5 - Brain Mechanisms of Emotion
(EN: No chapter introduction before the first section.)
How do Brain Mechanisms of Emotion Work?
The authors cite some outdated metrics about the number of cells and synapses in the human brain (EN: The numbers have grown much larger and the way in which cells communicate is no longer limited to synaptic connections) as a means of suggesting that it is a very complex organ whose functionality cannot be observed in detail.
Researchers have poked about the brain by largely indirect or general means. Dissection of a dead organ yields little insight into the functioning of a live organ. Temperature, electric current, and the movement of chemicals has been observed in a very general and superficial way. The effects of drugs or lesions can be observed.
The authors speak disdainfully of the tendency to analogize the brain to a computer - which becomes a tautology because computer logic is a pale and simplified version of human logic in the first place, and to compare the original to a poor imitation is bound to lead to confirmation of our assumptions and limitation of our perspective.
The air of scientific certainty about the function of the brain due to recent advances is steeped in hubris - even the most sophisticated modern technologies for analyzing the brain are laughably primitive and imprecise.
The foundational schema of the brain mechanisms and emotion can be traced to Descartes in 1649. His theory was that stimuli from the sensory nervous system are routed to the brain, where they provoke a reaction that is communicated to the motor nervous system that causes tension in muscles that poise the body to take action. "The history of neuropsychology has largely been that of showing how the mechanism proposed by Descartes occur by means of message carried by electricity and chemicals."
Which is to say that modern neuroscience is still guided and constrained by theories of a man who, nearly four hundred years ago based on his speculation and imagination of things that were impossible for him to observe.
This is not to say that science is entirely impotent, merely that its "conclusions" are merely observations, and its "facts" are merely theories that we do not have the means to fully confirm. One might imagine future research to confirm or refine the theories of the present day, but it is also entirely possible they will be contradicted.
Such is the state of "knowledge" about the human brain in the present day. It provides much greater insight than before - but it is still merely insight, and not firm and reliable answers.
Research: Brain Lesions and Stimulation
The authors refer to Canon and Bard's experiments in the 1920s which "deprived" cats of their neocortex and found that the creatures were perfectly capable of surviving. They were largely immobile and had to be force-fed, and their only spontaneous reactions were those of undirected hostility to any stimulus, but they did survive for quite some time.
These experiments supported the earlier notion of the structures of the brain: that the cerebellum was sufficient to maintain involuntary movements of the cardiopulmonary system, and that the hypothalamus supports basic stimulus-response necessary to react to danger (fight or flight mechanism), as well as the theory that all the higher functions are managed by the cerebrum.
It also supports the various theories of the function of the limbic system as being regulatory in nature and associated with negative emotions (anger and fear) - and that all other emotional states are cerebral in their origin.
Evolutionists got hold of the notion, and theorized that the structures in the brain developed along evolutionary pathways - with reptiles and amphibians being limited to the brain stem, lower orders of mammals using a "paleomammalian" brain consisting of the limbic system, and higher orders of mammals using the "neomammalian" brain that augments the cerebellum and introduces cerebral structures. As such, the complex brain of modern human beings developed incrementally along with other physiological changes.
Of particular note is the theory that the "reptile" brain did not evolve or atrophy, but remains fully resident in mammals and modern man. Instead, the cerebral structures are an entirely separate module that was added on, and the conflict we feel is literally a struggle for control between two separate brains - the limbic and cerebral structures - with out emotions and behavior being the results of a negotiation between hostile forces.
The Striatal System
The striatal system is reckoned to be the brain stem, the core of the limbic system which is present in reptiles. The authors turn to Paul MacLean (1990) and his extensive study of lizards, whose activities are limited to basic survival behaviors (marking and defending territory, foraging, hunting, hoarding, forming basic social groups, etc.) These are habitual and largely predictable behaviors that are followed with little variation by individual specimens.
The studies identified four expressions (identification, aggression, submission, and courtship) and six more specific behaviors (routine, imitation, tropism, repetitious behavior, reenacting, and deceiving) which are also evident in most bird species.
