The human brain is composed of billions of cells called neurons, which are linked to one another by neural pathways.
It used to be thought that the formation of new neurons cease shortly after birth. However, the current knowledge is that the brain possesses the capacity to reorganise pathways, create new ones and, in some instances, even create new neurons.
Brain plasticity, or neuroplasticity, refers to the reorganisation of its neural pathways by experience.
Permanent functional changes occur when new knowledge is learnt or committed to memory. These changes in the neural connections are akin to the changes during photography.
When a photograph is taken, the camera’s film changes to record the image of the subject to retain the image. Similarly, in order for something to be retained in memory, there are changes in the brain that represent the new knowledge or information.
There is rapid brain growth in the first few years of every child. As each neuron matures, it develops multiple branches, i.e. axons that send out information and dendrites that receive information. The junctions where each neuron connects to another neuron is called a synapse.
Each brain neuron in the newborn has an estimated 2,500 synapses. This increases to about 15,000 synapses by two to three years of age, which is about twice the number of the average adult brain neuron.
As a person gains new experiences, some synapses are kept and strengthened while others are eliminated. Synapses that are activated more often are preserved.
Neurons that do not receive or transmit information gets damaged and die through apoptosis, a process termed synaptic pruning.
By developing new connections and getting rid of weak ones, the brain adapts to the ever changing environment.
There are two features of brain development that are important to the understanding of how experiences can change its organisation.
Firstly, there are stem cells which remain active throughout life and can produce cells that can migrate into the brain (white or gray matter), even in adulthood. These cells remain quiescent for extended periods but can be activated to produce neurons.
The role of these cells is poorly understood at present, but they are probably the basis of one form of postnatal neuron formation, especially after injury.
Secondly, the branches of the neurons possess amazing plasticity when responding to experience and can form synapses in hours and even minutes after some experiences.
Whilst the vast majority of the brain’s cells are formed during foetal development, there are certain areas of the brain that continue to create new cells, a process termed neurogenesis, during infancy.
The hippocampus, which is a region of the brain associated with memories, learning and emotions, has been found to continue to create new cells into old age.
Features of plasticity
There are several features of neuroplasticity, which occur under two situations. Firstly, the immature brain processes sensory information in childhood through adulthood, i.e. learning and memory. Secondly, it occurs when there is a need to compensate for lost function and/or maximize remaining function following brain injury.
It includes many different processes taking place throughout life. It does not consist of a single change, but rather several processes occurring throughout an individual’s lifetime involving neurons, glia and vascular cells.
The neurons change independently of each other, and sometimes in opposite directions.
Neuroplasticity is influenced by age. Although it occurs throughout life, different types of plasticity are more prevalent during certain phases of a person’s life and are less prevalent during other phases.
It is generally presumed that the developing brain will be more responsive to experiences than the adult or ageing brain.
However, there are qualitatively different changes in the brain in response to what appears to be the same experience at different ages.
The environment influences plasticity considerably. In addition to each individual’s inherited genes, the brain is moulded by the characteristics of his/her particular environment and by his/her actions.
Each individual’s environment is unique. As humans have a lifetime of experiences throughout life until death, these experiences interact.
Whilst there is a tendency to think of plastic changes in response to experiences as widespread, this is rarely the case.
For example, while psychoactive drugs may have widespread acute effects on neurons, the chronic plastic changes are focal and largely confined.
Not all plastic changes are permanent and they may change markedly over time.
And, not all plastic changes are for the better. For example, although neuroplasticity support improved motor and cognitive functions, it can interfere with behaviour too, e.g. drug-induced changes in response to psychomotor stimulants.
Types of plasticity
There are two types of neuroplasticity – functional plasticity, which is the brain’s ability to move functions from a damaged area to other undamaged areas; and structural plasticity, which is the brain’s ability to actually change its physical structure as a result of learning.
It was believed that the brain’s networks become fixed with increasing age.
However, research has revealed that the brain never stops changing and adjusting.
Learning is the ability to acquire new knowledge or skills from instruction or experience.
According to some research, the changes in the brain (with learning) are changes in the internal structure of neurons, especially in the area of synapses, and an increase in the number of synapses between neurons.
Newly learned data are stored in short-term memory, which is the temporary ability to recall limited information.
After some time, the data is moved to more permanent, long-term memory, which is a consequence of structural or biochemical changes in the brain.
Subsequent to brain injury, the plastic changes maximise function despite the damaged brain.
In studies of rats in which one area of the brain was damaged, the surrounding cells of the damaged area underwent functional and structural changes that permitted them to take on the functions of the damaged cells.
Although this phenomenon has not been widely studied in humans, data indicates that similar changes occur in human brains following injury.
The brain is one of the last frontiers of medical science. Better understanding of the interaction between genetic and experiential factors that influence brain plasticity will provide insight into both normal and abnormal development.
To promote mental literacy and understanding of mind power, the Malaysia Mental Literacy Movement, Universiti Tunku Abdul Rahman and Tunku Abdul Rahman University College will be organising the “Festival of the Mind” on Aug 8-9 from 10am-5pm at Universiti Tunku Abdul Rahman, Jalan Universiti, Bandar Barat, Kampar, Perak.
For more information, visit www.facebook.com/malaysiamentalliteracymovement.
Dr Milton Lum is a member of the board of Medical Defence Malaysia. For more information, e-mail firstname.lastname@example.org. The information provided is for educational and communication purposes only and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader’s own medical care. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.