Chapter 10: Reproductive Behaviour
Hormonal Control of Sexual Behaviour
• Simply having the physique and genitals of a man or woman exerts a powerful effect on behaviour, but hormones also
affect behaviour by interacting with the nervous system
◦ Eg androgens present during prenatal development affect the development of the nervous system
Hormonal Control of Female Reproductive System
• Menstrual cycle – the female reproductive cycle of most primates; characterized by growth of the lining of the uterus,
ovulation, development of a corpus luteum and menstration
◦ Estrous cycle – female reproductive cycle of mammals other than primates, which, in rats, takes about 4 days
but is otherwise similar. The sexual behaviour of is linked to the cycle (while primates can mate at any time)
• These cycles are controlled by hormonal secretions of the pituitary gland and ovaries, where each one’s secretions effects
• Cycle overview:
1. Anterior pituitary gland (PG) secretes gonadotropins (eg FSH) stimulates growth of ovarian follicles (small spheres of
epithelial cells surrounding each ovum)
2. As these mature, release of estradiol cause growth of lining of uterus, in preparation for a possible fertilized ovum
3. Anterior PG stimulated by estradiol releases LH causing ovulation: ovarian follicle ruptures, releasing ovum
4. Also, LH causes ruptured follicle becomes a corpus luteum, produces estradiol and progesterone
1. Progesterone promotes pregnancy – maintains lining of the uterus, inhibits ovaries from producing another
5. Ovum enters a fallopian tube, heads towards uterus
1. If it encounters sperm on its way down the fallopian tube it will begin dividing and eventually attach itself to the
6. If ovum is not fertilized in time to develop sufﬁciently by the time it gets to the uterus, the corpus luteum ceases production
of estradiol and progesterone results in lining sloughs off = menstruation
Hormonal Control of Sexual Behaviour of Laboratory Animals
(talking about rats unless otherwise speciﬁed)
• Sexual behaviour is varied
◦ In mammals, all share essential features of intromission (entry of penis into vagina), pelvic thrusting, ejaculation
• Male rats reach sexual maturity after 45-75 days
• On encountering a receptive female:
◦ spend time nuzzling her, snifﬁng her face and genitals, mount her and engage in several rapid, shallow pelvic
thrusts. If he detects her vagina will make a deeper thrust, achieve intromission and then dismount
◦ will do this (intromission) 8-15 times (aprox 1 min apart) and then ejaculate
◦ refrains from sexual activity for a period (mins) then copulate again
◦ Finally pauses for a longer time: refractory period
• Coolidge effect – the restorative effect of introducing a new female sex partner to a male that has apparently become
“exhausted” by sexual activity
◦ eg a rat that is done with one female can respond quickly (often as fast as with original partner) to a new female
and can continue for a long period of time with successive females
◦ more often seen with species where males have harems
◦ Beamer, Bermant, and Clegg (1969) tested this successfully with rams (12 ewes) and the ram could have
continued. He was not tricked into mating with previous partners that were disguised (trench coats and
• Sexual behaviour of male rodents depends on
◦ Testosterone: Castrated males cease sexual activity, unless injected with testosterone
◦ Oxytocin: hormone secreted by posterior PG, released at orgasm for both sexes and contributes to
contractions of smooth muscle in male ejaculatory system and of vagina and uterus
■ Also contracts milk ducts in females
■ Plays a role in establishment of pair bonding
• Lordosis response – assuming a posture that exposes her genitals to the male (arching of back)
◦ Also move tail and stand rigidly to support male
• When receptive, nuzzle, sniff genitals and show other characteristic behaviours (rats: hop, ear wiggling)
• Sexual behaviour depends on estradiol and progesterone
◦ (in rats) estradiol increases ~40hrs before female becomes receptive
◦ immediately before receptiveness, lots of progesterone secreted (by corpus luteum)
■ *I’m going to call this sequence of a small amount of estradiol overtime followed by a large amount of
progesterone female hormone treatment - FHT
• Rats without ovaries are not sexually receptive
◦ Can be restored with large doses of estradiol alone (not true for progesterone, needs estradiol to “prime” its
◦ Most effective when doses of both hormones mimic normal sequence, FHT
• Rissman et al. (1997) found females w/o estrogen receptors were unreceptive to males even after FHT, Lydon et al.
