Do feelings arise out of physiological states to serve as warnings? Are they automatic mechanisms to quickly detect important changes in the body, such as hunger, thirst, and pain? Emotions, like fear, can be triggered from either external or internal information. What are feelings and emotions and how are they represented in the brain? How do physiological states integrate feelings and body maps in the brains of humans and animals?
Feelings and Emotions
The definitions of the two widely used terms, feelings and emotion, are not exact. Emotion generally refers to a subjective experience including mental states, bodily expressions, and neuronal and behavioral mechanisms. Emotion that is sustained is often referred to as mood, temperament, disposition, and if throughout life, personality.
Attempts have been made to define basic emotions in terms of specific physiology, facial expressions and behaviors, with primary candidates as sadness, surprise, happiness, fear, disgust and anger. A large number of combined and secondary emotions have also been described such as shame, contempt, and admiration.
But, no brain theory has exactly explained emotions and their function. Feeling first referred to the perception of touch, as in “feeling a table”. It is also used as a subjective experience, “the feeling of pain.” “Gut feelings”, referring to intuition, make the connection between physiological states, the thinking process and emotions.
Emotions/Feeling and Cognition
There appear to be some brain centers correlated with emotion, such as ventro medial pre frontal cortex (VMPFC,) and limbic regions; other regions are considered more closely correlated with cognition such as the dorso lateral pre frontal cortex (DLPFC.) But, as previous posts have shown, the hubs of the brain are now known to be very widely inter connected, making simple regional distinctions much more difficult.
In fact, studies of the visual system’s interpretation of incoming data are modulated by multiple different regions with an alternation between so-called emotional centers and so called cognitive centers, such that the finished product is based on both. Although two different types of decision-making have been elucidated, the fast, intuitive type and the slow rational type, it might be assumed that the intuitive type is more related to emotion, and the slow to rational thinking. But, in fact, it is very difficult to distinguish the brain’s emotional and cognitive decision-making.
Physiology and Emotion
Internal states based on bodily organ’s homeostasis are understood as a subjective mental experience or feeling. The need for food is a physiological event related to a subjective mental state called hunger. A physiological injury causes a subjective mental experience of pain. Breathing can trigger peacefulness in meditation or fear with shortness of breath in lung disease or drowning. Experiences from the external world are also associated with internal subjective mental states with danger producing a fearful feeling. Many complex feelings come from interactions with others, such as love, hate, and compassion.
A recent study showed that the way that fear is processed in the brain is dependent upon the specific moment in the heart cycle. If the fear is processed from a fearful looking face when the heart is pumping (systole), it is experienced as more severe than when the heart takes a brief rest (diastole). Also perception of the fearful nature of a face is also more pronounced on the heartbeat. This is similar to the rhythm research that shows learning and perception increased on an emphasized beat.
Signals from the body concerning important changes can be conscious or unconscious. The unconscious states include adjustments of electrolytes, sugar and blood pressure, which can be associated with a feeling of dizziness. Other reactions are automatic and conscious, a flinch occurring rapidly and hunger, pain, fear and thirst occurring gradually over time.
Body Maps and Feelings
A previous post (Body Consciousness) demonstrates that multiple different kinds of body maps exist in the brain without a central map. These brain maps change rapidly to adjust to circumstances.
When riding a horse, the horse becomes part of the body map. When using a tool or a musical instrument our body maps change to include this appendage. An example is the mechanic, lying under a car, who “feels” with the end of the wrench or screwdriver without being able to see the part. More permanent body maps occur with long-term use of a prosthetic or a wheelchair. Pianists have finger maps grow and merge with other fingers.
Detailed physiological maps are utilized in the responses to changes in blood pressure, blood sugar, the need for food, and other parameters. The maps are involved in triggering adjustments through autonomic nerves. Feelings are also related to these bodily maps and particularly to changes in physiological state that appear to be different, or abnormal. A new state perceived as better triggers a positive feeling, and perceived as worse a negative feeling.
The subjective feeling is more easily understood and remembered and can be associated with possible future events. Feelings are used as tags, a way of understanding important changes in our physiology. Feelings are also critical for our behavior and become an important part of our conscious awareness.
A well-known example of a brain map is the sensory homunculus in the cortex. Sensory information from all body parts travel to specific regions of the cortex to be analyzed. Note that in the picture the sensory representation of the mouth, thumb and tongue are much larger than the leg and arm even though the limbs are far greater in actual size. There are, however, many more sensory signals from these three crucial regions than from the relatively simple sensory apparatus of the arm and leg. Recently, a study showed that one third of the rat’s cortex is devoted to whiskers, occupying 1% of the body. In the humans the visual cortex is 40% of the total cortex for a very small organ the eyes.
