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Posts Tagged ‘Health’

Mood Broadcasting
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Like many folks, I generally feel better ever since I started practicing yoga.  Outwardly, my body is (slowly) growing stronger and more flexible and perhaps (hopefully) soon, I’ll even lose a few pounds.  However, even if I was to convince myself that looked slimmer (skinny mirrors?), the only way to really know if I’ve lost weight, is to stand on a scale and record my weight each day (darn! no fatness lost so far).

That takes care of the body right – but what about the inner, emotional improvements I might be experiencing?  How to measure these?

Here are some mobile- and web-based tools to help one track one’s emotions.  Most of these websites, like Moodstats, Track Your Happiness, MoodJam, MoodMill, Finding Optimism and MoodLog seem to function as online diaries which keep a running tab on aspects of ones moods and emotions.  Perhaps such tools – if used over long durations – would enable one to verify a shift toward a less anxious and more contented inner feeling?  I don’t know.

Perhaps the real proof of “inner” progress would be that I had closed my computer and put away my mobile device and, rather, was outside enjoying the sights and sounds of nature.  Perhaps best to avoid mixing yoga and digital distractions.

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** PODCAST accompanies this post**

I have a little boy who loves to run and jump and scream and shout – a lot.  And by this, I mean running – at full speed and smashing his head into my gut,  jumping – off the couch onto my head,  screaming – spontaneous curses and R-rated body parts and bodily functions.  I hope you get the idea.  Is this normal? or (as I oft imagine) will I soon be sitting across the desk from a school psychologist pitching me the merits of an ADHD diagnosis and medication?

Of course, when it comes to behavior, there is not a distinct line one can cross from normal to abnormal.  Human behavior is complex, multi-dimensional and greatly interpreted through the lens of culture.  Our present culture is highly saturated by mass-marketing, making it easy to distort a person’s sense of “what’s normal” and create demand for consumer products that folks don’t really need (eg. psychiatric diagnoses? medications?).   Anyhow, its tough to know what’s normal.  This is an important issue to consider for those (mass-marketing hucksters?) who might be inclined to promote genetic data as “hard evidence” for illness, disorder or abnormality of some sort.

With this in mind, I really enjoyed a recent paper by Stollstorff et al., “Neural response to working memory load varies by dopamine transporter genotype in children” [doi:10.1016/j.neuroimage.2009.12.104] who asked how the brains of healthy children functioned, even though they carry a genotype that has been widely associated with the risk of ADHD.  Healthy children who carry genetic risk for ADHD. Hmm, might this be my boy?

The researchers looked at a 9- vs. 10-repeat VNTR polymorphism in the 3′-UTR of the dopamine transporter gene (DAT1).  This gene – which encodes the very protein that is targeted by so many ADHD medications – influences the re-uptake of dopamine from the synaptic cleft.  In the case of 10/10 genotypes, it seems that DAT1 is more highly expressed, thus leading to more re-uptake and hence less dopamine in the synaptic cleft.  Generally, dopamine is needed to enhance the signal/noise of neurotransmission, so – at the end of the day – the 10/10 genotype is considered less optimal than the 9/9-repeat genotype.  As noted by the researchers, the ADHD literature shows that the 10-repeat allele, not the 9-repeat, is most often associated with ADHD.

The research team asked these healthy children (typically developing children between 7 and 12 years of age) to perform a so-called N-back task which requires that children remember words that are presented to them one-at-a-time.  Each time a new word is presented, the children had to decide whether that word was the same as the previous word (1-back) or the previous, previous word (2-back).  Its a maddening task and places an extreme demand on neural circuits involved in active maintenance of information (frontal cortex) as well as inhibition of irrelevant information that occurs during updating (basal ganglia circuits).

As the DAT1 protein is widely expressed in the basal ganglia, the research team asked where in the brain was variation in the DAT1 (9- vs. 10-repeat) associated with neural activity?  and where was there a further difference between 1-back and 2-back?  Indeed, the team finds that brain activity in many regions of the basal ganglia (caudate, putamen, substantia nigra & subthalamic nucleus) were associated with genetic variation in DAT1.  Neat!  the gene may be exerting an influence on brain function (and behavior) in healthy children, even though they do not carry a diagnosis.  Certainly, genes are not destiny, even though they do influence brain and behavior.