(1995) found similar results with missing progesterone receptors
• This hormone sequence causes increased
◦ receptivity (ability and willingness to copulate),
◦ proceptivity (eagerness to copulate)
◦ attractiveness (behaviour and physiology changes that affect male)
■ males most responsive to females in heat (estrus) ■ males ignore females w/o ovaries, unless given FHT
• Even women have slight physical changes
◦ Robert et al. (2004) found men found fertile women more attractive (from face photo)
Organizational Effects of Androgens on Behaviour: Masculinization and Defeminization
• Recalling that being female is the default: If not exposed to androgens during development, a rodent brain will engage in
female sexual behaviour as an adult (if given FHT)
◦ For rats this critical period is immediately after birth
■ Male rats that are castrated immediately and then given FHT when developed, will act as if female
• Brain exposure to androgens causes
◦ Behavioural defeminisation – the organisational effect that prevents the animal from displaying female sexual
behaviour in adulthood
■ Suppresses the development of neural circuits controlling female sexual behaviour
Eg a female rodent immediately ovariectomized (removed ovaries) after birth and given testosterone
will not respond to a male in adulthood (even when given FHT)
◦ Behavioural masculinisation
■ Androgens stimulate the neural circuits controlling male sexual behaviour
Eg the above female, given testosterone in adulthood instead will mount and attempt to copulate with
a receptive female
Effects of Pheromones
• Pheromones can affect reproductive physiology or behaviour
• Lee-Boot effect – The slowing and eventual cessation of estrous cycles in groups of females that are housed together,
caused by a pheromone in animal’s urine
• Whitten effect – the synchronization of the menstrual or estrous cycles of a group of females, occurs only in presence of
pheromone in males urine
◦ These mice start cycling together at the same time
• Vandenbergh effect – accleration of the onset of puberty in a female rodent caused by the odor of a male (urine
Castrated males have no effect
• Bruce effect – termination of pregnancy caused by this male odor, if its from a male other than the one that impregnated
• Vomeronasal organ (VNO) – very highly specialized sensory organ (smell), mediates the effect of some pheromone
In all mammals except whales and dolphins
◦ Contains over 200 G-protein coupled receptor molecules that detect chemicals (here, pheromones)
■ Responds extremely selectively (speciﬁc neurons ﬁre for speciﬁc individuals’ pheromones)
◦ Mostly sensitive to non-volatile compounds found in urine or other substances
• VNO projects to the accessory olfactory bulb (located behind the olfactory bulb)
◦ Removal of accessory olfactory bulb disrupts the above effects = vomeronasal system is essential for these
◦ The accessory olfactory bulb projects to the medial nucleus of the amygdala, which projects to preoptic area,
anterior hypothalamus, and ventromedial nucleus of hypothalamus
◦ Ie these areas play important roles in reproductive behaviour
• The main olfactory system detects volatile chemicals that signal the presence of another animal, vomeronasal organ
determines sex, estrous condition and identity
TRPC2 knockouts (affect VNO only) cannot determine sex, male knockouts attempt to mate with both males
and females, do not attack invading males, can and will still impregnate females though
• Affect behaviour of females
• Eg boar saliva elicits sexual behaviour of sows
◦ Still works if VNO destroyed
◦ (main olfactory still plays a role in pheromone detection)
soiled bedding from males stimulate neurogenesis in hippocampus and main olfactory system of
• Pheromones present in underarm sweat of men and women affect womens menstrual cycles
◦ have shorter cycles in the presence of men than those who rarely spent time with men
◦ Also men found shirts worn by fertile women smelled more pleasant and sexy
• Substances (androstadienone, “AND”) present in male sweat improve women’s moods, decrease men’s
• Human VNO does not appear to have sensory function, so we must be using main olfactory bulb
• Has so far have found no sex attractant pheromones, though we might recognize partners by familiar odours
Human Sexual Behaviour
Activational Effects of Sex Hormones in Women
• Ovarian hormones control not only the willingness of an estrous female to mate, but also her ability to mate
◦ Ie male rats cannot copulate with a female rate that is not in estrus (no lordosis response)
• In higher primates the ability to mate is not controlled by ovarian hormones
They probably inﬂuence quality and intensity of sex drive though
• Sexual proceptivity may be related to ovarian hormones, even in higher primates
◦ Seen with monkeys ◦ Studies with women suggest variations in these hormone levels across the menstrual cycle do affect sexual
