In type and psychopathology we saw that if we could understand just who from a typological point of view becomes a schizophrenic or manic-depressive, then it would be possible to begin to separate descriptions of the disease from the descriptions of the particular types that are mingled with them. Frankly, this particular problem is but one facet of a much wider one. Despite the enormous scientific progress that is taking place today it is rare when this scientific work averts to the question of human differences. It simply does not ask itself in an adequate way how its results are going to be skewed or obscured by the fact that there are important natural typological differences among the subjects they are examining.

For example, computerized tomography and magnetic resonance imaging, positron emission tomography, as well as other techniques, are unearthing potential differences between a schizophrenic brain and a normal brain in the form of ventricular enlargement, the number of dopamine D2 receptors and so forth. But we really have no idea how one normal brain differs from another. Will ectotonics have more frontal lobe activity than endotonics? Will introverted intuition types have more D2 receptors than extraverted sensation types? These questions are not farfetched, and if they appear so to the neuroscientist it is because this is but another aspect of his own biologically founded psychiatry that has not yet been rescued from the environmentalism of the past.

Recently C. Robert Cloninger has described a threefold typology based on novelty seeking, harm avoidance, and reward dependence. The person high in novelty seeking is impulsive and exploratory, and eager to take up new interests, but neglects details and quickly becomes distracted and bored. In contrast, the person low in novelty seeking is slow to make decisions, focuses on details, is frugal, orderly and slow tempered.

People high in harm avoidance are cautious, tense, inhibited, easily fatigable, shy and apprehensive worriers, while people low in harm avoidance are regarded as optimistic, outgoing, energetic and so forth.

The individual high in reward dependence is eager to please and help others, is warm, sympathetic and sensitive to social cues. The person low in reward dependence are tough minded, emotionally independent, socially detached, etc.

It is not farfetched to see in these descriptions, developed in more detail in three scales by Cloninger, similarities with Sheldon's three temperaments. The novelty seeker is closest to the mesotonic, the harm avoider to the ectotonic, and the reward dependent to the endotonic. It is also possible these descriptions have traces of Jung's psychological types. What kind of mesomorph is the novelty seeker? He looks like the extraverted intuition type. Cloninger describes the high rated novelty seeker: "Consistently seeks thrilling adventures and exploration; disorderly and unpredictable; intolerant of structure and monotony regardless of consequences; decisions and opinions based on vague global impressions and intuitions; consistently plays roles for dramatic effect so that real feelings and beliefs are uncertain; consistently spends on impulse in absence of external constraints; interests and friendships shift rapidly with the latest influence without any sustained commitments." ("A Systematic Method for Clinical Description and Classification of Personality Variants", p. 576)

But who is the person who is severely low in novelty seeking, who is disinterested in exploratory pursuits, and is highly orderly, highly frugal, slow to change interests and social attachments? We will not be far off if we look to the introverted sensation types, who are the typological opposites of the extraverted intuition types.

The person high in harm avoidance is inhibited by unfamiliar situations and strangers, and is easily fatigued. Here we find the ectotonic introverted intuition type. His opposite on the somatotype chart is the endomorphic-mesomorphic extraverted sensation thinking or feeling type, or extraverted thinking or feeling sensation type, that Cloninger describes as carefree meeting strangers and strange situations, and not fearful of risks, highly energetic, confident and optimistic, etc.

The reward dependent personality is closest to Jung's extraverted sensation type, and the low reward dependent person closest to the introverted thinking type, which is found opposite to the endomorphic pole on the somatotype chart.

While Cloninger does not relate his typology to Jung or Sheldon, he does give some indication of its biochemical foundations. He relates novelty seeking to dopamine and the brain's behavioral activation system, and harm avoidance to serotonin and behavioral inhibition: "Ascending serotonergic projections from the dorsal raphe nuclei to the substantia nigra inhibit nigrostriatal dopaminergic neurons and are essential for conditioned inhibition of activity by signals of punishment and frustrative nonreward." (p. 576) And reward dependence is correlated to norepinephrine and the acquisition and resistance to extinction of rewarded behavior.

