Motivation and emotion/Book/2017/Neurotransmitters and motivation

Neurotransmitters and motivation:
What is the effect of neurotransmitters on motivation?

Overview

From quite a young age we learn that nerves "send messages" around our bodies. When you touch something that's too hot, your nerves in your fingers send a message to your brain telling it "Ouch! Hot!" and you move your hand. This message travels fast! Or when you are hungry, your stomach sends a message to your brain that it's time to eat, and your eyes send your brain a message that "that donut looks REALLY DELICIOUS!" so you pick the donut up and eat it. Once you start learning more about anatomy and physiology, though, you soon come to realise that nerves are not actually single long strands like telephone wires, but long structures made of cells (neurons) that don't even actually touch each other end to end! So how do those messages we hear about get through? That is the job of the neurotransmitter. Neurotransmitters bridge the gap between neurons, helping to ensure the messages between cells and the brain get where they are going.

Neurotransmitters are not only involved in the physical functioning of our bodies, but also what we usually think of as psychological functioning as well. In this chapter we will learn more about the roles of neurotransmitters in motivation - that thing that gets us up in the morning ready to tackle our day, or the lack of which makes us sink under the doona wishing everyone would leave us alone because we just *can't* today. Of course, there are other factors involved in motivation, but they are for another chapter.

Science of neurotransmitters

Neurotransmitters are chemical substances released from a neuron into either another neuron, a muscle fibre or a gland (Tortora & Derrickson, 2014). They are similar to hormones - and some of them, for instance noradrenaline, can also act as hormones - but where hormones are stored in glands and carried in the blood, neurotransmitters are stored in synaptic vesicles and are released by a neuron (Craft et al., 2011). They are messenger chemicals, helping pass messages along the nerves in order to encourage or inhibit activity.

How they work

Figure 1: Diagram of a synapse showing how a neurotransmitter is released (Splettstoesser, 2015).

Figure 1 shows a diagram of how the neurotransmitter is released to the next location. Essentially, the neurotransmitter is stored in one of many synaptic vesicles located at the end of the axon. The action potential travelling down the axon stimulates the vesicle to open up, releasing the neurotransmitter so it can cross the synaptic cleft to the intended site, in this case a dendrite of the next neuron. There are receptors located on the dendrite, where the neurotransmitter can attach. If enough neurotransmitters attach to the receptors, a signal is triggered and the action potential again travels along the neuron to the next axon terminal and so on until the message is "delivered" (Craft et al., 2011).

Some important neurotransmitters and what they do

Neurotransmitter	Role	Notes
Serotonin	Found in the limbic system. Involved in arousal, sleep, and is important in “preventing depression and promoting motivation” (McKenna & Lim, 2012)	Serotonin produced for use as a neurotransmitter occurs in the brain, but 90% of the body's serotonin supply is actually produced in the gastrointestinal system! In schizophrenia, elevated levels of serotonin can cause positive symptoms such as delusions and hallucinations (Craft et al., 2011)
Dopamine	Involved in pleasure, addictive behaviours, and emotional responses (Tortora & Derrickson, 2014)	Parkinson’s Disease is marked by a significant reduction in the levels of dopamine being produced (McKenna & Lim, 2012). People with Parkinson’s experience loss of muscle tone and control due to lowered levels of dopamine in neurons controlling skeletal muscles (Tortora & Derrickson, 2014). While Parkinson’s disease can be treated with L-dopa, which increases dopamine levels, too much can cause schizophrenic symptoms (Craft et al., 2011).
Gamma-Aminobutyric Acid (GABA)	Inhibits nerve activity, helps prevent overactivity (eg seizures)(McKenna & Lim, 2012)	Diazepam (Valium) increases the action of GABA, which is how it helps relieve anxiety (Tortora & Derrickson, 2014).
Noradrenaline (also known as norepinephrine)	Involved in arousal (as in, waking up from deep sleep), dreams and mood regulation (Tortora & Derrickson, 2014).	Also a hormone when released from the adrenal glands (McKenna & Lim, 2012).
Acetylcholine	Communicates between nerves and muscles (McKenna & Lim, 2012)	Botulinum inhibits the release of acetylcholine, and thus can cause paralysis of muscles. This can be nice if you’re having a facelift using Botox but deadly if you get botulism (McKenna & Lim, 2012).
Endorphin	The body’s natural painkiller. It is also involved in the feeling of pleasure or euphoria (Tortora & Derrickson, 2014)	It is thought that acupuncture works by increasing the release opioid peptides including endorphin, which causes anaesthesia in the area being treated (Tortora & Derrickson, 2014).
Nitric Oxide	Works as a vasodilator (Craft et al., 2011)	Among other things, it is responsible for male erectile function! Viagra is an anti-hypertensive which works by enhancing the effect of nitric oxide: while it's designed to help lower blood pressure, it has the added side effect of allowing the penis to fill with blood more readily (Craft et al., 2011).