interest (but there are many other factors)
• Presence of androgens may facilitate the effect of estradiol on women’s sexual interest (studies showed women having
more sex, masturbation, fantasies and higher well-being)
◦ Ovaries also produce testosterone
Activational Effects in Sex Hormones in Men
• Testosterone levels
Normal: potent and fertile
◦ None: sperm production ceases and eventually so does sexual potency
■ Though males (men and monkeys) with experience and/or dominance could continue copulating for
much longer (and even indeﬁnitely with ejaculation, with highest-ranking male monkey)
Can rise when thinking about sex/females
• Generally believed to not be explained by social reasons
• May be inﬂuenced by prenatal exposure to androgens
Prenatal Androgenizaton of Genetic Females
• Congenital adrenal hyperplasia (CAH) – condition where adrenal glands secrete abnormal amounts of androgens
◦ Doesn’t seem to effect boys born with CAH
Girls have enlarged clitoris and possibly a partially fused labia
• Studies of prenatally androgenised girls suggest that organisational effects of androgens inﬂuence the development of
◦ Increased likelihood of becoming sexually attracted to women
Enhances interest in activities and toys usually preferred by boys
Failure of Androgenization of Genetic Males
• Recalling genetic males with androgen insensitivity syndrome
◦ Develop as females with female external genitalia
XY women have no reports of homosexuality or bisexuality
◦ The lack of androgen receptors appears to prevent both the masculinising and defeminising effects of
androgens on a person’s sexual interest
Effects of Rearing on Sexual Identity and Orientation of Prenatally Androgenized Genetic Males
• If androgens cannot act, the person’s anatomy and sexual orientation are female
• 50% (a huge percentage) of genetic males raised as females due to penis ablation or developmental abnormality end up
being expressing dissatisfaction and begin living as men and are (mostly) attracted to women
• No reported cases of genetic males with this raised as males becoming unsatisﬁed with their gender assignment
• Reiner: “genetic males with male-typical prenatal androgen effects should be reared male”
Sexual Orientation and the Brain
• The human brain is sexually dimorphic, probably due to differential exposure to androgens prenatally and during early
*** this does not mean this has to do with sexual orientation
• Differences in size of three subregions
◦ Suprachiasmatic nucleus (SCN)
Nucleus of hypothalamus
◦ Anterior commissure
■ Fibre bundle that connects parts of left and right temporal lobes
■ Hemispheres in women share more functions
* no good evidence for differences in brain structure that might account for differences in sexual orientation
• functional-imaging studies show differences in heterosexual men and women brain responses to AND and EST, two
chemicals that may serves as human pheromones
◦ homosexual male response similar to heterosexual females
• size of a particular region of the forebrain (central subdivision of the bed nucleus of the stria terminalis - BNST) relates to
sexual identity (not orientation)
• note that these things may not be the source of sexual identity, could be caused by any number of factors in common with
a certain sexual identity
Possible Causes of Differences in Brain Development
• prenatal stress in mother rats (which suppresses androgen production) can cause their male offspring to display female
play behaviour, and have increased chance of displaying female sexual behaviour when given FHT
◦ This stress also reduces the size of a sexually dimorphic nucleus of the preoptic area (involved in male sex
behaviour), which is normally larger in males
• Male homosexuals tend to have more older brothers than male heterosexuals
◦ No bias in number or sex of siblings is seen in heterosexuals
◦ Perhaps some women’s immune systems may become sensitized to a protein that is expressed only in male
Heredity and Sexual Orientation
• Heredity may play a role in sexual orientation in both men and women
• If homosexuality has a genetic basis, monozygotic (“identical”) male twins should both be homosexual (concordant, share
a trait) more often than dizygotic male twins, which it is (52% and 22% respectively)
• With females, concordance of monozygotic and dizygotic twins occurred at 48% and 16%
• The answer to the genetic basis of homosexuality will most likely come when we understand the basis for
Neural Control of Sexual Behaviour
Spinal Mechanisms • Sexual reﬂexes such as sexual posturing, erection and ejaculation are organized in the spinal cord
◦ Vibratory stimulation of the penis can elicit ejaculation in men with complete transection of the spinal cord, as
long as the damage is located above the 10 thoracic segment