Let's pursue this kind of neurobiological typology by looking at dopamine. The discovery of chlorpromazine led to the hope that its chemistry and that of other neuroleptic drugs would help us understand the chemistry of schizophrenia. Scientists soon found that chlorpromazine interfered with dopamine by binding to the dopamine receptors, and preventing dopamine from attaching to them. This led to the initial dopamine theory of schizophrenia which proposed that schizophrenia was caused by too much dopamine. However, post-mortem studies of schizophrenic brains did not, for the most part, bear this out. This, in its turn, led to the current dopamine theory in which schizophrenics have an increased number of dopamine D2 receptors. Dopamine research has been closely connected with Parkinson's disease, which is a motor disorder in which people have difficulty in initiating action. It was found that the dopamine neurons in the substantia nigra in Parkinson patients are fewer and that they have less dopamine.

Today any number of dopamine theories of schizophrenia have been proposed, including a lack of dopaminergic activity, or hyperdopaminergic activity in the limbic system, and hypoactivity in the prefrontal cortex. But do introverts and extraverts differ in dopamine activity? If dopamine helps initiate action, then we would imagine extraverts would have a higher level of it.

In 1975 Barchas, Ciaranello, Kessler and Hamburg examined the genetic aspects of catecholamine synthesis in mice. The catecholamines include dopamine, norepinephrine and epinephrine, which are important in normal behavior and psychiatric disorders. They stated:

"Strain differences exist in the activity of the enzymes involved in the synthesis of the catecholamines in mice. This variation has a genetic basis. Differential regulatory mechanisms of the enzymes involved in catecholamine formation exist in different strains and presumably the disvariation also has a genetic basis." (p. 27)

And they concluded:

"The present studies, taken together, represent the first demonstration that the activity of the enzymes involved in catecholamine biosynthesis are subject to the marked variation as a consequence of genetic differences. The experiments also provide the first suggestion that major differences in the physiological regulation of an enzyme involved in the formation of catecholamine exists within a single species." (p. 54)

But do these differences exist in humans? Roy King attempted to frame a hypothesis about dopamine function and temperament which can be summed up: "there may be genetic differences in mesolimbic dopamine cell numbers, as well as differences in dopamine release into the limbic striatum.", and 11mesolimbic dopamine lowers the response threshold to affectively significant cues, thereby initiating action." ("Motivational Diversity and Mesolimbic Dopamine", p. 363)

Later King and his colleagues studied the dopamine levels in cerebral spinal fluid of 16 male patients suffering from depression who were also given the Eysenck Personality Inventory. They found a significant correlation (R=0.58, P less than 0.01) between the dopamine level and extraversion.

A strong positive correlation has also been observed between 5-HIAA, the metabolite of serotonin and HVA, the metabolite of dopamine, in human cerebro-spinal fluid. In one study by Hans Agren and his colleagues 175 men and women with depressive disorders show this relationship between 5-HIAA and HVA, which was confirmed by brain studies on dogs, which found "highly significant and positive correlations between dopamine and serotonin in areas of the brain stem and hypothalmus. In the basal ganglia (except the substantia nigra) the correlations are negative." (p. 183) What makes this study particularly interesting from our point of view is that in the group of women, the 5-HIAA was effected by age, height and body size: "women show highly significant correlations with age (positive) and height (negative) for both 5-HIAA and HVA. Dividing height with the cube root of weight (the ectomorphy index) strengthens the correlation coefficients even more." (p. 179) In short, the taller the women the lower the levels of 5-HIAA. Is it possible to relate this lower level of 5-HIAA in the more ectomorphic women to the lower levels of dopamine found in cerebral-spinal fluid of those who scored higher in introversion? If this relationship could be borne out we have both introversion and ectomorphy related to dopamine levels.

Now let's create a somewhat fanciful example to illustrate the potential interactions that might exist between type and a disease like schizophrenia. It would be an ectomorphic introverted intuitive type who lacked mesomorphy and exhibited what Sheldon called asthenic characteristics, i.e., a failure of the organism to reach its full flowering, that would be most at risk for schizophrenia. Is it possible that this type's inhibition in terms of action is related to a low level of dopamine? And could he have more D2 receptors to make the most of what dopamine he does possess? Then if he suffered a metabolic insult that effected the dopamine system he would be more likely than other types to cross the critical threshold that leads to the overt symptoms of schizophrenia. He would be unable to mobilize his already weak extraversion of action in order to stay in contact with the world. In short, he would become a hebephrenic schizophrenic. And when he is treated with neuroleptic drugs the suppression of the already low dopamine level in the motor centers could lead to Parkinson-like symptoms, or even tardive dyskinesis.