Gut Feelings and Broken Hearts
The gut, heart, lungs and skin have very important effects on emotions, motivation and cognition. While internal states can change these organs, external events can cause heart pounding, heavy breathing, stomach pains, or skin crawling. We describe feelings as hurt feelings, cutting to the quick and heartache.
The two major branches of the autonomic nervous system, the sympathetic and parasympathetic, are intimately tied to all the visceral organs, such as the gut, heart, lungs, and the kidneys, and are also very connected to emotions. Only a very small part of this enormous innervation is perceived consciously, such as those circuits used for eating and bowel movements. Both the sympathetic (adrenaline – fight and flight) nervous system and the parasympathetic (rest, dreaming, rebuilding – acetylcholine) are important in emotions and were highlighted in the posts on sleep, dreaming, body consciousness and spiritual experiences.
The spinal reflexes and the nerves in the hypothalamic adrenal pathways are very important in both immune and emotional systems and communicate with the hypothalamus and amygdala. Brain–gut interactions are highly correlated with stress reactions and anxiety.
Which Evolved First – Body Maps or Feelings
Body maps are used to monitor changes in important parameters such as blood pressure and blood sugar, and when out of range in the map, alterations are made. One theory is that maps came first then emotions afterward. Conscious feelings are not needed to regulate glucose and blood pressure with a range. But, feelings are needed, perhaps, to have us eat a fruit or sit down.
Totally unconscious circuits of regulation include some aspects of immunity, smooth muscle control in the heart and digestion. Feelings may draw attention to what is necessary for the organism to attend to based on adjustments needed in the body map. One important example is the “sick feeling”. The very important relationship between the immune and nervous systems is discussed in my Guest Blog for Scientific American Mind. Feelings are also used to learn from experiences, and allow categorization of experience. With complex behavior, correction is easier with feelings than just body maps.
The changes triggered by emotions bring about actions, pre programmed to re establish balance. Internal actions include alterations of the heart, breathing and flow of blood. But, other actions are much more complex, such as meeting the needs for food, water, sex, mating. These involve brief and long term complex social behaviors. These behaviors can be triggered by feelings.
Where are the Maps and Feelings – The Cortex
The cortex has several regions that have body maps. Brainstem maps project up into the major somatosensory SI and SII, a detailed topographic map of the entire sensory system. However, if damaged, it doesn’t affect pain, heat and most emotions. These seem only to be a regulatory region for emotions, not critical for their existence. Likewise, the anterior cingulate have maps, but usually are related to specific motor responses to pain.
The insula is one region with complex maps that relate to emotions. Most of the information about internal states converges on the insula, which is the main place in the cortex for this information. The insula may be critical in the connection of intellect and emotion– the two avenues of human decision making that are also represented in two different regions of the frontal lobe
The insular cortex is a critical brain region in a wide range of emotions – negative emotions such as anxiety, fear, agitation, loss of balance, crying, dizziness – positive emotions such as laughter, and empathy. This region of the cortex is highly integrated with internal sensory information about the body, and is influenced by the gut. The insula integrates signals concerning the sensations of inflammation – pain, warmth, and physical swelling; heart rate; a full bladder; shortness of breath; swallowing; the ability to speak; disgust from smells; and gut sensations. The insula is also highly connected, as would be expected, to other cortex regions involved in memory, language and other higher brain functions.
The insula appears to modulate feelings, but not be critical for their existence.
Two different pain systems impact on the insula. The first is the sensory pain system in primary and secondary sensory cortex connecting to the posterior insula that codes the types of pain and how strong it is. The second system including the cingulate cortex, the limbic system communicating with the anterior insula codes for an affective aversive component of pain. Recently, a study of skin related acute pain (not disease related, or chronic) found signatures of physical pain in a definite widely distributed network, but these findings are tentative because of the rough sensitivity of the fMRI used.
But, children with no cortex (no insula) show feelings, and damage to the insula – complete bilateral destruction by herpes simplex – doesn’t destroy all feelings. In fact, bilateral insula destruction increases thirst and hunger, as well as pain, pleasure, sadness and happiness, caring and compassion, possibly because the insula is regulating and modulating the emotions and feelings from lower brain levels not creating them.
The Major Maps of the Internal Body are Below the Cortex in the Brainstem
In the brainstem, below the cortex, there are many different brain regions that are related to motivation, drive, actions, and emotions. Only some of these brain centers have a body map; the centers with the maps are closely correlated with specific bodily sensations. In the brainstem the important centers that have maps are Nucleus Tractus Solitarius (NTS), Parabrachial nucleus (PBN), Periaqueductal grey (PAG) and the Superior colliculus (SC.)
