Biological Perspective Studies

Biological Perspective Studies

Biological Perspective Studies How well does biological psychology explain others and you? Galvani (1791) It was through the accidental overlap of these two seemingly dissimilar areas of scientific effort that Galvani made his greatest discoveries. He noticed that the dissected legs of frogs in his laboratory seemed to jump to life under various conditions. For instance, when one of his assistants placed a scalpel against the exposed nerve of one specimen, which was sitting on a table previously used in electrostatic experiments, the legs of the frog suddenly kicked. In a similar event, when Galvani used a scalpel made of steel to cut the leg of a frog anchored on a brass hook, the leg visibly twitched. Based on such unusual observations Galvani concluded that there was a type of electrical fluid inherent in the body, which he dubbed animal electricity. According to his view, the nervous system delivered animal electricity to muscle tissue.

Von Helmholtz (1850) Helmholtz' technique was quite simple. He first cut out a muscle and an attached nerve fiber from a frog's leg. The experiment then consisted of stimulating the nerve at various distances from the muscle and measuring the length of time between nerve stimulation and muscle contraction. First, he electrically stimulated the nerve close to the point at which it attaches to the muscle, then he stimulated the nerve farther from this point of attachment. He found that the second reaction time (that is, the time between stimulation and contraction) was longer than the first. To obtain an estimate of the nerve impulse speed, he used a simple bit of reasoning: The difference in time between the two measurements must correspond to the time it takes the nerve impulse to travel the distance between the two points of stimulation (see Fig. 1). Hence, the distance between the point of stimulation divided by the time difference between the conditions of stimulating close to the muscle versus stimulating farther away should yield an estimate of nerve impulse speed. This is how he obtained his estimate of fifty to one hundred meters per second.

Golgi (1875) Camillo Golgi was responsible for inventing a specific staining technique for neurons, which he called "the reazione nera" (the black reaction). It consisted in fixing silver chromate particles to the neurilemma (the neuron membrane) by reacting silver nitrate with potassium bichromate. This resulted in a stark black deposit on the soma as well as on the axon and all dendrites, providing a exceedingly clear and well contrasted picture of neuron against an yellow background (see picture below). For the first time, neuroanatomists could follow where the ramifications went in and out a particular spot in the nervous system, and describe with exquisite detail all the richness of these ramifications. A marvelous picture of complexity emerged, and Golgi was able to explore it in full, describing for the first time, for example, that axons also gave collaterals, which provided a divergence of connexion which was heretofore suspected of, but not proven. Golgi defended the reticularist position, though, because he could not see with certainty that axons did not fuse to other cells. He wrote: There is certainly to be found a very widespread network of filaments anastomosing one with the other throughout the gray matter of the brain.

Ramon y Cajal (1906) Particularly relevant were Cajal s conclusions about the way action currents propagate in neuronal networks, always in the direction of dendrites to axons, and there to the dendrites or soma of other neurons. He called this the Law of Dynamic Polarization , which was another fundamental contribution to neurophysiology. The neuronal doctrine had four tenets: The neuron is the structural and functional unit of the nervous system; Neurons are individual cells, which are not continuous to other neurons, neither anatomically nor genetically; The neuron has three parts: dendrites, soma (cell body) and axon. The axon has several terminal arborizations, which make close contact to dendrites or the soma of other neurons; Conduction takes place in the direction from dendrites to soma, to the end arborizations of the axon Loewi (1921) Loewi's experiment

Loewi arranged two frog's hearts so that the baths they were in could be circulated through both preparations by way of a pump that could be turned on and off. One heart still had the vagus nerve attached. Stimulation of the vagus nerve slows the heart rate. If the pump was turned off, and one heart was stimulated, there was no effect on the second heart. If the pump was turned on, and one heart was stimulated, after a delay the second heart was also affected. This showed that something released by the nerve and that could circulate in the bath must be influencing heart rate. This had to be a chemical substance. Loewi was convinced the chemical substance was acetylcholine, since direct application of acetylcholine to the heart muscle also caused it to slow. But he couldn't prove it, so he called the chemical substance vagusstoff. Later it was demonstrated that vagusstoff was, in fact, acetylcholine. J.Z. Young (1936)

