Use it or lose it: the interplay of new brain cells, age, and activity

This 2015 German review was of aging and activity in the context of adult neurogenesis:

“Adult neurogenesis might be of profound functional significance because it occurs at a strategic bottleneck location in the hippocampus.

Age-dependent changes essentially reflect a unidirectional development in that everything builds on what has occurred before. In this sense, aging can also be seen as continued or lifelong development. This idea has limitations but is instructive with regard to adult neurogenesis, because adult neurogenesis is neuronal development under the conditions of the adult brain.

The age-related alterations of adult neurogenesis themselves have quantitative and qualitative components. So far, most research has focused on the quantitative aspects. But there can be little doubt that qualitative changes do not simply follow quantitative changes (e.g., in cell or synapse numbers), but emerge on a systems level and above when an organism ages. With respect to adult neurogenesis, only one multilevel experiment including morphology and behavior has been conducted, and, even in that study, only three time points were investigated.

In old age, adult neurogenesis occurs at only a small fraction of the level in early adulthood. The decline does not seem to be ‘regulated’ but rather the by-product of many age-related changes of other sorts.

From a behavioral level down to a synaptic level, activity increases adult neurogenesis. This regulation does not seem to occur in an all-or-nothing fashion but rather influences different stages of neuronal development differently. Both cell proliferation and survival are influenced by or even depend on activity.

The effects of exercise and environmental enrichment are additive, which indicates that increasing the potential for neurogenesis is sufficient to increase the actual use of the recruitable cells in the case of cognitive stimulation. Physical activity would not by itself provide specific hippocampus-relevant stimuli that induce net neurogenesis but be associated with a greater chance to encounter specific relevant stimuli.

Adult hippocampal neurogenesis might contribute to a structural or neural reserve that if appropriately trained early in life might provide a compensatory buffer of brain plasticity in the face of increasing neurodegeneration or nonpathological age-related functional losses. There is still only limited information on the activity-dependent parameters that help to prevent the age-dependent decrease in adult neurogenesis and maintain cellular plasticity.

The big question is what the functional contribution of so few new neurons over so long periods can be. Any comprehensive concept has to bring together the acute functional contributions of newly generated, highly plastic neurons and the more-or-less lasting changes they introduce to the network.”

I’ve quoted quite a lot, but there are more details that await your reading. A few items from the study referenced in the first paragraph above:

“The hippocampus represents a bottleneck in hippocampal neurogenesis occurs at exactly the narrowest spot.

We have derived the theory that the function of adult hippocampal neurogenesis is to enable the brain to accommodate continued bouts of novelty..a mechanism for preparing the hippocampus for processing greater levels of complexity.”

The role of the hippocampus in emotion was ignored as it so often is. The way to address many of the gaps mentioned by the author may be to Advance science by including emotion in research.

For example, from the author’s The mystery of humans’ evolved capability for adults to grow new brain cells:

“Adult neurogenesis is already effective early in life, actually very well before true adulthood, and is at very high levels when sexual maturity has been reached. Behavioral advantages associated with adult neurogenesis must be relevant during the reproductive period.”

When human studies are designed to research how “behavioral advantages associated with adult neurogenesis must be relevant” what purpose does it serve to exclude emotional content? “Activity Dependency and Aging in the Regulation of Adult Neurogenesis”

End draft registration – Now!

“The draft is morally wrong: the State doesn’t own us – we own ourselves.

Conscription is un-American, unconstitutional, and inimical to the principles of a free society.

Under no circumstances is it ever justified, period.

If a nation cannot find enough volunteers to defend itself against foreign invasion, then this tells us something about the nature of the regime – that it has lost whatever legitimacy it once had, and therefore doesn’t deserve to exist.”

Empathy, value, pain, control: Psychological functions of the human striatum

This 2016 US human study found:

“A link between existing data on the anatomical and physiological characteristics of striatal regions and psychological functions.