What was cooler to me though, is the way the investigators examined the role of genetic variation in the 1-back (easy or low load condition) vs. 2-back (harder, high-load condition) tasks.  Their data shows that there was less of an effect of genotype on brain activation in the easy tasks.  Rather, only when the task was hard, did it become clear that the basal ganglia in the 10/10 carriers was lacking the necessary brain activation needed to perform the more difficult task.  Thus, the investigators reveal that the genetic risk may not be immediately apparent under conditions where heavy “loads” or demands are not placed on the brain.  Cognitive load matters when interpreting genetic data!

This result made me think that genes in the brain might be a lot like genes in muscles.  Individual differences in muscle strength are not associated with genotype when kids are lifting feathers.  Only when kids are actually training and using their muscles, might one start to see that some genetically advantaged kids have muscles that strengthen faster than others.  Does this mean there is a “weak muscle gene” – yes, perhaps.  But with the proper training regimen, children carrying such a “weak muscle gene” would be able to gain plenty of strength.

I guess its off to the mental and physical gyms for me and my son.

** PODCAST accompanies this post** also, here’s a link to the Vaidya lab!

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The A-to-T SNP rs7794745 in the CNTNAP2 gene was found to be associated with increased risk of autism (see Arking et al., 2008).  Specifically, the TT genotype, found in about 15% of individuals, increases these folks’ risk by about 1.2-1.7-fold.  Sure enough, when I checked my 23andMe profile, I found that I’m one of these TT risk-bearing individuals.  Interesting, although not alarming since me and my kids are beyond the age where one typically worries about autism.  Still, one can wonder if such a risk factor might have exerted some influence on the development of my brain?

The recent paper by Tan et al., “Normal variation in fronto-occipital circuitry and cerebellar structure with an autism-associated polymorphism of CNTNAP2” [doi:10.1016/j.neuroimage.2010.02.018 ] suggests there may be subtle, but still profound influences of the TT genotype on brain development in healthy individuals.  According to the authors, “homozygotes for the risk allele showed significant reductions in grey and white matter volume and fractional anisotropy in several regions that have already been implicated in ASD, including the cerebellum, fusiform gyrus, occipital and frontal cortices. Male homozygotes for the risk alleles showed greater reductions in grey matter in the right frontal pole and in FA in the right rostral fronto-occipital fasciculus compared to their female counterparts who showed greater reductions in FA of the anterior thalamic radiation.”

The FA (fractional anisotropy – a measurement of white-matter or myelination) results are consistent with a role of CNTNAP2 in the establishment of synaptic contacts and other cell-cell contacts especially at Nodes of Ranvier – which are critical for proper function of white-matter tracts that support rapid, long-range neural transmission.  Indeed, more severe mutations in CNTNAP2  have been associated with cortical dysplasia and focal epilepsy (Strauss et al., 2006).

Subtle changes perhaps influencing long-range information flow in my brain – wow!

More on CNTNAP2 … its evolutionary history and role in language development.

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***PODCAST ACCOMPANIES THIS POST***

In his undergraduate writings while a student at Harvard in the early 1900’s E. E. Cummings quipped that, “Japanese poetry is different from Western poetry in the same way as silence is different from a voice”.  Isabelle Alfandary explores this theme in Cummings’ poetry in her essay, “Voice and Silence in E. E. Cummings’ Poetry“,  giving some context to how the poet explored the meanings and consequences of voice and silence.  Take for example, his poem “silence”

silence

.is
a
looking

bird:the

turn
ing;edge, of
life

(inquiry before snow

e.e. cummings

Lately, it seems that the brain imaging community is similarly beginning to explore the meanings and consequences of the brain when it speaks (activations whilst performing certain tasks) and when it rests quietly.  As Cummings beautifully intuits the profoundness of silence and rest,  I suppose he might have been intrigued by just how very much the human brain is doing when we are not speaking, reading, or engaged in a task. Indeed, a community of brain imagers seem to be finding that the brain at rest has quite a lot to say – moreso in people who carry certain forms of genetic variation (related posts here & here).

A paper by Perrson and colleagues “Altered deactivation in individuals with genetic risk for Alzheimer’s disease” [doi:10.1016/j.neuropsychologia.2008.01.026] asked individuals to do something rather ordinary – to pay attention to words – and later to then respond to the meaning of these words (a semantic categorization task). This simple endeavor, which, in many ways uses the very same thought processes as used when reading poetry, turns out to activate regions of the temporal lobe such as the hippocampus and other connected structures such as the posterior cingulate cortex.  These brain regions are known to lose function over the course of life in some individuals and underlie their age-related difficulties in remembering names and recalling words, etc.  Indeed, some have described Alzheimer’s disease as a tragic descent into a world of silence.

