Rewiring the brain: the power of neuroplasticity to adapt

By Ophelia Chan

Norman Doidge has said in his book that, “The brain is a far more open system than we ever

imagined, and nature has gone very far to help us perceive and take in the world around us.

It has given us a brain that survives in a changing world by changing itself”.

Healing. We all know that our body has the ability to repair itself as the immune system is

constantly fighting off bacteria and viruses. However, did you know that the brain can do so

too?

What is it?

Neuroplasticity is a biological process whereby the brain's activity and responses to stimuli

influence the strength or weakness of a specific synapse-to-synapse connections or even

grows new connections. The strengthening of relevant and weakening of irrelevant

connections allow the brain to response dynamically to different situations and improve its

efficiency when responding to repeated stimuli.

Furthermore, it also contributes towards the wider neural networks that are responsible for

distinct functions. For example, learning can result in various behaviours as a result of the

neural networks formed. The nervous system is able to change its activity in response to

intrinsic or extrinsic stimuli by reorganising its structure, functions or connections after

injuries, such as stroke or traumatic brain injury (TBI). This process is particularly evident in

explaining how learning and memory occur in the brain whilst implicating in some

neuropsychiatric disorders.

Significance of neuroplasticity

The brain is referred to as being ‘plastic’ as the cellular level (i.e. synaptic gaps) varies due to

creating and reinforcing neural networks. This means that the brain discards, retains and

changes information in response to new or repeated situations. Learning and memory are

interlinked, as with neuroplasticity.

There are mainly two types of neuroplasticity: structural (create connections to solidify the

learnt information); functional (constructing pathways around injured areas). The basic

mechanism of neuroplasticity includes neurogenesis, programmed cell death, and

activity‐dependent synaptic plasticity. Together with repetition of experiences learning,

memory and behaviour are shaped.

Memories are created by strengthening the connections between neurons or the growth of

new connections whereas repetition allows a group of neurons to create electrochemical

pathways that are specific to that activity. Using functional MRI, studies have shown that

experience is related to functional neural changes. A decrease in cortical activity can be

observed with increased training. This is because initially, processing requires central

resources to support but this response becomes more automatic. Hence, it results in

synaptic changes where relevant synapses are strengthened, leading to synaptic pruning –

elimination of excess synapses. Eventually, this action becomes more natural and

unconscious, becoming part of the long-term memory.

Since it is a process that involves adaptive structural and functional changes to the brain,

these changes can be either positive (the restoration of function after major injuries),

neutral or negative (having pathological consequences).

The malfunctioning of neuroplasticity is linked to major depression disorder, which can be

caused by faulty mood regulation by the brain, genetic vulnerability and stressful life events

(according to a research article published by Harvard Medical School). Some

antidepressants function by targeting the glutamatergic system and so helps to restore

cognitive function through neuroplastic effects. It works by increasing the BDNF levels –

brain-derived neurotropic factor, which is a key player in activating receptors (tyrosine

kinase receptors) that encourage synaptic plasticity. It partially corrects impairments in

structural plasticity, then facilitates re-adaptation through learning and memory

mechanisms, forming new synapse connections to combat the symptoms of depression.

Here, it reflects the power of neuroplasticity to recover from mental health disorders.

When does it take place?

This is an ongoing process in life that begins before birth and continues to adulthood. In the

first few years of life, more than 1 million new neural connections are formed every second.

Sensory connections such as basic vision and hearing are first to develop, then early

language skills and higher cognitive functions. These are important foundations of the brain

as the later more complex connections are formed upon these earlier circuits.

However, after which, connections are reduced through pruning, making the brain circuits

more efficient. For example, within one year of birth, the parts of the brain that

differentiate sound begin to specialise to the language that the baby has been exposed to.

Meanwhile, the brain starts to lose its ability to recognise sounds found in other languages.

Hence, the brain’s circuit becomes increasingly difficult to amend as time increases.

Some factors that alter the rate of neuroplasticity include childhood toxic stress. With

chronic and unrelenting stress in childhood, the neurons are damaged and so fewer

connections are formed.

Examples of neuroplasticity in a clinical context:

Activity-dependent neuroplasticity occurs throughout life, affecting the central nervous

system from cortex to spinal cord. It plays a vital role when trauma or disease such as stroke

impairs the motor function. Although the traditional rehabilitation predominantly focuses

on the intensive practice of the impaired motor skills in order to alleviate the consequences

of impairments, significant disabilities often remain. The use of neuroplasticity in

rehabilitation helps to address the underlying causes, acknowledging that it is impaired in

the stroke-affected hemisphere. The therapies, including the development of new neuronal

interconnections, acquiring new functions and compensation for impairing, are often

tailored to each patient to maximise the effect.

Through constraint-induced movement training (CIMT) and virtual-reality based training,

the brain’s plasticity is stimulated by the formation of new neural pathways and enhancing

connectivity between damaged and healthy brain regions. Other techniques, such as

transcranial direct current stimulation (tDCS), enrich cognitive functions via fostering

neuroplastic changes in the relevant brain networks. These changes help to improve

attention, memory and executive functions of the brain. Hence, neuroplasticity acts as a

foundation to rehabilitation nowadays to restore the lost functions.

However, not all forms of neutral plasticity result in pure motor recovery. The possibility of

maladaptive neuroplasticity can weaken motor function and limits recovery due to hyper

reliance on nonparetic side, proximal paretic side, or trunk movement to perform daily

tasks. Yet, this would prevent the affected limb from regaining daily activities. To prevent

this, bilateral movement training utilises both limbs to avoid exacerbating the maladaptive

plasticity.

Conclusion

Neuroplasticity is an important driving force in the human body, contributing from learning

and memory to recovery. It provides a fundamental explanation on how our brain works

and how connections are formed, reflecting the complexity in our brain. The ability of

reorganising connections illustrates the potential of humans to heal and grow, especially

considering rehabilitation. It is one of the most fascinating things about the brain – ability to

adapt and grow.