And if the already low dopamine levels of the introverted intuition type are lowered still more by the disease process, what will be the psychological effect on this type's already highly developed self-awareness? Will it reach a fever pitch as the introversion - extraversion balance is disrupted? Will the high arousal of the introvert go out of control, freewheeling without the normal enmeshment it has with everyday reality through its extraversion of action and affect?

Each of the salient characteristics of schizophrenia has to be evaluated according to the type of the person who has the disease. Schizophrenia has a heritable component, but what part of this component is due to genetic foundation of introversion and extraversion and somatotype? Schizophrenia seems to implicate the dopamine system, but what is the natural dopamine system like of those types most prone to it? Schizophrenia seems related to various brain abnormalities like ventricular enlargement and increased dopamine content in the amygdala on the left side of the brain, but what do normal introverted intuition brains look like?

These reflections on dopamine are indications that there are important and extensive biological foundations to introversion and extraversion, as well as the rest of our integrated typology. There may be even what could be called a biological introversion extraversion axis. Why, for example, did Kretschmer describe the pyknic and the asthenic? We have already seen how Sheldon broke down these types into more fundamental components, but from an observational point of view Kretschmer was on to something. The pyknic, or endomorphic mesomorph, is the most dramatic kind of extravert, the most visible. He draws comments down upon himself. It is almost as if he is the most extraverted of the extraverts, while the introverted intuition type is the most introverted of the introverts. There is a certain affinity that endomorphy and mesomorphy have for each other in virtue of both being related to temperamental extraversion and mass while ectomorphy is opposed both to mass and extraversion. Sheldon's somatotype diagram is, as he realized, an idealization of the actual relationships that exist between the components. We should really shorten the distance between the endomorphic and mesomorphic poles, and lengthen the triangle in the direction of ectomorphy. Then, if we draw a line from the ectomorphic pole to the middle of the now shortened leg between endomorphy and mesomorphy, this line would represent a tentative introversion - extraversion axis. On the extraverted end we find not only the pyknic, but the delinquent and criminal, the heart attack victim and the manic-depressive. All of them show a dynamic extraversion, often carried to the extreme. On the other end we have the extreme introversion of the introverted intuitive type and the schizophrenic.

If there is, indeed, a biological extraversion introversion axis, it will appear in many places once we begin to look for it. For example, there have been any number of studies which have attempted, however tentatively, to relate temperament to ABO blood groups. Gille-Maisini, again drawing on the work of Leone Bourdel, as well as compiling the results of various studies, describes the rhythmic temperament as having a predisposition to blood group B, while the complex temperament, which is a mixture of the rhythmic, melodic and harmonic, is mostly AB. The rhythmics are closest to the extraverted thinkers. The harmonics, which he related to introverted intuition, are predisposed to group A, while the melodics, which are closest to the endomorphic mesomorphs, or pyknics, have a high frequency of type 0. Eysenck relates the AB blood type to introversion, and finds that it has a much higher frequency in places like Japan and Egypt than in the United States and Italy. Our biological axis of introversion and extraversion would have at one end the 0 blood type, and at the other, the A and AB, while the B would represent a branching off closer to the 0, but also having intermediate characteristics. There is a relationship between affective diseases and blood group 0, and schizophrenia with A, and the predisposition to 0 among the affective diseases is especially strong in manic-depressives. There is also a relationship between 0 and duodenal ulcers. When Gille studied a group of male schizophrenics in Quebec, he found a greater frequency of paranoid schizophrenia among type 0, and a greater frequency of A among what he describes as simple and hebephrenic catatonic schizophrenics. Thus, he parallels the distinctions already made between these two basic classes of schizophrenics in virtue of differences in somatotype. There is some evidence, therefore, of an O-A dimension aspect in our introversion - extraversion axis, but it is overlaid with other tendencies and assertions that are hard to evaluate.

