FEELINGS & THE NEURO-CHEMISTRY OF EMOTION

What are feelings anyway? Neuroscientists, psychologists and philosophers alike have long puzzled over this question. The word feeling originally referred to the physical sensation of touch. The meaning was later expanded to include emotion, alluding to the way in which our emotions “touch” us in spite of being abstract internal sensations.

Neurologically speaking, the above connotation of sensuality is one and the same, translating into another genre of sensory neurological information that is received and responded to by the nervous system. Emotions occur as neurochemical reactions, either toward sensory information that is received from the environment or that is generated through thought.

In higher order animals, feelings typically modify behavior in a way that is beneficial to the organism for survival. For instance, an animal feeling fearful of a predator will flee as a result of experiencing the fear, and when feeling attracted to a potential mate, it will engage in reproductive behaviors. Emotions also contribute toward learning, memory, future behavior and decision-making by categorizing what constitutes either a negative or positive experience.

In humans, a higher rational capacity appears to have evolved in tandem with emotional depth and complexity. The ability to reflect on emotion is considered to be one of the primary traits that set humans apart from the animal kingdom and it goes hand-in-hand with forming a mental self-image or identity. Conscious reflection gives one the option to intervene during an undesirable emotional response and choose how one wants to react in the majority of situations.

It is also human complexity that makes the study of emotion a true challenge. Through decades of investigation, neuroscientists have only just begun to map out viable hormonal and neurological connections that are associated with producing an emotional feeling. In an attempt to better understand human feeling, the below review highlights what is presently known about the biological workings of emotion.

Physical Components of Emotion

Scientists know relatively little about emotion and there is still much to explore with regard to how emotional feelings are produced in the body. It is generally accepted that the basic components of emotion pertain to brain and body states generated by neurological impulses and the cellular release of biochemical substances.

The organism experiences a sensual (external) or conceptual (internal) situation that is received by the brain in the form of nerve impulses. The emotion is the consequent biological reaction to the situation, in which nerve impulses, as well as local and circulating neuro-chemicals, informs the cells of the body how to react. Changes in blood pressure, muscle tension, breathing rate, alertness and many other physiological variables are affected in order to create the lived experience of an emotional state of being.

The specific way in which neurons fire to produce an emotion are a result of the following:

Neurotransmitter Levels

Neurotransmitters are chemical messenger molecules produced by neurons to electrochemically deliver a message across a synapse. They are produced by neurons in advance and stored inside them until the appropriate moment.

The electrical gradient inside neurons is governed by the movement of Ca2+ (calcium ions) which works together with magnesium and ATP, the “energy molecule.” When calcium floods into the neuron, it increases the electrical potential of the cell which causes the stored neurotransmitters to move to the neuron’s membrane and be expelled across the synapse. The electrical potential gradient generated with calcium and ATP moves across to the next neuron to open up neurotransmitter receptors and is continuous to form nerve transmission. Neurotransmitters that are not absorbed by the next neuron as a result of closed receptors (each of which are specific to the molecule in question) are either recycled or degraded.

It has long since been acknowledged that certain levels of neurotransmitters in the brain are linked to inducing certain emotions. Neurotransmitters appear to be associated with maintaining states of perception, cognition, awareness and a number of bodily processes, having complex functions over and above that of emotion and behavior. It is the combination of neurotransmitters that get broadcast as well as their levels relative to one another that contributes to our experiential state, emotion included[1].

There are three basic neurotransmitters that are each associated with three basic states of emotion. Combinations of these neurotransmitters produce different types of emotion[2]. They include:

1. Serotonin associated with punishment/dislike and sadness.

2. Dopamine associated with pleasure/reward and joy.

3. Adrenaline and noradrenaline associated with surprise/arousal and fear or anger.

The emotional outcome is also dependent on the brain areas they engage with as well as the functionality of receptors.

Endocrine Activity

Hormones also contribute to producing hormones in a way similar to neurotransmitters, modulating the function and expression of neurons. Unlike neurotransmitters, hormones do not interact at neuronal synapses and are found in the bloodstream. Some hormones exert their influence at the cell’s membrane, some need to be taken up by the cell in order to do so and some can exert actions in both manners.

