The Adult Brain Does Grow New Neurons After All, Study Says
scientificamerican.com
scientificamerican.com
The case in point is the sciatic nerve is massive, and prone to constant stresses and strains, yet supposedly never regenerates.
Evolution doesn't try to head towards any global optima, so it is quite believable that certain things just don't work a certain way even if they sound 'obvious' to rational beings.
If one even exists. I don't think you could actually say a global optima exists in a lot of cases. Since there are a lot of compounding factors and the functions aren't required to be continuous.
I had some nerve damage a while back and went to a neurologist. He did an EMG test (https://en.wikipedia.org/wiki/Electromyography) and confirmed the nerve was damaged. He used electrodes to show that it did not conduct electricity like it was supposed to, nor did it conduct electricity like the corresponding one on the other side of my body. (Somewhere, I have a printout showing voltage and latency numbers.)
He then told me that if the damage is not too great, nerves can repair themselves, that the repair proceeds outward from the brain toward the periphery of the body, and that it happens at a rate of roughly 1 millimeter per day. So, he said, my problem would probably resolve itself but it would be a long time, think 6 months or a year, maybe even longer to finally be back to 100%.
And it basically happened just like he said it would. 6 months later, it was a lot better, and it continued to gradually improve from there.
He also mentioned that using the affected muscles would help encourage healing. I think he meant the nerve itself would heal faster this way, not just that it would help reverse muscle atrophy.
He said that if the outer layer is intact, the inner layer can be repaired. I'm not sure if that means more nerve fibers form or that existing nerve fibers are repaired but that the repair takes place incrementally instead of all at once. Intuitively it seems to make sense that a new fiber is growing, but I'm wary of speculating based on what seems to make sense to me.
We do not want nerves to regenerate in most cases because it could cause even worse results. If you start regrowing a batch of nerve, you have a chance of growing out nerves that transfer pain signals into places you don't want them to be, which could cause persistent neuropathic pain (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5290455/).
1) looking at people before and after 1 month of regular exercise.
2) healing of heart after large and invasive surgery.
Sciatica doesn't generally show up until people are in their 40s-50s. This is long after childbearing years for most people. At that point your sciatic nerve has done its job and gotten you across the finish line. What happens next is less important.
Isn't that given modern nutrition, hygiene, water access, tooth cleaning etc?
The other commenter said that people that survived childhood during these times usually were expected to live around 54 years.
Of course, old people can learn new things so I always thought the "neurons don't grow" thing was silly (although I guess it's possible that we have a set number of neurons and it's just our synapses that keep growing).
Those people who loose saliva production end up loosing teeth as well, because the enamel disappears.
I have no idea about corneas.
Apparently whatever mutation happened in the past in this regard was not good enough / human still didn't survive, or it didn't happen yet. It might be funny if we discover some remote tribe actually has this regenerative mutation.
I think its question of time (maybe very long time), look at our unique ability to process lactose in adult age.
This is definitely wrong. Individuals (e.g. grandparents or just random society members) can influence survival rates of other society members.
Some species(e.g. ants) even have sterile members that definitely exert evolutionary pressure.
Sterile ants do not exert evolutionary pressure unless they would attack weak queens before they are ready to reproduce. Evolutionary pressure (by scientific definition) is caused by things that reduce reproductive success in individuals or parts of population. Like a mutation that reduces fertility. Having the old individuals around might help relieve some of the pressure by infinitesimal amounts (helping raise offsprings) but that's about it. They cannot influence the outcome of a "defective" gene so they do not really drive evolution in any meaningful way.
Take this example. A genetic disorder that causes blindness soon after birth basically eliminates the individual from the population and the genetic defect along with it. Thus evolutionary pressure (genetic defect before the reproductive age) achieves the selection.
A genetic disorder that causes blindness at old age, any time after the next generation was raised, might also eliminate the individual but this doesn't matter as much. The gene already got passed along to the next generation(s). As long as it manifests only after reproduction then it does not reduce reproductive success, so exerts no pressure.
Or perhaps you want to take something like male impotence as an example. If humans were expected to bear offspring only in our 70s I'm certain Viagra wouldn't be a thing. Only the males that are still able to perform at that age pass along their genes, to the point where the males that can't are the exception.
I hope you can appreciate the difference in magnitude (many orders) between directly applying evolutionary pressure by removing the individual from the gene pool before the gene can be transmitted, and indirect evolutionary pressure via reduced support in society (which could conceivably affect reproductive success). For one, it stands to reason that solitary species or ones that do not form real societies would be completely unaffected by this indirect evolutionary pressure.
Doesn't seem that expensive
Do not ever let anyone tell you that you do not matter.
Do not ever let anyone tell you that you can't do something.
Be awesome, be like Rita.
Thanks!
Most of the activty of the dentate gyrus birthing new neurons is in during early development and when a baby. During these times there's a stream neurons from the sub-granular zone (beneath the granular cells in the dentate gyrus in the hippocampus). The perceptions of the external environment and the internal physiological state modulate the rate of survival of these new neurons.