Because we did not limit our metaanalysis to studies that specifically targeted striatal function, our results extend previous knowledge of the involvement of the striatum in reward-related decision-making tasks, and provide a detailed functional map of regional specialization for diverse psychological functions, some of which are sometimes thought of as being the exclusive domain of the PFC [prefrontal cortex].”

The analysis led to dividing the striatum into five segments:

Ventral striatum (VS):

  • Stimulus Value
  • Terms such as “reward,” “losses,” and “craving”
  • The most representative study reported that monetary and social rewards activate overlapping regions within the VS.
  • Together with the above finding of a reliable coactivation with OFC [orbitofrontal cortex] and ventromedial PFC, this finding suggests a broad involvement of this area in representing stimulus value and related stimulus-driven motivational states.

Anterior caudate (Ca) Nucleus:

  • Incentive Behavior
  • Terms such as “grasping,” “reaching,” and “reinforcement”
  • The most representative study reported a stronger blood-oxygen level-dependent (BOLD) response in this region during trials in which participants had a chance of winning or losing money in a card guessing game, in comparison to trials where participants merely received feedback about the accuracy of their guess.
  • This result suggests a role in evaluating the value of different actions, contrasting with the above role of the VS in evaluating the value of stimuli.

Posterior putamen (Pp):

  • Sensorimotor Processes
  • Terms such as “foot,” “noxious,” and “taste”
  • The most representative study reported activation of this region in response to painful stimulation at the back of the left hand and foot of participants. Anatomically, the most reliable and specific coactivation is with sensorimotor cortices, and the posterior and midinsula and operculum (secondary somatosensory cortex SII) in particular, some parts of which are specifically associated with pain.
  • Together, these findings suggest a broad involvement of this area in sensorimotor functions, including aspects of their affective qualities.

Anterior putamen (Pa):

  • Social- and Language-Related Functions
  • Terms such as “read,” “vocal,” and “empathic”
  • The most representative study partially supports a role of this area in social- and language-related functions; it reported a stronger activation of the Pa in experienced singers, but not when novices were singing.
  • It is coactivated with frontal areas anterior to the ones coactivated with the Pp, demonstrating topography in frontostriatal associations. These anterior regions have been implicated in language processes.

Posterior caudate (Cp) Nucleus:

  • Executive Functions
  • Terms such as “causality,” “rehearsal,” and “arithmetic”
  • The representative study reported this region to be part of a network that included dorsolateral PFC and ACC, which supported inhibitory control and task set-shifting.
  • These results suggest a broad, and previously underappreciated, role for the Cp in cognitive control.

The authors presented comparisons of the above striatal segments with other analyses of striatal zones.

One of the coauthors was the lead researcher of the 2015 Advance science by including emotion in research. The current study similarly used a coactivation view rather than a connectivity paradigm of:

“Inferring striatal function indirectly via psychological functions of connected cortical regions.”

Another of the coauthors was a developer of the system used by the current study and by The function of the dorsal ACC is to monitor pain in survival contexts, and he provided feedback to those authors regarding proper use of the system.

The researchers’ “unbiased, data-driven approach” had to work around the cortical biases evident in many of the 5,809 human imaging studies analyzed. The authors referred to the biases in statements such as:

“The majority of studies investigating these psychological functions report activity preferentially in cortical areas, except for studies investigating reward-related and motor functions.”

The methods and results of research with cortical biases influenced the study’s use of:

“Word frequencies of psychological terms in the full text of studies, rather than a detailed analysis of psychological tasks and statistical contrasts.” “Regional specialization within the human striatum for diverse psychological functions”

Which communities deserve your membership?

This 2015 California/Oxford review described the interplay between an individual and their group membership from an evolutionary biology viewpoint:

“Many central questions in evolutionary biology rely on understanding how individual-level and group-level selective processes interact to shape phenotypic variation and specialisation. Individuals can aggregate into groups, and the composition of these groups, populations, or communities (herein group phenotypic composition or GPC) can affect group-level dynamics and self-organisation.

