This content should include the following items:
- Brain development through the lifespan
- Drugs and the brain
- Stress and the brain
The human brain develops and changes in response to a variety of factors. 1. Genetic predispositions, for such diseases as alcoholism, make some brains more vulnerable to environmental factors. 2. In the grand scheme of brain development, the brain mostly develops due to environmental factors. 3. Within the fetus, genes and hormones control the formation of neural networks. Once exposed to the outside world, baby's brains are extremely sensitive to stimuli. What these humans learn throughout their development affects what gets pruned during apoptosis, which occurs in early childhood as well as in adolescence. 4. Cultural factors also have implications for development. 5. Exposure to drugs and stress physically changes neural structures, mostly in a negative way. Ultimately, physical changes in the brain and how the brain functions determine one's behavior.
The Developing BrainEdit
From conception the premature baby brain relies on cell migration. The trillions of brain cells line up in the brain based on how the other neurons around it are moving.
No two brains are alike. Even identical twins have differently structured brains by the time they are born (Patrick, 1997). While in the womb, exposure to sex hormones, such as androgens, shape the brain’s development and future sex behavior. Robert W. Goy of the University of Wisconsin studies the differences in male and female brain structure.
Description of Theory an Hypothesis
According to him, androgens help to create male brains and female brains develop in a lack of androgens. This exposure to sex hormones during early life produces lifelong changes between the sexes. The hypothalamus, which controls male and female reproductive behavior, is larger in males and smaller in females. In addition, men tend to be better at spatial tasks, mathematical reasonging, and target-directed motore skills. Women have better verbal abilities, workd recall, and precision manual skills. Women have larger corpus callosums, aiding in communication between right and left hemispheres for better speech abilities whereas men rely on the posterior portion of their left hemispheres for speech. For this reason, men are more likely to incur aphasia after a stroke, because it damages this region of the left hemisphere (Kimura, 1999).
Future Research on Womb Exposure Girls exposed to large quantities of adrenal androgens before birth develop the genetic defect called congenital adrenal hyperplasia (CAH). Sheri A. Berenbaum, who has studied CAH girls, notices more aggressive, male-like behavior in play- they prefer masculine toys and game over typical female ones (Kimura). Some researchers suggest that tastes can be primed by exposure to the residue of food in their mother’s blood. Babies born to drug addicts are addicted to drugs at birth and babies born to mothers eating curries and spicy foods have tastes for spicy foods themselves (Carter, 1998).
The fetal brain is sparse, with many non-myelinated neurons, and missing connections between the auditory and visual cortices, and between the retina and thalamus (Carter, 1998). The baby’s brains must finish developing in the external environment. Since the hippocampus is not fully developed until the age of three, a baby toddler cannot store long-term memories, only emotional memories in the amygdala. Heidelise Als, of Harvard Medical School, researches premature babies’ vulnerability to overstimulation. Bright lights and loud sounds, common in the ICU, impede the premies’ brain development. Als claims that for this reason, premies aften have difficulty in later life with learning, paying attention, and prioritizing. When premies were placed in an environment that imitated the womb- dark, quiet, with physical contact, the premies’ brains developed normally. When children lack physical contact or nurturing, psycho-social dwarfism may impede their growth. The hypothalamus does not stimulate the thyroid to produce enough growth hormone. In studies on Romanian orphanage children, the orphans had stunted growth, lower IQs, and more learning disabilities than average children (Groza et al., 1998). A few years after the orphans were adopted, they caught up in height and improved their learning abilities.
Early Childhood Brain Development
Neuroplasticity is the brain’s ability to create new neural pathways based on new experiences. It takes place over a lifetime, sometimes over genetically-determined critical periods. At birth, there are approximately 2,500 synapses in the cerebral cortex of a human baby.By three years old, the cerebral cortex has about 15,000 synapses (Gopnick et al., 1999). Because the infant brain has such a huge capacity for growth, it must eventually be pruned down. Synaptic pruning, or apoptosis, is the programmed neuron cell death that takes place during early childhood and adolescence. Pruning actually strengthens important connections and eliminates weaker ones, creating more effective neural communication (Brain Plasticity,2006). Many times children lose their eidetic or photographic memory during apaptosis. An incomplete pruning results in so-called idiot savantes while overkill apoptosis my strip too many connections and lead to Down’s syndrome (Carter, 1998).
Plasticity can also be demonstrated in any learning. For one to remember an experience, the circuitry of the brain must change. According the Durbach (2000) learning takes place when there is either a “change in the internal structure of neurons” or an “increase in the number of synapses between neurons.” Another name for this is Hebbian learning, where “the cells that fire together, wire together.” With repeated exposure, certain pathways in the brain permanent (Hebb, 1949).
