Limbic system Flashcards
The limbic system definition
The limbic system controls our behavioural responses
Responds to internal stimuli (drives) and external stimuli (emotion)
Integrates sensory information with cognitive evaluation and brings about an appropriate response
Motivation & the reward system Aggression Sexual behaviour Maternal behaviour Curiosity
Emotion and motivated behaviour
Emotions and motivated behavior are crucial for survival:
Emotional responses modulate the autonomic nervous system to respond to threatening stimuli or situations.
Emotional responses are adaptive. If you are prepared to deal with threatening stimuli, you are more likely to survive and reproduce.
Motivated behaviours underlie feeding, sexual and other behaviors integral to promoting survival and reproduction.
The hypothalamus and limbic system mediate these behaviors.
Limbic system anatomy
The limbic lobe comprises a ring (limbus = ring) of “primitive” cortex around the brainstem,
Subcortical limbic nuclei: amygdala, septal nucleus,
nucleus accumbens
Associated nuclei: mammillary bodies, anterior nucleus of the thalamus
Extensive interconnections
Hypothalamus and limbic system: clinical context (basic emotional drives)
A large number of clinical conditions have symptoms that arise from hypothalamic and/or limbic system brain circuits.
Fever
Need to detect temperature changes and modulate the ANS to either retain (shiver) or dissipate heat (sweat).
Addiction
Many recreational drugs evoke reward and motivated behaviours that form an important part of limbic system function.
Anxiety Disorders
Many anxiety disorders, such as Panic disorder and Post-traumatic stress disorder (PTSD) have physiological symptoms mediated by the ANS and by the limbic system.
Obesity
Feeding behavior is in part controlled by the hypothalamus and interactions between limbic reward circuitry and the hypothalamus are important to feeding behavior.
Emotion and reward
Emotional experience and the ability to reflect upon our emotions, forms an integral part of our lives, guiding our actions and enriching our sense of satisfaction.
Rewards, both good and bad, play an integral role in modulating emotions and motivated behaviour.
Emotions are mediated by the limbic system, which includes the hypothalamus.
The limbic system is a complex set of interconnected brain areas that integrate information about sensory stimuli, memories and cognitive plans to produce emotional learning and emotional experience.
Physiological changes associated with emotion
Emotional arousal: changes in the autonomic system.
Increase/decrease in heart rate
Cutaneous blood flow (blushing/ turn pale)
Sweating
Gastrointestinal motility
Changes in activity of the sympathetic, parasympathetic and enteric activity of the visceral motor system.
Few synaptic connections between the cerebral cortex and the limbic system
why we have so little conscious control over our emotions?
Limbic system anatomy and papez circuit
Neural circuit for emotion proposed by Papez (thick lines) and extended by P. McLean (thin lines)
Papez circuit: closed circuit of information flow between the limbic system and the thalamus and the hypothalamus
The amygdala is a key coordinator, linking cortical processing to the hypothalamus and other subcortical brain structures important for emotional behavior.
Mammillary body is important in memory recollection
Connections of limbic system
nputs:
All sensory systems,
Prefrontal and temporal cortex
Outputs:
Reticular formation (arousal)
Hypothalamus (autonomic and endocrine responses)
Neocortex (sensorimotor activity)
Extensive interconnections e.g. hippocampus and amygdala
Hypothalamus anatomy
Lines the walls of 3rd ventricle, above the pituitary.
Divided into medial and lateral regions by the fornix (bundles of axon fibres that connect the hippocampus to the mammillary bodies).
Role of hippothalamus
Hypothalamus regulates a broad range of functions Feeding and drinking Behaviour Reproductive function Endocrine and autonomic regulation Emotional responses
Lesions in the lateral hypothalamus (LH) lead to cessation of feeding
Lesions of the ventromedial hypothalamus (VMH) lead to uncontrollable aggression, hyperphagia, polydipsia
The amygdala coordinates emotional behaviour
Window of the limbic system
Many sensory inputs
Brain region most specifically involved with the emotional experience
Integrates sensory input, emotional response and cognitive evaluation
Displays LTP and is the site of conditioned fear
High expression of GABA receptors (potentiated by anxiolytics)
High expression of 5HT receptors (SSRIs lead to mood improvement)
Kluver-Bucy syndrome
Bilateral ablation of the temporal lobes, including the amygdala and hippocampus:
“Blunted/flattened” emotions – placidity, even when threatened.
Increased oral activity, including placing inedible objects in their mouth. Visual perception was intact but visual recognition was poor – exploring items orally.
Loss of appropriate evaluation of sensory input.
Increased and inappropriate sexual behavior.
Phineas Gage
Survived impalement with a metal rod through cerebral cortex, particularly frontal lobe.
Likely that connections between the cortex and the amygdala and hippocampus were damaged
Personality was severely altered – fitful, irreverent, indulging in profanity, impatient, obstinate… ‘no longer Gage’
The amygdala processes emotions
Micro-stimulation of the amygdala produces feelings of fear and apprehension.
Isolated lesions of the amygdala impairs learning how to discern emotions in facial expressions.