Research across a range of disparate topics will benefit from simultaneously developing an understanding of how GPC affects individual fitness [genetic fitness, not physical fitness] and exerts selection on individual phenotypes, and assessing how individual phenotypes respond to GPC.

GPC can be a function of the phenotypes of its members or an emergent property that is not attributable to any single individual, such as the mating system. GPC is also an emergent property of genotypes and their patterns of expression.

GPC can affect individual fitness by influencing the overall performance of the group on collective tasks, affecting all the members of any given group equally, or by affecting the relative performance of different phenotypes within groups. For instance, a group with more aggressive individuals can be more successful at foraging, but aggressive individuals can have a higher fitness than non-aggressive individuals because they can monopolise a larger share of the total resources.

Individuals can respond to the effect of GPC by altering the phenotypic composition of the group (for example by controlling access to the group) and/or by changing their own phenotype.”

See my Individual evolution page for more on the topic of human individuals “changing their own phenotype.”

The review provided specific examples to illustrate each point of the overall framework. The authors seldom mentioned human examples, although many of the discussion items applied. Two of their points that weren’t necessarily applicable to human groups were:

  • Benefits from reducing competition
  • Altruism wasn’t viewed as an individual trait.

The authors didn’t use human-specific examples in their framework. For example, they mentioned division of labor, which benefits both animals and humans. There was no mention of applying capital to efforts, which is thought to be specific to humans, although reuse of tools by crows and chimpanzees may be animal examples.

I’d guess that the authors didn’t refer to humans often because that may have added the human trait of unforced individual choice. Unlike other species, we have the capability to direct much of our own lives, and choose the communities to which we belong.

A few questions about our group membership decisions:

  • Do we choose group memberships based on how the group recognizes and facilitates the unique individual each of us is?
  • How do we benefit as an individual when we become default members of communities by not making choices?
  • What individual benefits may we receive by opting out of default groups? “From Individuals to Groups and Back: The Evolutionary Implications of Group Phenotypic Composition”

The mystery of humans’ evolved capability for adults to grow new brain cells

This 2016 German review discussed the evolution of human adult neurogenesis:

“Mammalian adult hippocampal neurogenesis is a trait shaped by evolutionary forces that have contributed to the advantages in natural selection that are associated with the mammalian dentate gyrus. Adult hippocampal neurogenesis in mammals originates from an ectopic precursor cell population that resides in a defined stem-cell niche detached from the ventricular wall.

Neurogenesis in the adult olfactory bulb generates a diverse range of interneurons, and is involved in the processing of sensory input. In contrast, adult hippocampal neurogenesis produces only one type of excitatory principal neuron and plays a role in flexible memory formation.

A surplus of new neurons is generated first from which only a subset survives. And it is exactly these new neuronal nodes that, at least for a transient period, are the carriers of synaptic plasticity.

For a number of weeks after they were born, the new neurons have a lower threshold for long-term potentiation. This directs the action to the new cells and results in a bias toward the most plastic cells in the local circuitry.

It is a highly polygenic trait, and numerous genes have already been identified to ultimately have essentially identical effects on net neurogenesis.

Adult neurogenesis is also an individualizing trait. Even before an identical genetic background, subtle individual differences in starting conditions and differential behavioral trajectories result in an increase in phenotypic variation with time.”

The author continued the penultimate paragraph above to pose a question about adult neurogenesis that’s incompletely answered by evolutionary biology theory and evidence todate:

“How genetic variation in single genes (or many genes) would be able to exert a phenotypic change in neurogenesis that can provide a large enough advantage to be selected for.”

The development of new brain cells throughout our lives helps us continually adapt and learn. The “increase in phenotypic variation with time” helps us maintain the unique individual that each of us is.

The review emphasized to me how “individual differences” should neither be viewed as a mystery, nor explained away, nor treated as an etiological factor as researchers often do. Focusing on what caused the differences may provide clearer information. “Adult Neurogenesis: An Evolutionary Perspective”

A problematic study of oxytocin receptor gene methylation, childhood abuse, and psychiatric symptoms

This 2016 Georgia human study found:

“A role for OXTR [oxytocin receptor gene] in understanding the influence of early environments on adult psychiatric symptoms.

