The Immortal Brain (revisited)
TLDR: Speculation on immortality, given the brain as a single point of failure.Previously we discussed the human brain as a single point of failure, that is hard to replace. And if true, this places a hard limit on human lifespan. And we then did some speculations, like “What if you replaced the neurons one at a time, as each neuron failed, with computer-type prosthetics?”
Eventually, these computer-type prosthetics would accumulate, and you would end up with a brain that was part biological and part computer. Or eventually, perhaps you end up with a computer hardware-based version of your brain, but with no loss of continuity. I have been told that this is a “Ship of Theseus” type of argument, whether this person is still “you”.
Some find this disturbing, but perhaps it’s just like having a leg replaced, then a hearing aid, then a heart pacemaker installed. What if you had 1 brain cell replaced? You wouldn’t object to that surely?
And you probably would not object to those prosthetics either? So at what point would you object? When you had one brain cell replaced with an electronic replacement? Two cells? Two thousand cells?
Perhaps it is only the machine type of replacement that gives you pause?
But what if you used a biological prosthetic instead?
What if you replace a hand, grown from your own stem cells. Then a lung. Etc. You can’t just replace your whole brain, and have it still be “you”. But…what if you did this brain replacement, one cell at a time, and did this from your own stem cells.
What if you induced stem cells to create new neurons as needed, and then had them migrate to the area where a neuron was struggling, and them matched up the connections?
Could that be done?
We do know there are neural stem cells. [1] At one time, biologists believed that brain cells could not be replaced, but now we know this does happen. In fact, new neurons are sometimes led to their final position, after generation, by following along the fibers of glial cells, and following chemical cues, until they reach their final destination. This sounds like an existing factory-type system that produces new brain cells, and then moves them into position. Perhaps such a natural system could be controlled and reprogrammed? Perhaps you could use this to replace failing brain cells - to bring new neurons into position as older ones wear out. [1]
In other words, you still repair the brain, one cell at a time, but in this scenario, you replace biological neurons with young biological neurons. Only the control system is computer based, and perhaps it only exerts enough control to replace damage, as it occurs, thus allowing the single point of failure that is your brain, to live on, by replacing failing parts, one cell at a time.
Or maybe it also adds interfaces to external computer systems, as well. Or maybe it thickens the cortex to produce a larger basic intelligence, and future research provides guidance on such techniques.
Upon reflection, this “control system” could likely be biological as well, and perhaps already exists in your DNA or your Brain cells? We really don’t know yet. However, there are steps in this direction. For example, here is a reference where engineered AAV viruses were used to target individual neuron types in the brain, allowing insertion of new genes into specific cell types. Some genes for optically active proteins were inserted, allowing detailed mapping of the brain cell shapes (see figure below). [2] I could see these thousands of new AAV tools, being used to target and alter the various brain cell types in new ways. This is making gene therapy for specific brain cell types much more feasible.
This is currently being used to insert and selectively map these brain cells, but once you can start selectively altering brain cells, you can do other things as well. For example, you could use this to insert surface marker genes to aid locating them later chemically - a sort of barcode for the brain? In any case, this is a step in the direction of understanding and selectively altering individual brain cells.
So, what do you think? Possible? Ethical? And if you end up replacing every brain cell with an identical but younger cell, or a very similar cell… are you still you?
For those who want to read more, I asked an AI about this, and it basically said, “We don’t really know” in a long-winded way, but below are the details. There are some hopeful ideas here however, in that the neural stem cells, extracellular matrix, chemical cues, vasculature network, support cells, can form a sort of distributed control system, that should outlast an individual neuron cell’s lifespan, but may themselves need some repair over a much longer span of time.
References
[1] https://www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-life-and-death-neuron
[2] https://www.scientificamerican.com/article/engineered-viruses-are-transforming-neuroscience-and-treating-brain-disease/?utm_source=Live+Audience&utm_campaign=1d9f1ccbe5-nature-briefing-translational-research-20250604&utm_medium=email&utm_term=0_b27a691814-1d9f1ccbe5-49258243
ME:
This article ( https://www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-life-and-death-neuron ) claims there is a system in the human brain to create new neurons and move them into position along fibers and chemical concentrations. Where is the control system for this repair?
gemini-2.0-flash-thinking-exp-01-21:
The article from the NIH is a good basic overview of neurons and brain function. When it discusses the brain creating new neurons in adults and moving them, it's referring to the phenomenon of adult neurogenesis. However, it's important to understand that the concept of a single, centralized "control system" for this repair process is an oversimplification. Instead, the regulation of adult neurogenesis is complex and distributed, involving multiple levels of control and acting at different stages of the process.