Some of the most fascinating evidence about these biological foundations center around the pineal gland. In ancient times the pineal was associated with clairvoyance. Descartes, in the 17th century, thought it was the bridge between body and soul, and for several centuries after him attempts were made to discover evidence in the anatomy of the pineal for mental derangement. After these attempts proved fruitless interest in the pineal waned, and it has only been in recent times that it has made a strong comeback. In 1958 Anton Lerner discovered a substance in the pineal that had a blanching effect on the melanin in frog skins, and he called it melatonin.

The pineal is a small, pea-sized, unpaired organ in the brain with close links with the hypothalmus and pituitary. Melatonin has a number of characteristics of great interest to the Jung-Sheldon typologist. First of all, the action of the pineal is primarily inhibitory. Melatonin, for example, diminishes the weight of the thyroid, reduces the uptake of iodine and inhibits thyroxin secretion. The pineal effects adrenal and thyroid glands which are involved in survival in the cold. Therefore, there are more complex pineal glands in penguins, seals, and walruses than in crocodiles, armadillos and manatees. ("Pineal Bodies and Thermoregulation", C.L. Ralph) Peak melatonin values occur in winter and summer, and lower levels in spring and autumn. Melatonin inhibits ovary function and lowers testosterone levels. It is lowest at ovulation and peaks at menstruation. It induces sleep and exacerbates the symptoms of depressed patients and those with schizophrenia and Parkinsonism, and is diminished by the anti-psychotic drug propranalol. ("Melatonin in Human Body Fluids", Waldhauser et al.) (P.E. Mullen) (Note: One reader has objected that propranalol is not an anti-psychotic drug.) In line with the transmethylaton theory of schizophrenia formulated by Smythes and Osmond an abnormality in the biochemical machinery that produces melatonin could lead, instead, to a hallucinogenic substance. LSD, in fact, which increased MBTI scores in intuition, augments melatonin synthesis.

The second major point is the close connection the pineal has with light and the eyes by both normal visual pathways and non-visually. Melatonin has an inverse relationship to light: the more light the less melatonin that is produced. This leads to a 24hour melatonin rhythm in which melatonin levels peak between one and three in the morning. Melatonin has been found in the retina of several animals and can be synthesized there. In the retina of rabbits it inhibits the release of dopamine so light which causes falling levels of melatonin leads, as well, to higher dopamine levels and to the down regulation of D2 dopamine receptors. (Dubocovich)

In order to see the implications of some of these facts let's look at the intriguing work of Morgan Worthy. Worthy was interested both in sports and in individual differences. He noticed that blacks and whites appeared to differ in their sport abilities, and then he went further and concluded that it was not really racial differences that were primary, but differences in eye color. Those sports which seemed to depend on quick and immediate reactions appeared to have a higher percentage of dark-eyed leaders, while the sports that were self-paced and demanded a certain inhibition before action seemed to have many light-eyed champions. For example, the light-eyed basketball players were significantly more accurate on shooting free throws than the dark-eyed. With this clue in mind Worthy ranged over an enormous variety of studies and eventually drew them together in his Eye Color, Sex and Race: Keys to Human and Animal Behavior. He found that light-eyed birds of prey differed from dark-eyed birds of prey in their methods of hunting, and two different survival patterns could be found among animals, as well. He called these patterns the react-approach-flee and the wait-freeze-stalk, with cats being a good example of the latter. He cites the work of Tyron, who in 1931 compared pigmented and albino rats on their maze learning ability. The rats with the lack of pigmented eyes did better, presumably because they could ignore extraneous stimuli. All in all, Worthy "found strong evidence of an eye darkness/reactivity relationship in such scattered areas as human athletic performance, hunting and escape tactics of birds and mammals, behavioral traits in different breeds of dogs, and laboratory studies of rodents." (p. 65)

But what was causing these differences? Wasn't eye color a relatively superficial characteristic? Perhaps not. Worthy felt that eyes with heavy pigmentation would have better visual acuity but less visual sensitivity, and be more responsive to the red end of the spectrum, while light-eyed creatures would respond to the blue end, and have more visual sensitivity than visual acuity. A certain amount of evidence has appeared linking light eyes with form perception and dark eyes with color perception. The dark eyed are described as more "interpersonally spontaneous and emotionally reactive". (p. 92)