Data on 18 OXTR CpG sites, 44 single nucleotide polymorphisms, childhood abuse, and adult depression and anxiety symptoms were assessed in 393 African American adults. The Childhood Trauma Questionnaire (CTQ), a retrospective self-report inventory, was used to assess physical, sexual, and emotional abuse during childhood.

While OXTR CpG methylation did not serve as a mediator to psychiatric symptoms, we did find that it served as a moderator for abuse and psychiatric symptoms.”

From the Limitations section:

  1. “Additional insight will likely be gained by including a more detailed assessment of abuse timing and type on the development of biological changes and adverse outcomes.
  2. The degree to which methylation remains fixed following sensitive developmental time periods, or continues to change in response to the environment, is still a topic of debate and is not fully known.
  3. Comparability between previous findings and our study is limited given different areas covered.
  4. Our study was limited to utilizing peripheral tissue [blood]. OXTR methylation should ideally be assessed in the tissues that are known to express OXTR and directly involved in psychiatric symptoms. The degree to which methylation of peripheral tissues can be used to study methylation changes in response to the environment or in association with behavioral outcomes is currently a topic of debate.
  5. Our study did not evaluate gene expression and thus cannot explore the role of study CpG sites on regulation and expression.”

Addressing the study’s limitations:

  1. Early-life epigenetic regulation of the oxytocin receptor gene demonstrated – with no hint of abuse – how sensitive an infant’s experience-dependent oxytocin receptor gene DNA methylation was to maternal care. Treating prenatal stress-related disorders with an oxytocin receptor agonist provided evidence for prenatal oxytocin receptor gene epigenetic changes.
  2. No human’s answers to the CTQ, Adverse Childhood Experiences, or other questionnaires will ever be accurate self-reports of their prenatal, infancy, and early childhood experiences. These early development periods were likely when the majority of the subjects’ oxytocin receptor gene DNA methylation took place. The CTQ self-reports were – at best – evidence of experiences at later times and places, distinct from earlier experience-dependent epigenetic changes.
  3. As one example of incomparability, the 2009 Genomic and epigenetic evidence for oxytocin receptor deficiency in autism was cited in the Introduction section and again in the Limitations section item 4. Since that study was sufficiently relevant to be used as a reference twice, the researchers needed to provide a map between its findings and the current study.
  4. Early-life epigenetic regulation of the oxytocin receptor gene answered the question of whether or not an individual’s blood could be used to make inferences about their brain oxytocin receptor gene DNA methylation. The evidence said: NO, it couldn’t.
  5. It’s assumed that oxytocin receptor gene DNA methylation directly impacted gene expression such that increased levels of methylation were associated with decreased gene transcription. The study assumed but didn’t provide evidence that higher levels of methylation indicated decreased ability to use available oxytocin due to decreased receptor expression. The study also had no control group.

To summarize the study’s limitations:

  1. The study zeroed in on childhood abuse, and disregarded evidence for more relevant factors determining an individual’s experience-dependent oxytocin receptor gene DNA methylation. That smelled like an agenda.
  2. The study used CTQ answers as determinants, although what happened during the subjects’ earliest life was likely when the majority of epigenetic changes to the oxytocin receptor gene took place. If links existed between the subjects’ early-life DNA methylation and later-life conditions, they weren’t evidenced by CTQ answers about later life that couldn’t self-report relevant experiences from conception through age three that may have caused DNA methylation.
  3. There was no attempt to make findings comparable with cited studies. That practice and the lack of a control group reminded me of Problematic research with telomere length.
  4. The researchers tortured numbers until they confessed “that CpG methylation may interact with abuse to predict psychiatric symptoms.” But there was no direct evidence that each subject’s blood oxytocin gene receptor DNA methylation interacted as such! Did the “may interact” phrase make the unevidenced inferences more plausible, or permit contrary evidence to be disregarded?
  5. See Testing the null hypothesis of oxytocin’s effects in humans for examples of what happens when researchers compound assumptions and unevidenced inferences.