Rosenweig's study More Experience = Bigger Brains, illustrates in rats how the brain changes in response to experience. Rats who lived in more enriched environments had larger neurons, more DNA and RNA, a heavier cerebral cortex, and larger synapses than rats who lived in sparse environments (Rosenweig et al., 1972).
Drugs and the BrainEdit
Drugs directly affect the physiology of the brain’s composition and functioning and therefore human behavior.
Types of Drugs and Effects on the Brain and Behavior
The chemical THC in marijuana stimulates cannabinoid receptors in the brain, which affects the release of the neurotransmitters norepinephrine and dopamine. The effects of these two hormones eases pain and creates a euphoric-like sensation. However, marijuana impairs memory in the hippocampus. It lowers the functioning of the cerebral cortex, lowering concentration and judgement. The THC slows down the cerebellum, impairing movement and affects perception in the sensory cortex, enhancing sensations and creating hallucinations.
The depressant, alchohol, in low doses, relaxes people, lowers inhibitions, and slows down reflexes. In medium doses, alchohol also stimulates the release of norepinephrine and dopamine and causes a quick reuptake of acetylcholine and GABA. The effect is relaxation, but loss of coordination, impaired memory, and impaired reason. Even in monderate consumption, alchohol may cause brain shrinkage, according to a study on rats. When chronically abused, alcohol damages the frontal lobes, decreases brain mass, decreases the size of ventricles which pump blood to the brain. This may lead to permanent impairment of memory and speech, causing such disorders as Wernicke’s Encephalopathy and Korsikoff’s Syndrom.
Drinking during pregnancy can alter the genes of the fetus. Babies with Fetal Alcohol Syndrome have smaller brains, lower IQs, and mental retardation. The neurogenesis of the hippocampus is affected, and there are less overall neurons, leading to impaired learning and memory, as well as depression. Also, the development of the corpus callosum is disrupted.
Stimulants such as cocaine and crack prevent the reuptake of dopamine, norepinephrine, and serotonin, creating a euphoric rush. But after a while this depletes the brain’s supply of these neurotransmitters, creating a “crash” effect.
Dr. Hans Brider took FMRI scans of cocaine users, revealing changes in the amygdala, nucleus accumbens, hippocampus, and anterior singulate. These parts of the brain create the deep desire to do cocaine- especially the amygdala, which creates deep emotional memories concerning drug use. Dr. Anna Rose Childress of the University of Pennsylvania also studied cocaine users, trying to trigger memories of drug use to see what parts of the brain it affected. When participant were shown pictures of drug use or drug dealers, PET scan images also showed activity in the amygdala and nucleaus accumbens, which reveals where relapse cravings originate.
Nicotine, another excitatory drug, is a competitive inhibitor for acetylcholine receptors in the brain. Therefore, nicotine acts like acetylcholine and affect many functions, such as muscle movement, breathing, heart rate, learning, and memory. Continually, acetylcholine stimulates the release of other neurotransmitters and hormones that play a role in mood, appetite, and memory. Nicotine also raises levels of dopamine in the brain, which creates a feeling of euphoria. Dopamine is present in cocaine and heroin and scientists suggest that the changes in dopamine play a role in why addiction occurs.
Amphetamines like ecstasy (MDMA) increase neurotransmitter activity in the brain. Ecstasy stimulates the release of serotonin, dopamine and norepinephrine. Serotonin, the neurotransmitter greatly impacted by ecstasy, "plays an important role in the regulation of mood, sleep, pain, appetite, and other behaviors" (NIDA). Repeated use of ecstasy or abuse of the drug can lead to a depletion of serotonin, an important neurotransmitter, and brain imaging of heavy users show that there are changes in regions involved in cognition, emotion, and motor function (McCann 2000, and Morgan 1999, 2000).
Research on Addiction
Steven Hyman of the National Institute of Health proposes that some people may have higher endogenous stress levels or may lack dopamine receptors, making drug addiction and abuse more likely. Genetics and family environments can also increase vulnerability to addiction. According to Dr. Mark Shuckett, those people with an alcoholic parent are 60% more likely to become alcoholics themselves.
Certain cultural norms and environments foster alcohol and drug use. Around 50% of college students consider themselves binge drinkers, with even higher percentages for those in fraternities, sororities, or military academies. While binge drinking is more prevalent in the United States, cigarettes and other drugs are more common. An estimated 20% of Europeans use marijuana. Stress and traumatic events make drug and alcohol use more likely. For example, there were widespread reports of increased alcholism after Hurricane Katrina and 9/11.