Ultimately, his hypothesis has been that the striatal region of the brain is involved in species-characteristic behavior patterns that are supportive of basic functions (eating, mating, controlling territory, avoiding danger, and aggression) - and more, that these functions remain the same in human subjects, as observations of subjects with damage to the striatal system show impairment in these regards.
The Limbic System
Still referring to McLean, comparative studies of lower species of mammal to reptile found there to be three additional behaviors - things that mammals do and reptiles do not: maternal caregiving, vocal signaling, and play. (EN: "play" in this sense is modeling or practicing behavior outside of the circumstances in which it is useful.)
In this sense, the limbic system provides support for behaviors common to social coexistence, primarily caring for infants and competing with others for resources. This is largely unique to mammals because reptiles are largely solitary - they are not nurtured by their parents after they hatch from eggs and while they may share territory they do not behave as members of a social group.
There is some niggling over details here, as some species of mammal have a solitary life after maturing to adulthood - so the level of socializing and interdependence varies among species and individuals. Even man, whose social interaction is more extensive and complex than any other mammal, is able to persist in solitude albeit with great inefficiency.
As to the limbic system itself, it represents evolution of the basic structures of the striatal system - which is to say that it is not, like the cerebrum, an entirely different nature of tissue, but merely an "evolutionary enlargement" of striatal components.
Kluver and Barcy (1937) removed the neocortex of primates and found their behavior to be distinctly different than those of the cats in Canon and Bard's experiments (described earlier in the chapter):
- The monkeys did not become inert, but remained animated
- They became docile rather than hostile
- They continued to eat, but did so indiscreetly - any item that could be chewed or swallowed (feces, rotten meat, etc.) would be ingested
- They also continued to mate, but also indiscreetly - coupling with members of the same sex, mounting or displaying when not in estrus
It's noted that the same symptoms are seen when the amygdala is removed or damaged in primates, even if there is no damage to the cerebrum. The specific effects above have been named Kluver-Barcy syndrome. Also, these experiments caused the amygdala to be included in the limbic system (it was previously believed to be a portion of the cerebrum).
Some follow-up studies by Hess are mentioned, particularly in the early use of electrodes to stimulate brain activity. The way that electrodes function is to deliver a charge to a specific area of the brain that is assumed to stimulate activity - the initial "foreign" energy that has no purpose is "translated" by neurons into normal and contextual impulses. In a literal sense, it short-circuits the brain. In that way an electric charge to the hypothalamus of a cat will provoke it to attack a nearby object.
Experiments with rats (Olds and Milner 1954) demonstrated that electrical stimulation causes ritual behaviors to occur. When a specimen receives stimulation in a given situation (eating, moving to a different location, to press a lever, etc.) the specimen tends to repeat that behavior even when it is otherwise unnecessary.
(EN: This casts some light, and likely some doubt, on the use of rats in addiction studies - that is, rats that prefer drugs to food do so because the drugs provide greater stimulation - in that sense there's nothing particularly special about the drug, it's just another method of stimulating the brain, as the same effect can be achieved by electrical stimulation.)
These experiments led to the notion of the brain having "pleasure centers" and behavior being driven not by functional outcomes, but merely by the desire to experience stimulation.
Further experimentation (Kakolewski 1970) added greater refinement, and found that stimulation to certain parts of the brain created more specific drives: anger, hunger, and thirst could be aroused by stimulating specific parts of the limbic system.
There's also a brief mention that routine behaviors can also be effected by providing other rewards - if a subject is given a reward for visiting a certain area of its enclosure (to a rat, a food pellet, marble, or bit of wood is a reward) it will repeat the behavior.
Though it's noted at this point that statistical probability became involved as a method to differentiate stimulated behavior from naturally occurring behavior (drinking was more likely to occur with electrical stimulation than without it - it was not an automatic result). Given that the outcome was probable but not certain, it was reckoned that stimulation was similar to creating a "mood" that caused the specimens to be more inclined to perform a given action rather than guaranteed to perform it as a matter of course.