The study’s institution, Emory University, and one of the study’s authors also conducted Conclusions without evidence regarding emotional memories. That 2015 study similarly disregarded relevant evidence from other research, and made statements that weren’t supported by that study’s evidence.

The current study used “a topic of debate” and other disclaimers to provide cover for unconvincing methods and analyses in pursuit of..what? What overriding goals were achieved? Who did the study really help? “Oxytocin Receptor Genetic and Epigenetic Variations: Association With Child Abuse and Adult Psychiatric Symptoms”

This post has somehow become a target for spammers, and I’ve disabled comments. Readers can comment on other posts and indicate that they want their comment to apply here, and I’ll re-enable comments.

Early-life epigenetic regulation of the oxytocin receptor gene

This 2015 US/Canadian rodent study investigated the effects of natural variation in maternal care:

“The effects of early life rearing experience via natural variation in maternal licking and grooming during the first week of life on behavior, physiology, gene expression, and epigenetic regulation of Oxtr [oxytocin receptor gene] across blood and brain tissues (mononucleocytes, hippocampus, striatum, and hypothalamus).

Rats reared by high licking-grooming (HL) and low licking-grooming (LL) rat dams exhibited differences across study outcomes:

  • LL offspring were more active in behavioral arenas,
  • Exhibited lower body mass in adulthood, and
  • Showed reduced corticosterone responsivity to a stressor.

Oxtr DNA methylation was significantly lower at multiple CpGs in the blood of LL versus HL males, but no differences were found in the brain. Across groups, Oxtr transcript levels in the hypothalamus were associated with reduced corticosterone secretion in response to stress, congruent with the role of oxytocin signaling in this region.

Methylation of specific CpGs at a high or low level was consistent across tissues, especially within the brain. However, individual variation in DNA methylation relative to these global patterns was not consistent across tissues.

These results suggest that:

  • Blood Oxtr DNA methylation may reflect early experience of maternal care, and
  • Oxtr methylation across tissues is highly concordant for specific CpGs, but
  • Inferences across tissues are not supported for individual variation in Oxtr methylation.


Individual DNA methylation values were not correlated across brain tissues, despite tissue concordance at the group level.

For each CpG, we computed the Pearson correlation coefficient r between methylation values for matched samples in pairs of brain regions (bars). Dark and light shaded regions represent 95% and 99% thresholds, respectively, of distributions of possible correlation coefficients determined from 10,000 permutations of the measured values among the individuals. These distributions represent the null hypothesis that an individual DNA methylation value in one brain region does not help to predict the value in another region in the same animal.

(A) Correlations based on pyrosequencing data for matched samples passing validation in both hippocampus (HC) and hypothalamus (Hypo). Correlations for individuals at each CpG were either weak (.2 < r < .3) or absent (r < .2), and none were significant, even prior to correction for multiple comparisons.

(B) Correlations for matched samples passing validation in both hippocampus and striatum (Str). Two correlations (CpG 1 and 11) were individually significant prior to but not following correction, and this result could be expected by chance.

Correlations between hippocampus and blood (described in the text) yielded similar results, and no particular CpG yielded consistently high correlation across multiple tissues.”

The study focused on whether or not an individual’s experience-dependent oxytocin receptor gene DNA methylation in one of the four studied tissues could be used to infer a significant effect in the three other tissues. The main finding was NO, it couldn’t!

The researchers’ other findings may have been strengthened had they also examined causes for the observed effects. The “natural variation in maternal licking and grooming” developed from somewhere, didn’t it?

The subjects’ mothers were presumably available for the same tests as the subjects, but nothing was done with them. Investigating at least one earlier generation may have enabled etiologic associations of “the effects of early life rearing experience” and “individual variation in DNA methylation.” “Natural variation in maternal care and cross-tissue patterns of oxytocin receptor gene methylation in rats” (not freely available)