Evolutionary paradox of mental disorders Flashcards
Explanation 1: Direct vs. inclusive fitness
Reduced direct fitness - fertility rates of those with MDs.
Potentially enhanced inclusive fitness - increased fertility of relatives.
Explanation 2: paternal age effect - mutation accumulation
Most MDs associated with a genetic component.
Accumulation of chance mutations - increased levels with fathers age (eg. schizophrenia).
Explanation 3: early prenatal preparation and early plasticity - human brain development
High levels of plasticity before birth and during early stages (synaptogenesis and myelination) .
- more vulnerable to environmental effects.
Explanation 3:… genes and environment
Stressors (eg. drugs, stress, infection etc) enhance risk of MDs.
- risk of CNS disorders increased: ASD (childhood), schizophrenia (adolescence), MDD (lifelong), diabetes/alzheimers (later life).
Explanation 3:… prenatal preparation effects
Adaptive development plasticity and unanticipated environments.
- foetal development suggests a neonate is primed to expect a certain environment (inconsistent = illness).
Explanation 3:… may be neurodevelopmental disorders
On a continuum (eg. ASD, ADHD etc).
- why is development often between childhood and adolescence?
Explanation 3:… brain development in adolescents
Limbic system plays role in: emotions, motivation, emotional learning.
PFC in: working memory, planning, inhibiting inappropriate responses, risk taking etc.
PFC development believed to underlie age-related changes in: cognitive function, judgement, decision making.
- mismatch usually leads to stress - may be due to lacking development.
Explanation 3:… why do changes happen so late?
Neurodevelopmental hypothesis: infant -> brain damage -> to DLPFC.
- age one year - little effect of lesion, performs almost as well as undamaged monkeys.
- 2 years - clear effect, performs worse.
Explanation 3:… synaptic pruning in schizophrenia
Synaptic over-pruning hypothesis (Feinberg, 1982): too excessive neural pruning in PFC in post-natal development prior to onset of disorder .
- Glanz & Lewis (2000) - healthy adult = dendrites with many spines; schizophrenic adult = only a few spines.
Explanation 3:… white matter reduction in schizophrenia
Loss of myelin sheath and reduced white matter in schizophrenic patients - eg. reduced corpus callosum volume.
Leads to disrupted disrupted communication with the brain -> loss of timing.
Basic ideas of evolution of MDs
Continuum of mental illness.
Initially adaptive traits become maladaptive - adaption theories.
Mismatch between adaptive trait and current environment - mismatch theories.
MD as a by-product of an adaption - by-product theory.
MD due to random noise (mutations) - eg. paternal age effect.
THEORIES NOT EXCLUSIVE OF EACH OTHER.
Evolutionary theory 1: The dopamine theory (An adaption theory) - human migration out of Africa
Enhanced brain size.
Homo-neatheralenis coexisted/interbred with homosapiens but died out 28000 years ago.
Migrated from Africa -> Europe -> Australia -> North America -> South America.
As human species evolved, brain enlarged (especially PFC).
Evolutionary theory 1:… adaption of people
Migration (for resources) requires individuals to be adaptive, curious, risk taking etc.
- trade off - more likely to be killed.
- these traits vary in monkey species and humans (Fairbanks, 2001).
Dopamine levels linked.
Evolutionary theory 1:… rise of dopamine levels in human evolution
Risk taking related to increased dopamine.
Goal directed behaviour/cognitive capacities related to increased dopamine, increased PFC.
Pathways:
- nigostriatal - motor action.
- mesolimbic - emotions, exploratory behaviour, motivational drive, creative impulse.
- mesocortical - reward-seeking behaviour, planning, problem solving etc.
Evolutionary theory 1:… why did levels increasing during evolution?
Dopamine is important for attending to distant space and time (Pevic, 2009) - migration?
Near vs distant space - planning to reach something far away; imagination of more distant and abstract worlds.
Near vs distant time - planning behaviour (eg. food hoarding); distant goals (motivational behaviour); imagining the large time scale of evolution.
