidence for brain maintenance at different levels: cellular, neurochemical, gray- and white-matter integrity, and systems-level activation patterns. Various genetic and lifestyle factors support brain maintenance in aging and interventions may be designed to promote maintenance of brain structure and function in late life.

The aging hippocampus: interactions between exercise, depression, and BDNF

Late adulthood is associated with increased hippocampal atrophy and dysfunction. Although there are multiple paths by which hippocampal deterioration occurs in late life, the authors discuss the evidence that a single nucleotide polymorphism in the brain-derived neurotrophic factor (BDNF) gene and age-related changes in BDNF protein or receptor expression contribute to hippocampal atrophy. The authors conclude that few studies have tested whether BDNF mediates age-related hippocampal atrophy and memory impairment. However, there is strong evidence that decreased BDNF is associated with age-related hippocampal dysfunction, memory impairment, and increased risk for depression, whereas increasing BDNF by aerobic exercise appears to ameliorate hippocampal atrophy, improve memory function, and reduce depression. Importantly, the most consistent associations between BDNF and hippocampal dysfunction have emerged from research on BDNF protein expression in rodents and serum and plasma concentrations of BDNF in humans. Current research suggests that the BDNF val66met polymorphism may be only weakly associated with hippocampal atrophy in late adulthood. These conclusions are interpreted in relation to age-related memory impairment and preventions for hippocampal atrophy.

Val/Val genotype of brain-derived neurotrophic factor (BDNF) Val⁶⁶Met polymorphism is associated with a better response to OROS-MPH in Korean ADHD children

Research on psychostimulants, analysis of animal models and genetic association studies all suggest that the brain-derived neurotrophic factor gene (BDNF) may be a good candidate for pharmacogenetic studies of attention deficit hyperactivity disorder (ADHD). Yet to date there have been no pharmacogenetic studies of BDNF in ADHD. A total of 102 drug-naive ADHD children (8.7±2.1 yr) were treated with osmotic release oral system-methylphenidate (OROS-MPH) for 12 wk, and four kinds of response criteria were applied, based first, on a combined threshold of the ADHD Rating Scale - IV (ARS) and the Clinical Global Impression - Improvement scale (CGI-I); second, on scores of 1 or 2 vs. 3-7 on the CGI - Severity scale; third, on a >50% reduction in ARS scores; and fourth, on satisfaction of all of the aforementioned criteria. The Val⁶⁶Met polymorphism of BDNF and six single nucleotide polymorphisms from the SLC6A2, ADRA2A and NTF-3 genes were tested for association with each criterion. Relative to other genotypes, homozygosity for the Val allele of the BDNF Val⁶⁶Met polymorphism was associated with a greater relative frequency of good response under all four response criteria (after controlling for baseline ARS score, age, gender, final dose (mg/kg) of OROS-MPH at 12 wk, and level of academic functioning). This association was significant at the uncorrected level for the first and third response criteria (p=0.013 and p=0.018, respectively) and significant at a Bonferroni-corrected level for the second and fourth response criteria (p=0.0002, p=0.0003, respectively). Our findings support an association between homozygosity for the Val allele of BDNF and better response to OROS-MPH in Korean ADHD children as assessed by four different response criteria.

Genetic Modulation of Training and Transfer in Older Adults: BDNF ValMet Polymorphism is Associated with Wider Useful Field of View

Western society has an increasing proportion of older adults. Increasing age is associated with a general decrease in the control over task-relevant mental processes. In the present study we investigated the possibility that successful transfer of game-based cognitive improvements to untrained tasks in elderly people is modulated by preexisting neuro-developmental factors as genetic variability related to levels of the brain-derived neurotrophic factor (BDNF), an important neuromodulator underlying cognitive processes. We trained participants, genotyped for the BDNF Val⁶⁶Met polymorphism, on cognitive tasks developed to improve dynamic attention. Pre-training (baseline) and post-training measures of attentional processes (divided and selective attention) were acquired by means of the useful field of view task. As expected, Val/Val homozygous individuals showed larger beneficial transfer effects than Met/-carriers. Our findings support the idea that genetic predisposition modulates transfer effects.

Minimal peroxide exposure of neuronal cells induces multifaceted adaptive responses

Oxidative exposure of cells occurs naturally and may be associated with cellular damage and dysfunction. Protracted low level oxidative exposure can induce accumulated cell disruption, affecting multiple cellular functions. Accumulated oxidative exposure has also been proposed as one of the potential hallmarks of the physiological/pathophysiological aging process. We investigated the multifactorial effects of long-term minimal peroxide exposure upon SH-SY5Y neural cells to understand how they respond to the continued presence of oxidative stressors. We show that minimal protracted oxidative stresses induce complex molecular and physiological alterations in cell functionality. Upon chronic exposure to minimal doses of hydrogen peroxide, SH-SY5Y cells displayed a multifactorial response to the stressor. To fully appreciate the peroxide-mediated cellular effects, we assessed these adaptive effects at the genomic, proteomic and cellular signal processing level. Combined analyses of these multiple levels of investigation revealed a complex cellular adaptive response to the protracted peroxide exposure. This adaptive response involved changes in cytoskeletal structure, energy metabolic shifts towards glycolysis and selective alterations in transmembrane receptor activity. Our analyses of the global responses to chronic stressor exposure, at multiple biological levels, revealed a viable neural phenotype in-part reminiscent of aged or damaged neural tissue. Our paradigm indicates how cellular physiology can subtly change in different contexts and potentially aid the appreciation of stress response adaptations.

Performance-related increases in hippocampal N-acetylaspartate (NAA) induced by spatial navigation training are restricted to BDNF Val homozygotes

Recent evidence indicates experience-dependent brain volume changes in humans, but the functional and histological nature of such changes is unknown. Here, we report that adult men performing a cognitively demanding spatial navigation task every other day over 4 months display increases in hippocampal N-acetylaspartate (NAA) as measured with magnetic resonance spectroscopy. Unlike measures of brain volume, changes in NAA are sensitive to metabolic and functional aspects of neural and glia tissue and unlikely to reflect changes in microvasculature. Training-induced changes in NAA were, however, absent in carriers of the Met substitution in the brain-derived neurotrophic factor (BDNF) gene, which is known to reduce activity-dependent secretion of BDNF. Among BDNF Val homozygotes, increases in NAA were strongly related to the degree of practice-related improvement in navigation performance and normalized to pretraining levels 4 months after the last training session. We conclude that changes in demands on spatial navigation can alter hippocampal NAA concentrations, confirming epidemiological studies suggesting that mental experience may have direct effects on neural integrity and cognitive performance. BDNF genotype moderates these plastic changes, in line with the contention that gene-context interactions shape the ontogeny of complex phenotypes.