Behavioral Neuroscience, lecture on Fear and Fear behavior
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Behavioral Neuroscience
Summers
Fear
Afferent Path for Fear
Amygdala
Fear Conditioning
Pavlovian potentiated startle Afferent Shock (US) Pathway
Efferent Output
Neuromuscular Production of Fear Potentiated Startle
Integration of Fear Conditioning
BDNF
Substance P
ACh
Fear figures
Fear Conditioning Circuitry
end     Acronyms/Abbreviations
Fear Conditioning
I. Fear  		

	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  Fear  Terror
		
			a. Annoyance  Anger  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. raph (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  startle
				
				iii. fear + loud sound  bigger startle

III. Afferent Path for Fear