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=Neuroscience of Gender Differences=

Intro Paragraph
Until around 21 years ago, scientists did not think that sex had any impact on how the human brain performs daily tasks, but through fMRI and PET scan studies, they have uncovered a great deal of information regarding the differences between male and female brains and how much they differ in regards to both structure and function. Recent studies have shown that gender influences how the brain carries out several components of our physical being such as emotion, memory, vision, hearing, processing faces, pain perception, navigation, neurotransmitter levels, stress hormone action on the brain and disease states.There are several sexual dimorphisms present in the brain. Some of these dimorphisms are present in the cognitive regions of the brain such as the neocortex, hippocampus, and amygdala.

The vast amount of evidence supporting sex differences in brain morphology and functionality has forced scientists to realize that they cannot simply assume that the male and female brain can be treated the same from neither a therapeutic nor functional perspective. .

From before birth, human brains are structurally asymmetric. These asymmetries could account for gender differences in brain anatomy and functionality. Male brains, for example, exhibit asymmetries on the right superior temporal and inferior frontal cortices more so than females; this asymmetry " sexual dimorphism in brain lateralization"

Oxytocin
Oxytocin is a hormone that induces contraction of the uterus and lactation in mammals. It is also a characteristic hormone of nursing mothers. Studies have found that oxytocin improves spatial memory. Through activation of the MAP kinase pathway, oxytocin plays a role in the enhancement of long-term synaptic plasticity and long-term memory. Consequently, this hormone helped mothers remember where food the location of distant food sources so they could better nurture their offspring

Sexual Selection

 * Maximizing offspring by controlling behavior
 * Females have a subtle approach where they are able to recall fine details-such as social cues- when competing against other females for a mate.
 * Sex related functional asymmetry
 * May provide an explanation how homologous brain regions differ in how they process information and shaped our brains to meet the demands of both the sexes with unique reproductive and social roles.”

Amygdala

 * Sexual dimorphism exists in the left amygdala
 * In males, the left side is more active than in females. Males possess up to 80% more excitatory synapses in the left medial amygdala than do females.
 * Gonadal hormones during puberty increase the number of proteins related to synapse formations
 * protein called Post synaptic density 95 increased dramatically in the amygdala of male hamsters.

Hippocampus
Several studies have shown the hippocampi of men and women to differ anatomically, neurochemically, and also in degree of long-term potentiation. Such evidence indicates that sex should influence the role of the hippocampus in learning. One experiment examined the effects of stress on Pavlovian conditioning performance in both sexes and found that males’ performance under stress was enhanced while female performance was impaired. The hippocampus’s relationship with other structures in the brain influences learning and has been found to be sexually dimorphic as well. .

Limbic Brain

 * Discuss Koskic et al. paper: “Sex related functional asymmetry in the limbic brain”
 * Ventromedial prefrontal cortex (VPMC)
 * Important for social-emotional processing
 * Exhibits sexual dimorphism on a functional level
 * Right VPMC-critical for social-emotional functioning and decision making in men
 * Left VPMC-more dominant in social-emotional functioning in women
 * How left limbic dominance affects women’s social functioning (interpersonal relationships)

White/Grey Matter

 * Women exhibit a higher ratio of grey to white matter
 * They also exhibit greater volumes and concentrations of localized and regional grey matter
 * Women have greater cortical thickness than men
 * Discuss Luders et al. paper
 * Global and regional grey matter (GM) in women versus men
 * Women have larger left orbitofrontal GM volumes than men

Orbital Prefrontal Cortex
Positron emission tomography studies have shown that men and women ranging from the ages of 19 to 32 years old metabolize glucose at significantly different rates in the orbital prefrontal cortex. Furthermore, MRI images display reduced hemispheric brain volumes, specifically in the frontal and temporal regions, in men more so than women. Infant males who exhibited lesions on their orbital prefrontal cortex struggled with object reversal experiments, but females exhibiting such lesions did not have impaired performance in object reversal.

Hormones
Steroid hormones have several effects on brain development as well as maintenance of homeostasis throughout adulthood. One effect they exhibit is on the hypothalamus, where they increase synapse formation. . Estrogen receptors have been found in the hypothalamus, pituitary gland, hippocampus, and frontal cortex, indicating the estrogen plays a role in brain development. Gonadal hormone receptors have also been found in the basal forebrain nuclei. .

