The science of happiness: Everything you need to know about the feeling we all crave

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The prospect of a new year inspires many people to make resolutions and transform their lives. In doing so, we are all essentially chasing happiness.

But what causes this emotion, and others, and could this help us capture the emotion we all crave?

Human emotions are governed by a complex mixture of chemicals and electricity.

The human brain weighs over a kilogram (2.2 pounds) and has an estimated 86 billion neurons. Signals are transmitted along each nerve electrically, by gradients of charged ions, and each neuron makes hundreds of connections to those around it.

At each of the 300 trillion synapses in the human brain, chemicals known as neurotransmitters relay messages from one nerve to another. Each neurotransmitter has a set of corresponding receptors, which can be activatory or inhibitory, helping nerves to fire, or preventing them from working. This enormous chemical and electrical network provides the complexity that enables us to feel emotion, from the all-consuming addiction of love, to the raw devastation of grief.

Imaging techniques have helped to reveal the areas of the brain involved in processing different emotional responses. This data, in combination with case studies of patients with damage to certain areas of their brains, and information gathered from investigations in animals, has enabled us to draw up a rough map of the emotional connections in the brain.

A notable area of the brain when it comes to our mood is the limbic system, a small cluster of interconnected regions involved in memory processing and decision-making. It also has a role in motivation and the processing of emotion. The limbic system is directly connected to the olfactory bulb, which processes incoming smell signals from the nose, providing the biological link that allows smells to bring back a memory. Recent research at the Kavli Institute for Systems Neuroscience in Norway suggests smell-based memories are triggered with corresponding brain waves.

The nucleus accumbens links the limbic system to other areas of the brain also known to have an involvement in the processing of emotion. For instance, the basal ganglia, at the base of the forebrain, has been well studied for its role in the planning and co-ordination of movement, but certain areas also light up in response to positive emotional stimuli, and are thought to be involved in reward and reinforcement. Damage to part of the basal ganglia, known as the ventral pallidum, causes anhedonia – the inability to experience pleasure.

The orbitofrontal cortex, meanwhile, located just above the eyes, also lights up in response to positive experiences, and is thought to play a role in evaluating reward versus punishment.

Another approach to the study of complex emotions, like happiness, is to break them down into smaller parts. Pleasure is evolutionarily ancient and is based on a chemical reward system that acts as a biological incentive to repeat beneficial behaviour. There are several ‘reward pathways’ in the brain, but the best studied is the mesolimbic pathway.

The pathway transmits dopamine signals from nerves in the middle of the brain, upward and forward, to the limbic system and the prefrontal cortex, both of which are involved in emotional processing. Under normal conditions, this pathway serves as a motivator for positive actions, producing pleasurable feelings that reinforce evolutionarily beneficial behaviour like eating high-calorie food, social interaction and reproduction.

Activation of the pathway also aids in memory storage, increasing the likelihood that the action will be repeated in the future.

It’s not all about the brain though. The feelings associated with emotions are the result of a complex mixture of incoming sensory messages from all over the body.

A natural high - Six major hormones and chemicals associated with emotion

•    Dopamine

This neurotransmitter feeds the reward pathway in the brain, and is involved in motivation, drive, pleasure and addiction. Abnormally high levels of dopamine are linked to loss of contact with reality, delusions and lack of emotion, while low levels have been associated with addictive behaviour and risk taking.

•    Noradrenaline

Chemically related to adrenaline, this neurotransmitter is a stress hormone that co-ordinates the fight-or-flight response. It mediates many of the physical components of emotion, including raised heart rate, and also acts in the brain enhancing alertness, cognition and decision-making behaviour.

•    GABA

Gamma amino butyric acid (GABA) is the main inhibitory neurotransmitter in the brain – it decreases nerve transmission, allowing neurons time to recover. Increased GABA activity in the brain relieves anxiety and reduces stress.

•    Serotonin

First recognised for its ability to constrict blood vessels, serotonin has become widely known as the "happiness hormone." Chemically known as 5-hydroxytryptamine (5-HT), increasing the available serotonin level in the brain is the main target of the most commonly used antidepressants.

•    Beta-endorphin

Endorphins are natural opioids, produced by the body in response to pain, excitement and even exercise. Beta-endorphin binds to the same mu receptors as the pain-relieving drug morphine. These receptors, present on nerves in the brain and spinal cord, modulate the activity of nerves, causing mild sedation, relieving pain and giving a sense of wellbeing.

•    Oxytocin

Often described as the "bonding hormone", the "trust hormone", or sometimes even the "love hormone", oxytocin is unique to mammals. Although research is still in its infancy, oxytocin is thought to play an important role in human intimacy, childbirth, sexual arousal, trust and pair bonding.

The autonomic nervous system (ANS) is the subconscious arm of the peripheral nervous system, and controls bodily functions that are not under voluntary control, such as heart rate, digestion and sweating, and it is connected to the limbic system.

The ANS has two distinct components with opposing functions. The sympathetic nervous system uses the neurotransmitters adrenaline and noradrenaline to prepare the body for "fight or flight", raising the heart rate and mobilising resources to fuel the muscles. The parasympathetic nervous system uses acetylcholine to allow the body to rest and digest, slowing the heart and breathing, and diverting the blood supply to the gut.

Sensory feedback produced by the effects of the ANS contribute to many of the familiar feelings associated with emotions. Stimulation of the heart by adrenaline and noradrenaline as part of the fight-or-flight response produces the rapid palpitations associated with anger, fear and embarrassment. Its actions on the digestive system cause "butterflies in the stomach", and activity at the glands on the hands, feet and in the armpits, leads to nervous sweating.

More passive emotions, like sadness or contentment, on the other hand, require little physical response, and the parasympathetic nervous system takes control of the heart, decreasing its rate. Feelings of contentment and relief are often accompanied by deep, slow breathing – another indicator of parasympathetic activity.

The limbic system is also connected to the body via the hypothalamus. This small region, located on the underside of the brain, links the nervous system to the endocrine system – which produces hormones, some of which are key mediators of mood and emotion. For example, corticotropin-releasing hormone is produced in response to stress, and leads to the release of the stress-hormone cortisol from the adrenal glands above the kidneys.

The regulation of emotion is not just restricted to one area of the brain – it involves almost the entire body. Reducing the bewildering complexity of human emotion down to anatomy, physiology, and ultimately, brain chemistry, might seem cold and clinical, but in reality, the fact that humans are capable of experiencing such an extraordinary range of abstract feelings is one of the greatest wonders of biology, with many chemical puzzles waiting to be solved.

Jodie Tyley is the Editor of How It Works Magazine. Issue 79 out now, RRP £4.25. Follow the magazine on Twitter: @HowItWorksmag