Genetics of Behavior

The Brain and Behavior Genes contribute to behavioral traits via effects on the brain Remember: genes are recipes for proteins

Neurons

The Brain: Neurons and Glia

The Synapse

Synapses

Where do things go wrong? Myelin Neurotransmitter synthesis Reuptake Postsynaptic receptors …anywhere there are proteins

Behaviors are Often Multifactorial Traits Environment, environment, environment! Polygenic Genetic heterogeneity Same collection of symptoms may have different causes Epistasis Influenced by temperament and personality What is “normal”? Some disorders have various symptoms

Autism 3 major symptoms, each likely has its own underlying gene Impaired communication Usually no speech or interaction with others Social problems Interaction with others is difficult Rigid repetitive behaviors Comfortable only with repetitive behaviors Incidence is per 10,000 (<0.1%) Higher for siblings (2-4%) Twin studies indicate 90% heritability 4-5 major genes contributing genes

Eating Disorders Anorexia nervosa Person perceives themselves as obese Highest risk of death of any psychiatric disorder (15-20%) Bulimia Person binges and purges 90% of eating disorders are in females heritability Little sister may mimic big sis’s or mom’s eating habits Christy Henrich

Sleep Sleep is “a vital behavior of unknown function” Strong heritability for sleep characteristics

Narcolepsy Individual falls asleep suddenly Sleep paralysis Inability to move after awakening Gene for narcolepsy + cataplexy in dogs discovered in 1999 Is polygenic in humans Cataplexy Muscle weakness following excitement Mutation in the gene for the hypocretin/orexin receptor

Drug Addiction Compulsively seeking and taking a drug despite knowing its adverse effects Tolerance Need to take more of the drug to have the same effects as time goes on Dependence Withdrawal symptoms if drug use stopped Heritability is 0.4 to 0.6 Brain changes occur in the limbic area of the brain

Major Depressive Disorder (MDD) Mood disorders may appear to be extremes of normal behavior Many “normal’ people have “highs” and “lows” to some degree Lethargy, sadness, no joy from favorite activies 15% of people hospitalized for MDD end their lives Partly due to malfunction of the serotonin transporter

The Neurotransmitter Serotonin Can affect mood, emotion, appetite, and sleep Many antidepressive drugs are serotonin reuptake inhibitors (SSRIs)

Bipolar Affective Disorder The “effects” of this drug may “affect” my “affect” Bouts of depression and bouts of mania Manic behavior is reckless and excited Much less common than MDD Genetic cause still unknown

Schizophrenia Loss of ability to organize thoughts and perceptions Delusions and hallucinations Inappropriate affect Difficult to pinpoint heritability (~0.8) Some symptoms associated with other illnesses Polygenic Environmental factors my mimic it (phenocopies)

Genetic Contribution

Environmental Risk Factors for Schizophrenia Deficit subtype Associated with summer births Negative symptoms Lack of emotion Lack of facial expressions Non-deficit subtype Associated with winter births Positive symptoms Paranoia Hallucinations Delusions Table 8.3

In Conclusion Behavioral traits involve disruption in brain proteins Behavioral traits are multifactorial and often polygenic