• Lumbar spinothalamic (LSt) cells, a group of neurons in the lumbar region of the rat spinal cord, play a critical (and
necessary) role in triggering an ejaculation
• In lab animals, different brain mechanisms control male and female sexual behaviour
• The medial preoptic area (MPA) is the forebrain region most critical for male sexual behaviour
◦ Electrically stimulating this area produces copulatory behaviour
◦ Destruction abolishes male sexual behaviour
• The sexually dimorphic nucleus (SDN) of the MPA develops only if an animal is exposed to androgens early in life
A SDN is found in humans as well
◦ Destroying this in lab animals impairs mating
• The medial amygdala is sexually dimorphic, where a region containing a high concentration on androgen receptors is 85%
larger in male rats than female rats
Destruction disrupts the sexual behaviour of male rats
• MPA activity
◦ receives chemosensory input from vomeronasal organ and main olfactory system through connects with medial
amygdala and BNST
Neurons in MPA contain testosterone receptors
◦ Copulatory activity causes an increase in activity of neurons
◦ Implantation of testosterone directly into MPA reinstates copulatory behaviour that was previously abolished by
castration in adulthood
Neurons in MPA are part of a circuit that includes
■ periaqueductal gray matter (PAG)
■ Region of the midbrain that surrounds the cerebral aqueduct
■ Excites nPGi
nucleus paragigantocellularis (nPGi) of the medulla,
■ receives input from MPA and is connected to the below mentioned motor neurons
■ connections of nPGi with spinal cord are inhibitory (MPA suppresses this by inhibiting PAG)
■ motor neurons that control genital reﬂexes in spinal cord (suppressed by nPGi)
• Ejaculation in men is accompanied by increased behaviour in many brain regions. Activity of the amygdala decreases
• The ventromedial nucleus of the hypothalamus (VMH) is the forebrain region most critical for female sexual behaviour
◦ Similar to MPA
Destruction abolishes copulatory behaviour
◦ Stimulation facilitates this behaviour
◦ Estradiol and progesterone facilitate female sexual behaviour in this region (which contains their receptors)
◦ “priming” effect of estradiol is caused by an increase in progesterone receptors in VMH
steroid sensitive neurons of VMH send axons to PAG
■ through their connects with the medullary reticular formation, control particular responses that
constitute female sexual behaviour
■ lesions that disconnect VMH from PAG abolish female sexual behaviour
• Medial amygdala activity similar to male
◦ receives info from vomeronasal system and genitals, sends efferent axons to MPA and also VMH
• lordosis response pathway was as predicted
◦ VMH PAG nPGi motor neurons in spinal cord
• Orgasms in women accompanied by increased activity in regions similar to those activated during ejaculation in men, in
addition, in the PAG
Formation of Pair Bonds
• Vasopressin and oxytocin, peptides that serves as hormones and as neurotransmitters in the brain, appear to facilitate
• Insertion of the gene for vasopressin receptors in the basal forebrain of polygamous male voles induces monogamous
• Vasopressin plays the most important role in males, while oxytocin plays the most important role in females
• In humans, oxytocin appears to increase trust in other people
Maternal Behaviour of Rodents
• This includes nest building, delivery of pups (a very extensive and delicate process), cleaning them, keeping them warm,
nurse them, retrieve them if they are moved out of the nest, induce pups’ urination and defecation (where the mother
ingestion of the urine recycles water, lost to the milk)
• Paturition – the act of giving birth
• In normal conditions, paturition is a main stimulus of inducing maternal behaviour
◦ Also stimulated by artiﬁcially distending the birth canal in nonpregnant females
◦ Can be retarded by cutting the sensory nerves that innervate the birth canal
Hormonal Control of Maternal Behaviour
• No evidence that organizational effects of hormones play a role
◦ Males will care for pups under the right conditions
• Though maternal behaviour is affected by hormones, it is not controlled by them
◦ Exposure of virgin females to young pups stimulates maternal behaviour within a few days
Females will still build new nests after blood level progesterone drops
• Stimuli that normally induce maternal behaviour are those produced by the hormones present during pregnancy and
around the time of birth ◦ Injections of progesterone, estradiol, and prolactin, the hormone responsible for milk production, (duplicating
the pregnancy sequence) facilitate maternal behaviour
◦ Appear to act in the MPA
• Oxytocin, involed in pair bonds between female rodents, is also involved in formation of a bond between mother and her
Neural Control of Maternal Behaviour
• Stimuli that facilitate pup care activate the MPA