The brain produces hormones that often lead to the release of other hormones in distant body sites. For instance, cortisol releasing hormone stimulates for the adrenal glands to produce cortisol. The blood levels of cortisol then affect brain function by binding on neuronal receptors. Adrenal hormones, reproductive hormones and thyroidal hormones are the main influencers that affect the brain and their levels are also associated with different emotional states.

Immune System Signaling

Interestingly, recent research findings confirm that immune cell signaling molecules, such as interleukins and other cytokines, can modulate the neuro-anatomical components of the above-described circuits and contribute toward producing an emotional state of being. Our state of health and immune function thus also modulates mood and our emotional state of reactivity.

Biological Clock

The release or activity of many hormones and some neurotransmitters is highly dependent on our daily (and nightly) rhythms and therefore so is our emotional state of being[3] [4]. The sleep-wake cycle that sets the body’s daily bio-rhythms is operated by the sympathetic nervous system and the primordial circuitry of the brain that governs our state of arousal.

In the average person, cortisol peaks first thing in the morning in tandem with a few other hormones, signaling for the body to wake up and be alert. This is why many feel at their most energized in the morning and become progressively more tired as the day wears on. Interfering with the sleep-wake cycle can make the body release hormones and neurotransmitters at the wrong time, potentially interfering with one’s emotional state of being. 

Nervous System Circuitry

The brain operates through neuronal communication in which neurons from unique brain compartments connect to one another. The constant back and forth creates observable nervous system feedback loops between brain areas, which are paramount to overarching brain function. Basic circuits exist that are common to all higher order animals which sustain sensory experience, movement, learning, body function and survival.[5]

Emotion arises from this same basic neuro-circuitry and is suggested to modify behavior in such a way that is conducive to the survival of the organism. Feeling fearful of an imminent threat and running away as a result of the feeling is a clear example of how an emotional reaction might enhance the survival of an organism.

Interestingly, the majority of brain circuitry involved in generating either positive or negative feelings is virtually the same with some minor variances. Either ends of the emotional spectrum are brought into being through two overarching circuits that are joined at central brain areas associated with emotional processing and learning. [6] These circuits fall within the limbic system in the brain, comprising of some forebrain areas, the cingulate cortex, the amygdala, the hippocampus, the habenula and various other brain regions, such as specific parts of the grey matter.

The one circuit or network is associated with generating emotional reactions that elicit behavior most likely to help the organism avoid undesirable circumstances (misery fleeing), while the other is associated with behavior that seeks out desirable ones (reward seeking). The precise way in which these circuits fire, with their respective neurotransmitter ratios and other chemical components, is ultimately what is responsible for producing a negative or positive emotional reaction.

The two circuits integrate and are connected to primordial brain networks, including the hypothalamus and brain stem, which regulate body function and contribute to the physical sensations brought about by emotional states of being. These primordial areas are responsible for receiving physical motor and sensory feedback from the body in order to generate our basic physical experience of the five senses (sight, taste, touch, sound and smell).

When we experience an emotion, these areas send feedback toward the rest of the body that alters cellular function and in turn our physical experience. Classically this is achieved through central nervous system communication with the autonomic nervous system; inducing either a sympathetic (stressed) or parasympathetic (relaxed) nervous response. These responses constitute the experiential physicality behind an emotional state of being. Examples include shock-induced labored breathing, an excitement-induced increase in heart rate and trust-induced muscle relaxation.

The higher cognitive compartments of the human brain allow for us to experience more complex emotions than other lifeforms, such as guilt or awe, and modify them through self-reflection and reasoning. These areas are also linked to the primordial parts of the brain when experiencing emotion, allowing for primal emotional reactions to be generated purely from thought alone, as well as for thought to intervene with emotional reactivity. Ultimately, complex emotions appear to be modifications or extensions of the same set of primordial emotional reactions seen in other higher order animals.

Neuroplasticity & Neurogenesis

As an animal learns throughout its life, it develops a memory that is deeply linked to emotional states of being[7]. When an emotional reaction generates a successful or positive outcome, it tends to be reinforced, with there being a higher chance of the same reaction being produced to similar stimuli in the future. Neural circuits that are fired often become wired more strongly in the brain, with adaptations arising as required. This is foundational to all bodily learning and remembrance, whether conceptual, emotional, behavioral, physical or otherwise.