The disease does not affect the ability to discriminate fine differences in faces, nor the ability to recognize faces (controlled by a separate brain region – inferotemporal cortex).
maging studies show differential activation of the amygdala by emotional facial expressions.
The amygdala responds to emotionally arousing stimuli.
The amygdala has appropriate anatomical connections for mediating fear conditioning and may also modulate emotional memories
Memories of emotionally arousing events are more poignant than unemotional events.
Emotionally arousing events activate the sympathetic nervous system and the HPA axis
Epinephrine and glucocorticoids - improve emotional memory via the amygdala.
The basolateral nucleus is reciprocally connected with the hippocampus and the neocortex
both implicated in memory processes.
Other areas in the limbic system
Nucleus accumbens: target for the dopaminergic pathway in reward system and motivation.
Hippocampus: CA1 neurons display LTP and set up reverberating circuits very easily
Consolidation of verbal memory - Papez circuit.
Korsakoff’s syndrome: bilateral damage to Papez circuit -anterograde amnesia and confabulation (L&M lecture)
Limbic Cortex: links neocortex to other limbic structures
E.g. the cingulate gyrus links to sensorimotor areas, the prefrontal cortex is essential for cognitive evaluation and ‘working memory’.
Emotional behaviour and positive reward
Emotional behaviour occurs in response to positive rewards as well as negative rewards.
Positive rewards can modulate the autonomic nervous system and behaviour.
Positive reinforcement, is a far more effective reinforcer than fear and negative rewards.
Drugs of abuse increase dopamine release in the brain
Cocaine and amphetamines increase dopamine release in the brain - nucleus accumbens.
The nucleus accumbens shell receives dopaminergic input from midbrain dopamine neurons, and it projects to the hypothalamus and limbic structures mediating emotional responses.
Both drugs block the dopamine transporter responsible for dopamine reuptake, thus leaving dopamine present in the synapse.
Nicotine also enhances dopamine release, by acting on presynaptic cholinergic receptors.
Motivation
that which energizes and directs behaviour
Drive
an arousal state resulting from a biological/psychological need.
Drive-reduction theory
Based on concepts of homeostasis
Deviation from the optimal state activates a drive which brings about corrective action
Return to optimal state leads to drive reduction
However, it doesn’t explain why we often seek arousal
Optimal level of arousal – deviation in either direction motivates corrective action
Boredom can be as powerful a motivator as hunger and people function best at their optimal level of arousal
Behaviour may be motivated by biological/psychological needs (motives) or by emotion
Maslow’s hierarchy of needs
Abraham Maslow suggested some needs have priority over others:
Physiological needs like breathing, thirst and hunger come before psychological needs like achievement, self-esteem and need for recognition.
Motives below must be at least partially satisfied before those above become important.
Reward system
Old’s & Milner (1950’s):
Rats with electrodes implanted in lateral hypothalamus (LH) very quickly learn to self-stimulate at high rates (2,000/hr x 15-20 hrs!) until they collapse!
Even hungry rats self-stimulate in preference to food – Lateral hypothalamus is the ‘pleasure centre’
Periaqueductal grey matter (PAG): strong stimulation is aversive, rats learn to escape/avoid it – ‘punishment centre’
Involves both noradrenergic and dopaminergic pathways (dorsal noradrenergic bundle, mesolimbic DA pathway)
Highly diffuse system which facilitates all brain areas to activate behaviour
Amphetamines, cocaine lead to increased DA release ‘high’
Aggression-nature vs nurture
Cats: Strong stimulation of lateral hypothamaus
or stimulation of amygdala leads to a rage response,
which is inhibited by ventromedial hypothalamic /septal stimulation
Rats: Lab-bred rats live peacefully with mice until hypothalamic stimulation → kills mouse by biting neck- suggests an innate killing response.
Role of hormones: Dihydotestosterone applied to amygdala → increased aggression
Castration → decreased play fighting, decreased aggression
Monkeys:
Stimulation of aggression areas leads to attack or flight, depending on position in dominance hierarchy i.e. learning influences behaviour
Humans:
Learning greatly influences the expression of aggression, i.e. its under cognitive control
Theories of aggression in humans
Basic instinct/innate drive (Freud):
Death instinct – aggression, self-destructive acts
Modified by positive emotional attachments, substitute outlets e.g. sports
Frustration-aggression hypothesis:
Frustration leads to aggressive drive – aggression leads to reduction in drive (does it?)
Aggression is usual response but there may be others if aggression doesn’t work
Social Learning theory:
Aggression is a learned response to frustration or other unpleasant emotional arousal – learned through observation and imitation (vicarious learning)
Positive reinforcement increased the likelihood of occurrence
Evidence supports social learning theory
Young children imitate aggression observed in adults, films and cartoons
If aggression is a drive, then expression should result in decreased aggression (drive-reduction)
In fact, aggression increases with positive reinforcement (victim’s response!)
On-screen violence and aggression
Positive correlation between amount of viewing of violence in childhood and aggressiveness in later life?
WHY?
