Biological concepts and terminology

Acetylcholine: The most common neurotransmitter. Acetylcholine receptor sites are found in the hippocampus. It appears that acetylcholine plays a key role in memory consolidation from STM to LTM.

Adrenaline: Also called epinephrine, adrenaline is secreted by the adrenal glands and stimulates the sympathetic nervous system, and prepares the body for fight or flight.

Agonist: a chemical or a drug that binds to receptors in the brain and causes a reaction. Agonists can occur naturally in the body as neurotransmitters (endogenous agonists) or come from exterior sources like drugs and toxins (exogenous agonists).

Amygdala: Part of the limbic system, this part of the brain is believed to play a key role in emotion and memory. In addition, there is evidence that it plays a role in aggression, sexual orientation, trust, and alcoholism.

Antagonist: A chemical or drug that binds to receptors in the brain and prevents a neurotransmitter from having an effect on behaviour. For example, scopolamine is an antagonist for acetylcholine.

Concordance rate: the probability that the same trait will be present in both members of a pair of twins.

Cortisol: a stress hormone that is secreted by the adrenal cortex. Responsible for the breakdown of glucose in the fight or flight response. Appears to be linked to hippocampal cell loss and memory dysfunction.

Dizygotic twins: The clinical term for fraternal twins; this occurs when two fertilized eggs are implanted in the uterus wall at the same time. When two eggs are independently fertilized by two different sperm cells, fraternal twins result. The genetic similarity is the same as any other siblings.

Dopamine: A neurotransmitter that helps control the brain's reward and pleasure centers. Dopamine also helps regulate emotional responses. Dopamine deficiency results in Parkinson's Disease and people with a lower number of dopamine receptor sites may be more prone to addiction.

Epigenetics: A branch of genetics that focuses on "gene expression" - that is, how environmental factors may "activate" genes.

Equal environment fallacy: environmental similarity between twins does not have much of an impact on trait similarity.

Excitatory function: When a neurotransmitter increases the likelihood that the neuron will fire an action potential.  This depends on the receptor site.  Many neurotransmitters are excitatory when they act on some receptor sites, and inhibitory when they act on others. For example, serotonin is an excitatory neurotransmitter that regulates sleep and wakefulness and is found in neurons in the pons and upper brain stem -  but it is inhibitory in mood and emotion.

Family studies: Researchers trace a phenotype over several generations in a family tree to determine the likelihood that a behaviour is inherited

Fight or flight response: a physiological reaction that occurs in response to perceived harm or threat to survival. It is triggered by the sympathetic nervous system activation that innervates the adrenal medulla, producing a hormonal cascade that results in the secretion of glucocorticoids. The animal is then reading for fighting or fleeing. This response is recognized as the first stage of Seyle's General Adaptation Syndrome.

Genome-wide association studies (GWAS): an examination of a genome-wide set of genetic variants in a large sample of individuals to see if any variant is associated with a trait.

Glucocorticoids: stress hormones that help with the metabolism of glucose. They are released during stress to assist with the "Fight or Flight" response.

Hippocampus: Part of the limbic system, this part of the brain appears to play a key role in the consolidation of memory from short-term to long-term, as well as play a role in spatial navigation. There are several acetylcholine receptor sites in the hippocampus. Hippocampal cell loss plays a role in dementia, including Alzheimer's Disease.

Hormone: A chemical released by a gland directly into the bloodstream which has an effect on behaviour.

HPA axis: a complex set of interactions between two parts of the brain—the hypothalamus and the pituitary glands—and the adrenal glands that are located at the top of each kidney. This is the basis of the human stress response.

Human Genome Project: the international, collaborative research program whose goal was the complete mapping and understanding of all the genes of human beings. All our genes together are known as our "genome."

Inhibitory function: When a neurotransmitter decreases the likelihood that the neuron will fire an action potential.  This depends on the receptor site.  Many neurotransmitters are inhibitory when they act on some receptor sites, and excitatory when they act on others. For example, serotonin is an inhibitory neurotransmitter when it is involved in emotion and mood, but excitatory in sleep and wakefulness.

Linkage analysis: Matching genetic variations (polymorphisms) with the frequency of a behaviour

Melatonin: Secreted by the pineal gland, melatonin forms part of the system that regulates the sleep-wake cycle by chemically causing drowsiness and lowering the body temperature.

Monozygotic twins: The clinical term for identical twins; they share 100% of their DNA.

Natural selection: the process whereby organisms better adapted to their environment tend to survive and produce more offspring

Neural network: Usually called a neural circuit, a group of neurons interconnected by synapses to carry out a specific function when activated.

Neural pruning: Usually referred to as synaptic pruning refers to the process by which extra neurons and synaptic connections are eliminated in order to increase the efficiency of neuronal transmissions.

Neuroplasticity: the brain’s ability to alter its own structure following changes within the body or in the external environment.

Neurotransmitter: A neurotransmitter is a chemical messenger that carries signals between neurons. Neurotransmitters are released from the terminal buttons at the end of an axon after the action potential has sent an electrical charge down the neuron. The neurotransmitter then crosses the synaptic gap to reach the receptor site on another neuron.

Nucleus Accumbens: A section of the basal forebrain, the nucleus accumbens plays a key role in addiction, pleasure, reinforcement learning, aggression, impulsivity, and the placebo effect. The nucleus accumbens has a significant number of dopamine receptors.

Oxytocin: Secreted by the pituitary gland, oxytocin plays a role in social recognition, pair bonding, and maternal attachment. For this reason, it is sometimes referred to as the "love hormone". There is some evidence that oxytocin promotes trust and empathy in in-groups.

Permissive effect: When the mere presence of the hormone allows for a behaviour, rather than the amount of the hormone. In the case of testosterone, Sapolsky argues that it not how much testosterone an animal has that determines whether it is aggressive, it is whether they have testosterone.

Pheromone: a chemical substance produced and released into the environment by an animal affecting the behaviour or physiology of others of its own species. 

Polymorphism: a genetic variation (mutation) resulting in the occurrence of several different forms or types of individuals among the members of a single species

Reuptake: The reabsorption of a neurotransmitter by the terminal buttons of the pre-synaptic neuron after it has performed its function of transmitting a neural impulse. This prevents further activity of the neurotransmitter. Prozac is an SSRI - that is, a selective serotonin reuptake inhibitor, allowing more serotonin to remain in the synaptic gap.

Selective placement: a limitation of adoption studies in which children are placed with families that are very similar to the original family.

Serotonin: A neurotransmitter that works to regulate mood, appetite, and sleep. Low levels of serotonin have been linked to Clinical Unipolar depression and high levels of aggression. High levels of serotonin have been linked to hallucinations.

Sexual selection: natural selection arising through preference by one sex for certain characteristics in individuals of the other sex

Testosterone: The male sex hormone. Secreted by the testes in males and the ovaries in females.

Transgenic mice: a mouse that has had a single gene changed or removed