Omar Khalid
Plasticity, also known as neural plasticity or brain plasticity, is the ability of the brain to undergo changes and reorganize neural connections. The brain's plasticity allows it to adapt and function differently from its prior state. This can occur in response to learning new skills, environmental changes, injury recovery, or adapting to cognitive deficits. Theorists who emphasize plasticity believe in the potential for change and development through influential experiences, challenging the notion that behaviour is solely determined by heredity.
| Characteristics | Values |
|---|---|
| Definition | "The ability of the nervous system to change its activity in response to intrinsic or extrinsic stimuli by reorganizing its structure, functions, or connections" |
| Synonyms | Neural plasticity, brain plasticity |
| Discovery | The term 'plasticity' was first applied to behaviour in 1890 by William James in 'The Principles of Psychology'. The first person to use the term 'neural plasticity' appears to have been the Polish neuroscientist Jerzy Konorski. |
| Development | The concept of neural plasticity was developed based on Santiago Ramón y Cajal's neuron doctrine, which describes the neuron as the fundamental unit of the nervous system. |
| Occurrence | Neuroplasticity occurs throughout the lifetime, but certain types of changes are more predominant at specific ages. |
| Influencing factors | Environmental factors, genetics, sleep, physical exercise, mindfulness |
| Types | Experience-independent plasticity, experience-expectant plasticity, experience-dependent plasticity, homeostatic plasticity, adult neurogenesis, functional plasticity, structural plasticity, homologous area adaptation, cross-modal reassignment, map expansion, compensatory masquerade, synaptic plasticity, Hebbian plasticity |
| Impact | Neuroplasticity can have significant implications for healthy development, learning, memory, and recovery from brain damage. |
| Theories | Plasticity theorists emphasise the malleability of individuals and their capacity for growth and change throughout their lives. They challenge the notion that behaviour is solely determined by heredity, instead highlighting the role of environmental factors. |
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What You'll Learn
Plastic deformation
In physics and materials science, plasticity is also referred to as plastic deformation. It is the ability of a solid material to undergo permanent and irreversible deformation, a non-reversible change of shape in response to applied forces. Plastic deformation is observed in most materials, particularly metals, soils, rocks, concrete, and foams. However, the mechanisms that cause plastic deformation vary widely.
In crystalline materials, plasticity is caused by slip and twinning. Slip is a shear deformation that moves atoms through multiple interatomic distances relative to their initial positions. Twinning is plastic deformation that occurs along two planes due to a set of forces applied to a metal piece. In amorphous materials, plasticity can still occur, despite the absence of long-range order. When these materials are pulled in tension, the regions of free volume or wasted space open up, leading to a hazy appearance caused by crazing.
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Yield point
In the field of mechanical engineering, the yield point is a critical concept that defines the load at which a solid material undergoing stretching begins to flow or change shape permanently. This deformation is typically divided by the material's original cross-sectional area. The yield point, also known as the elastic limit, marks the transition from elastic behaviour to plastic behaviour in a material. When the load applied is below the yield point, the material will return to its original shape once the load is removed. However, when the load exceeds the yield point, the material undergoes permanent deformation, and further increase in stress beyond this point will lead to greater deformation and eventually fracture.
The yield point is not a constant value and can vary for different materials. Some materials may exhibit a well-defined yield point, while others may not. In cases where a distinct yield point is absent, the concept of yield strength is introduced. Yield strength represents the stress at which a material undergoes a predetermined amount of permanent deformation, commonly set at 0.2 percent. This value serves as a standard for comparison and provides a quantitative measure of a material's resistance to permanent deformation.
The presence of dislocations and lattice defects within a material's crystal lattice structure influences the yield point. As a dislocation moves through the lattice, it encounters other defects, and their stress fields interact. This interaction leads to an increase in local lattice yield stress, making it more challenging for the dislocation to move. The concentration of dislocations and their behaviour contribute to the existence of a yield point and the subsequent plastic deformation.
The yield point is an essential consideration in materials science and engineering. Understanding the yield point allows engineers to predict and manipulate a material's behaviour under stress. For example, metals typically exhibit work-hardening, where their microstructure changes as plastic deformation occurs, making them more resistant to further deformation. On the other hand, thermoplastic polymers may demonstrate work-hardening or work-softening characteristics, depending on factors such as temperature, strain rate, and the polymer's chain structure and organisation.
The yield point is a critical factor in designing structures and selecting appropriate materials. Engineers can utilise materials' knowledge of the yield point to ensure safety, durability, and optimal performance in various applications. By considering the yield point, they can determine the maximum load a material can withstand before permanent deformation occurs, guiding decisions about material choices and structural designs.
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Malleability
The term plasticity was first used in 1890 by William James in 'The Principles of Psychology', where it was described as "a structure weak enough to yield to an influence, but strong enough not to yield all at once". The term neural plasticity was perhaps first used by Polish neuroscientist Jerzy Konorski. However, the concept of plasticity was controversial in the early 1900s, when the brain was commonly viewed as a non-renewable organ. Pioneering neuroscientist Santiago Ramón y Cajal used the term neuronal plasticity to describe changes in the structure of adult brains, including degeneration and regeneration, which went against the prevailing view at the time.
The brain exhibits a higher degree of plasticity during gestation and childhood than in adulthood. However, research has shown that the brain can be altered even in adulthood, with the potential for growth and transformation throughout life. For example, learning multiple languages has been shown to restructure the brain and boost its capacity for plasticity.
Plasticity can be observed in the brain's ability to recover from injuries such as strokes or traumatic brain injuries (TBIs). These changes can be beneficial, neutral, or negative. Synaptic plasticity, for instance, can aid in learning and regaining function in the brain. Plasticity can also be observed in the development of new neurons in adult animals, such as rats, birds, and other small mammals. While there is currently no convincing evidence of new neuron development in humans, there are two proposed sites of adult neurogenesis: the olfactory bulb and the hippocampus.
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Elasticity
The behaviour of elastic materials can be understood through stress-strain diagrams. When a load is gradually increased, the behaviour is linear and elastic up to a certain point, after which the relationship between stress and strain becomes nonlinear but still elastic. This region is known as the “nonlinear elastic region”. As the load continues to increase beyond the elasticity limit, the material will undergo plastic deformation and will not return to its original shape and size when the load is removed.
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Ductility
The ductility of a metal can be improved by adding certain alloys that increase hardness and strength without compromising ductility. Additionally, ductility increases with temperature up to a certain point, after which excessive heating can weaken the material or reduce ductility.
On the other hand, some materials, such as cast iron, exhibit brittle failure instead of ductile failure. These materials are characterized by their inability to withstand plastic deformation due to strong ionic or covalent bonds that maintain atoms in a rigid, densely packed arrangement. Polymers, on the other hand, are generally considered ductile materials as they allow for plastic deformation.
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Frequently asked questions
Plasticity is the ability of the brain to change and adapt in response to external stimuli.
Neuroplasticity, also known as neural plasticity or brain plasticity, is the ability of neural networks in the brain to change through growth and reorganisation.
There are three main types of neuroplasticity that shape the developing brain: experience-independent plasticity, experience-expectant plasticity, and experience-dependent plasticity.
Neuroplasticity allows the brain to recover from injuries, adapt to cognitive deficits, and learn new skills. It also enables the brain to compensate for injury and disease by adjusting its activities in response to new situations or changes in the environment.
Plasticity theorists believe that individuals have the potential to develop new skills and behaviours through their interactions with the environment. They argue that early experiences and learning can shape the brain's plasticity and influence later behaviour, but it is not a lifelong pattern set in stone.