The circuits themselves are not firing all at once, all the time. Certain neurons have the ability to withdraw from a circuit and connect into another one as required.

This ability of brain neurons to be plastic, flexible or adaptive in moving between neural firing patterns is known as neuroplasticity[8]. Neuroplasticity also allows for the brain to efficiently house numerous neuronal circuits and also gives a little insight into how a sudden memory flashback or a mood swing works.

Neurons and neural patterns that are not used that much tend to shrivel and eventually die off. The nervous system is equally equipped with reservoirs of neuronal stem cells that allow for neurogenesis[9] or the regeneration of neurons. Thus in this way, when something completely new is learned that challenges old emotional reactions and consequent behavioral patterns, the brain is able to create and/or switch to a different neural network.

It would seem that the capacity for neurogenesis and neuroplasticity naturally affects the extent to which each person perceives and reacts to life situations at the emotional level. Neuroplasticity has been linked to emotional control as well and is thought to become better with practice.[10]

Loss of emotional control is highlighted in neurodegenerative disorders such as dementia, with which faulty neurogenesis and neuroplasticity are associated[11]. Patients commonly experience drastic mood swings, forgetfulness, reduced life satisfaction and other emotionally related symptoms.

Dissecting 5 Basic Bodies of Emotion

Emotion is difficult to dissect as it is subjective, in spite of the physiological reactions that states of feeling produce. In order to study an emotion, a plausible definition has to first be generated and applied to each type. With this in mind, scientists can then look into the brain and body, puzzling over the many thousands of chemical and neurological associations they see when the subject is experiencing an emotional state.

It’s not always easy for us to understand what emotion we are feeling or to predict what stimuli will produce an emotional state of being; which is why it has taken decades for this field to advance to where it is today.

The following attempts to summarize what is currently known about the neuroanatomy and chemistry of 5 basic states of emotion. It should be noted that this review is not exhaustive and much remains to be answered about the workings of emotion.

1. Happiness

What is happiness? This question never has and likely never will be answered with surety. It is very difficult to discern what makes a person happy as happiness is a rather subjective emotion.

Biologically, the study of happiness was originally confused with the study of pleasure[12]. It was soon realized that pleasure does not necessarily equate happiness and that the neuro-circuitry responsible for motivation is a crucial second factor that contributes to overall happiness. Motivation begins to enter an abstract realm as it pertains to life meaning and purpose.[13]

Pleasure has also been neurologically distinguished from desire; however desire also appears to be an important component in feeling happy. Studies reveal that those who maintain a balance between pleasure and desire are happier on average. Those who only seek pleasure for pleasures sake (e.g. addicts) are generally not very happy and those who constantly desire without ever reaching fulfilment also tend to suffer from unhappiness. Desire relates to motivation, being augmented by one’s perception. Perception is likewise physically altered by one’s emotional state of being.

Other models of happiness state that happiness is merely the absence of negative emotion and turmoil in one’s life. In other words, when we are not feeling sad, stressed or fearful, we are happy. This theory concurs with the emotional circuitry of the brain.

The pleasure component of happiness tends to arise from the reward seeking network and is inhibited by the misery fleeing networks of the brain. On the experiential front, many would agree that it is easier to experience reward and feel pleasure when one is not able to escape from troubling or stressful circumstances. That is because the misery fleeing circuit of the brain dominates. This circuit is classically associated with the sympathetic nervous system stress response (fight or flight), which is known to stifle the parasympathetic nervous response of relaxation (rest and digest).

In this context, the emotion of happiness can be seen as the absence of fear, the presence of motivation, and the continued (uninterrupted) process of desiring, seeking reward and experiencing pleasure.

Of course, this description still does not answer what happiness is for any individual person as what could constitute any negative or positive stimulus for generating emotion is highly subjective and unique to the individual’s exposures. It merely offers a useful conceptual framework that allows for neuroscientists to study emotion in the context of brain function.