He then made a careful study of the anatomy of the mantles, and in his classical paper on `The functioning of the giant nerve fibres of the squid' (Young, 1938), he showed that the third order giant axons served to bring about the precisely coordinated contraction of the mantle causing expulsion of a powerful jet of water propelling the animals rapidly backwards or forwards according to the position of the funnel, sometimes accompanied by a slug of `ink' to assist the animal's escape. Having confirmed that the squid giant axons did conduct action potentials, and having with R. J. Pumphrey in 1938 (Young and Pumphrey, 1938) looked at the effect of their diameter on the rate of conduction, the only respect in which J.Z. subsequently involved himself in research on the ionic basis of conduction was to measure their electrolyte content (Young and Webb, 1945). Hodgin and Huxley (1939, 52) Hodgkin and Huxley's work with the giant squid axon was the first to use mathematical models to represent biological

systems. Due to Hodgkin and Huxley's findings, we are able to understand how an action potential propagates along a nerve and the functions of their associated ion channels. The Resting Potential The Model Cell The Constant Field Equation The Resting Membrane Potential The Action Potential Harlow In 1848, Gage, 25, was the foreman of a crew cutting a railroad bed in Cavendish, Vermont. On September 13, as he was using a tamping iron to pack explosive powder into a hole, the powder detonated. The tamping iron43 inches long, 1.25 inches in diameter and weighing 13.25 poundsshot skyward, penetrated Gages left cheek, ripped into his brain and exited through his skull, landing several dozen feet away. Though blinded in his left eye, he might not even have lost consciousness, and he remained savvy enough to tell a doctor that day, Here is business enough for you. Gages initial survival would have ensured him a measure of celebrity, but his name was etched into history

by observations made by John Martyn Harlow, the doctor who treated him for a few months afterward. Gages friends found himno longer Gage, Harlow wrote. The balance between his intellectual faculties and animal propensities seemed gone. He could not stick to plans, uttered the grossest profanity and showed little deference for his fellows. The railroad-construction company that employed him, which had thought him a model foreman, refused to take him back. So Gage went to work at a stable in New Hampshire, drove coaches in Chile and eventually joined relatives in San Francisco, where he died in May 1860, at age 36, after a series of seizures. Read more: tml#ixzz2kySYrhR3 Broca (1860s) Broca is most famous for his discovery of the speech production center of the brain located in the ventroposterior region of the frontal lobes (now known as Broca's area). He arrived at this discovery by studying the brains of aphasic patients. His first patient in the Bictre Hospital was Leborgne, nicknamed "Tan" due to his inability to clearly speak any words other than "tan".

In 1861, through post-mortem autopsy, Broca determined that Tan had a lesion caused bysyphilis in the left cerebral hemisphere. This lesion was determined to cover the area of the brain important for speech production, affecting syntactic skills of patients. (Although history credits this discovery to Broca, another French neurologist, Marc Dax, made similar observations a generation earlier.) Today the brains of many of Broca's aphasic patients are still preserved in the Muse Dupuytren, and his collection of casts in the Muse d'Anatomie Delmas-Orfila-Rouvire. Broca presented his findings on the localisation of language at the 1868 British Association meeting in Norwich, chaired by Joseph Dalton Hooker, and the subsequent discussions included Hughlings Jackson. Wernicke (1870s) In 1873, Wernicke studied a patient who had suffered a stroke. Although the man was able to speak and his hearing was unimpaired, he could barely understand what was said to him. Nor could he understand written words. After he died, Wernicke found a lesion in the rear parietal/temporal region of the patient's left brain hemisphere. Wernicke concluded that this region, which is close to the auditory region of the brain, was involved in speech comprehension. Wernicke named the

