Psychosurgery and its Effects

Psychosurgery and the Biology of Behavior

• No psychosurgery should be done without a detailed assessment of its effects on a large sample of patients.
• Psychosurgery refers to any brain surgery performed for the treatment of a psychological problem.
• Patients were often judged as improved if they were more manageable, but this did not necessarily mean they were cured.

The Origins of Dichotomous Thinking

• Dichotomy: a simple way of thinking in terms of two opposing extremes, such as good-bad or right-wrong.
• Examples of dichotomous thinking include:
  • Is it physiological or is it psychological?
  • Is it due to nature or nurture?
• Studies have shown that dominant males in some species copulate more and are more effective in passing on their characteristics to future generations.
• In some species, dominant females are more likely to produce more and healthier offspring.

Courtship Displays and Evolution

• Courtship displays are important for evolution because they can promote the formation of new species.
• A species is defined as a group of organisms that are reproductively isolated from other organisms.
• The evolution of an idiosyncratic courtship display can form a reproductive barrier that is as effective as geographical separation.

Mendelian Genetics

• Gregor Mendel discovered the mechanisms of inheritance through his work with pea plants.
• Dichotomous traits: characteristics that occur in one form or another, never in combination.
• True-breeding lines: interbred members will always produce offspring with the same trait generation after generation.
• Mendel's key findings:
  • When true-bred brown and white peas are crossed, all the offspring from the first cross have brown seeds, whereas 25% of the offspring from the second cross have white seeds.
  • The concept of dominant and recessive traits.
  • Each organism possesses two genes for each of its dichotomous traits.
  • One of the two kinds of genes for each dichotomous trait dominates the other in heterozygous organisms.

Chromosomes

• Chromosomes are threadlike structures in the nucleus of each cell.
• Humans have 23 pairs of chromosomes, with an allele on each chromosome.
• Meiosis: the process of cell division that produces gametes (egg and sperm cells).
• Genetic recombination: the crossover of chromosomes to exchange genetic material, creating diversity.

Genetic Code and Gene Expression

• Structural genes: contain information for the synthesis of proteins.
• Proteins: long chains of amino acids that control the physiological activities of cells and are important components of cellular structure.
• Promoters and enhancers: determine whether particular structural genes are converted into proteins through a two-phase process called gene expression.
• Gene expression involves two phases:
  1. Transcription: the process of transcribing DNA code into RNA code.
  2. Translation: the process of translating RNA code into a protein.

Human Genome Project

• The Human Genome Project was launched in 1990 to compile a map of the sequence of all 3 billion nucleotide bases that compose human chromosomes.
• The project has led to important insights into evolution and the discovery of the number of structural genes in humans and other species.### Human Proteome and Epigenetics
• Human proteome: a nearly complete map of the entire set of proteins encoded by our genes
• Only about 1% of human DNA constitutes protein-encoding genes, while the remaining 99% is considered "junk DNA"
• Many genes have been linked to each disease, but together, they often account for only a small portion of its heritability
• 18 different gene variants have been linked to adult-onset diabetes, but these variants account for only 6% of the heritability of the disease

Growth of Epigenetics

• Epigenetics focuses on mechanisms that influence the expression of genes without changing the genes themselves
• 4 factors that led to the rise of epigenetics:
  • Human Genome Project generated new research techniques
  • Discovery that protein coding genes constitute only about 1% of human DNA
  • Most RNA molecules are small, with only 1.2% being of the large protein-encoding variety
  • Mechanisms of gene-experience interactions unknown
• 5 important discoveries in epigenetics:
  • Nongene DNA is not "junk DNA", but rather active DNA that controls structural gene expression
  • Epigenetic mechanisms can modulate gene expression, including DNA methylation and histone remodeling
  • Worldwide effort to catalogue the epigenome of each cell type
  • Epigenetic modifications of messenger RNA and transfer RNA are prevalent
  • Epigenetic mechanisms can be induced by experiences, such as neural activity, hormonal state, and changes to the environment

Epigenetics of Behavioral Development

• Behavioral development is a consequence of genetic potential interacting with the experience of an individual organism
• Ontogeny refers to the development of an individual through their lifespan
• Phylogeny refers to the evolutionary development of a species through the ages

Selective Breeding of Maze-Bright and Maze-Dull Rats

• Cooper and Zubek's (1958) study on maze-bright and maze-dull rats
  • Reared maze-bright and maze-dull rats in one of two environments: impoverished or enriched
  • Maze-dull rats made more errors than maze-bright rats only if they had been reared in the impoverished environment
• Tryon's (1934) study on selective breeding of behavioral traits
  • Bred fittest maze-bright rats together and dullest maze-dull rats together for 21 generations
  • By 8th generation, there was almost no overlap in the maze learning performance of the two groups of rats
  • Used cross-fostering control procedure to demonstrate that genetic factors contribute to behavioral traits

Phenylketonuria (PKU)

• PKU is a single-gene metabolic disorder that affects brain development
• Symptoms of PKU include intellectual disability, vomiting, seizures, hyperactivity, irritability, and brain damage
• PKU is transmitted by a single gene mutation and develops only in homozygous individuals
• PKU homozygotes lack phenylalanine hydroxylase, leading to an accumulation of phenylalanine in the body and low levels of dopamine
• Behavioral symptoms result from an interaction between genetic and environmental factors
• A phenylalanine-restricted diet can reduce the development of intellectual disabilities in PKU homozygotes
• Sensitive period: a period during which a particular experience must occur to have a major effect on the development of a trait