Neurochemicals of Happiness

At the chemical level, happiness is associated with the following neurotransmitters and hormones[14]:

• Dopamine is thought to be a major driver of happiness from a pleasure perspective; however it is not always absent during negative emotional states. It is also involved in generating motivation through invoking reward anticipation. Dopamine is inhibited and regulated by serotonin to ensure that addiction does not ensue.
• Serotonin is a major neurotransmitter that is involved in regulating many emotions alongside our baseline state of arousal, mood, memory formation and cognition. This chemical promotes the relaxed state of being associated with having confidence and good self-esteem. Feelings of confidence, self-acceptance and self-significance are brought about by serotonin. Estrogens are known to stimulate serotonin formation.
• GABA (Gamma Amino Butyric Acid) is the main neurotransmitter responsible for calming the nervous system down. The nervous system is designed to be alert at all times and is more prone to becoming overactive, which tends to detract from positive emotion and add onto stressful ones. GABA regulates mood indirectly by keeping the nervous system calm and running smoothly. Progesterone is known to act on GABA receptors and work in a similar fashion, relaxing the nervous system.
• Endorphins are peptide hormones that are associated both with pain relief and pleasurable emotional states. Endorphins are released when one laughs, exercises, feels love, consumes certain mood-modulating foods like chocolate and after intercourse.

Stress chemicals are required for all emotion, but can of course be detrimental toward feelings of happiness. Most emotions require a basic state of arousal and some energy to be felt, which is what ordinary levels of stress contribute toward. Low levels can result in boredom, restlessness, lethargy, etc; while higher levels are obviously associated with increased stress and emotional volatility.

2. Fear (and Anxiety)

It would seem that the neural wiring of the brain and nervous system gives preference to fear and fear-based learning. This is evident when understanding that fear chemicals largely drive the waking state. However, the emotion of fear is only felt in response to a threat, whether that threat is real or imaginary. Many negative emotions are spin-offs from the primordial emotion of fear and many positive emotions are dependent on the absence of fear.

Anxiety appears to be a type of fear that is more generalized. It is usually distinguished from fear as it is felt without an external queue present and is often linked to the anticipation of a fearful outcome that has not occurred yet.

By contrast, fear arises as when one is faced with an imminent threat and has to respond swiftly. Anxiety is also felt with a degree of uncertainty, either for no apparent reason or because the future has not yet occurred. Fear is far more certain, with a response directed at avoiding harm from the potential threat. [15]

It is suggested that anxiety is the product of fear-based learning that helps us to adapt and prepare for future threats, forming a part of healthy cognitive processing of fearful or traumatic events. This is not to be confused for anxiety disorders in which the feeling is chronic and detrimental to cognitive function.[16]

Fear is typically used to describe the sympathetic nervous response that causes the organism to react by fleeing, freezing on the spot and in some cases, fighting with the perceived threat (fighting is more commonly seen with anger). Much research points to the amygdala’s key role in promoting fearful responses and learning from them.[17] While this circuit is fully active, the brain’s reward seeking pathways are unable to operate.

Which reaction the nervous system expresses in response to fearful stimuli depends on the type of stimulus encountered. Freezing is classic of an inescapable threat; however it also occurs in response to an environmental queue that is predictive of an inescapable threat, such as when an animal temporarily freezes from observing an approaching predator from a perceptually safe distance. Fleeing tends to express in response to an escapable threat, whereas fighting manifests when one is cornered but the threat is perceived to be escapable through aggression, assertion or persuasion.

Individual differences also affect the expression of fear on the behavioral level. Neurochemical profiles appear to predispose the individual to reacting to fearful stimulus, contributing toward either a passive or active coping mechanism. More research is required however before distinctions can be drawn. In animal studies, it appears that in certain breeds, genetics plays a role in disposing the animal to either a passive or active reaction when faced with fear-inducing stimuli. 

Neurochemicals of Fear

Fear has been largely associated with the following chemical components:

• Adrenaline and noradrenaline are hormonal promoters of the fight or flight response and activate the sympathetic nervous system. These are seen as the main components of fear and perhaps constitute the fine line between feeling stressed and fearful.
• Cortisol and similar adrenal hormones regulate our state of arousal and are increased in order to promote the feeling of fear.
• Serotonin is implicated in fearful feeling yet there are contradictory results with regard to its exact role. In some areas of the brain, serotonin promotes a fearful response, while inhibiting it when acting on other areas. Serotonin can be viewed as a regulatory and facilitative neurotransmitter in the context of fear. It is also associated with producing the feeling of disgust, dislike or avoidance, naturally in the context of the self in relation with something.
• GABA is crucial for putting an end to the fear response by inhibiting the nervous system and if a lack is present, it may interfere with one’s ability to stop feeling anxious or fearful.