It's kind of open in the sub-granular zone and the stem cells are able to move freely and assume multiple intermediate cell architectures before finally becoming dentate granule neurons that migrate to and integrate with the existing hippocampal circuitry along the other parts of the two nesting C shapes. They're even somewhat glia-like during part of this intermediate development. It's a complex process that's easy to interrupt. Most of the cells die and do not become integrated into the hippocampus.
So, to get to and restate the question: how do neuroactive chemicals and things like ECT potentially alter the rate of new sub-granular zone stem cells? If the current development state of the cell has receptors or the glia around it are effected by chemicals that bind to those receptors it's easy to see how things could be thrown off.
It is not necessarily a good thing to increase the rate of cell survival of new neurons in the adult. The rate of new neurons has important effects on the ability of the neuronal circuits in the rest of the hippocampus (involving CA1, CA3, etc) to do the types of memory encoding tasks researchers call pattern separation and pattern completion. So while there are indeed chemical and electrophysiological ways to increase the the survival rate of new neurons there should be reasons to believe the balance needed to be adjusted up.
Just as a throwaway, THC is one of the chemical compounds found to increase new dentate granual neuron survival and integration.
Many thanks.
1) It seems to mostly be focused on neurogenesis in the hippocampus, not necessarily elsewhere in the brain.
2) It seems the key item these researchers hit on to invalidate the previous study was the method of preservation for brain tissue in deceased individuals, not study of tissue in living humans. I think new studies in that latter area in the future will put the matter to rest.
For an up to date review/link-set of neurogenesis in humans as compared to other mammals check out the summary write-up over at http://blogs.discovermagazine.com/neuroskeptic/2019/01/30/ne... which makes the case that human neurogenesis isn't found in adulthood because of relative lifespan differences.
Sides during first week or so: increase in blood pressure, slightly higher heart rate, decreased appetite, teeth grinding, could feel a "crash" in late afternoon, some difficulty sleeping ~1030pm
After the second week: unsure about blood pressure, body has adjusted some and I believe it to be more normal now. Heart rate still increases slightly, appetite still suppressed throughout the day (I eat a banana early and try and get ~20g protein by noon), not getting those "Crashes" that i had first week (or if anything, not so bad), I can sleep now and I am aware of the teeth grind thing but that has definately decreased.
Overall I think body adjusted to this well, may consider 40mg instead of 30mg. Don't think i'll go over 40mg personally. The focus benefit throughout the day really helps me with my productivity
Oh I should note I kept drinking coffee during all of this. When I first started (with those sides) I went from 4 to 2 cups a day. Now I'm back at around 3ish cups a day.
Idk if that helps, overall I feel great
These medications are often strong enough and have enough addiction potential that even people _with_ ADHD end up abusing them. Be careful.
A general question I've been wondering about -- ever since it seemed half of some CS departments' undergrads were on meds, at the start of the dotcom bubble -- is what are the costs to discretionary use of meds as performance enhancers, by people who don't have abnormal brain situations to start with?
I'd like to know in general, and it might be important to public health or societal direction. But this doesn't seem the kind of thing that a non-researcher/doctor can ask individuals about, since it can be extremely personal.
And you have to keep in mind with any sort of pharmaceutical there's a major bias in research. There's billions of dollars to be made by showing that things are effective and safe. There's much less of an incentive to to show that things are ineffective or unsafe. Even for those who are genuinely completely altruistically motivated, there's far more interesting research to pursue and topics that don't come with lovely consequences such as making influential enemies within the industry you're dependent upon grants for.
Consider things like cigarettes, leaded fuel, or whatever else. There's invariably decades of "science" proving it completely harmless before some crisis points triggers a 'reevaluation'. And for things intended to interact with your cognitive abilities, if there are negative effects it's entirely possible we might never reach that crisis point as any negatives effects may likely manifest in ways that are rather less apparent than the effects of e.g. lead or tobacco consumption.
The two alternative conclusions presented are skepticism of any new neurons in the target area after toddlerhood and the conclusion that neuron development seems to be lifelong, though reduced in and with the progress of Alzheimer's.
That's why I mentioned you should always be wary of anything that purports to increase neurogenesis, as even if it does, that can lead to significantly increased probabilities of cancer development. And brain cancer specifically, is one of if not the most difficult types of cancer to treat, with extremely limited survival outlooks.
I was always curious about it, and this piece shed some light over it: as death is a process where all cells undergo chemical transformation, all you add to stop the process and preserve some state also induces changes. So, depending on how you preserve something, you will also lose information and won't be able to further study something.
Interesting how we have a long road regarding preservation of bodies and how much we still can improve about it.
The best way to reconstitute neurons is to eat plenty of raw fish, specifically saltwater fish.
[1] https://www.nature.com/articles/nature25975 "Human hippocampal neurogenesis drops sharply in children to undetectable levels in adults"
still, "a growing body of reseach" vs "a nature paper last year"?
This seems to explain why that situation happened, nothing more.