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
Feelings associated with emotions: James-Lange theory
- An emotion inducing stimulus of event triggers physiological responses that are controlled by the autonomic nervous system
- The brain receives feedback from sensory receptors in the skin, muscle, and internal organs that produce these responses,
- This feedback from sensory receptors generates the subjective feeling of emotion
in 1927 physiologist Walter Cannon criticised this theory. He proposed that internal organs only provide diffuse and very slow feedback which cannot account for the immediacy of emotional feelings
Feelings associated with emotions: Cannon- Bard Theory
The emotion inducing stimulus has two independent effects. They excite a feeling of emotion and also a range of physiological effects controlled by the somatic and autonomic nervous systems
The orbitofrontal cortex and the somatic marker hypothesis
- Decision making is guided by emotional evaluation of the consequences of our actions (Damasio 1994)
- When we are faced with the same decision memories of past events are activated (recollection of the outcome of previous choices)
- These representations activate traces of the bodily reaction to previous behaviour
- Feelings steer us towards decisions that decrease negative feelings and increase positive feelings (somatic marker)
- This allows us to anticipate the emotional consequences of our actions
Autonomic response to affective stimuli
Damasio et al. (1994) measured the skin conductance response (SCR) of patients with lesions in the orbitofrontal cortex
- These patients had normal SCR to innately negative stimuli such as loud sounds, but showed no SCR to stimuli with learned affective value, such as pictures of mutilated bodies, disaster scenes and nudity.
- Normal control participants by contrast showed an increase SCR to affective stimuli compared with pictures of neutral stimuli such as the countryside.
Emotional responses on a gambling task
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Fear conditioning
Fear conditioning: a previously neutral stimulus acquires aversive properties because it has been paired repeatedly with an aversive event, such as a painful stimulus
Fear conditioning
Before conditioning:
NS (light)—————————————- no relevant response
UCS (electric shock) ————————- UCR (fear)
During conditioning:
NS (light)
+
UCS (electric shock) ———————————— UCR (fear)
After conditioning:
CS (light) ——————————————————— CR (fear)
potentiated startle reaction: natural startle reactions such as a response to a loud noise can be exaggerated in animals that are already in an anxious state. E.g. the rat shows a potentiated (much greater) startle reaction when the noise is proceeded by the light, which elicits a fearful state.
Effects of amygdala lesions on conditioned fear responses
it is a misconception that the amygdala impairs conditioned fear responses as amygdala damage does not disrupt the normal unconditioned response to an aversive stimulus.
- Instead the amygdala blocks the ability of the individual to learn a conditioned response to a neutral stimulus that is paired with an aversive unconditioned stimulus
Amygdala pathways and fear conditioning
model proposed by Joseph Le Doux
‘low road’, involves information direct transmission of information from the sensory thalamus to the lateral nucleus of the amygdala (information is in a crude form)
‘high road’, conveys information from the sensory thalamus to the primary sensory cortex and association cortex, which together analyse the stimulus in much more detail, before sending the information on to the lateral nucleus of the amygdala
The low road is thought to ready or prime the amygdala quickly, so that it is ready to respond to the more detailed information from the high road if this corresponds to the conditioned stimulus. This two-pathway mechanism allows for both fast and accurate responses to potentially threatening events.
Six basic categories of facial emotion
- happiness
- surprise
- fear
- sadness
- disgust
- anger
- Facial expressions appear to be innate
- Facial emotion conveys important information about the feelings and intentions of others
- The human limbic system, particularly the amygdala plays a crucial role in the expression and recognition of emotion
- Damage to the amygdala impairs the ability to recognise facial expressions of emotion, particularly expressions of fear
The facial feedback hypothesis
- Afferent information from the muscles of the face is conveyed back to the brain and interpreted as reflecting an emotional state
- Facial expressions can influence our emotional experience
- Idea that having a happier expression can induce higher level of happiness and vice versa.
The ‘lie detector’ (polygraph)
- Emotional reactions to questions are used to determine ‘truthfulness’ of answers
- Measures physiological responses associated with activity of the autonomic nervous system e.g. heart rate, breathing, blood pressure, skin conductance etc.
- Still routinely used by law enforcement authorities in many countries
Lie detectors ‘Control- question’ technique
This technique assumes the lying will be associated with greater activity by the sympathetic branch of the autonomic nervous system. This technique has a success rate of 80%
control question e.g. Have you been in jail before?
key question e.g. Did you steal that car?
guilty-knowledge technique.
This requires that the questioner has some specific pieces of information concerning a crime that only the guilty person could know. Instead of trying to detect a lie, the questioner simply uses the polygraph to assess a suspect’s emotional reaction to a series of actual and contrived details of the crime. People who are innocent will react in the same way to all details because they have no knowledge of the crime; by contrast, the guilty person should show an emotional reaction to the actual details.