Where do the neurotransmitters act?

Figure 2: Dopamine and serotonin pathways

Essentially, wherever there is a neuron there will be at least one kind of neurotransmitter. Some work only between neurons while others communicate between neurons and muscles or glands. Since we will be looking mostly at serotonin and dopamine and the way they affect motivation, this is a good opportunity to see where these neurotransmitters act within the brain. Figure 2 shows the dopamine and serotonin pathways, which are mostly contained within the limbic system and frontal cortex. This makes sense, as the limbic system is commonly associated with emotions, and the frontal cortex with personality (Urban, 2017).

If you want to learn more about the brain, its structure and functioning, check out this highly readable account by Tim Urban (external webpage).

The role of neurotransmitters in motivation

Motivation is essentially the "why" behind behaviour (Reeve, 2015). When we see people act a certain way and wonder why they do that, we are wondering about their motivation. Why does someone get up at 5 am and go for a jog before work? Why does someone keep arriving late at work even though they know it annoys their boss? Why does one person become a nurse while their sister becomes a doctor, and their other sister becomes a laser lass at Woolworths? It's all about motivation - or the lack of it. There are many sources of motivation, whether internal or external, according to Reeve (2015), and some neurotransmitters play a part in that process.

How neurotransmitters increase motivation

One neurotransmitter that helps to increase motivation is Dopamine. Dopamine acts as a motivator in order to activate a reward pathway in the brain. this was demonstrated in a study with rats which showed they would stimulate there pathways manually after a stimulation device was put in their brains. the feeling they received from this was enough motivation for them to continue doing it over and over again (Love, 2014).

When neurotransmitters decrease motivation

Even though dopamine is pretty great, when it is is firing improperly it can lead to a lack of concentration and motivation (Love, 2014)

Mental Health

When neurotransmitters are firing improperly they can affect emotions and motivation drastically and cause severe mental health issues for the individual involved. The following are just some of the mental health issues that can develop from neurotransmitter activity.

Depression: Depression can be brought on by different means such as trauma and chemical imbalances. When the neurotransmitter serotonin is firing too little it can lead to the development of depression (Leo & Lacasse, 2008). Many people who suffer from depression experience a lack of motivation, they have no drive to get up in the morning, to bathe or even to eat. This can be due to not perceiving anything as important or thinking everything is too difficult so why bother trying (Smith, 2013). In some ways it is surprising how something as simple as a neurotransmitter can make us go against natural survival instincts (Frey, Savage, & Torgler, 2011).

Misophonia

Misophonia has been linked with glutamate, a neurotransmitter which when secreted in excess can lead to abnormal sensitivity, Noises that others may perceive as normal such as breathing or eating can be distressing to listen to for people who suffer from misophonia (Maxwell, 2014). When distress occurs in a person they may start to avoid a situation so as not to experience the negative emotions. This motivates people to isolate themselves to feel better. Given that humans are usually very social animals it is not good individuals mental health to be isolated. (Love, 2014).

Addiction

Studies have been performed on animals investigating drug addiction and motivation. It has been shown that the animals were motivated to continue the drug use due to the feelings they experienced while on the drugs. Dopamine is secreted during many drug trips which leave individuals seeking that high they experience while on drugs (LeBlanc, Maidment, & Ostlund, 2013).

Play

A study involving rats showed that dopamine secretion related directly to the motivation to play with other rats (Achterberg, et al, 2016).

When things go right

When neurotransmitters are being fired correctly they do wonderful things for motivation. People whose brain chemistry is statistically normal will have positive motivation, helping the individual to succeed in their goals and help improve their life (Richard, Castro, DiFeliceantonio, Robinson, & Berridge, 2013).

Conclusion

Neurotransmitters are very interesting in their functions. Sometimes they don't work well and cause more problems than they solve but on the whole they keep us going. They communicate with areas of our brain to perform many wonderful tasks and all in all they are pretty nifty.

References

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