COGNITIVE

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COGNITIVE SCIENCE 17 Why Sex is
Necessary Part 2 Jaime A.
Pineda, Ph.D.
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Hormonal Control of Reproductive Cycle

• Menstrual cycle
• Begins with secretion of FSH to stimulate growth
  of ovarian follicles (epithelial cells
  surrounding each ovum)
• As ovarian follicles mature they secrete
  estradiol causing the growth of the lining of the
  uterus (preparation for fertilization)
• Increasing levels of estradiol triggers the
  release of LH causing ovulation (release of ovum)
• Ovum enters a Fallopian tube and starts migrating
  towards uterus.
• If it meets sperm and becomes fertilized it
  begins to divide and then attaches itself to
  uterus wall
• If it is not fertilized, the ruptured ovarian
  follicle (corpus luteum) and the lining of the
  uterine wall will be expelled

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Menstrual Cycle
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Sexual Behavior

• Hormones have organizational effects on sexual
  behavior
• They exert these effects by altering the
  development of the brain
• In most female mammals (other than higher
  primates) sexual behavior (willingness and
  ability to mate) is controlled by
• Ovarian hormones estradiol and progesterone
• Pheromones odor and smell

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Effects on Human Females

• The ability to mate is not strictly controlled by
  ovarian hormones
• No physical barriers (such as lordosis)
• Hormones may affect sexual interest
  (female-initiated sexual activity peaks during
  ovulation estradiol levels are highest)
• Other factors are important
• Pleasure, affection, attraction, and love
  (emotions)
• Desire to get pregnant confidence in birth
  control method
• Cognition (how a stimulus is interpreted
  romantic vs sexual interest?)
• Learning (e.g., Fear of rejection) and culture

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Effects on Human Males

• Males (in contrast) resemble other mammals in
  their response to sex hormones
• Normal levels of testosterone ? potent/fertile
• No testosterone ? reduction in sexual interest,
  sexual fantasy, and intercourse
• Sexual activity (even imagining it) affects
  levels of testosterone which affects levels of
  sexual activity

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Neural Control of Sexual Behavior Role of the
Brain
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Neural Control of Sexual Behavior

• Human males
• Erection and ejaculation are controlled by spinal
  reflexes
• Spinal nucleus of the bulbocavernosus (SNB)
  controls the muscle that attaches to penis
• SNB is controlled by the level of androgens
  present
• Brain mechanisms can control reflex circuits
• Medial preoptic area (MPA) of the hypothalamus
• Sexually dimorphic nucleus (SDN) larger in
  males than females
• Medial amygdala, bed nucleus of the stria
  terminalis (BNST), periaqueductal gray (PAG) and
  nucleus paragigantocellularis (PGi)

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Medial Preoptic Area (MPA)
Lesions impair sexual and parenting
behaviors Controls mating behavior Contains
estrogen receptors What is its role?
Involved in both consummatory (execution) and
appetitive (motivational) aspects of masculine
sexual behavior.
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Neural Control of Sexual Behavior

• Females
• Ventromedial nucleus of the hypothalamus (VMH)
• Medial amygdala
• Periaqueductal gray matter (PAG)
• PGi

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Sexual Orientation

• Sexuality is best regarded as a continuum with
  most people being primarily heterosexual, some
  bisexual, and others primarily homosexual.
• Homosexuality was thought of as a choice or the
  result of faulty upbringing.
• There is now evidence that it is not a choice or
  the result of upbringing.
• Biological events appear to play a major role in
  determining sexual orientation.
• LeVay found evidence of a structure in the
  hypothalamus (MPA) that is smaller in women and
  in homosexual males than in heterosexual males.
• This study is supported by animal research
  linking atypical sexual behavior when the MPA was
  removed.
• These and other data suggest a biological
  predisposition for some people to become
  homosexual.
• The evidence for biological underpinnings to
  sexual orientation is not sufficient to rule out
  a role for the environment.

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Sex Differences in Cognitive Function

• Female superiority tests that emphasize
  perceptual, psychomotor abilities, face
  recognition, object memory, object location
  memory, language and processing speed
• Male superiority tests that emphasize
  visual-spatial functions, mental rotation,
  navigation, targeting, mechanical reasoning, and
  mathematical skills

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Anatomic Differences Behavior

• Lateralization of verbal functions to the left
  hemisphere and visual-spatial functions to right
  is more pronounced in males, beginning in
  childhood
• Less hemispheric lateralization in females
  greater need for interhemispheric communication
  (larger corpus callosum?)

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Theories of Functional Differences

• Perhaps specific functions that show male
  superiority require relatively large volumes of
  brain tissue
• Whereas functions that show female superiority
  may be independent of tissue volume but
  critically dependent on circuit organization.

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• Neuronal density may be normally greater in
  certain critical areas of the female brain,
  reducing volume without reducing efficacy
• Males greater hemispheric lateralization may
  confer certain functional advantages but result
  in male intrahemispheric brain tissue redundancy
  for other functions

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Sagittal MRI