In their recordings of brain activity of subjects (60 healthy participants aged 49-79), the team noticed something extraordinary.  They found that there were differences not in how much the brain activates during the task – but rather in how much the brain de-activates – when participants simply stare into a blank screen at a small point of visual fixation.  The team reports that individuals who carry at least one copy of epsilon-4 alleles of the APOE gene showed less de-activation of their their brain (in at least 6 regions of the so-called default mode network) compared to individuals who do not carry genetic risk for Alzheimer’s disease.  Thus the ability of the brain to rest – or transition in and out of the so-called default mode network – seems impaired in individuals who carry higher genetic risk.

So, I shall embrace the poetic wisdom of E. E. Cummings and focus on the gaps, empty spaces, the vastness around me, the silences, and learn to bring my brain to rest.  And in so doing, perhaps avoid an elderly descent into silence.

***PODCAST ACCOMPANIES THIS POST***

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We are all familiar with the notion that genes are NOT destiny and that the development of an individual’s mind and body occur in a manner that is sensitive to the environment (e.g. children who eat lots of healthy food grow bigger and stronger than those who have little or no access to food).  In the case of the brain, one of the ways in which the environment gets factored into development – is via so-called “sensitive periods” where certain parts of the brain transiently rely on sensory experience in order to develop.  Children born with cataracts, for example, will have much better vision if the cataracts are removed in the first few weeks of life rather than later on.  This is because the human visual system has a “sensitive period” early in development where it is extra-sensitive to visual input and, after which, the function and connectivity of various parts of the system is – somewhat permanently – established for the rest of the person’s life.  Hence, if there is little visual input (cataracts) during the sensitive period, then the visual system is somewhat permanently unable to process visual information – even if the cataracts are subsequently removed.  (To learn more about this topic, visit Pawan Sinha’s lab at M.I.T and his Project Prakash intervention study on childhood blindness.)

What the heck is an “in”sensitive period then?   Well, whereas visual input is clearly a “good thing” for the sensitive period of visual development, perhaps some inputs are “bad” and it may be useful to shield or protect the brain from exposure.  Maybe some environmental inputs are “bad” and one would not want the developing brain to be exposed to them and say, “OK, this (bad stuff) is normal“.  As a parent, I am constantly telling my children that the traffic-filled street is a “bad place” and, like all parents, I would not want my children to think that it was OK to wander into the street.  Clearly, I want my child to recognize the car-filled street as a “bad thing”.

In the developing brain, it turns out that there are some “bad things” that one would NOT like (the brain) to get accustomed to.  Long-term exposure to glucocorticoids is one example – well-known to cause a type of neuronal remodelling in the hippocampus, that is associated with poor cognitive performance (visit Bruce McEwen’s lab at Rockefeller University to learn more about this).  Perhaps an “in”sensitive period – where the brain is insensitive to glucocorticoids – is one way to teach the brain that glucocorticoids are “bad” and DO NOT get too familiar with them (such a period does actually occur during early post-natal mammalian development).  Of course, we do need our brains to mount an acute stress response, if and when, we are being threatened, but it is also very important that the brain learn to TURN-OFF the acute stress response when the threat has passed – an extensive literature on the deleterious effects of chronic exposure to stress bears this out.  Hence, the brain needs to learn to recognize the flow of glucocorticoids as something that needs to be shut down.

OK, so our developing brain needs to learn what/who is “good vs. bad”.  Perhaps sensitive and insensitive periods help to reinforce this learning – and also – to cement learning into the system in a sort of permanent way (I’m really not sure if this is the consensus view, but I’ll try and podcast interview some of the experts here asap).  In any case, in the case of the visual system, it is clear that the lack of visual input during the sensitive period has long lasting consequences.  In the case of the stress response, it is also clear that if there is untoward stress early in development, one can be (somewhat) destined to endure a lifetime of emotional difficulty.  Previous posts here, here, here cover research on behavioral/genomic correlates of early life stress.

Genes meet environment in the epigenome during sensitive and insensitive periods?

As stated at the outset – genes are not destiny.  The DNA cannot encode a system that knows who/what is good vs. bad, but rather can only encode a system of molecular parts that can assemble to learn these contingencies on the fly.  During sensitive periods in the visual system, cells in the visual system are more active and fire more profusely during the sensitive period. This extra firing leads to changes in gene expression in ways that (somewhat) permanently set the connectivity, strength and sensitivity of visual synapses.  The expression of neuroligins, neurexins, integrins and all manner of extracellular proteins that stabilize synaptic connections are well-known tagets of activity-induced gene expression.  Hence the environment “interacts” with the genome via neuronal firing which induces gene expression which – in turn – feeds back and modulates neuronal firing.  Environment –> neuronal firing –> gene expression –> modified neuronal firing.  OK.