• Connections between the MPA and the medial amygdala are responsible for the suppression of the aversive effects of the
odour of pups
• A different circuit starting with the MPA is involved in establishing the reinforcing effect of pups and enhancing motivation
to care for them
◦ MAP maps onto two regions of the midbrain, ventral tegmental area (VTA) and retrorubral ﬁeld
◦ The VTA sends axons to the nucleus accumbens (NAC)
■ This connection is critically involved in motivation and reinforcement
■ Cocaine will activate this in virgin rats, but lactating females are preoccupied with their pups
◦ MAP > VTA > NAC > ventral pallidum (region of the basal ganglia involved in control of motivated behaviours)
• fMRI study with rats showed activation of brain mechanisms of reinforcement when the mothers were present with their
◦ Women who look at photos of their infants show similar effects
Neural Control of Paternal Behaviour
• Paternal behaviour is relatively rare in mammalian species
◦ but research indicates that sexual dimorphism of the MPA is less pronounced in male voles of monogamous,
but not promiscuous, species
■ recall that the size of the MPA plays an essential role in maternal behaviour
◦ Lesions of the MPA abolish paternal behaviour of male rats
• Thus, MPA plays a similar role in parental behaviour of both males and females
Chapter 11: Emotion
Lateral Nucleus (LA): A nucleus of the amygdala that receives sensory information from the neocortex, thalamus, and
hippocampus and sends projections to the basal, accessory basal, and central nucleus of the amygdala.
Central Nucleus (CE): The region of the amygdala that receives information from the basal, lateral, and accessory basal nucleus
and sends projections to a wide variety of regions in the brain, involved in emotional responses.
Conditioned Emotional Response: A classically conditioned response that occurs when a neutral stimulus is followed by an
aversive stimulus; usually includes autonomic, behavioural, and endocrine components such as changes in heart rate, freezing and
secretion of stress-related hormones.
Threat Behaviour: A stereotypical species-typical behaviour that warns another animal that it may be attacked if it does not ﬂee or
show a submissive behaviour.
Defensive Behaviour: A species-typical behaviour by which an animal defends itself against the threat of another animal.
Submissive Behaviour: A stereotyped behaviour shown by an animal in response to threat behaviour by another animal; serves to
prevent an attack.
Predation: Attack of one animal directed at an individual of another species on which the attacking animal normally preys.
Ventromedial Prefrontal Cortex (vmPFC): The region of the prefrontal cortex at the base of the anterior frontal lobes, adjacent to
Affective Blindsight: The ability of a person who cannot see objects in his or her blind ﬁeld to accurately identify facial expressions
of emotion while remaining unconscious of perceiving them; caused by damage to the visual cortex.
Volitional Facial Paresis: Difﬁculty in moving the facial muscles voluntarily; caused by damage to the face region of the primary
motor cortex or its subcortical connections.
Emotional Facial Paresis: Lack of movement of facial muscles in response to emotions in people who have no difﬁculty moving
these muscles voluntarily; caused by damage to the insular prefrontal cortex, subcortical white matter of the frontal lobe, or parts of
James-Lange Theory: A theory of emotion that suggests that behaviours and physiological responses are directly elicited by
situations and that feelings of emotions are produced by feedback from these behaviours and responses.
• Emotions consist of patterns of physiological responses and species-typical behaviour.
• In humans these responses are accompanied by feelings.
• The useful purposes served by emotional behaviours are what guided the evolution of the brain, feelings came later.
11.2 EMOTIONS AS RESPONSE PATTERNS
• Emotional response consists of three types of components:
• Behavioural Component: Consists of muscular movements that are appropriate to the situation that elicits them.
• Ex Dog’s aggressive posture when defending territory. Dog running and attacking.
• Autonomic Response: Facilitate the behaviours and provide quick mobilization of energy for vigorous movement.
• Ex Activity of sympathetic branch increases while that of parasympathetic branch decreases; heart rate increases, change in
size of blood vessels shunt circulation of blood way from digestive organs toward muscles.
• Hormonal Response: Reinforce the autonomic responses. • Ex Hormones secreted by adrenal medulla (epinephrine/norepinephrine) further increase blood ﬂow to muscles and cause
nutrients stored in muscles to convert to glucose. Adrenal cortex secretes steroid hormones, also helps make glucose
available to muscles.