The authors feel that Glickman and Schiff propose "the most comprehensive theory of the effects of brain stimulation." They proposed that stimulation activates species-typical patterns of behavior but the encouragement od discouragement to act relies on the nature of the stimulation (positive or negative reinforcement). They further proposed that curiosity is a quality that leads mammals to experiment with behavior to determine the outcome.
Turning to human studies, it is found that damage to the amygdala coincides with defective social decision making and a diminished skill to recognize emotional expressions in others.
There is also mention of epilepsy in the limbic system that causes temporary lapses and, over time, spreads to a larger area of the brain, such that the onset of a seizure can be experienced as an emotional state. Dostoyevsky, an author who suffered from epilepsy described the onset of a seizure as a feeling of "happiness ... entirely in harmony with myself and with the whole world." It is further suggested that epileptic patients progress from physical behavior to emotion, to mood, and even to personality changes as a result of their condition.
(EN: I skimmed and skipped the remainder of the section because the authors carry on like this for a while, drawing further away from the topic to explore peripheral issues.)
Emotions and the Neocortex
The neocortex represents a significant evolutionary advance. In humans, it represents 80% of the whole brain mass. Anatomically, it is an outer layer that wraps the brain, about a tenth of an inch thick. But folded and creased such that it would cover an area of about 310 square inches if laid flat.
The brain is generally described as being a symmetrical organ with two hemispheres, and there is a switching effect such that stimuli from and motor control of the right side of the body is processed in the left side of the brain and vice-versa. This has been well established by both observation and dissection.
There is also the general notion that the hemispheres of the brain have different cognitive functions, the left side being more rational and the right being more creative. (EN: More recent findings support the basic premise, but not to the same degree. That is, both sides of the brain are engaged, but activity in the neocortex is higher on one side for certain stimuli and activities.)
It is common to evaluate subjects as being predominately left- or right-brain oriented. The hemispheres are not entirely isolated in normal individuals, though cognition and behavior tend to favor one side or the other.
It's noted that some individuals develop a "split brain" through developmental defect or injury that impairs the brain's ability to pass data from one hemisphere to the other. One subject with such a disorder was unable to describe images when their left eye was covered, as the data was unable to reach logical and language centers in the left hemisphere.
Emotions are considered to be predominately a right-brain phenomenon. While the left-brain is effective in identifying people by their facial features, the right brain is more effective in interpreting emotional expressions (as demonstrated by Escoff 1992). But at the same time, the left brain is more effective in determining emotional overtones in language.
Another bit of trivia (Bloom 1989) is that babies begin speaking around the age of 13 months, but lack emotional expression until 19 months.
Its also suggested that positive emotions are more strongly represented by the left side of the brain and negative ones are on the right, based on the electrical activity in response to stimuli (Davidson 1990). An in terms of motivation, the left brain is more engaged in seeking gain whereas the right brain is more engaged in avoiding loss.
The author presents a string of experimental evidence that the left/right positive/negative correlation is evident in emotional episodes, moods, and even personalities: those who are left-brained are more positive than those who are right-brained.
The Amygdala
The amygdala was previously described as a section of the limbic system that is closely associated to survival-based emotions: fear and aggression. Additional observations suggest that the amygdala, along with the hypothalamus, process basic sensations of pleasure and pain, and react accordingly.
It is further theorized that the amygdala is the foyer to the neocortex, though which all stimuli pass prior to processing (LeDoux 1993) and that emotions within the amygdala precede and sometimes supersede cerebral emotions.
This may explain the effectiveness of conditioning - in that a conditioned response is triggered in the lower brain (the association of pleasure or pain to a given stimulus) prior to the higher brain's ability to process the sensory input and develop a cerebral emotion. This also suggests the reason that conditioning is more effective on lower orders of mammals than on humans, as human beings have greater capacity to analyze, override, and reprogram their reactions by virtue of a more substantial neocortex.