In order to try to explain these kinds of findings Worthy turned to the early results of pineal research. Why did spring seem to bring about an outburst of sexual activity among Eskimos? Why were blind people and prisoners often obese? The answers all seem to lie in the pineal gland. He reports one experiment in which slow-running rats were distinguished from fast-running rats by observation of how much they used an activity wheel. Autopsies showed that the slow-running rats had higher cell densities in the pineal glands and lower cell densities in the adrenal glands compared to the fast-running group. He speculates that light-eyed people have a different level of pineal functioning than dark-eyed people, and he suggests a tentative link between eye color and height in terms of "an inverse relationship between eye darkness and height of human populations." And he pursues this possibility by examining the eye color and length in birds. Worthy also describes a New Zealand lizard, the tuatara, the sole survivor of an ancient line, who has a well developed pineal eye and takes an hour between breaths. Much like the view extraverts have of introverts!

Worthy's work is strengthened by other data. Raymond Cattell, for example, summarizes work on eye color that indicates the possibility of a relationship between light eye color and quantitative reasoning, and dark eyed color and quicker reaction time, and lower flicker fusion speed. The light-eyed are more highly field independent and the dark-eyed more susceptible to being influenced by the opinions of others. He reports that Havelock Ellis surveyed the British National Portrait Gallery, looking for relationships between eye and hair color and field of eminence. He found more mathematical and scientific performance among the light-eyed, and language and religious eminence among the dark-eyed. Perhaps melatonin, like dopamine, represents another area where an integrated typology of psychological types and somatotypes could begin to organize these disparate pieces into a coherent picture.

Let's speculate. Just who are the people who have high natural levels of melatonin? Just who are the most biologically inhibited types? Is it our old friend the introverted intuition type who anchors one end of the biological introversion - extraversion axis? Sheldon surmised that the ectotonia of the pronounced ectomorph kept his mesotonia and endotonia in check. Here we would expect to find a higher proportion of light-eyed people and a special manifestation of length which, as we remember, became one of the final criteria of ectomorphy in Sheldon's objectification of somatotypes. It is the ectomorph, as well, who is the late sexual maturer. David McNeill and Norman Livson found a positive relationship between endomorphy and sexual maturation and a negative relationship between ectomophy and sexual maturation. They felt that height over the cube root of weight accounted for most of the relationship between somatotype and sexual maturation.

Further, the administration of melatonin has been known to increase growth hormone levels and pineal hyperplasia manifests itself in dental and skin abnormalities, abdominal distentions, phallic enlargement, thickened nails, hirsutism and dental precocity, many of which point to the ectodermal layer of the embryo from which the pineal itself derives. Melatonin induces sleep, lowers activity levels, and testosterone levels. It is the ectomorph who sleeps more, acts less, and is mesopenic. The more androgynous males, in contrast to the more virilized males, have more highly developed spatial ability, and Sheldon thought the ectomorph more resistant to cancer than the endomorphic-mesomorph, and melatonin does exert an inhibitory effect on tumor growth.

The ectomorph also has difficulty tanning. Do the higher levels of melatonin mediate this quality, as well? Melanin deposited in human skin does not change as rapidly as it does in certain animals, but melatonin does inhibit the pituitary secretion of melanocyte-stimulating hormone (MSH). It has been suggested that in humans "the pineal hormones may have shifted their target organ from the pigmentary melanocyte cell to a cell sharing a common embryonic and evolutionary origin, the neuron" (Mullen and Silman, p. 410) so while the melatonin does not change skin color it could inhibit tanning. Interestingly, one of the diagnostic signs of Type A behavior at the other end of the introversion - extraversion axis is a "browning of skin of eyelids and of skin immediately below the eyelids. This tan pigmentation is due to a chronic excess discharge of a pigment inducing hormone (MSH) by the pituitary gland. Unlike the tan coming after exposure to excess sunlight, this type of periorbital pigmentation never seems to disappear. Although it is by no means common to all persons exhibiting Type A behavior, its presence in Caucasians invariably indicates severe Type A behavior and usually a relatively high level of serum cholesterol." (Friedman and Ulmer, p. 58) In women it is the lower eyelid that is more likely to be involved. (p. 95)