Special behaviours that serve to communicate emotional states to other animals, such as threat gestures that precede an actual
attack and the smiles and frowns made by humans.
The integration of the components of fear appears to be controlled by amygdala.
Brain Region Behavioural and Physiological Responses
Lateral Hypothalamus Sympathetic activation; increased heart rate, blood pressure,
Dorsal Motor Nucleus of Vagus Parasympathetic activation; ulcers, urination, defecation.
Parabrachial Nucleus Increased respiration.
Ventral Tegmental Area Behavioural arousal (dopamine).
Locus Coeruleus Increased vigilance (norepinephrine).
Dorsal Lateral Tegmental Nucleus Cortical activation (acetylcholine).
Nucleus Reticularis Pontis Caudalis Augmented startle response.
Periaquductal Gray Matter Behavioural arrest (freezing).
Trigeminal, Facial Motor Nuclei Facial expressions of fear.
Paraventricular Nucleus ACTH, glucocorticoid secretion.
Nucleus Basalis Cortical activation.
11.2.3 RESEARCH WITH LABORATORY ANIMALS
• Amygdala plays special role in physiological/behavioural reactions to objects and situations that have biological signiﬁcance.
• Shown that single neurons in various nuclei of amygdala become active when emotionally relevant stimuli are presented.
• Amygdala is involved in effects of olfactory stimuli on reproductive physiology/behaviour, in addition to role of amygdala in
organizing emotional responses produced be aversive stimuli.
• Amygdala (amygdaloid complex) located in temporal lobes.
• Consists of groups of nuclei, each with different inputs and outputs and different functions.
• ~12 Regions of subdivision.
• Only looking at 3 major ones:
1. Lateral Nucleus
2. Basal Nucleus
3. Central Nucleus
• Lateral Nucleus (LA):
• Receives info from all regions of neocortex (including ventromedial prefrontal cortex, thalamus, hippocampal formation).
• Sends info to basal nucleus (B) and other parts of brain, including ventral striatum (region involved in effects of reinforcing
stimuli on learning) and the dorsomedial nucleus of thalamus (projection region is prefrontal cortex).
• LA and B nuclei send info to ventromedial prefrontal cortex and the central nucleus (CE).
• CE projects to regions of hypothalamus, midbrain, pons, medulla that are responsible for the expression of the various
components of emotional responses.
• CE of amygdala is the single most important part of the brain for the expression of emotional responses provoked by aversive
• When threatening stimuli are perceived, increases are seen in neural activity of CE and the production of Fos protein there.
• Damage to CE (or nuclei that provide it sensory info) reduces/abolishes a wide range of emotional behaviours/physiological
• Ex no longer showing signs of fear when confronted with aversive events, lower blood stress-hormone levels, less likely
to develop stress-induced illnesses.
• Stimulation to CE (electricity or by excitatory amino acid), makes animal shows physiological/behavioural signs of fear/
agitation, and long-term stimulation produces stress-induced illnesses.
• Thus autonomic and endocrine responses controlled by CE are among those responsible for harmful effects of long-term
• A few stimuli automatically activate CE of amygdala and produce fear reactions.
• Ex loud unexpected noises, heights, large animals, speciﬁc sounds/odors.
• There is also the ability to learn that a particular stimulus/situation is dangerous/threatening. Once learned, that stimulus/
situation will evoke fear (behavioural and physiological responses).
• Conditioned Emotional Response: Most basic form of emotional learning, produced by neutral stimulus that has been
paired with an emotion-producing stimulus.
• Classical Conditioning: Occurs when a neutral stimulus is regularly followed by a stimulus that automatically evokes a
response. • Amygdala plays a role in development of classically conditioned emotional responses.
• Behavioural Arrests: A species-typical defensive response called “freezing.”
• Research indicates that physical changes responsible for classical conditioning take place in the lateral nucleus of
• Neurons in LA connect with neurons in CE, which in turn communicate with regions in hypothalamus, midbrain, pons,
medulla that are responsible for behavioural, autonomic, and hormonal components of conditioned emotional response.
• Learning takes place in CE as well as LA.
Amygdala appeared early in evolution of brain, involved in responses vital to survival.