Adaptation to new environments due to:
- environmental pressures - increased consumption of meat and fish - greater supply of dopamine precursors - increased longevity in humans.
- population pressures.
- migration.
- stress levels - physiological responses to increasingly stressful and new environments.
Evolutionary theory 1:… support
Dopamine level adaptation can be due to:
- genetic and epigenetic inheritance (eg. mothers can pass prenatal high dopamine levels to their offspring).
Dopamine levels across species (Previc, 1999; 2009).
- high dopamine - intelligent non-human species (eg. dolphins).
- very high - primates and humans.
Dopamine levels across societies (Previc, 2009; 1999) - modern industrial societies might have higher dopamine levels compared to agricultural societies.
- higher achievement motivation, increased competition.
Evolutionary theory 1:… mental disorders and dopamine
Schizophrenia: clear relation between D2 receptor blocking and therapeutic effect.
- accounts for positive symptoms.
Other hyper DA disorders: autism, OCD, mania etc.
May be originally adaptive trait of mild dopamine levels, has become maladaptive.
Evolutionary theory 2: by-product theory - mental illness = by-product
Eg. creativity: capacity to create new valuable ideas.
- Includes intrinsic motivation, expertise, intelligence, personality, psychopathology, etc.
Intelligence: humans - positively correlated between creative and IQ up to 120.
Thinking style: convergent and divergent thinking, use of analogies.
- chimp Sarah chose can opener instead of paint brush for closed paint can (Holyark & Thagard, 95).
Personality differences: Drives, Big5, capacities etc (Runco, 2007).
- some male vervet monkeys are bold and novelty seeking temperament (King et al, 1999).
Psychopathology: abnormal and maladaptive thought process; in mild form can contribute to creativity.
- eg. filtering out irrelevant info - increased odds of new ideas.
Evolutionary theory 2:… creativity
Schizophrenia link (Previc, 2009; Carson et al, 203).
Reduced latent inhibition - reduced tendency to filter out irrelevant info.
Enhanced divergent and convergent thinking - lots of memory for ideas, observations, objects etc.
Loosened associations - more jumping from one topic to another.
- creativity - associations between remote ideas, well sorted and explained.
- psychosis - not organised, unusual, bizarre.
Evolutionary theory 2:… creativity in high moods (bipolar disorder)
Hypomania - often part of bipolar disorders: manic/depressive.
- intense enthusiasm.
- overactivity.
- pressure to talk.
- flight of ideas etc.
Mania - often grandiosity and other traits take over and hospitalisation and medication is required.
Evolutionary theory 2:… mental illness is a by product of creativity
Shared vulnerability model (Shelley & Carson, 2011):
- reduced latent inhibition - psychoactive drugs (Eg. LSD).
- novelty seeking - drugs and alcohol to stimulate creativity.
- hyper connectivity - synaesthesia.
Evolutionary theory 3: Mismatch theory - mismatch theory
Adaptive trait in our ancestral environment becomes maladaptive in current environment.
- fears, phobias, depression etc.
Evolutionary theory 3:… specific phobias
Ancient world - low fear threshold might have been advantageous.
- although includes false alarms, there is high cost of death/injury so beneficial to be wary.
Specific phobias - oversensitive fears(eg. spiders-hardly any harmful to humans).
- primary (inherent/unconditioned) - once posed a threat to ancestors maybe due to evolutionary stress.
- secondary (learned/modern) - eg. flying, dentists etc.
Evolutionary theory 3:… depression
Associated with reduced serotonin levels.
Depression due to unfavourable changes:
- eg. loss of partner/child.
- one’s place in social hierarchy - vervet monkeys: changing serotonin levels with ranking (McGuire & Troisi, 1998) - humans: social place, pride and shame.
Hypothesis = depression and anxiety increased in modern society.
- because media bombards with info about those in better places than us?
- always hierarchy happening in bigger circle.
- social comparison theory (Festinger, 1954).