Imitation
Arousal (increased if frustrated or annoyed)
Desensitisation to effects of violence
Decreased inhibition of aggressive behaviour
Distorted views of conflict resolution
Cognitive factors: guilt, self control, influence the expression of aggression
Disinhibition by alcohol
Sexual behaviour: role of the limbic system
A powerful motivator, necessarily for the survival of the species.
Hypothalamus controls sexual arousal, and more complex behaviours:
Sexually dimorphic nucleus (SDN): larger in male brains 2:1.
Differentiation occurs ~ age 2 to 4 in humans (corresponds to Freud’s ‘phallic stage’).
Suprachiasmatic nucleus (SCN) - sexual and reproductive behaviour:
Larger in female compared to male brains, 2:1
Larger in homosexual male brains as compared to heterosexual male brains
Amygdala: stimulation leads to complex sexual activity, lesion lead to inappropriate hypersexuality
Sexual behaviour: Role of hormones
Hormonal control of sexual behaviour decreases from lower to higher vertebrates:
Male
Rats: castration leads to greatly decreased sexual activity.
Primates: little or no decline
Humans: complicated by emotional, social factors, most studies report little or no decline.
Female
Oopherectomy: complete cessation of sexual activity in all animals from reptiles to monkeys.
Human is the only exception: most studies report no decrease in sexual motivation after menopause, may in fact increase (due to lack of fear of pregnancy).
Ovulatory cycle: Most female animals are receptive only during period of ovulation i.e. when ‘in heat’.
Primates: all phases of cycle, but most intense during ovulation.
Role of learning in sexual behaviour
learning plays n increasingly important role from lower to higher mammals.
Humans: secure attachment to primary care-giver leads to the development of trust and good relationships with peers, which are essential for healthy adult sexual relationships
Cultural variations in acceptable sexual activity e.g. incest –taboo in most cultures, premarital sex etc.
Maternal behaviour
In many species the most powerful motivator of all.
Regulated in the hypothalamus
Preoptic area, VMH, mesolimbic DA pathway.
Hormones vs environment:
Virgin rats presented with pups take ~1 week to develop maternal behaviours, but if given plasma from a post-natal rat, it happens in 1 day
Maternal behaviour is induced by gonadal steroids and increased by oxytocin, prolactin and environmental stimuli
Maternal behaviour pattern is innate
Neural circuitry of maternal behaviour
Like other motivated behavior, maternal behavior is dependent on the hypothalamus
Medial preoptic area (MPOA)
Lesions of MPOA will abolish maternal behavior
Regulated by the POA, VMH, DA pathway
Maternal behaviour: Hormones v Environment
Primates
Experience is much more important
Monkeys reared in isolation make very poor first-time mothers, if they mate at all
They need to practice the movements of mating in play with other young monkeys to mate efficiently as adults
They need to form an affectionate bond with mother in order to develop maternal behaviour in adulthood
Humans
Experience far overrides whatever influence hormones may have
E.g. parents who abuse their children and often victims of abuse themselves
Harry Harlow…The monkey love experiments
Harlow evaluated whether feeding or contact comfort was more important to infant attachment.
The young animals were “raised” by two kinds of surrogate monkey mother machines.
One ‘mother’ was made of soft terry cloth, the other made of wire mesh
Harlow’s research showed that the need for affection created a stronger bond between mother and infant than did physical needs (food).
Monkeys raised without their mothers or other monkeys were socially maladjusted for the rest of their lives.
When confronted with fear, they displayed institutionalized behaviors-throwing themselves on the floor, clutched themselves, rocked back and forth, and screamed in terror.
They were incapable of having sexual relations and they were also unable to parent their offspring, either abusing or neglecting them.
Harlow’s work suggested that the development of a child’s love for their caregiver was emotional rather than physiological
Harlow showed that the development of attachment was closely associated with critical periods in early life.
It is difficult or impossible to compensate for the loss of initial emotional security
Curiosity (sensation-seeking)
Curiosity is a motive in itself
We are motivated to seek stimulation, to actively explore the environment, even when it satisfies no biological need – e.g. 3 month old infants have learnt to shake a rattle and to turn on a musical toy
There is enormous individual variation in need for stimulation
Sensation-seeking scales: wide individual variation but good consistency across different situations
Compatibility on sensation-seeking is a good predictor of marital adjustment, incompatibility leads to marital discord, especially if female is higher than male!
Do people choose pain over boredom?
Just think: The challenges of the disengaged mind – Wilson et al, Science 2014
People are unhappy in their own company and some prefer painful experiences to their own thoughts!
Nearly half the subjects gave themselves mild electric shocks during 15 minutes of quiet time
18 of 42 people, more of them men than women, chose to give themselves at least one mild shock on the ankle when left alone for 15 minutes.
These were all people who had experienced the same shock already and declared that, if given $5, they would part with some of it in order not to be zapped again.
People who didn’t think they’d pay to avoid the shock were excluded - as was one man who pushed the button 190 times!
Sensory deprivation
Exploration and manipulation leads to a variety in sensory input:
Sensory deprivation leads to visual hallucinations, difficulty in thinking, feelings of unreality, disorientation in time and place
Most subjects refuse to continue with experiment after a few days, no matter what reward they’ve been promised
Variety in sensory input is necessary for proper mental functioning.
