The biological or physiological level explains behavior in terms of physiology meaning that it explains behavior in terms of the brain, genes, neurotransmitters and hormones


  • Behavior is biologically determined by physiological processes such as the nervous system neurotransmitters (e.g. serotonin) and the endocrine system (hormones e.g. testosterone)
  • The above principle was expressed as "all that is psychological is first physiological" (Sperry)
  • Patterns of behavior can be inherited through genetics
  • The study of animals can inform our understanding of human behavior

Principles of the Biological Level Demonstrated in Theories and Research

  • Localization of function (Broca's Area in speech production) discovered through post mortem analysis of brains
  • Genetic predisposition of schizophrenia using correlational twin research (Gottesman and Shields, 1976)
  • The dopamine hypothesis of schizophrenia - amphetamines increase positive symptoms of schizophrenia in normal patients and increases positive symptoms further in schizophrenic patients (Laruelle //et al//., 1996)
  • The monoamine hypothesis of depression

Research Methods

  • Experiments
  • Observations
  • Correlational Studies
    • Twin studies
    • Adoption studies
    • Family studies
  • Ethical Concerns

Physiology and Behaviour

Localization of Function

  • Broca's Area - Involved in speech production
  • Wernicke's Area - Involved in speech comprehension
    • Patients can produce speech but not comprehend it

Effects of Neurotransmission on Behavior

  • Dopamine
    • Voluntary movement
    • Learning
    • Pleasure
  • Serotonin
    • Sleep
    • Arousal Levels
    • Emotion
      • Happiness
    • Monks hallucinated after 48 hours of no food or water - linked to increased serotonin levels (Kasamatsu & Hirai, 1999)

Functions of Two Hormones on Behavior

Effects of Environment on Physiological Processes

  • Brain plasticity - ability to rewire connections between neurons
    • Enriching environment leads to increased cortical thickness in rats compared to boring environment (Rosenzweig & Bennett, 1972)
  • Environmental stressors at work can increase our susceptibility to disease (e.g. heart disease). Do Google employees have this problem? Check out this video
  • Eating disorders can disrupt the menstrual cycle - can be considered an evolutionary mechanism to prevent an unprepared woman from conceiving a child
  • Sleep deprivation in rats causes increased metabolism (210-270%) despite increased food intake and for most rats eventual death __(Rechtschaffen & Bergman, 1995)
  • Menstrual Synchronicity

Interaction between Cognition and Physiology in Terms of Behavior

  • Meditation produces gamma waves found using a PET scan with monks (Davidson, 2004)
    • Did not account for confounding variable of practice since monks meditate a lot

Brain Imaging Techniques

  • EEG - records brain waves
    • Cannot show what is happening in deeper brain regions
    • Cannot show actual functioning of brain regions
  • PET - monitors glucose metabolism in brain via injection of radioactive glucose
    • Can record ongoing activity like thinking
  • fMRI - provides 3D image of brain
    • Easier to carry out compared to PET
    • Higher resolution than PET
    • Cannot record ongoing activity - just snapshots

  • MRI scanners are unnatural environments for cognition - ecological validity
  • Colors in images may exaggerate activity in brain regions
  • Equipment may not be sophisticated enough to detect subtle brain activity
  • Brain areas activate for various reasons because the brain is highly interconnected so you cannot conclude that just because the amygdala is activated the patient is experiencing fear

Genetics and Behavior

Extent of Genetic Inheritance on Behavior

  • Huntington's - Only neurodegenerative disease with a 100% genetic cause
  • Schizophrenia - DISC1 implicated (Hennah_//et al//., 2006)
    • Diathesis stress model - environment and genetics
  • Affective Disorders - Short and Long Serotonin Transporter Genes implicated in disposition to depression (Caspi_//et al//., 2003) (Du_//et al//., 1999)
    • Diathesis stress model is most accepted

  • Both genetics and environment play crucial role
    • Poverty tends to correlate with low IQ
  • Meta-analysis of 111 studies found highest correlation for IQ was kinship (Bouchard & McGue, 1981)
  • Minnesota Twin Study __(Bouchard_//et al//., 1990)
    • MZ twins raised together compared to MZ twins raised apart longitudinal study
    • Estimate that heritability accounts for about 70% of intelligence
    • Criticism
      • Media coverage to recruit participants - possible sample bias
      • Ethical concerns about how he reunited the twins who were reared apart
      • No control over how often the twins reared apart visited each other prior to study
      • Equal environment assumption - cannot assume twins raised together experience same environments (e.g. treatment from parents, experience with friends and peers in school and at home)
  • Adoption studies (Scarr & Weinberg, 1977; Horn et al., 1979)
    • No significant difference found in correlations despite adoptive parents being wealthy, white and with high IQ and adopted children being from poor backgrounds

Ethical Considerations for Research into Genetic Influences

  • Undue stress on patients being tested for Neurodegenerative diseases (Alzheimer's, Parkinson's but less with Huntington's because of reliability of prognosis)
  • Parents can feel responsible for fate of the child
  • Patient may feel less responsible for their disease and make less of an effort to recover, instead relying on medications to do the psychological work

Evolutionary Explanation of Behavior: Disgust

  • Promotes survival (Fessler, 2006)
  • Confirmed by online survey that found participants had the strongest disgust reaction to stimuli which threatened the immune system __(Curtis_//et al//., 2004)
  • Has also been related to biological preparedness and phobias because animals that elicit a disgust response can be poisonous and avoiding these creatures because they evoke disgust further promotes survival

Evaluation of Evolutionary Arguments
  • Testing evolutionary theories of behavior is empirically difficult so researchers may be led astray by confirmation bias
  • We know little, if anything, about Homo sapiens’ behavior - it is purely speculative
  • Disregard the role of culture in shaping behavior

Additional Resources