Neurochemicals, Modulation, and the Emotions
It's been observed that nerve fibers transmit information to one another by means of electricity and chemicals, and it's currently theorized that the electricity is generated from within a cell whereas chemicals are used to transmit information from one cell to the next. There are three basic types of neurotchemical:
- Transmitter substances - Primarily glutamates and amino acids (such adrenaline, dopamine, and serotonin) that are emitted from a nerve cell to carry information across synaptic gaps to other cells
- Hormones - Substances that are carried in the bloodstream that affect organs and tissues. Most hormonal systems are controlled by the hypothalamus.
- Neuromodulators - These chemicals, primarily peptides, have not garnered much attention from researchers, but it is theorized that they are involved with sensing and reacting to pain and pleasure, and thus have emotional effects
These chemicals are also important to emptions i- but more importantly, because they are chemicals they can be augmented by drugs and medications that can directly affect systems related to emotions, moods, arousal, and other psychological states - though it is worth considering that this impacts the physical symptoms of emotions, but do not substitute for actual emotions (that is, the drug can help the body not to experience panic, but it does not address the psychological factors that cause panic to be felt naturally).
Restoration of Transmitter Functions in the Striatal Region
The author gives a rather extended account of experimentation with L-Dopa, a precursor of dopamine, in patients with encephalitis lethargic (which causes constant sleep) who were experiencing periods of wakefulness during which they were normally despondent.
The effect of the drug was a dramatic restoration of mental functions - but unfortunately, the patients also demonstrated "passions and strong appetites" as well as severe psychotic episodes. And overtime, they developed a tolerance to the drug which rendered it ineffective.
(EN: the film "Awakenings" considered this incident, but in a highly inaccurate way. The actual patients regained awareness and responsiveness, but in an extremely limited degree and for a short period of time, which was quite a change from being unconscious and unresponsive, but still significantly impaired comparative to a normal individual.)
What the authors find striking about this incident is that it demonstrates the ability of drugs to restore function to the striatal system.
Peptide Effects on Fear
The authors consider the effects of peptides on panic attacks, which are sudden onsets of intense fear lasting around half an hour. Unlike phobia, which relates to a specific object or situation, panic is a fee-floating sense of fear that mimics much the same cognitive and physical symptoms.
Researchers found that a peptide called cholecystokinin (CCK) induces panic attacks without external cause, and injections can reliably induce anxiety, apprehension, and fear in simians and rodents.
Various test s have been done to confirm the effects of CCK, and it seems that this peptide is responsible for spreading the effects of fear through the brain and central nervous system, particularly localized to the limbic system. (EN: The authors have nothing further to add to this observation.)
Integration of Neurochemical and Anatomical Information
It is highly likely that human brains contain "a small number" of emotional mechanisms that are common to other species: basic emotion such as anger, fear, attraction, sexuality, attachment, and anxiety are all closely related to the limbic and striatal systems, and each has specific neurochemical profiles.
The basic set of material emotions involved in procreation, nurturing, and mother-child interactions are common to many species of mammal. They have most often been studies in rats, whose infants are born blind and immature. Not only do mothers nurture and care for the infants, but the infants themselves have specific behaviors such as squeals of distress that vary between hunger and separation anxiety, that cue maternal behaviors.
Researchers measuring the brain chemicals of rats show a dramatic increase in peptides during late pregnancy. These chemical changes cause physical changes in the maternal rat (like the production of milk) but also cause behavioral changes. Female rats who have not recently given birth do not act in a nurturing manner toward rat pups, and in fact have been observed to actively avoid them.
It is also observed that certain maternal behaviors are learned rather than hormonal, as a mother rat whose hormone levels have returned to normal still behave in a nurturing way toward their young, and female rats who have never given birth will, if placed in an enclosure with young rats, eventually overcome their aversion to them and display material behaviors such as grooming and physical proximity.
The researchers have conclude that the maternal instinct is in the hypothalamus, principally the pre-optic region, and involves the hormones of estradiol and prolactin. However, this does not mean that maternal behavior is exclusive to that area or to those chemicals, as it is a highly complex set of behaviors that includes both instinctive and learned patterns.