syndrome sensory aphasia, although now it is usually called Wernicke's aphasia. The affected region of the brain is known as Wernicke's area. The syndrome is sometimes called fluent aphasia since the victim is capable of speech; however words may be misused and the speech may be disordered or even without content. For this reason, scientists now believe that Wernicke's area may be involved in semantic processing, and it is sometimes called the receptive language area. Read more: Carl Wernicke - Describes Wernicke's aphasia, Describes Wernicke's encephalopathy - Right Hemisphere Of The Brain, Right Brain, and Brain - JRank Articles Heath (1950s) Abstract (1963) Studies are described of two human patients under treatment with ICSS. Their subjective reports in association with stimulation to reward areas of the brain are presented. The data indicate that patients will [See Figure 6. in Source PDF] [See Figure 7. in Source PDF] stimulate regions of the brain at a high frequency for reasons other than to obtain a pleasurable response. These data

extend information obtained from ICSS in animals. Olds and Milner (1954) POSITIVE REINFORCEMENT PRODUCED BY ELECTRICAL STIMULATION OF SEPTAL AREA AND OTHER REGIONS OF RAT BRAIN. Journal of Comparative and Physiological Psychology, Vol 47(6), Dec 1954, 419-427. doi: 10.1037/h0058775 After implantation of electrodes at various points in the brains of rats, the animals were placed in a Skinner box, arranged in such a manner that they could stimulate themselves by pressing the lever. The results indicate that various places exist in the brain "where electrical stimulation is rewarding in the sense that the experimental animal will stimulate itself in these places frequently and regularly for long periods of time if permitted to do so." The reward phenomenon appears most reliably when the electrodes are placed in the septal region, where an extreme degree of control was observed.

Hetherington and Ranson (1940s) A.W Hetherington and S.W Ranson conducted one of the first experiments studying regulation of feeding behavior in the 1940s in which they used a HorselyClark instrument to make hypothalamic lesions. They found that lesions in the lateral hypothalamus caused the rats to stop eating, while lesions in the ventromedial hypothalamus caused the animals to overeat, leading to obesity. 4/Historical+Background Milner (1957) and Corkin (1997) H.M. is probably the best known single patient in the history of neuroscience. His severe memory impairment, which resulted from experimental neurosurgery to control seizures, was the subject of study for five decades until his death in December 2008. Work with H.M.

established fundamental principles about how memory functions are organized in the brain. Gazzaniga and Sperry (1960s) Each hemisphere is still able to learn after the split brain operation but one hemisphere has no idea about what the other hemisphere has experienced or learned. Today, new methods and technology in split brain operation make it possible to cut off only a tiny portion and not the whole of the corpus callosum of patients. The studies demonstrated that the left and right hemispheres are specialized in different tasks. The left side of the brain is normally specialized in taking care of the analytical and verbal tasks. The left side speaks much better than the right side, while the right half takes care of the space perception tasks and music, for example. The right hemisphere is involved when you are making a map or giving directions on how to get to your home from the bus station. The right hemisphere can only produce rudimentary words and phrases, but contributes emotional context to language. Without the help from the right hemisphere, you would be able to read the word "pig" for instance, but you wouldn't be able to imagine what it is. Rosenzweig and Bennett (1972) rats Davidson et al. (2004) monks Vestergaard-Poulsen et al. (2009) meditation Gallese (1996) rhesus monkeys Iacoboni (2004) fMRI humans Bouchard (1990) twins Newcomer et el. (1999) cortisol Fisher (2004) dopamine Martinez and Kesner (1991) Ach rats Baumgartner et al (2008) oxytocin Bremner et al. (2003) PTSD Ashtari (2009) MRI substance abuse Harris and Fiske (2006) fMRI students Caspi et al. (2003) 5-HTT gene

Fessler et al. (2005) pregnancy sensitivity Rosenzweig and Bennett (1972) rats The differences in cortical weights among groups were caused by differences in cortical thickness: animals exposed to the EC environment developed slightly but significantly thicker cerebral cortices than their SC or IC littermates had (M. C. Diamond, 1967; M. C. Diamond et al., 1964). More-refined neuroanatomical measurements were soon undertaken on pyramidal cells in the occipital cortex, including sizes of cell bodies, counts of dendritic spines, measurements of dendritic branching, and measurements of the size of synaptic contacts (M. R. Rosenzweig et al., 1972). Each of these measurements showed significant effects of differential experience, as we will see shortly. Kasamatsu and Hirai (1999) Aim: to see how sensory deprivation affects the brain