3. Anger

Anger can be viewed as a mixed emotional state of stress and hostility, sometimes (but not necessarily) coupled with aggression. It is strongly associated with dislike, disgust, punishment, judgement and criticism.

The sympathetic stress response, or a fight or flight reaction, is the most studied component of anger. From this perspective, anger has neurochemical roots in fear and is theorized to be part of an adaptive survival mechanism when facing an imminent threat that causes the organism to defend itself. [18]

While the fight response and heightened aggression are very much characteristic of the anger expressed in animals, humans have a more sophisticated nervous system that allows for anger to be felt in non-threatening situations and without aggression. [19]

The frontal lobe of the human brain appears to be able to skillfully intervene in the primordial fear pathway and moderate the response, toning down aggression and allowing for anger to be expressed in many different ways. Humans tend to experience anger when treated unfairly, when their goals are being blocked and, like other animals, when threatened. When the limbic system cannot control this pathway and an anger-inducing stimulus is present, aggression and even violence[20] can arise very quickly as it pertains to circuitry that is not in the realm of the conscious mind.

The feeling of anger is generally short lived, however the state can be perpetuated by thought, which is another aspect of anger that separates man from beast. Unfortunately, fear and anger inhibit cognitive functions by narrowing one’s focus in a way that tends to give rise to more of the same. High speed processing occurs in this state with many mental associations being created around the source of provocation from within the confines of this limited, yet highly focused state of arousal. This is thought to be another evolutionary advantage for mankind that evolved alongside language and higher order cognitive functions, allowing for verbal fighting and aggressive bargaining tactics.

Aggression is generally the result of increased provocation and/or low emotional control from the prefrontal lobe and emotional centers of the brain. The prefrontal lobes tend to intervene in anger by allowing for reflection of self and other or of the provocation, which in turn re-evaluates the stimulus and modifies the response. A provocation big enough is likely to inhibit the emotional control centers of the brain in favor of generating a fight response for optimal survival outcomes.

It is interesting to note that in infants, anger seems to be necessary for developmental cognition. Anger promotes infantile learning when a goal is blocked or an obstacle is encountered, as well as a sense of self and a sense of mastery or control over the self. This emotion only tends to occur toward the end of the first year of life, with other emotions taking precedent until then. As anger is more rehearsed, it progresses into the heightened reaction of rage, becoming easier to access as an emotional state and even defining baseline personality traits in some people.[21]

Frustration and irritation are minor forms of anger. Frustration occurs when one expects a reward and does not receive the reward in spite of continued effort[22]. Irritation is more of a generalized form of anger and can arise with little to no provocation (a bit like anxiety is a spin-off from fear).

Neurochemicals of Anger

Anger is comprised of many of the same components of fear, such as adrenaline and noradrenaline.

• Serotonin is especially implicated in aggressive anger as it promotes heightened self-confidence, feelings of dislike and is associated with punishment[23]. Aggression is linked to heightened levels of serotonin and perhaps serotonin levels at the time of getting a fright play an important role in determining whether one will have a fight or flight reaction.
• Dopamine may have an indirect role in facilitating anger, particularly when the anticipation of reward is not met causing dopamine levels to drop in relation to serotonin (which would then be increased resulting in anger or frustration).

Patients receiving cytokine therapy reported heightened levels of hostility, anger and irritability, suggesting a role for increased immune activity in contributing toward volatile emotional states like anger.[24]

4. Love

Love is a very complex emotional state that arises from and bridges the reward-seeking circuits to the stress centers of the brain. It is seen as a mixture of stress, reward, pleasure, joy, bonding and attachment.[25]

All love tends to begin as a state of stress after a person is attracted to another person or responds well and identifies that other person as unique to them. The increased arousal and stress encourages spending time with the special other, as well as the anticipation of reward and the positive feeling produced when with them. Spending more time with the other increases feelings of bonding and relaxes this response.

