CHAPTER 8. ISSUES IN BRAIN RESEARCH

 

Besides a general knowledge of the human nervous system and the role of neurotransmitters, social scientists need to know certain concepts about the structure of the brain that impact on such key areas as sexual behavior and measurement.

The reason why dimorphism in the brain is so important is that so many problems of deviancy are particularly attributable to men. Sexual deviation is gender-dependent and not only much more frequent but also much more varied in its manifestations in the male than in the female. Certain deviations such as voyeurism, exhibitionism, homicidal sadism, and fetishism are virtually never encountered in women. Excepting female homosexuality, transsexuality and masochism (yet these last two are still more frequent in men) it is a remarkable fact that sexual deviations occur exclusively in men (Flor-Henry, 1987:50)

But it is not just in the field of deviancy that men have a poorer record than women. The Y-chromosome itself probably evolved from the X. Ounsted and Taylor (1972) suggest that the Y-chromosome slows down the growth rate in the male fetus. This allows more time for genomic information to be transcribed. However, it also means that the male fetus is born relatively more immature compared with the female. This slowing of the growth rate means more health problems for the male than the female. For instance, males have higher rates of perinatal mortality, accidental death, mental handicap (including autism and epilepsy). Later in life males suffer from an increased vulnerability to cardiac disease and certain forms of cancer. To balance the excess male damage and loss 5 percent more males are born than females in the human population. (Goodman, 1987:29)

The development of a male brain involves more processes than that involved in the creation of a female brain and naturally, this increases the possibility of something going wrong (Goodman, 1987:29).

Male Sex Hormones

Since many of the acts that are considered deviant in America involve sex it is important to cover the basics of this system. We start the story of sex in the male with the hypothalamus.

The hypothalamus is the site that controls many of the sexual processes in humans. This organ produces luteinizing-releasing hormone (LnRH) and corticotropin-releasing factor (CRF). A special system of blood vessels transports these hormones to the anterior lobe of the pituitary gland.

In the anterior lobe the LnRH stimulates the biosynthesis of luteinising hormone (LH) and follicle-stimulating hormone (FSH). CRF stimulates production of adrenocorticotropic hormone (ACTH). (ACTH stimulates the adrenal glands to produce adrenocortical hormones, especially glucocorticoids and male hormones known as androgens.)

From the anterior lobe of the pituitary gland, via the circulating blood, LH and FSH arrive at the testicles. The testicles have specific receptors for these hormones. The receptors for LH occur only on Leydig (interstitial) cells, whose primary secretion is testosterone. Testosterone effects its action after conversion to dihydrotestosterone, a more potent androgen. The receptors for FSH are found only in the Sertoli cells of the seminiferous tubules, which produce spermatozoa. The feedback loop from these sites modulates production of these two hormones.

Development of the Male

The differentiation of sexual orientation or status is a sequential process. The prenatal stage of this process, with a possible brief neonatal extension, takes place under the aegis of brain hormonalization. It continues postnatally under the aegis of the senses and social communication and learning. (Money, 1988:49)

In the early stages of the development of the mammalian embryo, the fetus is sexually bipotential. The undifferentiated gonads can differentiate into either testes or ovaries. On several important dimensions, male and female brains develop differently. In the brain the principle of feminization takes priority over the principle of masculinization. Something must be added to induce masculinization. (Money, 1988:14-15) remarks that this puts Eve first, then Adam! In mammals male specialization hinges on testosterone slowing the developmental pace of the left hemisphere. Hucker and Bain, 1990:93-95

In mammals the ability of the male to display masculine behavior depends on two processes, masculinization and defeminisation (Goodman, 1987:33). Masculinsation behaviors consist of mounting the female, penetrating her vagina, thrusting, and ejaculation, and depend on E (converted from T) and DHT. Defeminsation is the obliteration of feminine behaviors, e. g. presenting, lordosis, and allowing penetration, in a male.

Successful development of the male actually depends on two processes that affect the brain: defeminization and masculinization. This development proceeds largely via two different types of gonadal hormones normally secreted by the male baby's own testicles. One of these two masculinizing hormones is actually a defeminizing hormone, mullerian-inhibiting hormone (MIH). It atrophies the embryonic mullerian ducts and thus prevents them from growing into a uterus (Money, 1988:15). The second hormone, testosterone, is a masculinizing hormone and induces the growth of masculine sexual organs.

The stage in development when hormones influence the differentiation of the human brain as dimorphically male or female remains to be discovered. It may be in the third trimester of pregnancy, or it may extend through the first three postnatal months of age when, in boys, there is a transient surge of testosterone released from the testicles to circulate in the bloodstream, which would carry it to the brain. (Money, 1988:23)

The critical importance of testosterone and in effects on personality can be illustrated in the case of fraternal twins of different sexes. Females situated near males have more aggression later in life, while those further away have less, due to being exposed to T that is secreted from the fetal male testis. Goodman, 1987:35

Brain dimorphism as regards sex is especially located in hypothalamus, more specifically, the interstitial nuclei of the anterior hypothalamus (Money, 1988:23). The nucleus is larger in men than in women, the male's containing slightly more than twice as many cells. Scientists are not sure of its function, but it is located within an area that is essential for gonadotropin release and sexual behavior in other mammals.