Studied a group of Buddhist monks who went on a 72 hour pilgrimage to a holy mountain in Japan. Monks did not consume food or water, they did not speak, and they were exposed to the cold, late autumn weather. After about 48 hours, they began to have hallucinations, often seeing ancient ancestors or feeling a presence by their sides. Researchers took blood samples before the monks ascended the mountain, and then again immediately after having hallucinations. Findings: serotonin level increase that activated parts of the hypothalamus and frontal cortex resulting in hallucinations Conclusions: Sensory deprivation triggered release of serotonin. Crane, John and Hannibal, Jette. IB Diploma Programme Psychology Course Companion. Martinez and Kesner (1991) The aim of this experiment was to determine the role of the NT acetylcholine (ACH) on memory. ACH is believed to have a role in memory formation. Rats were trained to go through a maze, to the end, where they received food. Once the rats were able to do this, they were divided into 3 groups.

Group 1: rats were injected with scopolamine, which blocks ACH receptor sites (decreasing available ACH) Group 2: rats injected with physostigmine (fis-o-stig-mean) which blocks the production of cholinesterase (chol-in-ester-aise) which cleans-up ACH from the synapse and returns the neuron to a resting state. Without this, there was more ACH to excite the neurons. Group 3: control group, rats were given no injections. The results: Group 1 rats were slower in the maze, and made more errors. Group 2 rats ran through the maze, found food even quicker, made fewer errors, and were even better than the control group. Researchers concluded that ACH plays an important role in creating a memory of the maze. 0Biological%20Perspective.pdf Gallese (1996)

Action recognition in the premotor cortex. Gallese V, Fadiga L, Fogassi L, Rizzolatti G. Source Istituto di Fisiologia Umana, Universit di Parma, Italy. Abstract We recorded electrical activity from 532 neurons in the rostral part of inferior area 6 (area F5) of two macaque monkeys. Previous data had shown that neurons of this area discharge during goal-directed hand and mouth movements. We describe here the properties of a newly discovered set of F5 neurons ("mirror neurons', n = 92) all of which became active both when the monkey performed a given action and when it observed a similar action performed by the experimenter. Mirror neurons, in order to be visually triggered, required an interaction between the agent of the action and the object of it. The sight of the agent alone or of the object alone (three-dimensional objects, food) were ineffective. Hand and the mouth were by far the most effective agents. The actions most represented among those activating mirror neurons were grasping, manipulating and placing. In most mirror neurons (92%) there was a clear relation between the visual action they responded to and the motor response they coded. In approximately 30% of mirror neurons the congruence was very strict and the effective observed and executed actions corresponded both in terms of general action (e.g. grasping) and in terms

of the way in which that action was executed (e.g. precision grip). We conclude by proposing that mirror neurons form a system for matching observation and execution of motor actions. We discuss the possible role of this system in action recognition and, given the proposed homology between F5 and human Brocca's region, we posit that a matching system, similar to that of mirror neurons exists in humans and could be involved in recognition of actions as well as phonetic gestures. Iacoboni (2004) A similar phenomenon takes place when we watch someone experience an emotion and feel the same emotion in response, says Marco Iacoboni, a neuroscientist at the University of California, Los Angeles. The same neural systems get activated in a part of the cortex called the insula, which is part of the mirror neuron system, and in the emotional brain areas associated with the observed emotion. However, the amount of activation is slightly smaller for the mirrored experience than when the same emotion is experienced directly, Iacoboni adds. A recent study by Iacoboni and colleagues highlights the impor-tance of mirror neurons

and their role in the development of autism spectrum disorder (ASD). ASD is a pervasive developmental disorder characterized by impaired social interactions. Iacobonis team used functional magnetic resonance imaging (fMRI) to investigate neural activi-ty of 10 highfunctioning children with ASD and 10 normally developing children as they observed and imitated facial emotional expressions. Although both groups performed the tasks equally well, children with autism showed reduced mirror neuron activity, particularly in the area of the inferior frontal gyrus. Moreover, the degree of reduction in mirror neu-ron activity in the children with autism correlated with the severity of their symptoms. Iacoboni says, these results indicate that a healthy mirror neuron system is crucial for normal social development. Davidson et al. (2004) monks