Estrogen and the Female Brain
Estradiol influences cognitive function, specifically by enhancing learning and memory in a dose-sensitive manner. Too much estrogen can have negative effects by weakening performance of learned tasks as well as hindering performance of memory tasks; this can result in females exhibiting poorer performance of such tasks when compared to males.

It has been suggested that during development, estrogen can exhibit both feminizing and defeminizing effects on the human brain; high levels of estrogen induce male neural traits to develop while moderate levels induce female traits. In females, defeminizing effects are resisted due to the presence of α-fetoprotein (AFP), a carrier protein proposed to transport estrogen into brain cells, allowing the female brain to properly develop. The role of AFP is significant at crucial stages of development, however. Prenatally, AFP blocks estrogen. Postnatally, AFP decreases to ineffective levels; therefore, it is probable that estrogen exhibits its effects on female brain development postnatally.

Ovariectomies, surgeries inducing menopause, or natural menopause cause fluctuating and decreased estrogen levels in women. This in turn can “ attenuate the effects” of endogenous opioid peptides. Opioid peptides are known to play a role in emotion and motivation. β-endorphin (β-EP), an endogenous opioid peptide, content has been found to decrease (in varying amounts/brain region),post ovariectomy, in female rats within the hypothalamus, hippocampus, and pituitary gland. Such a change in β-EP levels could be the cause of mood swings, behavioral disturbances, and hot flashes in post menopausal women.

Testosterone and the Male Brain
Testosterone has been found to play a big role during development but may have independent effects on sexually dimorphic brain regions in adulthood. Studies have shown that the medial amygdala of male hamsters exhibits lateralization and sexual dimorphism prior to puberty. Furthermore, organization of this structure during development is influenced by the presence of androgens and testosterone. This is evident when comparing medial amygdala volume of men and women, adult male brains have a medial amygdala of greater volume than do adult female brains which is partially due to androgen circulation. It also heavily influences male development; a study found that perinatal females introduced to elevated testosterone levels exhibited male behavior patterns. In the absence of testosterone, female behavior is retained. Testosterone's influence on the brain is caused by organizational developmental effects. It has been shown to influence proaptotic proteins so that they increase neuronal cell death in certain brain regions. Another way testosterone affects brain development is by aiding in the construction of the "limbic hypothalamic neural networks".

Similar to how estrogen enhances memory and learning in women, testosterone has been found to enhance memory recall in men. In a study testing a correlation between memory a recall and testosterone levels in men, "fMRI analysis revealed that higher testosterone levels were related to increased brain activation in the amygdala during encoding of neutral pictures".


 * Females, menstrual cycle
 * Short-term hormone-dependent structural brain changes during the menstrual cycle

Stress
Stress has been found to induce an increase in serotonin, norepinephrine, and dopamine levels within the basolateral amygdala of male rats, but not within that of female rats. Furthermore, object recognition is impaired in males as a result of short term stress exposure. Neurochemical levels in the brain can change under the influence of stress exposure, particularly in regions associated with spatial and non-spatial memory, such as the prefrontal cortex and the hippocampus. Dopamine metabolite levels decrease post stress in male rats’ brains, specifically within the CA1 region of the hippocampus.

In female rats, both short term (1 hour) and long term (21 days) stress has been found to actually enhance spatial memory. Under stress, male rats exhibit deleterious effects on spatial memory, however female rats show a degree of resistance to this phenomenon. Stressed female rats’ norepinephrine (NE) levels go up by about 50% in their prefrontal cortex while that of male rats goes down 50%..

Iowa Gambling Task

 * Provide a general summary of what the Iowa card task is and what it is used for (link to page)
 * Reavis et al. paper
 * Studies have found sex differences in orbital prefrontal cortex in adolescents, young children, and adults
 * Men outperformed women in Iowa Card Task
 * Negative correlation between testosterone levels and performance in card task

A study conducted on men and women of various age groups, " children below the age of three years, adolescents between the ages of 12 and 18, young adults in their twenties, and older adults over 55 years", who were asked to perform the Iowa Gambling Task revealed data showing that man and women differ in their decision making processes on the neurological level. The study suggests that decision-making in females may be guided by avoidance of negativity while decision making in males is mainly guided by assessing the long term outcome of a situation.

Math, Science, & Literature

 * Men perform better on spatial tasks
 * Women perform better on phonological tasks