The word neuroplasticity breaks down as neuro for “neuron”, the nerve cells in our brain and nervous system. Plastic is for “changeable, malleable, modifiable.” Neuroplasticity refers to the brain’s ability to change in response to experience. The brain does this by strengthening the connections between some nerve cells while weakening the connections between others. This is how the brain stores memories, learns, unlearns and adapts to a changing environment. Two principles govern brain plasticity:
First, ‘nerve cells that fire together wire together’ means that two events can become strongly connected if they occur at the same time. For example, a toddler touching a hot stove for the first time activates both nerve cells that process the visuals of a stove-top and nerve cells that experience burning pain. These two previously unconnected events become permanently wired together in the brain via nerve cell branches. Seeing sexually stimulating images for the first time will cause a fixed memory in a child’s brain and start to mould his and her sexual arousal template.
Second, ‘use it or lose it’ is most apt during certain windows of development. It is why it is much easier to learn particular skills or behaviours at certain ages. We don’t see Olympic gymnasts starting at age 12 or concert musicians beginning at age 25. Not unlike the toddler, a porn-watching teen connects external objects with his innate circuit for sexual excitement. Adolescence is the time to learn about sexuality. The nerve cells involved in surfing the internet and clicking from scene to scene fire together with those for sexual excitement and pleasure. His or her limbic system is just doing its job: touching stove = pain; surfing porn sites = pleasure. Ceasing an activity helps weaken the associations.
Our brain is part of an extended nervous system. It consists of the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and the spinal cord. It is essentially the control centre receiving all the sensory information from throughout the body that it can then decode to activate the relevant responses- approach, withdraw or ‘as you are’. In regard to specific responses it sends signals via the PNS. So an erotic image, smell, touch, taste or word association will fire up the sexual arousal pathways from the brain to the genitals via the nervous system in a fraction of a second.
The brain has around 86 billion nerve cells or neurons. The neuron or nerve cell has a cell body that contains the nucleus with DNA material. Importantly, it also contains proteins that change shape as they adapt to the input of information from elsewhere.
Neurons differ from other cells in the body because:
1. Neurons have specialised cell parts called dendrites and axons. Dendrites bring electrical signals to the cell body and axons take information away from the cell body.
2. Neurons communicate with each other through an electrochemical process.
3. Neurons contain some specialized structures (for example, synapses) and chemicals (for example, neurotransmitters). See below.
Neurons are the messenger cells in the nervous system. Their function is to transmit messages from one part of the body to another. They constitute about 50% of the cells in the brain. The other approximately 50% are glial cells. These are non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons in the central nervous system and peripheral nervous system. Glial cells do the maintenance such as cleaning up dead cells and repairing others.
The neurons form what we think of as ‘grey matter’. When the axon, which can be very long or short, is insulated by a white fatty substance (myelin), this allows the signals to pass along more rapidly. This white coating or myelination, is what is often referred to as ‘white matter’. Dendrites which receive information do not get myelinated. The adolescent brain integrates brain regions and pathways. It also speeds up connectivity through myelination.
Electrical and chemical signals
Our neurons carry messages in the form of electrical signals called nerve impulses or action potentials. To create a nerve impulse, our neurons have to be excited enough, because of a thought or an experience, to send a wave firing down the length of the cell to excite or inhibit the neurotransmitters at the end point of the axon. Stimuli such as light, images, sound or pressure all excite our sensory neurons.
Information can flow from one neuron to another neuron across a synapse or gap. Neurons don’t actually touch each other, the synapse is a small gap separating neurons. Neurons each have anywhere between 1,000 and 10,000 connections or ‘synapses’ with other neurons. A memory will be created with mix of neurons conveying smell, sight, sounds and touch firing together.
When a nerve impulse or action potential moves along and reaches the end of the axon at its terminal, it triggers a different set of processes. At the terminal there are small vesicles (sacs) filled with a variety of neurochemicals that cause different types of responses to take place. Different signals activate the vesicles containing different neurotransmitters. These vesicles move to the very edge of the terminal and release their content into the synapse. It moves from this neuron across the junction or synapse and excites or inhibits the next neuron.
If there is a decline in either the amount of neurochemical (e.g. dopamine) or number of receptors, the message becomes harder to pass on. People with Parkinson’s Disease have poor dopamine signalling capacity. Higher levels of neurochemicals or receptors translate into a stronger message or memory pathway. When a porn user binges on very emotionally stimulating material, those pathways become active and strengthened. The electrical current passes down them very easily. When a person quits a habit, it takes some effort to avoid that path of least resistance and easy flow.
Neuromodulation is the physiological process by which a given neuron uses one or more chemicals to regulate diverse populations of neurons. This is in contrast to classical synaptic transmission, in which one presynaptic neuron directly influences a single postsynaptic partner, one-to-one transmission of information. Neuromodulators secreted by a small group of neurons diffuse through large areas of the nervous system, affecting multiple neurons. Major neuromodulators in the central nervous system include dopamine, serotonin, acetylcholine, histamine, and norepinephrine/noradrenaline.
Neuromodulation can be thought of as a neurotransmitter that is not reabsorbed by the pre-synaptic neuron or broken down into a metabolite. Such neuromodulators end up spending a significant amount of time in the cerebrospinal fluid (CSF), influencing (or “modulating”) the activity of several other neurons in the brain. For this reason, some neurotransmitters are also considered to be neuromodulators, such as serotonin and acetylcholine. (see wikipedia)