Abstract Practitioners understand meditation, or mental training, to be a process of familiarization with one's own mental life leading to long-lasting changes in cognition and emotion. Little is known about this process and its impact on the brain. Here we find that long-term Buddhist practitioners self-induce sustained electroencephalographic high-amplitude gamma-band oscillations and phase-synchrony during meditation. These electroencephalogram patterns differ from those of controls, in particular over lateral frontoparietal electrodes. In addition, the ratio of gamma-band activity (25-42 Hz) to slow oscillatory activity (4-13 Hz) is initially higher in the resting baseline before meditation for the practitioners than the controls over medial frontoparietal electrodes. This difference increases sharply during meditation over most of the scalp electrodes and remains higher than the initial baseline in the postmeditation baseline. These data suggest that mental training involves temporal integrative mechanisms and may induce shortterm and long-term neural changes. Little is known about the process of meditation and its impact on the brain (1, 2). Previous studies show the general role of neural synchrony, in particular in the gamma-band frequencies (25-70Hz), in mental processes such as attention, working-memory, learning, or conscious perception (3-7). Such synchronizations of oscillatory neural discharges are thought to play a crucial role in the constitution of transient networks that integrate distributed neural processes into highly ordered cognitive and affective functions (8, 9) and could induce synaptic changes (10, 11). Neural synchrony thus appears as a promising

mechanism for the study of brain processes underlining mental training. Vestergaard-Poulsen et al. (2009) Long-term meditation is associated with increased gray matter density in the brain stem. Vestergaard-Poulsen P, van Beek M, Skewes J, Bjarkam CR, Stubberup M, Bertelsen J, Roepstorff A. Abstract Extensive practice involving sustained attention can lead to changes in brain structure. Here, we report evidence of structural differences in the lower brainstem of participants engaged in the long-term practice of meditation. Using magnetic resonance imaging, we observed higher gray matter density in lower brain stem regions of experienced meditators compared with age-matched nonmeditators. Our findings show that longterm practitioners of meditation have structural differences in brainstem regions concerned with cardiorespiratory control. This could account for some of the cardiorespiratory parasympathetic effects and traits, as well as the cognitive, emotional, and immunoreactive impact reported in several studies of different meditation

practices. Newcomer et. al (1999) A total of 51 people participated in the study -- 25 men and 26 women between ages 18 and 30. They were assigned to one of three groups. One group of seven men and eight women received a high daily dose of cortisol. A second group of eight men and eight women took a lower dose, and the remaining 10 men and 10 women received an inactive substance. All took their capsules twice daily for four days. The amounts mimicked cortisol levels secreted in response to stressful medical procedures. The high dose corresponds to cortisol secretion after events like abdominal surgery. The lower dose was similar to cortisol secretion during a minor medical procedure such as getting stitches or having a skin growth removed. The volunteers also were asked to listen to and recall parts of a paragraph so the researchers could assess their verbal declarative memory. This type of memory involves several brain regions, including the hippocampus, a seahorse-shaped brain structure related to memory and learning. The memory test, as well as tests of other cognitive functions, were given before the cortisol treatment, after one day of treatment, after four days of treatment and six days after the subjects stopped taking cortisol. Newcomer, who also is a staff psychiatrist at Barnes-Jewish Hospital, found that memory performance suffered only in those subjects who received the high dose of cortisol and only after the subjects had

received the hormone for several days. Fourteen of the 15 individuals taking the high dose experienced a decrease in memory performance after four days of treatment. No effects were found on the other cognitive tests. Fisher (2004) dopamine and love es/13JourCompNeur.pdf Baumgartner et al (2008) Oxytocin shapes the neural circuitry of trust and trust adaptation in humans. Trust and betrayal of trust are ubiquitous in human societies. Recent behavioral evidence shows that the neuropeptide oxytocin increases trust among humans, thus offering a unique chance of gaining a deeper understanding of the neural mechanisms underlying trust and the adaptation to breach of trust. We examined the neural circuitry of trusting behavior by combining the intranasal, double-blind, administration of oxytocin with fMRI. We find that subjects in the oxytocin group show no change in their trusting behavior after they learned