• The ventromedial prefrontal cortex (vmPFC) plays important role in controlling the expression of emotional responses.
• Involved in process of extinction.
• The value of a conditioned emotional response is that it prepares an animal to confront (or avoid) an aversive stimulus.
If CS occurs repeatedly but the aversive stimulus does not follow, then it is better for the emotional response (which
itself is disruptive/unpleasant) to disappear (extinction).
• Extinction is not the same as forgetting. Expression of conditioned response is inhibited, but the memory for the
association between the conditioned stimulus and the aversive stimulus is not erased.
This inhibition is supplied by medial prefrontal cortex.
• Lesions of prefrontal cortex impair extinction, stimulation inhibits conditioned emotional responses, and extinction
training activates neurons there.
11.2.4 RESEARCH WITH HUMANS
• Humans can also acquire conditioned emotional responses.
• Speciﬁc Responses are aimed at terminating the painful stimulus.
• Nonspeciﬁc Responses are controlled by autonomic nervous system (dilation of eyes, hr/bp increase, faster breathing, etc.,
release of stress-related hormones).
• Amygdala is involved in emotional response in humans.
• Studies show that stimulation of parts of brain produced autonomic responses associated with fear/anxiety, but only when
stimulating amygdala did people FEEL fear.
Lesions of amygdala decrease people’s emotional response. People with such lesions also showed impaired acquisition of
conditioned emotional response.
• Study showed a man with lesion of right amygdala had startle response not augmented by unpleasant emotion when looking
at unpleasant pictures (as normally occurs).
Most human fears are probably acquired socially, not through ﬁrsthand experience of painful stimuli.
• Vicarious acquisition; someone get painful stimulus (shock) when seeing danger stimulus, people watching this can start
to show signs of fear when danger stimulus presented but when they have never been shocked.
• Acquisition through instruction; told a person they will be shocked when countdown played when a danger stimulus was
show, instructions given by experiments sufﬁcient to evoke a fear response (increased activation of amygdala) when danger
colour appeared even though no shock was actually given.
• Medial prefrontal cortex plays critical role in extinction of conditioned emotional response in humans as well as animals.
• Increased activity of amygdala correlated with acquisition of a conditioned emotional response.
Increased activity of medial prefrontal cortex correlated with extinction of conditioned response.
• Damage to amygdala interferes with the effects of emotions on memory. Patients with damaged to amygdala show no increase in
memory when the encounter events that should produce a strong emotional response.
• More a patient’s amygdala is degenerated (in Alzheimer’s), the less likely patient will remember emotional events.
Amygdala participates in the formation of emotional memories.
• Looking a threatening words can also cause bilateral increase in the activity of the amygdala.
• Amygdala lesions impair recognition of a musical style that is normally associated with fear.
11.2.5 ANGER, AGGRESSION, AND IMPULSE CONTROL
• Aggressive behaviour are species-typical; patterns of movements are organized by neural circuits whose development is largely
programmed by an animal’s genes.
• Many aggressive behaviours are related to reproduction. Others are related to self-defense.
Threat behaviours consists of postures/gestures that warn an adversary to leave or it will get attacked. More often displayed
than actually attacking.
• Used to reinforce social hierarchies or protecting territory.
• Advantage is that does not involve actual ﬁghting which can harm one/both combatants.
Defensive behaviours are threat behaviours or an actual attack against the aggressor.
• Submissive behaviours indicate that the animal accepts defeat and will not challenge the other.
• Predation is the attack of a member of 1 species on a member of another, usually because latter serves as food to the former.
• Prey is aroused/excited; activity of sympathetic branch of autonomic nervous system is high.
Predator is “cold-blooded”; efﬁcient, not high sympathetic activation; attacking is a means to an end (food).
11.2.6 RESEARCH WITH LABORATORY ANIMALS
11.2.7 NEURAL CONTROL OF AGGRESSIVE BEHAVIOUR
• Neural control of aggressive behaviour is hierarchal.
• Particular muscular movements that an animal makes in attacking/defending itself are programmed by neural circuits in
Whether animal attacks depends on nature of stimuli and previous experience, among other things.
