Biological basis of emotion

What are emotions?

• perception of environmental stimuli
• cognitive appraisal of the situation
• neural and hormal responses to perceptions (feelings)
• outward expression of the state (behaviour)

Emotion is any relatively brief conscious experience characterised by intense mental activity and a high degree of pleasure or displeasure. According to some theories, they are states of feeling that result in physical and psychological changes that influence our behaviour.

The sympathetic nervous system is one of the 2 main divisions of the autonomic nervous system. It's primary role is to stimulate the body's fight-or-flight response. These are its functions:

• dilates pupils to better vision by letting more light in
• increases heart rate and force of contraction
• increases respiration to allow more oxygen in the blood
• activates sweat secretion
• slows down digestive system to allow blood to transfer to muscles

The parasympathetic nervous system is responsible for regulating the body's unconscious actions. It is responsible for stimulation of "rest-and-digest" or "feed and breed" activities that occur when the body is at rest

• slows and calms the body
• slows heartbeat
• stimulates digestion
• contracts bladder
• stimulates digestion

The amygdala has been shown in research to perform a primary role in the processing of memory, decision-making, and emotional reactions. It is part of the limbic system.

• located in the medial temporal lobe
• small almond shaped collection of nuclei
• is a "protection device" - it appears to play a role in inhibiting an organism's approach to novel objects or other organisms
• plays a role in: emotion processing, formation and storage of emotional memories, threat processing and learning about aversive things
• amygdala damage can result in deficits in recognising fear, reduction or removal of many emotional behaviours and their related physiological responses, and impaired memory for emotional events
• amygdala damage in animal studies showed that the animals were: not afraid of normally aversive stimuli, less aggressive when handled, lower stress levels, and had less stress-related illnesses

The hippocampus is located under the cerebral cortex and in primates in the medial temporal lobe. It belongs to the limbic system.

• nicknamed "the seahorse" due to its resemblance to the seahorse
• it has dense connections to the amygdala
• it is involved in memory functions including short-term memory, long-term memory, and encoding and retrieval of declarative memories
• understanding of spatial relations in environment
• hippocampus damage can result in difficulties in forming new memories - in alzheimer's diesease the hippocampus is one of the first regions of the brain to suffer damage
• severe stress can impair hippocampal size
• animal studies have shown the role of the hippocampus in spatial memory and navigations. Neurons in the rat and mouse hippocampus fire bursts of action potentials when the animals passes through a specific part of its environment

The hypothalamus contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland

• located below the thalamus
• links mind to body
• it is the main output from the limbic system
• has connections with the frontal lobes
• hub for automatic and endocrine homeostatic systems, controlling appetite, body temperature, endocrine hormonal levels and sleep

The prefrontal cortex is the cerebral cortex which covers the front part of the frontal lobe. It's responsible for the control and regulation of emotional responses.

• this region has also been implicated in will to live, personality, planning complex cognitive behaviour and decision making. The most typical psychological term for functions carried out by the prefrontal cortex area is executive function
• it is widely accepted that a function of the brain's prefrontal cortex is that it serves as a store of short-term memory. This was formulated by Jacobsen (1936) who reported that damage to the primate prefrontal cortex caused short-term memory deficits
• damage to the prefrontal cortex leads to executive function deficits like: poor planning, poor organisation, poor attention, and poor memory performance
• classic case of Phineas Gage: iron rod blasted through his head which damaged his frontal lobe. The damage made him impulsive, unreliable and he used profanity in excess

Testosterone

• a steroid which is part of the androgen group
• it is primarily a sex-hormone
• it is secreted in the testes and ovaries
• it is involved in muscle and bone strength and density, and is important for development of male secondary sex characteristics
• men produce about 40-60x more testosterone than women
• testosterone affects aggression - Archer (1994) reviewed the literature and found that most studies found a relationship between testosterone levels in males and females and their level of aggression
• however, individuals receiving testosterone doses report increases in happiness, sexual activity, irritability, hostility but not aggression