Laterality or Asymmetry in Brain Organization

There are many processes that the brain performs. These functions are asymmetrically organized between hemispheres of the brain. The left cerebral hemisphere is involved in processing verbal and linguistic material, while the right deals with spatial and analytic processing. The right hemisphere determines emotionality, aggression and sexual arousal while the left hemisphere exercises regulatory inhibition (Flor-Henry, 1987:51). Even neurotransmitters are lateralised in the brain. Dopaminergic systems, which activate sexual drive, have a left-hemisphere bias, while serotoninergic systems, which inhibit sexual drive, are right-hemisphere biased.

Lateralisation of the brain gives rise to the possibility of lateralised cerebral dysfunction. Male specialization hinges on testosterone/left hemisphere interactions whereby the developmental pace of the left hemisphere is slowed, it follows, theoretically, that the cerebral locus of sexual deviations is probably determined by unusual patterns of neural organization in the dominant hemisphere (Flor-Henry, 1987:50)

Males have more specialized right brains while females are more bilaterally organized. Goodman, 1987:39 Left handedness is more common in men and is thought to reflect the effect of intrauterine T, which suppresses the growth of the left hemisphere and promotes that of the right. The left hemisphere controls the sex drives in the right hemisphere. Sexual deviation is linked to the differential cerebral organization of the male and female brains, which, in turn, is the result of neurochemical interactions that are testosterone-dependent. This carries with it an increased susceptibility to aberrant sexual programming. Flor-Henry, 1987:60-61

Epileptic studies show that sexual deviation is often the result of lateralised, often astonishingly specific disturbances of temporal/limbic neural sets. Kolarsky, Freund, Machek et al. (1967), in a study of 86 males, have noted that sexual deviation was significantly associated with temporal lobe epilepsy occurring before the first year of life. All categories of sexual deviations were found: voyeurism, exhibitionism, homosexuality, heterosexual and homosexual paedophilia, sadism and masochism, as well as fetishism and transvestism. Hyposexuality was also significantly associated with temporal lesions. Flor-Henry, 1987:57-58

Imprinting-like Processes in Sexual Development

There appears to be at least two instinctual mechanisms in the process of sexual attachment. Ethologists Lorenz and Tinbergen came to two major conclusions about sexual attachments. First, the range of potential sex objects is restricted to certain broad classes of stimuli by inborn neural circuits called innate releasing mechanisms (IRMs). In humans Wickler (1967) and Morris (1971) have proposed that female buttocks and breasts as innate sexual stimuli for the human male (Wilson, 1987:104).

The second instinctual mechanism is imprinting. Particularly in early infancy, imprinting details the blueprint for arousal, broadly sketched by the innate releasing mechanisms. This imprinting-like mechanism partly depends upon the visual stimuli that are available in the environment (Immelmann and Suomi, 1981). For example, zookeepers may become the sexual targets of a wide variety of animals in their care if these animals do not have sufficient exposure to members of their own species at the sensitive period of development (Wilson, 1987:104-105).

Human imprinting-like processes in humans are undoubtedly more complex than in other species. Nevertheless, there are similar mechanisms that operate at sensitive periods in infancy. Money (1988) calls the result of the imprinting-like processes, love maps. These love maps are seen in masturbation fantasies and pornographic preferences (Wilson, 1987:110).

Either of these instinctual mechanisms (IRMS or imprinting- like processes) can go wrong so that sexual responses can be attached to classes of stimuli that are either peculiar or socially unacceptable. It is necessary that sexual imprinting be impersonal, otherwise there would be a risk of the male child fixating upon the mother as an identity rather than a displayer of certain attributes of universal female application. Wilson, 1987:110 An example of a disturbance in sexual attachment is the case of fetishism, in which some article or material becomes the focus for sexual arousal. These attachments commence very early in life, often being recalled as well established by the age of four, and are very resistant to change. Wilson, 1987:105

There is some evidence that sexual preferences can be modified in adulthood. D'Udine (1987) describes how adult sexual preferences in rodents can be permanently altered through experimental manipulation of their early environment by cross- fostering among different species. Domjan (1987) demonstrates experimentally in the adult Japanese quail that sexual behavior can be modified in some degree through conditioning to inanimate objects. In general, altricial species are more behaviorally plastic than nonaltricial species, and experiences in adulthood as well as in early life can affect adult sexual preferences.