Eventually the stress response dies down completely once the other becomes more familiar, moving love into less intense emotional grounds in which bonding and engaging in new experiences keeps the feeling “alive.” This is generally true of platonic friendship or romantic partnership; however the latter yields components of attraction, lust and stronger forms of attachment and bonding.[26]

The stress response to love is a pleasant one and this is because the neurotransmitters involved in stress are moderated with ones that promote trust and security. It is also speculated that the initial stress is mostly in response to novelty and that the other chemicals associated with love help one to face an unknown situation with optimism and joy – the reaction to which would normally be one of fear or anxiety.

It is theorized that love is a motivational state that is there to promote survival of oneself and of the species at large through reproduction. Those who have long-lived partnerships tend to lead longer lives than those who don’t have a dedicated partner. Likewise, maintaining friendships are associated with living longer and being happier on average, while having no friends is associated with depression, loneliness and a decreased lifespan.

Rejection in love typically results in anger followed by sadness as the anticipation of reward is first dashed, followed by despondent feelings related to self-punishment.

Neurochemicals of Love

Love is chemically produced in the nervous system by the following neurotransmitters:

• Oxytocin is a peptide hormone that is known to be the major inducer of feelings of trust, safety, security, relaxation, bonding and attachment, particularly with regard to others. Without oxytocin, there would be no bonding or attachment and love would not endure[27]. Thus it is the main component of love, whether plutonic or romantic.
• Dopamine is mainly involved in initiating and sustaining the motivational force of love. Reward in relationships is characterized by dopamine release. Oxytocin and other regulatory mechanisms ensure that love does not become addictive as a result of dopamine dependence.
• Serotonin is not as involved in the emotion of love as dopamine, however it helps to regulate its actions. When the intensity of a new relationship dies down after a year or two, dopamine levels decrease and serotonin increases in response to the significant other. This may promote confidence in the relationship and is kept in check thanks to occasional rewards and oxytocin-induced bonding. Serotonin may be a key chemical in the biology of rejection and heartbreak.
• Testosterone and Estrogen modulate serotonin levels in the brain, having an indirect effect on dopamine and social reward anticipation. Testosterone inhibits serotonin, giving rise to more dopamine, optimistic thinking and anticipation of reward. Estrogen promotes serotonin, which increases confidence, self-awareness and dislike. In this regard, women are more inclined to reject suitors than men and men are more inclined to seek out partners than women.

Love has been associated with invoking the release of many opioid compounds, like endorphins, that are associated with pain relief and elated states of being.

5. Sadness

Sadness is commonly known as the emotional reaction to loss. While sadness is often seen as a simple negative feeling, it is arguably the most complex of all emotion and there is still much debate about its neurochemistry. This is likely due to the many expressions of sadness, with some pertaining to fear (anguish and distress), love (grief and heartbreak), and even joy (feeling ‘touched’). [28]

When sadness ensues, it interrupts the reward seeking pathway, preventing laughter, humor, and joy as well as decreasing motivation and pleasure. Sadness is provoked by loss which occurs neurologically as loss of future anticipation (dreams, goals and expectations), highlighting the way in which sadness inhibits reward seeking. This has led to the theory that sadness is there to move attention away from a reward that is unattainable, inhibiting the drive to pursue fruitless endeavors.

Sadness can be linked to any other emotional state but has a unique neurological relationship with anger. The emotion promotes a strong sense of punishment, generally related to self, which overlaps with anger, particularly that seen in frustration. This correlates with an overlap in brain regions that specifically regulate anger and sadness. Sadness also is known to disconnect many areas of the brain that are connected during the processing of other emotional states while still maintaining body function.

When loss is coupled with a big surprise or sudden change, such as the death of a loved one, it can increase the basic state of arousal and activate the fear/anxiety network, causing separation distress, fear of the sudden new situation and grief or intense sorrow.

The way in which intense sadness modulates the brain causes it to signal via the autonomic nervous system to produce feelings of physical pain in the body. This is why heartache is common when feeling heartbroken.

Neurochemicals of Sadness

Not much is known about the role of neurotransmitters in sadness and much of the research is directed at looking at depressive disorders[29]. However, the following implications have been drawn about ordinary forms of sadness:

• Higher serotonin levels relate to sadness due to the neurotransmitter’s role in punishment, dislike and it’s antagonism of reward systems.
• Dopamine is low and the reward pathway is inhibited.
• Adrenaline and noradrenaline could be high or low, depending on whether sadness is coupled with surprise.

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