In X-linked ectodermal dysplasia males show an absence of teeth and sweat glands, and Darwin described a case "of a Hindoo family in Scinde, in which ten men, in the course of four generations, were furnished in both jaws taken together, with only four small and weak incisor teeth and with eight posterior molars." (McKusick, 1985, 1347/30510) And it is intriguing that many of these patients are short and have hyperpigmentation around the eyes. Are there some light-eyed ectomorphs who are hypopigmented around the eyes?

In another X-linked disease, steroid sulfatase deficiency or ichthyosis, a drying and scaling of the skin, certain cases show deep corneal opacities. And it has been suggested that there is a reduction of cholesterol content of the stratum corneum. (McKusick, 1985, 1400/30810)

Gary and Glover report some anecdotal information on the relationship between light eyes and various illnesses. These included the higher incidence of hypoglycemia among light-eyed, light-haired and fair-skinned children (p. 112) and the story of a mother who said that when her autistic child was very withdrawn "her eyes which were normally brown became lighter in color, had no depth, lacked luster and seemed fuzzy." (p. 114) But when the eyes became darker the child would learn rapidly. In a study of learning disabilities, despite the fact that following Morgan Worthy they would have expected that light-eyed students would be better at tasks of discrimination and dark-eyed students better at problems that have to do with resolving power, they found that dark-eyed students are less likely to be learning disabled than light-eyed students, which we can relate to the possibility of their lower lateralization.

Happy and Collins investigated 25 autistic children and 65 normal children in Australia and found that there was an over-representation of hypopigmented children among the autistic group and under-representation of hyperpigmented children. They hypothesized that autism represented extreme introversion and that introversion was connected with the ascending reticular activating system, especially in connection with its dopamine and melanin content, and therefore was related to eye, skin and hair color.

The removal of the pineal gland results in higher blood sugar and blood pressure levels, and the pineal probably plays a role in the immune system. If high melatonin levels are connected with ectomorphy we would expect them to be connected to more psycho, logical ectotonic qualities, as well. Rosenthal and his colleagues studied 29 patients who suffered depressions in the fall and winter which disappeared in the spring or summer. Their study grew out of their experience with a woman patient who suffered winter depressions and summer manias, which were effected by the latitude of where she was living. The winter depression would disappear if she went south for a vacation. She was treated with light therapy with good effect. When the research team advertised for people with similar problems by means of an article in the Washington Post, they got more than 2,000 replies. The resultant 29 subjects contained a large proportion of manic-depressives, and those who were treated with light therapy benefited from it.

Did manic-depressives in this sample suffer from an inability to handle melatonin, which induced in them lethargy and depression? In other studies patients suffering from depression and who stayed up all night were more talkative in the morning. Did a similar reduction in melatonin levels play a role here, as well?

Tyron's albino-eyed rats did better than pigmented rats in mazes, and in another study melatonin itself was connected to maze ability. Given the proclivities of the light-eyed and presumably more highly pineal active people for science and mathematics which we have already seen connected with the introverted intuition thinking and the introverted thinking intuition types, is intuition a prerequisite for maze ability? If it is, then the myth of Daedalus, who built the maze to contain the Minotaur, and Icarus, his son, the archetypal intuitive, would take on a new meaning. Perhaps the ancient link between the pineal and clairvoyance has its biological foundation in the connection between high melatonin levels and the introverted intuition type.

In Turner's syndrome where a woman suffers a partial or complete loss of one of her X chromosomes, there is often an impairment of visualizing ability. Can this be connected with the diminished melatonin levels that have been found in Turner's syndrome patients? Higher ranges of melatonin have been found in boys than in girls, and might point to a similar link with visual abilities.

Again we have strayed in fanciful flights of speculation, but the underlying point is important. Once we link Jung's psychological types to Sheldon's somatotypes we become sensitized to the issue of a complementary biological typology, the pieces of which are emerging all around us.