Similarly, in the stress response system, the environment induces changes in the firing of cells in the hypothalamus which leads (through a series of intermediates) to the release of glucocorticoids.  Genes induced during the firing of hypothalamic cells and by the release of glucocorticoid can modify the organism’s subsequent response to stressful events.  Environment –> neuronal firing –> gene expression –> modified neuronal firing.  OK.

Digging deeper into the mechanism by which neuronal firing induces gene expression, we find an interesting twist.   Certainly there is a well-studied mechanism wherein neuronal firing causes Ca++ release which activates gene expression of neuroligins, neurexins, integrins and all manner of extracellular proteins that stabilize synaptic connections – for many decades.  There is another mechanism that can permanently mark certain genes and alter their levels of expression – in a long-lasting manner.  These are so-called epigenetic mechanisms such as DNA methylation and acetylation.  As covered here and here, for instance, Michael Meaney’s lab has shown that DNA CpG methylation of various genes can vary in response to early-life stress and/or maternal care. In some cases, females who were poorly cared for, may, in turn, be rather lousy mothers themselves as a consequence of these epigenetic markings.

A new research article, “Dynamic DNA methylation programs persistent adverse effects of early-life stress” by Chris Murgatroyd and colleagues [doi:10.1038/nn.2436] explores these mechanisms in great detail.  The team explored the expression of the arginine vasopressin (AVP) peptide – a gene which is important for healthy social interaction and social-stress responsivity.  Among many other interesting results, the team reports that early life stress (using a mouse model) leads to lower levels of methylation in the 3rd CpG island which is located downstream in a distal gene-expression-enhancer region.  In short, more early-life stress was correlated with less methylation, more AVP expression which is known to potentiate the release of glucocorticoids (a bad thing).   The team reports that the methyl binding MeCP2 protein, encoded by the gene that underlies Rett syndrome, acts as a repressor of AVP expression – which would normally be a good thing since it would keep AVP levels (and hence glucocorticoid levels) down.  But unfortunately, early-life stress removes the very methyl groups to which MeCP2 binds and also the team reports that parvocelluar neuronal depolarization leads to phosphorylation (on serine residue #438) of MeCP2 – a form of MeCP2 that is less accessible to its targets.  So, in  a manner similar to other examples, early life stress can have long-lasting effects on gene expression via an epigenetic mechanism – and disables an otherwise protective mechanism that would shield the organism from the effects of stress.  Much like in the case of Rett syndrome (as covered here) it seems that when MeCP2 is bound – then it silences gene expression – which would seem to be a good thing when it comes to the case of AVP.

So who puts these epigenetic marks on chromosomes and why?

I’ll try and explore this further in the weeks ahead.  One intriguing idea about why methylation has been co-opted among mammals, has to do with the idea of parent-offspring conflict.  According to David Haig, one of the experts on this topic, males have various incentives to cause their offspring to be large and fast growing, while females have incentive to combat the genomic tricks that males use, and to keep their offspring smaller and more manageable in size.  The literature clearly show that genes that are marked or methylated by fathers (paternally imprinted genes) tend to be growth promoting genes and that maternally imprinted genes tend to be growth inhibitors.  One might imagine that maternally methylated genes might have an impact on maternal care as well.

Lastly, the growth promoting/inhibiting effects of paternal/maternal genes and gene markings is now starting to be discussed somewhat in the context of autism/schizophrenia which have have been associated with synaptic under-/over-growth, respectively.

Building a brain is already tough enough – but to have to do it amidst an eons-old battle between maternal and paternal genomes.  Sheesh!  More on this to come.

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arch_fatesAm having a wonderful time reading, “Your Inner Fish” by Professor Neil Shubin – an exploration into the deep evolutionary roots of the human body.  Amazed to contemplate the embryonic structures known as the branchial arches, or gill arches – which we share with sharks! – and the role of the gcm2 gene that is expressed in these arches and controls salt balance in humans and fish.  Pharyngula has a wonderful post on this !! 

Hoping to find more deep evolutionary roots of mind and brain.
innershark

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personality1With more and more genes being directly associated with personality or as moderators of correlations between personality and brain structure/function (here, here, here, here) it was fun to try out the latest online “big-5 personality profiler“.

10 mins of self-reflective fun.  My profile displayed at left.

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