Behavioral Neuroscience, lecture on Fear and Fear behavior
Fear Conditioning
I. Fear back to Syllabus
A. Fear is an emotional response
1. hypothetically 8 basic emotions (Plutchik 1994)
a. four pairs of opposites
i. joy : sadness
ii. affection : disgust
iii. expectation : surprise
iv: anger : fear
2. 7-8 human universal facial expressions (Kelter & Eckman 2000)
a. happiness : sadness, disgust, contempt, surprise,
embarrassment, anger : fear
B. Fear is an emotional response that follows experience of aversive stimuli
1. A response to threat or danger
2. Novel stimuli may be benign, beneficial or aversive
a. \ novel stimuli are stressful
b. novel stimuli may also be fearful
if aversive novel stimuli have been previously experienced
i. \ fearful stimuli need not have been
experienced previously
(1) but, presumably only if other fearful stimuli
have been experienced
ii. ambiguity = stimuli that have more than one
possible interpretation
(1) may contribute to fear
iii. uncertainty
(1) expected - known unreliability
of predicitive cues within a context
(2) unexpected - unsignaled context switches that
produce strongly unexpected results
3. Anxiety is the anticipation of a fearful stimulus
a. includes conditioning to fear
4. fearful stimuli may be physically or psychologically painful
a. nociceptive thresholds vary
b. psychologically aversive stimuli also have varying thresholds
i. experience and controllability are important factors
c. \ responses to fearful stimuli are also variable
B. Intensity of Fear
1. Apprehension Þ Fear Þ Terror
a. Annoyance Þ Anger Þ Rage
2. contollability of enviromental factors
a. influences intensity of fear
i. fearful stimulus that can not be controlled
is more terrifying
ii. fearful stimulus that can be absolutely controlled
is only annoying
b. partly modulated via stress neurocircuitry
C. Fear is stressful
1. uncontrollable stressors cause the largest
neuroendocrine stress response
a. social stress is the most potent stressor
2. fear and stress are both modulated by the amygdala
a. limbic structure
3. LHPA axis
a. Limbic system in the brain regulates both neural
and endocrine stress responses
i. Hippocampus inhibits/terminates
endocrine stress responses
(1) via the bed nucleus of the stria terminalis
(BNST)
(a) hippocampal neurotransmitter is Glu
(b) BNST transmitter is GABA
ii. Amygdala stimulates endocrine stress responses
(1) transmitter is GABA
(2) via the BNST
iii. Amygdala modulates brain stress responses
(1) central amygdala (CeA) produces
corticotropin releasing factor (CRF)
(2) CRF neurons project
to many other brain regions
(a) e.g. raphé (5-HT) and
locus ceruleus (NE)
iv. Amygdala also modulates emotional experience
(1) more specifically than other limbic regions
(2) especially fear, anxiety and anger
(3) including fear learning and memory
b. Hypothalamus produces the 1st hormone CRF (CRH)
in the stress endocrine cascade
i. hormonal CRF from the paraventricular nucleus (PVN)
of the hypothalamus travels via the blood the pituitary
c. Piuitary: CRF stimulates adrenocorticotropic hormone (ACTH)
d. Adrenal Cortex: ACTH stimulates corticosteroids
i. cortisol (F) in humans, fish and sheep
ii. corticosterone (B) in rats, mice, birds, reptiles
iii. bind to glucocorticoid receptors (GR)
and mineralocorticoid receptors (MR)
e. feedback
i. short-term negative feedback
(1) F/B inhibit activity at the PVN directly
(a) and via the hippocampus (GR & MR)
(2) bind MR during normal baseline homeostasis
(a) pulsatility
(3) bind GR during stress or circadian peak
ii. longer-term positive feedback
(1) binding to GR in the amygdala
(2) chronic stress
II. Fear Behavior
A. immobility/feezing
1. rats and mice freeze in response to foot shock
2. hamsters become immobile after social defeat
a. submissive postures in reponse to social fear
i. some submissive behaviors are active
3. learned helplessness
a. lack of control
B. flight/escape
1. hamsters increase locomotor activity to foot shock
2. social aggession promotes fearful escape in many animals
C. Aggression
1. hostility may be tempered by fear
a. may change to fear
D. Fear potentiated startle
1. unexpected sensory stimulus can produce abrupt motor response
a. sharp noise will make rats or humans jump
2. Fear/anxiety/stress increases the motor repsonse to the same stimulus
E. Place Avoidance
F. Fear Learning
1. powerful learning and memory mechanisms are associated with fear
and stress
a. involve the amygdala
2. associative ambiguity - learning situations which have
more than one possible interpretation
a. angry face - presence and source of threat
b. fearful face - presence but not source of threat
3. place avoidance - spatial memory
4. classical conditioning: Fear Conditioning
a. shock paired with light or sound
i. freezing to light or sound
b. fear potentiated startle
i. shock paired with sound
ii. loud sound Þ startle
iii. fear + loud sound Þ bigger startle