The neural basis of emotion Flashcards
The concept of emotion
- emotions consist of patterns of physiological response and species-typical behaviours
- In humans these physiological responses are accompanied by feelings
- Feelings are powerful motivators
- Emotions are likely to have evolutionary significance (Charles Darwin (1872 - emotional expressions convey an animal’s intentions. (predictive value) may evolve to enhance communicative value
He also suggested that particular stereotyped responses tend to accompany similar emotional states in all members of the same species. E.g. in humans facial expressions tend to accompany the same feelings.
Three components of emotional responses
- Behavioural
- Autonomic
- Hormonal
Behavioural component of an emotional response
muscular changes that are appropriate to the situation that elicits them. For example, a dog may seek to defend its territory in the face of an intruder by adopting an aggressive posture (growling, ears forward, back and tail up, teeth bared). If this behavioural display is sufficiently effective, the intruder may in turn adopt a submissive posture (ears back, back and tail down). If it is not effective, the defending dog may run towards the intruder and attack. Note that the displays of aggression and submission are clearly distinguishable by the opposite movements and postures (what Darwin called the principle of antithesis)
Autonomic component of an emotional response
Physiological changes induced by the autonomic nervous system facilitate the behavioural responses. In the example of the dog defending its territory, activity of the sympathetic branch of the autonomic nervous system increases whereas activity of the parasympathetic branch decreases; the dog’s heart rate increases, and blood is diverted from the digestive system to the muscles.
Hormonal component of an emotional response
These reinforce the autonomic changes. To continue the example, the dog’s adrenal medulla secretes epinephrine and norepinephrine, which act to further increase blood flow to the muscles and cause nutrients stored in the muscles to be converted into glucose.
Neural control of emotional response patterns
Bard (1929) found that cats who had their cerebral cortex surgically removed in both hemispheres (decortication) behaved in an excessively aggressive manner. A simple touch would make cats hiss etc. This behaviour can be considered abnormal as it is not elicited by an environmental stimulus that would normally elicit this response
This aggressive behaviour was termed ‘sham rage’ by Bard. When removal of brain tissue also included the hypothalamus, sham rage was no longer elicited. This implies that the hypothalamus is responsible for the expression of aggressive behaviour, and that the cortex normally inhibits and controls such behaviour.
The limbic system of emotion
The neuroanatomist James Papez suggested that the circuit that elicited emotion included the hypothalamus, anterior thalamus, cingulate gyrus, fornix and the hippocampus
Paul Maclean in 1949 extended the circuit to include the amygdala, orbitofrontal cortex, and some nuclei of the basal ganglia. (this circuit was called the limbic system)
The hippocampus played an important role in Maclean’s limbic system. It was believed to receive inputs from the various senses, as well as from the internal organs. Although the concept of the ‘limbic system’ is still used, it is now clear that it has several shortcomings, including the fact that the hippocampus plays a much more important role in learning and memory than in emotion.
Kluver-Bucy syndrome (1939) and the amygdala
- Bilateral ablation of the anterior temporal lobes of rhesus monkeys (damaging the amygdala)
- impaired visual recognition (psychic blindness)
- oral exploration of objects; hyperphagia
- impulsive and stereotyped actions; aberrant sexual behaviour
- absence of fear
Structure of the amygdala
- medial nucleus
- lateral/ basolateral nucleus
- central nucleus
- lesion of central nucleus: abolishes fear response
- stimulation of central nucleus: induced fear and agitation
Medial nucleus
receives sensory input (including information from the olfactory system concerning odours and pheromones) and relays information to the basal forebrain and the hypothalamus.
Lateral/ basolateral nucleus
receives sensory information from the primary sensory cortex, association cortex, thalamus and hippocampus. They send axons to parts of the basal ganglia, thalamus and the central nucleus of the amygdala
Central nucleus
sends axons to the axons of regions of the hypothalamus, midbrain, pons and medulla that are responsible for the expression of various emotional responses.
- the central nucleus is the most important part of the brain for the expression of emotional responses to aversive or threatening stimuli. Damage to the central nucleus abolishes fear responses to stimuli that have been associated with aversive events. By contrast electrical stimulation of the central nucleus induces a reaction of fear of agitation.
Basal nucleus
receives axons from the lateral and basolateral nuclei and sends axons to other amygdaloid nuclei and to the midbrain.
Consequences of prefrontal leucotomy
serious cognitive side effects such as apathy (lack of motivation), emotional unresponsiveness, disinhibition (lack of self control), lack of foresight and inability to plan etc.
The orbitofrontal cortex and decision making
The human orbitofrontal cortex is located on the ventral surface (underside) of the frontal lobes
medial region = ventromedial prefrontal cortex
lateral region = lateral-orbital prefrontal cortex
involved in regulating our ability to evaluate social and emotional information, inhibit inappropriate responses and develop plans for acting appropriately. ‘decision making’ role
there is evidence that patients with orbiotfrontal cortex damage tend to engage in antisocial behaviours