Here's a breakdown of where the "control" resides and how it works, based on current scientific understanding:
1. Within the Neural Stem Cells (NSCs) Themselves:
Intrinsic Genetic Programming: NSCs are genetically programmed to divide, differentiate, and migrate. This intrinsic program is the foundation of neurogenesis. Genes regulate cell cycle, lineage commitment, and responsiveness to external signals.
Epigenetic Regulation: Epigenetic factors (like DNA methylation and histone modifications) influence gene expression within NSCs. These factors can be modulated by experience and environment and play a crucial role in determining the fate of NSCs.
Cell-Autonomous Mechanisms: NSCs have internal mechanisms that sense their own state and regulate their behavior. For instance, they can sense their own metabolic status, stress levels, and developmental stage.
2. The Local Microenvironment (Niche):
This is arguably the most critical level of "control." The areas where adult neurogenesis primarily occurs, the subventricular zone (SVZ) lining the lateral ventricles and the subgranular zone (SGZ) of the hippocampus, are specialized niches. These niches provide the necessary signals and support for neurogenesis.
Growth Factors and Signaling Molecules: The niche is rich in growth factors (like BDNF, VEGF, FGF2, EGF), neurotransmitters (like GABA), and other signaling molecules secreted by neighboring cells (astrocytes, microglia, ependymal cells). These molecules act as signals, telling NSCs when to divide, differentiate, and where to migrate. These are not controlled by one central system, but rather by the local needs and conditions within these specific brain regions.
Cell-Cell Interactions: NSCs interact directly with neighboring cells within the niche. Astrocytes, for example, provide structural support, nutrients, and signaling molecules crucial for NSC maintenance and differentiation. Microglia can modulate neurogenesis by releasing cytokines and clearing debris.
Extracellular Matrix (ECM): The ECM provides a physical scaffold and influences cell migration and differentiation. Chemical gradients within the ECM, as mentioned in the article (implicitly through "chemical concentrations"), guide the movement of new neurons.
Vascular System: Blood vessels are closely associated with neurogenic niches and provide essential nutrients and signaling molecules. They also act as migration routes for newborn neurons.
3. Systemic Factors and Brain Activity:
Neurogenesis is not solely regulated locally. It is also influenced by broader brain activity and systemic factors:
Neural Activity: Activity in existing neural circuits can influence neurogenesis in the hippocampus and SVZ. For example, learning and memory (hippocampus-dependent) can promote hippocampal neurogenesis. Olfactory stimulation can influence SVZ neurogenesis.
Hormones: Hormones like glucocorticoids (stress hormones), estrogen, and growth hormone can modulate neurogenesis.
Neurotransmitters: Systemic neurotransmitter levels can influence neurogenesis. For example, serotonin and dopamine can have both positive and negative effects depending on the context.
Experience and Environment: Environmental enrichment, exercise, learning, and social interactions generally promote neurogenesis. Stress, sleep deprivation, and chronic inflammation tend to suppress it.
Age: Neurogenesis declines with age in humans, suggesting an age-related decline in the efficiency of these control mechanisms.
It's Important to Understand There's No Single "Control Center":
The term "control system" can be misleading if you think of it as a single brain region or organ responsible for orchestrating neurogenesis like a central computer. Instead, think of it as a distributed and multi-layered regulatory network.
Decentralized Control: The "control" is distributed across different levels, from the intrinsic programming within NSCs to the local niche environment and systemic influences.
Context-Dependent Regulation: Neurogenesis is highly context-dependent. The specific signals and mechanisms that are dominant at any given time will depend on the location, the age of the individual, their experience, and the overall state of their brain.
Ongoing Research: The precise mechanisms and full extent of control over adult neurogenesis are still being actively researched. It's a complex and dynamic process that scientists are still working to fully understand.
In summary, while the article correctly points out the brain's capacity for adult neurogenesis, the "control system" is not a single location but a complex interplay of intrinsic cellular programs, local niche signals, and broader systemic influences. It's a beautifully orchestrated process operating at multiple levels within specific brain regions rather than a centralized command center.