Stress and the BrainEdit
Stress has many definitions, but according to Richard Lazarus, stress is a state of anxiety produced when events and responsibities exceed one’s coping abilities. In this way, stress relies not only on environmental factors, but on cognitive appraisals of these factors (Myers, 2004). The cerebral cortex percieves the stressor, the hypothalamus stimulates the pituitary gland to release epinephrine and norepinephrine. This in turn stimulates the adrenal glands to release the hormone cortisol (Myers, 2004). Stress effects many other areas of the body, such as the amygdala, which produces a fear response. It seems to hardwire the brain differently. Middle-aged rats that had undergone early life stress had abnormal brain-cell activity and memory loss (Brunson et. al., 2005).
The sources of stress are numerous: from catastrophes such as Hurricane Katrina, significant life changes, poverty and inequality, to daily hassles like traffic tie-ups and demanding jobs (Myer, 2004). Especially in urban and overcrowded environments, psychologists see links between everday stressors and hypertension, and unhealthy behaviors such as lack of sleep and alcoholism (Lazarus & Folkman, 1984). In fact, the leading causes of death today in America are linked to lifestyle and stress. According UNSEC, about half of the world’s children grow up in extremely stressful environments (poverty, violence, war, abuse), which means that these children may have impaired cognitive abilities later on in life.
Certain personalities are more susceptible to stress. Friedman and Rosenman found that Type A people, who are characterized as competitive, impatient, and aggressive, are more physically reactive to stress- they produce more hormones and have a higher blood pressure. Type B people, who are more relaxed and easygoiong, are less prone to stress. Most significantly, Type A's were 69% more likely to suffer from a heart attack (Myers, 2004). Type A's typically feel like they are less in control of situations.
Accordint to research by Janet Rodin, the less percieved control of a situation, the greater the stress. The elderly that lived in nursing homes, were lonely, and had to be fed, dressed, and changed, felt significantly more stress and had shorter lifespans than their independent, active counterparts.
The Canadian scientist Hans Seyle was among the first to discover the link between stress and physical effects. In studying stressed rats, Seyle observed the same reaction: shrinkage of the thymus gland, bleeding ulcers, and an enlargement of the adrenal glands. His continued research led him to naming the body’s response to stress General Adaptation Syndrome. During phase one, one experiences an alarm reaction, the initial activation of the sympathetic nervous system. In phase two, resistance, the body tries to cope with stress and there is an outpouring of stress hormones. In the third and final stage, exhaustion, stress depletes the body’s reserves and wears down the immune system. Additional research has shown that prolonged stress shrinks the hippocampus, which helps make memories explicit.
Females seem to be more susceptible to stress and depression. After experiencing traumatic events, females are twice as likely as men to develop Post Traumatic Stress Disorder, where humans develop maladaptive behaviors such as avoidance, reduced responsiveness and guilt (Myers, 2004). Researcher Tracey Shors concluded that in response to stress, females memory formation is more inhibited than that of male rats because of the fluctation of estrogen during and following the traumatic event. In typical experiments, the rats were exposed to inescapable stressors such as tailshocks or swimming. Later on, Shors would try to condition eyeblinks. The stressors, in contrast to the females, actually improved the male rat’s learning and eyeblink responses. Glucocorticoids, stress neurotransmitters in the brain, seemed to increase dendritic spine density in the hippocampus of male rats, but decreased the dendritic spine density in female rats (Shors, 2001).
However, mindful exercise, such as Tai Chi, meditation, and aerobic exercise decrease stress response and promote overall well-being (Sandlund and Norlander, 2000). In a University of Wisconsin study, participants who did meditative exercises showed more electrical activity in the left side of the frontal lobe, indicating that they had a lower anxiety and a more positive emotional state (Davidson, 2003). Meditation, yoga, and other relaxation exercises also assist in autonomic reflexes. This is called conscious control. Through these practices, it is possible to gain control over the sphincter muscles in the anus and bladder. Yoga has been shown to help control heart rate, blood pressure, and other autonomic functions. These are learned behaviors - they involve the formation of new pathways in the brain.
Researchers have also found the correlation between a social support network of close friends and family and less physiogical stress effects (Brown and Harris, 1978). Stress Inoculation Training and Hardiness Training are cognitice behavioral techniques that work to improve stress resistance through analysing stressors, teaching coping techniques, and changing behavior so that the patient feels more assertive and in control (Meichenbaum, 1977) (Kobasa, 1986). Drugs, such as beta-blockers, which reduce stress arousal, anxiolytic drgus, such as minor tranquilisors, and anti-depressant drugs, which treat severe anxiety, can also be used to combat stress.
How do drugs effect behavior? What physical effects and changes on the brain can be observed?
Looking through the lens of the biological perspective, explain how genetics influences brain development.
What are the implications of Rosenweig's study More Experience = Bigger Brains study? Triungalate other research that goes in accordance to this theory.
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