• Activity of limbic system controlled by perceptual systems that detect the status of the environment (incl. presence of other
• Shaikh/Siegel experiments: Used cannula electrodes in brain of cat. Found that aggressive attack and predation can be elicited
by stimulation of diff parts of periaqueductal gray matter (PAG) and the hypothalamus and amygdala inﬂuence these behaviours
via excitatory/inhibitory connections with PAG.
• Found that 3 principal regions of amygdala and 2 regions of hypothalamus affect defensive rage and predation, both of
which are organized by PAG. • Possible connection between lateral hypothalamus and ventral PAG (unveriﬁed).
• See chart 11.6 on pg 373.
11.2.8 ROLE OF SEROTONIN
• Activity of serotonergic synapses inhibits aggression.
• Destruction of serotonergic axons in forebrain facilitates aggressive attack, by removing inhibitory effect.
• EXPERIMENT: Removed CSF of monkeys, analyzed it for 5-HIAA (a metabolite of serotonin 5-HT).
When 5-HT is released, most of neurotransmitter is taken back by terminal buttons by reuptake, but some broken down to 5-
HIAA, which goes to CSF.
• High levels of 5-HIAA in CSF indicate elevated level of serotonergic activity.
• Experiment showed serotonin does not simply inhibit aggression, but rather exerts a controlling inﬂuence on risky behaviour
• Applications of this is selective breeding for tame animals; animals will have increased level of serotonin and 5-HIAA.
11.2.9 RESEARCH WITH HUMANS
11.2.10 ROLE OF SEROTONIN
• Several studies found that serotonergic neurons play an inhibitory role in human aggression.
• A depressed rate of serotonin release (indicated by low levels of 5-HIAA in CSF) associated with aggression and other forms
of antisocial behaviour (assault, arson, murder, child beating).
Men with low serotonergic activity more likely to have close relatives with a history of similar behavioural problems.
• Application: Low levels of serotonin release contribute to aggression, drugs that act as serotonin agonists reduce antisocial
behaviour. Ex ﬂuxetine (serotonin agonist) decreases irritability/aggressiveness.
• Functional-imaging studies found association between differences in genes responsible for production of serotonin transporters
and reaction of amygdala to viewing facial expression s of negative emotions.
• Serotonin transporters play regulatory role in amount of serotonin that remains in synaptic cleft after released by terminal
• Serotonin transporter gene has 2 common alleles, 1 short and 1 long.
Having at least 1 short allele makes people more likely to show higher levels of anxiety or develop affective disorder (ex
• Investigators found that right amygdala of people with short form showed higher rate of activity in viewing faces task.
• PET scanner measured levels of serotonin transporter in brains, found people higher levels of transporter in amygdala
showed less activation (by fMRI) of amygdala when people looked at emotional faces.
11.2.11 ROLE OF THE VENTROMEDIAL PREFRONTAL CORTEX
• Impulsive violence is a consequence of faulty emotional regulation.
Ventromedial prefrontal cortex plays important role in regulating our responses to frustrations.
• Analysis of social situations involves much more than sensory analysis; skills involved are complex, and not localized in any one
part of cerebral cortex.
• But research suggest that right hemisphere more important than left.
Ventromedial prefrontal cortex (incl orbitofrontal cortex, subgenual anterior cingulate cortex) plays special role.
• vmPFC receives direct inputs from dorsomedial thalamus, temporal cortex, ventral tegmental area, olfactory system,
• Inputs provide it with info about what is happening in environment and what plans are being made by rest of frontal
• vmPFC outputs go to cingulate cortex, hippocampal formation, temporal cortex, lateral hypothalamus, amygdala.
• Outputs permit it to affect a variety of behaviours and phsyiological responses, incl emotional responses organized by
vmPFC communicates with regions of frontal cortex (incl dorsolateral prefrontal cortex - dlPFC).
• vmPFC has inhibitory connections with amygdala; this is responsible for extinction. These inhibitory connections appear to be
involved in suppressing emotional responses in other situations too.
• Ex Phineas Gage; had accident that largely destroyed the vmPFC bilaterally.
People whose vmPFC damaged by disease/accident still able to accurately assess signiﬁcance of particular situations but only
• vmPFC serves as an interface between brain mechanisms involved in automatic emotional responses (both learned and
unlearned) and those involved in control of complex behaviours
This role incl using our emotional reactions to guide our behaviour and controlling occurrence of emotional reactions in
various social situations.
• Damage to vmPFC causes serious impairments of behavioural control and decision making.