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Neuroplasticity

Q: How does neuroplasticity work in the human brain?

Krishna: Neuroplasticity is the brain's lifelong ability to reorganize its structure, functions, and connections in response to learning, experience, or injury. It works by strengthening active neural pathways (synaptic plasticity) and forming new ones while eliminating unused connections, driven by molecular changes like increased brain-derived neurotrophic factor (BDNF).
The adult brain retains the capacity for neuroplasticity, allowing structural and functional changes in response to experience, learning, and injury. This adaptability is shaped by factors such as practice, physical exercise, sleep, and stress, but operates within biological limits. Neuroplasticity is experience-dependent, value-neutral, and persists throughout life, though meaningful change requires sustained effort.
Neuroplasticity involves changes in how existing brain cells communicate with one another.

When you learn a new skill, specific synapses, the tiny junctions where neurons pass signals to each other, become stronger and more efficient. Neural networks, which are groups of neurons that work together, become better organized. Communication between brain regions involved in that skill improves.

At the cellular level, plasticity involves changes in synaptic structure, the release of chemical messengers called neurotransmitters, and the sensitivity of receptors that receive those signals. So, it changes how neurons communicate with each other.

In a few areas of the adult brain, particularly the hippocampus, which plays a key role in memory, limited adult neurogenesis, the creation of new neurons, also occurs. Although influenced by factors such as stress, sleep and physical activity, its significance in humans is still debated.

Image source: Adobe stock

Key Mechanisms of Neuroplasticity (3)
Synaptic Plasticity: The fundamental mechanism where connections between neurons (synapses) strengthen or weaken based on activity levels (long-term potentiation or depression).
Structural Changes: The brain physically changes by sprouting new synaptic connections, remodelling existing ones, or growing new neurons (neurogenesis), particularly in the hippocampus.
Functional Reorganization: The brain assigns functions to new areas after damage or consistently new experiences, shifting neural networks to adapt.

Factors Driving Neuroplasticity (4)
Learning and Experience: Acquiring new skills or storing memories physically alters neural circuitry.
Repetition: Consistently repeating an action or thought strengthens the neural pathways involved, making the change permanent.
Exercise & Environment: Physical activity boosts BDNF, a protein that supports neuron health, while stimulating environments encourage connection growth.
Focus and Intent: Focused attention on a task enhances the speed and extent of brain reorganization.

Types of Plasticity
Functional Plasticity: The brain's ability to move functions from a damaged area to undamaged areas.
Structural Plasticity: The brain's ability to actually change its physical structure through learning.

Neuroplasticity allows the brain to remain flexible, adapting to new information and recovering from injuries, though its rate tends to slow with age.

What strengthens and weakens this plasticity? (2)

1. Practice and challenge are essential.
Repeatedly engaging in tasks that stretch your abilities leads to changes in both brain activity and brain structure, even in older adults.

2. Physical exercise is one of the most powerful enhancers of plasticity.
Aerobic activity increases levels of brain-derived neurotrophic factor, or BDNF, which supports neuron survival and strengthens synaptic connections. Regular exercise is consistently linked to better learning, memory and overall brain health.

3. Sleep plays a critical role in consolidating brain changes.
During deep sleep, important neural connections are strengthened while less useful ones are weakened, supporting learning and emotional regulation, as shown in neuroscience research.
4. Chronic stress can seriously impair plasticity.
Long-term exposure to stress hormones is associated with reduced complexity of neural connections in memory-related brain regions and heightened sensitivity in threat-processing systems, undermining learning and flexibility.

However, some neuroscientists say that brains can't actually 'rewire' themselves (1).

Writing in eLife, two neuroscientists – Tamar Makin and John Krakauer – argue that the most influential experiments in this field don't conclusively show that the brain can functionally reorganize itself.

The idea that our brain has an amazing ability to rewire and reorganize itself is an appealing one. It gives us hope and fascination, especially when we hear extraordinary stories. This idea goes beyond simple adaptation, or plasticity – it implies a wholesale repurposing of brain regions. But while these stories may well be true, the explanation of what is happening is, in fact, wrong, they argue. In their view, none of the key studies meet the strictest definition for cognitive reorganization, where a part of the brain usually dedicated to one type of computation becomes capable of an entirely different type of cognition, marked by a change in function or behaviour.

In their experiments, the neural inputs from the ferrets' eyes were surgically connected to the auditory cortex of the brain instead of the visual cortex. Despite this mix-up, the ferrets had some vision in a follow-up study. The auditory neurons had reorganized themselves to perform a new function.

"But is this true reorganization…?" the scientists ask. The type of processing done in the visual cortex might be just like that done by the auditory cortex, meaning that this surgical rewiring isn't really challenging the brain to change its functions.

If the same input were to be delivered to a part of the brain responsible for completely different processes, such as the prefrontal cortex, the results might be far less impressive.

When a study participant miraculously recovers cognitive functions that were thought to be lost due to injury or impairment, it's likely that the brain is adding computational capacity by leaning on neural connections or functions that previously existed but were very quiet or under-utilized, the authors argue.
If it looks like part of the brain is doing something it never did before, that could just be an illusion produced by the fact that we didn't know the brain had that additional capability in the first place, the authors propose.

The researchers also doubt that the brain 'takes over' neurons that aren't being used and 'rewires' them to perform other functions.

For example, children with congenital cataracts (who are born blind) can have their sight immediately restored following surgery.

"If the visual cortex is re-appropriated to support new functions, then it follows that restoration of visual input will be futile (or will at least require substantial reversal of reorganization)," the authors write.
But this is not the case. Not only are the children immediately able to perceive some visual information, they show susceptibility to visual illusions.

While the brain is more interconnected and "fuzzy" than we give it credit for, Makin and Krakauer argue different parts of the brain are destined to perform certain functions, and it's not possible to deviate from this underlying "architecture" or "blueprint", even in early development.

"So many times, the brain's ability to rewire has been described as 'miraculous' – but we're scientists, we don't believe in magic," they say.

"These amazing behaviours that we see are rooted in hard work, repetition and training, not the magical reassignment of the brain's resources." they conclude.

It is my responsibility to put all points of view before you.
Now you can analyse them and come to your own conclusion.

Footnotes:

1. https://elifesciences.org/articles/84716

2. https://theconversation.com/scientists-once-thought-the-brain-could...

3. https://www.ncbi.nlm.nih.gov/books/NBK557811/#:~:text=Neuroplastici....

4. https://www.physio-pedia.com/Neuroplasticity#:~:text=The%20ability%....

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