that their trust had been breached several times while subjects receiving placebo decrease their trust. This difference in trust adaptation is associated with a specific reduction in activation in the amygdala, the midbrain regions, and the dorsal striatum in subjects receiving oxytocin, suggesting that neural systems mediating fear processing (amygdala and midbrain regions) and behavioral adaptations to feedback information (dorsal striatum) modulate oxytocin's effect on trust. These findings may help to develop deeper insights into mental disorders such as social phobia and autism, which are characterized by persistent fear or avoidance of social interactions. Rosenthal (1987) Seasonal Affective Disorder Abstract Seasonal affective disorder (SAD) is a recently described mood disorder characterized by recurrent winter depressive episodes and summer remissions. The symptoms of SAD include DSM III-R criteria for recurrent major depression, but atypical depressive symptoms

predominate with hypersomnia, hyperphagia and carbohydrate craving, and anergia. Seasonal affective disorder is effectively treated by exposure to bright light (phototherapy or light therapy), a novel antidepressant treatment. The authors review the syndrome of SAD, hypotheses about its pathophysiology, and the use of phototherapy to treat the disorder. Bouchard (1990) Sources of human psychological differences: the Minnesota Study of Twins Reared Apart Since 1979, a continuing study of monozygotic and dizygotic twins, separated in infancy and reared apart, has subjected more than 100 sets of reared-apart twins or triplets to a week of intensive psychological and physiological assessment. Like the prior, smaller studies of monozygotic twins reared apart, about 70% of the variance in IQ was found to be associated with genetic variation. On multiple measures of personality and temperament, occupational and leisure-time interests, and social attitudes, monozygotic twins reared apart are about as similar as are monozygotic twins reared together. These findings extend and support those from numerous other twin, family, and adoption

studies. It is a plausible hypothesis that genetic differences affect psychological differences largely indirectly, by influencing the effective environment of the developing child. This evidence for the strong heritability of most psychological traits, sensibly construed, does not detract from the value or importance of parenting, education, and other propaedeutic interventions. Bremner et al. (2003) Abstract OBJECTIVE: Animal studies have suggested that early stress is associated with alterations in the hippocampus, a brain area that plays a critical role in learning and memory. The purpose of this study was to measure both hippocampal structure and function in women with and without early childhood sexual abuse and the diagnosis of posttraumatic stress disorder (PTSD). METHOD: Thirty-three women participated in this study, including women with early childhood sexual abuse and PTSD (N=10), women with abuse without PTSD (N=12), and women without abuse or PTSD (N=11). Hippocampal volume was measured with magnetic resonance imaging in all subjects, and hippocampal function during the performance of hippocampal-based verbal declarative memory tasks was measured by

using positron emission tomography in abused women with and without PTSD. RESULTS: A failure of hippocampal activation and 16% smaller volume of the hippocampus were seen in women with abuse and PTSD compared to women with abuse without PTSD. Women with abuse and PTSD had a 19% smaller hippocampal volume relative to women without abuse or PTSD. CONCLUSIONS: These results are consistent with deficits in hippocampal function and structure in abuse-related PTSD. Ashtari (2009)

Abstract BACKGROUND: There is growing evidence that adolescence is a key period for neuronal maturation. Despite the high prevalence of marijuana use among adolescents and young adults in the United States and internationally, very little is known about its impact on the developing brain. Based on neuroimaging literature on normal brain developmental during adolescence, we hypothesized that individuals with heavy cannabis use (HCU) would have brain structure abnormalities in similar brain regions that undergo development during late adolescence, particularly the fronto-temporal connection. METHOD: Fourteen young adult males in residential treatment for cannabis dependence and 14 age-matched healthy male control subjects were recruited. Patients had a history of HCU throughout adolescence; 5 had concurrent alcohol abuse. Subjects underwent structural and diffusion tensor magnetic resonance imaging. White matter integrity was compared between subject groups using voxelwise and fiber