Methodological Techniques

The electroencephalogram (EEG) measures the rhythmic electrical activity of the cerebral cortex of the brain. A current theory contends that the rhythmic character of the activity is the result of a pacemaker (believed to be located in certain nuclei of the thalamus) which "drives" the cortical neurons. The pacemaker consists of an aggregate of neurons having the unique ability to generate rhythmic discharges. The neurons in these thalamic nuclei project diffusely to the cerebral cortex.

In an EEG electrodes are attached to the scalp and the oscillations of the brain are recorded on an oscillograph. These waves or rhythms are of several different types. When the subject is alert the EEG records beta waves that have a frequency of 18 to 30 cps (cycles per second). The alpha wave is the most common wave form, often occurring in the parietooccipital area. These waves occur when the subject is awake, but at rest. The waves are smooth and regular and at a frequency of 8 to 12 cps (cycles per second). The mu wave measures from 7 to 11 cps. The theta rhythm is 4 to 7 cps and often appears in the temporal region of the brain. It indicates drowsy or light sleep. The delta rhythm is an abnormal rhythm with a frequency slower than 4 cps and indicates deep sleep.

In the EEG the brain waves are recorded by electrodes placed on the scalp. There is a numbering system to identify the location of the electrodes. Imagine yourself standing behind the testee. Looking at the top of the head one can place nine electrodes in three rows and three columns. The rows are labeled (from the front of the head to the back) F, C, and P. The columns are labeled (from left to right) 3, Z (or 2), and 4. Therefore, the nine cells (from top to bottom and left to right) are: the first row is F3, FZ, F4; the second row is C3, CZ, C4; and the last row is P3, PZ, and P4.

There are additional placements for electrodes along the sides of the head. One can imagine all four sides of the head as constituting a time clock with the 12 o'clock position at the middle of the front of the head. On either side of 12 o'clock are electrodes Fp1 and Fp2. At three o'clock the electrode is T4. On either side of six o'clock (from left to right) are positions 01 and 02. At the 9 o'clock position is T3. At the 10 and 2 o'clock positions are electrodes F7 and F8. And at the 7:30 and 4:30 positions are electrodes T5 and T6.

When reading about brain research, one often comes across the abbreviations EP, ERP, and AEP. These all refer basically to the same phenomenon. An evoked potential (EP) or an event-related potential (ERP) is a brain wave response to auditory stimuli, such as a light flash, a musical tone, a click, or a photograph. As recorded from the surface of the scalp, EPs are exceedingly low level electrical signals. They have to be averaged before a reliable waveform can be obtained. Among the many usages of the AEP is the investigation of perceptual dysfunction in patients, such as those suspected of having schizophrenia.

The EP is a complex waveform. One way to label the ups and downs of the waves is to designate positive deflections by the letter P and negative deflections by the letter N. Then the ups and downs are labeled consecutively with numbers, the first up being P1, the next one being P2, etc. The third upward wave is the P3 waveform. Because this component occurs around 300 milliseconds after the presentation of the stimulus, it sometimes is referred to as P300. P3 appears to reflect active cognitive processing of stimulus information by the subject. Its latency and amplitude shows considerable variability from one person to another. The presence of this variability has suggested that P3 might serve as a physiological index of an individual's "cognitive style." The waveforms up to P3 are known as exogenous components, and as endogenous components from P3 onward. The endogenous components are related to the personality characteristics of the subjects.

In addition to EPs, there is a far-field potential, or brain stem auditory ERP. This occurs within the initial 10 milliseconds following the presentation of an auditory stimulus such as a click. There is evidence that the waveform of a typical brain stem auditory ERP consists of six or seven distinctive, positive waves. Each of these waves signifies the arrival of the stimulus at a particular anatomical location within the brain. Wave I signals the occurrence of activity in the auditory nerve consequent to stimulation; wave II originates from the cochlear nucleus in the medulla; wave II marks the arrival of the stimulus at the superior olivary complex in the pons; wave IV denotes arrival at the lateral lemniscus, also in the pons; wave V signals arrival at the inferior colliculus in the midbrain; and wave VI denotes arrival at the medial geniculate body in the thalamus. These are helpful in diagnosing a variety of neurological disorders. For instance, the far-field potential can help pinpoint a lesion in the brain.

Another area of brain research involves using brain mapping techniques. One technique is tomography, which presents a detailed x-ray map. During exposure, the X-ray tube is moved in a curve synchronous with the recording plate but in the opposite direction. As a result, the shadow of the selected plane remains stationary while all others are displaced and thus blurred or obliterated. A CAT scan is a computerized axial tomography scan. The CT (computerized tomography) scan is often used as a basic screening device for suspected neurological disorders such as brain tumor.

Computed tomography and magnetic resonance imaging (MRI) show images of brain structure, not brain functioning. Positron emission tomography (PET) shows aspects of brain functioning, but requires the injection of radioactive tracers.

 

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