Neuroscience: Patience ‘determined by brain’s SEROTONIN levels’

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Patience is determined by the levels of the hormone serotonin, dictating whether you can calmly anticipate a reward or crave instant gratification, a study has found.

Researchers from Japan found that artificially triggering the release of the hormone in mice made the rodents more patient when waiting for food in lab experiments.

Furthermore, the team found that two different areas of the brain are responsible for separately evaluating the benefits of waiting patiently for a reward. 

The findings may help to refine the development of antidepressants that modulate serotonin levels in humans — such as by targeting specific areas of the brain.

Patience is determined by the levels of the hormone serotonin, dictating whether you can calmly anticipate a reward (pictured) or crave instant gratification, a study has found

In their study, neuroscientist Katsuhiko Miyazaki of the Okinawa Institute of Science and Technology Graduate University and colleagues worked with special mice with light-sensitive neurons that release serotonin when triggered.

In a previous study, the researchers trained the mice to perform a waiting task called a ‘nose poke’ — one in which they held their snout inside a hole until a food pellet was delivered.

In three-quarters of tests, the mice were rewarded for this action — but in the remainder, the scientists did not provide any food.

The team found that the release of serotonin in a brain region called the dorsal raphe nucleus increased the amount of time mice were happy to wait for food when the probability of receiving the reward was high but the timing of such was uncertain.

The dorsal raphe nucleus is the brains central hub of serotonin-releasing neurons — and contains neurons that reach out into other areas of the brain.

‘Serotonin is one of the most famous neuromodulators of behaviour, helping to regulate mood, sleep-wake cycles and appetite,’ explained Dr Miyazaki.

‘Our research shows that release of this chemical messenger also plays a crucial role in promoting patience — increasing the time that mice are willing to wait for a food reward.’

The team also explored the impact of releasing serotonin in different areas of the mice’s brains, with a particular focus on areas of the brain that are known to lead to an increase in impulsive behaviour when damaged.

These included two parts of the frontal lobe called the orbitofrontal cortex and the medial prefrontal cortex.

The researchers found that serotonin release in the orbitofrontal cortex was as effective at promoting patience as release of the same in the dorsal raphe nucleus.

The team found that the release of serotonin in a brain region called the dorsal raphe nucleus (orange) increased the amount of time mice were happy to wait for food when the probability of receiving the reward was high but the timing of such was uncertain. The dorsal raphe nucleus is the brains central hub of serotonin-releasing neurons — and contains neurons that reach out into other areas of the brain — including the orbitofrontal cortex (pink) and the medial prefrontal cortex (blue), as well as the nucleus accumbens (yellow)

The team found that the release of serotonin in a brain region called the dorsal raphe nucleus (orange) increased the amount of time mice were happy to wait for food when the probability of receiving the reward was high but the timing of such was uncertain. The dorsal raphe nucleus is the brains central hub of serotonin-releasing neurons — and contains neurons that reach out into other areas of the brain — including the orbitofrontal cortex (pink) and the medial prefrontal cortex (blue), as well as the nucleus accumbens (yellow)

The team found that the release of serotonin in a brain region called the dorsal raphe nucleus (orange) increased the amount of time mice were happy to wait for food when the probability of receiving the reward was high but the timing of such was uncertain. The dorsal raphe nucleus is the brains central hub of serotonin-releasing neurons — and contains neurons that reach out into other areas of the brain — including the orbitofrontal cortex (pink) and the medial prefrontal cortex (blue), as well as the nucleus accumbens (yellow)

In the medial prefrontal cortex, however, an increase in patience more serotonin with was only seen when the timing of the reward was varied — and not in fixed time trials in which the mice had been trained to expect food after a given time.

‘The differences seen in how each area of the brain responded to serotonin suggests that each brain area contributes to the overall waiting behaviour of the mice in separate ways,’ Dr Miyazaki said.

‘This confirmed the idea that these two brain areas are calculating the probability of a reward independently from each other, and that these independent calculations are then combined to ultimately determine how long the mice will wait.’

‘This sort of complementary system allows animals to behave more flexibly to changing environments.’

The researchers found that serotonin release in the orbitofrontal cortex (red) was as effective at promoting patience as release of the same in the dorsal raphe nucleus (yellow). In the medial prefrontal cortex (blue), however, an increase in patience more serotonin with was only seen when the timing of the reward was varied (top left) — and not in fixed time trials in which the mice had been trained to expect food after a given time (bottom left)

The researchers found that serotonin release in the orbitofrontal cortex (red) was as effective at promoting patience as release of the same in the dorsal raphe nucleus (yellow). In the medial prefrontal cortex (blue), however, an increase in patience more serotonin with was only seen when the timing of the reward was varied (top left) — and not in fixed time trials in which the mice had been trained to expect food after a given time (bottom left)

The researchers found that serotonin release in the orbitofrontal cortex (red) was as effective at promoting patience as release of the same in the dorsal raphe nucleus (yellow). In the medial prefrontal cortex (blue), however, an increase in patience more serotonin with was only seen when the timing of the reward was varied (top left) — and not in fixed time trials in which the mice had been trained to expect food after a given time (bottom left)

Understanding how different areas of the brain are affected by serotonin could help to improve the development of so-called selective serotonin reuptake inhibitors (SSRIs) — a commonly-used form of antidepressant medication.

‘This is an area we are keen to explore in the future, by using depression models of mice,’ said Dr Miyazaki.

‘We may find, under certain genetic or environmental conditions, that some of these identified brain areas have altered functions.’

‘By pinning down these regions, this could open avenues to provide more targeted treatments that act on specific areas of the brain, rather than the whole brain.’

 The full findings of the study were published in the journal Science Advances.

WHAT IS THE NEUROTRANSMITTER SEROTONIN AND WHAT DOES IT DO?

Serotonin, also known as 5-hydroxytryptamine, is a neurotransmitter – a chemical substance that transmits nerve impulses across the space between nerve cells or neurons – known as a synapse.

It plays an important part in the regulation of learning, mood, sleep and helps control blood vessels.

It has also been linked to anxiety, migraine, vomiting and appetite. 

Serotonin is the chemical which can help with feelings of low-self esteem as well as a sense of not belonging.

As a neurotransmitter, once the first molecule makes its way across the synapse, the cell stops accepting any further chemicals or signals.

Once the process is completed, the remaining serotonin is reabsorbed into the original neuron. 

Chemicals and tablets, such as Prozac, tackle depression by stopping the cell fromshutting off and not accepting any more serotonin. 

By keeping the avenues open for more of the neurotransmitter to pass through, it increases the strength and duration of the signal. 

This, at least theoretically, increases happiness.     

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