Processes like up-regulation and down-regulation (see "Agonist" and "Antagonist") are evidence of the plasticity of receptors in the brain (i.e., the fact that each subtype of neurotransmitter receptor can vary in number and distribution in the brain). Receptor plasticity occurs during development and throughout adulthood. Therefore, a neuron's sensitivity to different transmitters can vary throughout the lifespan. 

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After the transmitters have been released due to exocytosis, they bind to proteins called receptor molecules (or receptors). This binding is similar to how a key fits into a lock. If a transmitter, known as a ligand during this process, is not the correct shape, it will not be able to bind with a receptor. If a transmitter is the correct shape, it will be able to bind with the receptor at ligand-binding sites. Each transmitter is able to bind to a group of different receptors.

Receptor Molecules

Plasticity is how the brain is able to learn and adapt to environments. It exists throughout a person's lifetime, though it tends to be more active in early development when the brain is still forming. Plasticity is one of the key concepts within behavioral neuroscience that affects nearly all systems of the brain and brain functions.

Plasticity

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

A molecule that acts like a transmitter and binds to a receptor, causing a response similar to one caused by a transmitter. These molecules are usually drugs.

Agonist

A molecule that blocks a transmitter from binding with a receptor. These molecules are usually drugs.

Antagonist

A ligand is a substance that binds to receptor molecules, like agonists and antagonists when they mimic neurotransmitters. Agonists and antagonists are usually drugs; because they originate outside of the body, they are referred to as exogenous ligands. If an agonist or antagonist were to originate inside of the body, however, they would be referred to as endogenous ligands. 

Agonist and Antagonist Characterization 

Receptor Plasticity

Plasticity of the sensory cortex refers to a characteristic of the cortex, that the cortical maps can change with experience. This was demonstrated in an experiment by Merzenich and Jenkins (1993), where they surgically removed the middle finger of the monkey, then found later that the region of cortex that responded to each remaining, adjacent finger expanded.

Plasticity of the Sensory Cortex

The nervous system's capacity to change and adapt is known as neuroplasticity. This adaptation can be triggered by various factors, such as personal experiences, normal developmental stages, or in response to damage or injury. The underlying mechanisms of neuroplasticity include the formation of new synapses, the elimination of unused ones, modifications in glial cells, and even the generation of new neurons. While the brain's plasticity is at its peak during early life, it retains a significant capacity for change and reorganization throughout adulthood.

Neuroplasticity

Infants have diverse hearing capbilities in early life. If that hearing ability isn't used, for example if they have damage or deformity in their ears, their ability to distinguish or interpret sounds disappears. 

Musicians show higher sensitivity and activation to musical notes, with bigger differences in brain imaging if the musician was trained from an early age.

Plasticity, auditory perception and auditory pathways

Studies utilizing Art Therapy  as part of a treatment for brain diseases or injuries can lead to promotion in brain plasticity

Mindfulness Based Art Therapy for Individuals with Traumatic Brain Injuries and other Brain Diseases

One example of culture’s influence on brain function involves the use of the abacus in East Asian cultures. Giyoo Hatano, a Japanese developmental psychologist, hypothesized that abacus users relied on a mental representation of an abacus to solve arithmetic problems. In an fMRI study, Japanese participants, all of whom were familiar with the abacus, demonstrated increased activation in the parietal lobe. The magnitude of activation was positively correlated with the difficulty of the arithmetic problem. By contrast, individuals with no abacus experience tend to engage brain regions associated with linguistic processing when tasked with arithmetic problems (i.e. Broca’s area, Wernicke’s area). These findings support Hatano’s theory and illustrate the influence of culture on neuroplasticity.

Cultural neuroscience and arithmetic processing

A significant example of cultural neuroplasticity involves the famous “taxi driver” study by Maguire et al. (2000). They used structural MRI to compare the brains of experienced London taxi drivers to controls who did not drive taxis. Taxi drivers had larger posterior hippocampi, but smaller anterior hippocampi, compared to controls. Posterior and anterior hippocampal volume was positively and negatively correlated, respectively, with time spent as a licensed taxi driver. These findings support the hypotheses that a) the posterior hippocampus is involved in spatial/navigational memory and b) environmental stimuli can essentially “reshape” the brain.

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