Study Notes on Sex Differences: Animals and Humans

Learning Objectives

  • Understand emergence of brain and behavior sex differences
  • Recognize significance of these differences

Sex Differences in Disease

  • Prevalence varies by sex:
    • Schizophrenia, Autism, ADHD, Parkinson's: M > F
    • Depression, Multiple sclerosis, Alzheimer's: F > M
  • Clinical presentations differ:
    • Depression in women: atypical symptoms
    • Heart attack symptoms vary by sex
  • Drug responses differ; women have higher adverse reactions

Female Exclusion in Research

  • Females historically overlooked in biomedical research
  • Myths about female utility and variability
  • Evidence suggests significant differences impacting disease

Policy Changes in Research

  • 1993: NIH mandated women in clinical trials
  • 2016: NIH required preclinical research to include both sexes and consider sex as a biological variable

Behavioral Sex Differences

  • Reproduction: Males - mounting, Females - lordosis
  • Cognitive functions:
    • Verbal: F > M
    • Visuospatial: M > F
  • Social behavior:
    • Nurturing: F > M
    • Aggression: M > F

Types of Brain Differences

  • Volumetric: Size differences in brain regions
  • Connective: Synaptic connections
  • Neurochemical: Hormonal/neurotransmitter variations

Causes of Brain Sex Differences

  • Result from organizational effects of gonadal hormones
  • Influenced by genetic, environmental factors
  • Involves mechanisms like neurogenesis, apoptosis, myelination

Specific Brain Regions and Their Sex Differences

  • Spinal Nucleus of the Bulbocavernosus (SNB): Larger in males
  • MPOA: Connective differences; influenced by hormones
  • SDN-POA: Size differences linked to hormone effects
  • AVPV: Involves maternal behavior and neural mechanisms of sex differences

Genetic Contributions

  • Four core genotypes model shows genetic influence on behavior and diseases independent of gonadal sex

Non-Reproductive Brain Differences

  • Sex differences also seen outside reproductive contexts (e.g., language, spatial reasoning)
  • Neuroanatomical variations exist in human brains; e.g. differences in surface area, gray/white matter proportions

Conclusion on Brain Sexual Differentiation

  • The brain is not strictly male or female but a mosaic of traits; distinct regions exhibit varying sexual differentiation processes.