For a long time, scientists believed that no part of the human brain could regenerate. What have we learned since our technology improved? This article explores whether new research offers hope for brain injury and goes over various factors that may either shrink or grow the brain.
“Once again, a flurry of new research is suggesting neurogenesis may be more common than previously thought.”
Comb jellyfish can regrow their rudimentary brains [ 1 ]. But in most mammals (including humans), neurogenesis largely ceases in adulthood. It has been observed in a few places, including the hippocampus, a relatively ancient part of the brain many animals share. In comparison, only humans have a developed neocortex [ 2 ].
The party line in neuroscience has been observational. First, we believed no part of the human brain could regenerate. And we’ve added exceptions as our technology has improved.
Who’s to say we won’t find more exceptions?
Nothing in neuroscience is absolute because the brain is still a black box.
When we sleep, the hippocampus reactivates and connects with various brain regions, including the cortex – the brain’s “crust” or outer layer – all the while emitting delta brainwaves. Scientists think that this may explain, in part, how our memories stabilize while we’re asleep. A study published in Science in 2019 suggests just this [ 3 ].
One part of the cortex is called the occipital cortex is smaller than a speck of dust and it revealed cell types we had never seen before. Nor do we know exactly how memories are stored, though various scientific theories have been proposed [ 3 ].
An older but widely accepted working theory stands on long-term potentiation ( LTP ): neurons that fire together wire together. But that’s more a description than an explanation. We don’t know what induces LTP. When scientists temporarily block certain kinases to prevent neuronal connection (reconsolidation), it often reverts back [ 4 ].
So, researchers emphasize that the brain is more than its connectome (set of neuronal connections). But exactly what–that’s a focus of ongoing research.
Does new research give hope to people struggling with brain injury? Perhaps, but it’s still too early to say. Research findings are mostly limited to animal experiments.
Further studies need to clarify the relevance of neurogenesis after traumatic brain injury in humans. Until then, people with brain injury shouldn’t keep their hopes too high.
For example, induction of adult neurogenesis has been observed in normally non-neurogenic regions of the brain in response to injury and death of neurons – in animals [ 5 ].
Scientists say that upon injury in the non-neurogenic regions, there have been reports of local precursor cells generating new neurons and migrating from the neurogenic to the non-neurogenic region [ 5 ].
This has been suggested to occur in the neocortex [ 6 ], striatum, and hippocampus as a result of ischemic brain injury in rats [ 7 , 8 ].
Neurons that were being generated in the subventricular zone were able to migrate to the injured striatum and differentiate into mature neurons in these animal experiments. Scientists have hypothesized that these migrated and matured cells may help repair neurological deficits, but this remains unproven [ 9 ].
Another study suggested that mice, in response to cortical lesions, may produce new neurons in the ventricular areas. The new neurons then migrated and populated to the cortical areas [ 10 ].
The authors mention that the migration and differentiation of neurons to nonneurogenic regions suggests the brain might have much more potent regenerative capabilities than previously imagined. How and whether this is relevant in humans is still highly uncertain [ 10 ].
Further studies need to clarify the relevance of neurogenesis after traumatic brain injury in humans.
This post explores associations between neurogenesis and aspects of health.
The majority of studies we discuss deal with associations only, which means that a cause-and-effect relationship hasn’t been established.
For example, just because memory and learning have been linked with neurogenesis doesn’t mean that increasing neurogenesis will improve these processes, unless clinical data about a direct link are available. However, data are lacking to make such claims.
Additionally, even if a study did find that neurogenesis contributes to brain recovery after TBI, neurogenesis is unlikely to be the only contributing factor. Complex processes like post-stroke or post-TBI recovery always involve multiple possible factors – including symptom severity, therapeutic modalities, brain chemistry, environment, health status, and genetics – that may vary from one person to another.
If your goal is to increase neurogenesis to improve your neurological issues – including those of traumatic brain injury – it’s important to talk to your doctor, especially your symptoms are significantly impacting your daily life.
Your doctor should diagnose and treat the condition causing your symptoms.
The existing evidence does not suggest that reduced neurogenesis causes any disease.Additionally, changes in brain chemistry are not something that people can change on their own with the approaches listed below. Instead, the factors listed here are meant to reduce daily stress and support overall mental health and well-being. Therefore, you may try the additional strategies listed below if you and your doctor determine that they could be appropriate . None of these strategies should ever be done in place of what your doctor recommends or prescribes.We’re providing a summary of the existing research below, which should guide further investigational efforts.The studies listed in the sections below were mostly done in animals and should not be interpreted as supportive of health benefits in humans. Factors to Avoid that May “Shrink” the Brain It’s always a good idea to avoid unhealthy habits – such as smoking, fast food, overeating, being under a lot of stress, and drinking too much – that can bring your body and mind out of balance. Look to get regular exercise , enough nutrients, sleep, and keep a healthy circadian rhythm . Alcohol Avoid in excess. Drinking 3-4 drinks a day (rather, having an alcohol percentage of .08%) could reduce the number of cells produced in the hippocampus by 40% in one human study [ 11 ]. Stress […]