Many other very important regions without maps are probably not directly forming feelings, but rather modulate feelings and initiate correct action. These include the ventral tegmental area (VTA), monoamine regions (serotonin, norepinephrine, dopamine), the red nucleus, and the hypothalamus. Other important regions that don’t have maps amygdala, nucleus accumbens, basal ganglia and basal forebrain.
The brainstem is involved in continually monitoring the internal workings of the body. This includes senses from organs, mainly temperature, touch, proprioception and vestibular sense. The most important internal monitoring nerves are:
- The vagus connected to heart, lungs, gastro intestinal, and urinary systems.
- Spinothalmocortico pathway – senses thermo and chemo info of body to spinal cord, brainstem trigeminal nucleus.
- Circumventricular organs – special brain circuits for energy metabolism, water and salt balances where brain sits on the unimpeded shores of the spinal fluid
- The first place where whole body maps exist are regions of the PBN, PAG, and reticular formation. These are critical region for body regulation, and might be for feelings.
- The superior colliculus (SC) receives vision, auditory, somatosensory data with three superimposed correlated spatial maps spatial. This may be were the first integrated sensory map occurs between the outside data and the internal landscape – visual, tactile and auditory attention, mind and self.
Damage to the posterior brainstem results in coma. This includes several regions that have complete body mapping, such as the PBN, PAG and SC, as well as the reticular activating system and centers of release of neurotransmitters serotonin, norepinephrine and acetylcholine. Damage to the anterior brainstem region, causes the “locked in” state where emotions, feelings and other cognition exist but communications to the outside is blocked.
Animals With No Cortex Have High Intelligence and Emotions
There are increasing animal studies showing advanced cognition and feelings/emotions without a cortex at all. Lizards, birds and bees do not need a cortex for advanced decision-making, symbolic language, complex nurturing social life, and emotions.
The small-brained animals have unique brainstem structures unlike human brains. These unique brainstem structures have neurons that are as advanced and complex as the human neurons. (A summary is in a recent article I co wrote with Marc Bekoff Ph.D in Psychology Today.) This article notes that because animals without a cortex have unique brain regions that function as if they are a hippocampus and frontal cortex, current brain evolutionary theories must be re evaluated. These animal brainstems are very different from humans, and do not have a cortex, but have feelings and advanced cognition.
In humans it appears that a cortex is important for advanced cognition but not for feelings.
Individual Neurons and Feelings
Do individual neurons participate in feelings?
Most neuronal axons travelling to and from internal organs are unmyelinated (or very slightly myelinated, which means one Schwann cell surrounds many neurons). This includes the sympathetic, parasympathetic, and the hormone regions, which affect the internal organs. The major spinal paths are similar and includes the very important vagus nerve including its cranial nerve branches.
Not having myelin is unusual since these axons are critical for internal homeostasis and myelination increases the speed by up to eight times. However, myelin also insulates the axon membrane from any ionic exchanges. Newly discovered mechanisms send information sideways from the axon itself (ephaptic communication is described in several posts) when myelin is damaged and in un-myelinated axons.
The internal milieu benefits from the axons, without myelin, being able to sense important chemical changes, and allows much greater communication about internal states including complex immune function. Without myelin the entire axon can respond to the extracellular matrix, energy flow and ionic status (Please see a previous post Brain Electricity and the Mind.)
Previous posts on the relation of immune and nervous systems have noted how important the vagus nerve is in connecting immune and nervous system processes which often occur along the axon. My recent article summarized extensive data about important immune communications with back and forth signaling in the vagus nerve, which respond to local immune activity. The vagus needs these ephatic mechanisms to accomplish local communication for immune activity in inflammation. Specific chemicals stimulate the vagus along the axons, including receptors for ATP, serotonin, acetylcholine and capsaicin. None of this could happen with myelin.
Conclusion – Feelings and Body Maps in the Brain
Feelings are integrally related to internal body states including connections with the heart, lungs, skin and gastro-intestinal tract. The body maps are very significant in the body’s attempts to regulate the internal milieu including all of the organs. They continually attend to the homeostasis of important parameters such as blood pressure and blood sugar.
The insula in the cortex modulates body maps and feelings with connections to both intellect, emotion memory, language and other higher brain functions. It has the most detailed overlapping body maps.
But, feelings exist without an insula. It appears that feelings begin in the brainstem regions, the same as other animals. The entire evolutionary relationships of animal and human brains need to be re evaluated because animals without a cortex have evolved more advanced brainstem structures that perform as if they are a cortex and the hippocampus. In humans feelings start in the brainstem but are modulated by higher cognition with the cortex.