tractography analysis. RESULTS: Voxelwise and tractography analyses revealed that adolescents with HCU had reduced fractional anisotropy, increased radial diffusivity, and increased trace in the homologous areas known to be involved in ongoing development during late adolescence, particularly in the fronto-temporal connection via arcuate fasciculus. CONCLUSIONS: Our results support the hypothesis that heavy cannabis use during adolescence may affect the trajectory of normal brain maturation. Due to concurrent alcohol consumption in five HCU subjects, conclusions from this study should be considered preliminary, as the DTI findings reported here may be reflective of the combination of alcohol and marijuana use. Further research in larger samples, longitudinal in nature, and controlling for alcohol consumption is needed to better understand the pathophysiology of the effect of cannabis on the developing brain. Harris and Fiske (2006)

Dehumanizing the lowest of the low: neuroimaging responses to extreme out-groups. Abstract Traditionally, prejudice has been conceptualized as simple animosity. The stereotype content model (SCM) shows that some prejudice is worse. The SCM previously demonstrated separate stereotype dimensions of warmth (low-high) and competence (low-high), identifying four distinct out-group clusters. The SCM predicts that only extreme out-groups, groups that are both stereotypically hostile and stereotypically incompetent (low warmth, low competence), such as addicts and the homeless, will be dehumanized. Prior studies show that the medial prefrontal cortex (mPFC) is necessary for social cognition. Functional magnetic resonance imaging provided data for examining brain activations in 10 participants viewing 48 photographs of social groups and 12 participants viewing objects; each picture dependably represented one SCM quadrant. Analyses revealed mPFC activation to all social groups except extreme (low-low) out-groups, who especially activated insula and amygdala, a pattern consistent with disgust, the emotion predicted by the SCM. No objects, though rated with the same emotions, activated the mPFC. This neural evidence supports the prediction

that extreme out-groups may be perceived as less than human, or dehumanized. Caspi et al. (2003) Influence of life stress on depression: moderation by a polymorphism in the 5-HTT gene. Abstract In a prospective-longitudinal study of a representative birth cohort, we tested why stressful experiences lead to depression in some people but not in others. A functional polymorphism in the promoter region of the serotonin transporter (5-HT T) gene was found to moderate the influence of stressful life events on depression. Individuals with one or two copies of the short allele of the 5-HT T promoter polymorphism exhibited more depressive symptoms, diagnosable depression, and suicidality in relation to stressful life events than individuals homozygous for the long allele. This epidemiological study thus provides evidence of a gene-by-environment interaction, in which an individual's response to environmental insults is moderated by his or her genetic makeup.

Fessler et al. (2005) Abstract By motivating avoidance of contaminants, the experience of disgust guards against disease. Because behavioral prophylaxis entails time, energy, and opportunity costs, Fessler and Navarrete [Evol. Hum. Behav. 24 (2003) 406417] hypothesized that disgustsensitivity is adjusted as a function of immunocompetence. Changes in immune functioning over the course of pregnancy offer an opportunity to test this notion. Relative to later stages, the first trimester of pregnancy involves substantial suppression of the maternal immune response, and both maternal and fetal vulnerability to pathogens are greatest during this phase; food-borne illnesses, in particular, pose a threat during the first trimester. Using a Web-based survey of 496 pregnant women, we compared participants in the first trimester with those in later stages of pregnancy. Results reveal heightened disgust sensitivity in the first trimester, notably including disgustsensitivity in the food domain. This pattern is notsimply a consequence of elevated nausea during the first trimester, as, although disgust sensitivity and current level of nausea are correlated, first trimester women remain more easily disgusted in the food domain even after controlling for the greater incidence of nausea. These results provide preliminary support for the hypothesis that disgust sensitivity varies during pregnancy in a manner that compensates for maternal and fetal vulnerability to disease. Biological Bits A-k&list=PLEE6E3B5E90A6A5AF 94&list=PLEE6E3B5E90A6A5AF jU&list=PLEE6E3B5E90A6A5AF

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