Lecture 24: Emotion and Reward Flashcards
Brief history of the amygdala
- “amygdala” comes from the Greek word for “almond”
- Formed of many nuclei → each have their own function, hard to differentiated each of their functions.
- Up until mid -20th century, was believed to be associated primarily with smell function.
- A conglomerate of nuclei that are involved in a vast array of functions, therefore some researchers suggest it should be called “amygdaloid complex” to avoid thinking it is one structure.
- Very close to olfactory bulb and piriform cortex
- In the medial temporal lobe
What techinues can be used to visualize the subdivisions of the amydala?
What is the flow of information through amygdala circuits modulated by?
- Different histological techniques can be used to visualize the subdivisions (e.g., studies of cytoarchitecture, myeloarchitecture, and specific connectivity fingerprints).
- The flow of information through amygdala circuits is modulated by a variety of neurotransmitter systems. Thus, norepinephrine, dopamine, serotonin and acetylcholine released in the amygdala influence how excitatory and inhibitory neurons interact. Can excite or inhibit the neuron
→ See different hormones, enzymes and NTs that are in the amygdala. - Striatum is very close to amygdala
What is basolateral?
“basolateral” can be used to refer to a region – basal nucleus + accessory basal nucleus + lateral nucleus OR the basal nucleus itself because the accessory basal nucleus is sometimes referred to as basomedial nucleus.
* Multiple sections in amygdala → basal lateral is equivalent to the basal nucleus
* Amygdala is like the thalamus, receives a lot of information.
* Amygdala is connected to the auditory cortex → therefore can activate the amygdala through auditory stimulation
basolateral side of amygdala vs the medial side?
- Evolutionarily older medial side is associated more with olfactory function; basolateral side more recently evolved processing.
- To some, the basolateral region is viewed as a nuclear extension of the cortex (higher order cognition) —not just amygdala regions related to the cortex (pallial amygdala) — while the central and medial amygdala are said to be ventral extensions of the striatum (subpallial amygdala). Just know it is connected to striatum.
- can have higher order function.
- Striatum coordinates many aspects/ functions (planning, decision making, motivation, reinforment, reward…) → amygdala is connected to hippocampus
- The Amygdalo-striatal neurons in the basolateral nucleus have a very similar structure to cortical pyramidal neuron!
- When you look at the structure of the neuron, even though it is a deep structure and subcortical structure, it can have higher order functions.
The inputs of the amygdala
- Each nucleus of the amygdala has unique inputs and outputs (major ones shown here).
- The lateral nucleus is viewed as the “gatekeeper” through which all sensory information passes - from the thalamus and sensory cortex (association cortex) - to dorsal subnucleus.
- lateral nucleaus is viewed as receiving all og the sensory information from the Thalamus, from the sensory cortex and to the dorsal sub nuclei.
➢Dorsal subnucleus plays key role in fear conditioning
- lateral nucleaus is viewed as receiving all og the sensory information from the Thalamus, from the sensory cortex and to the dorsal sub nuclei.
Snesory, auditory information, visual information, somatosensory information, gustative information, Taste and olfaction all project to the amygdala.
- makes sense because are senses are associated with our emotions.
Lateral nucleus = inputs
Learn the inputs and outputs
The outputs of the amygdala
- Central nucleus an important output region, especially for expression of emotional responses (e.g., freezing) and associated physiological responses.
- drives a lot of are behaviour when we have to react to a stimulas that is dangerous/adversive.
- Even if it is a positive response we want to respond to it.
- Central nucleaus is associated with arousal, freezing, sympatthethic system and hormones and the parasympathetic neural system –> associated with our physiological responses.
Central nucleus = output region that drives a lot of projections to other regions
*Do not need to learn all the regions associated with central nucleus.
Basal Nucleus
- Basal nucleus projects to striatum to control instrumental learning behaviours associated with specific stumulation, which also important for emotional responses (e.g., running away from stimulus).
- ex: running away from dangerous things - need ur basal nucleus - will activate all your physiological responses so that you can run faster than you ever could in daily life.
- The basal nucleus that is associated with the ventral striatum associated with actions
behavioural functions associated with amygdala
-
Fear processing (including fear conditioning, fear perception, and unconditioned fear response to predators) →
- Taste aversion
- Emotional memory (with its connection to hippocampus)
- Reward and motivation
- Aggression
- Social and sexual behaviour
Kluver-Bucy syndrome
- lesion to MTL (amygdala is completely rremoved) Has to be bilateral
- Symptoms include:
lack of fear, hyperorality (anything in its mouth)* – strong compulsion to place objects in mouth, flat affect – reduced response to emotional stimuli, hypersexuality, hypermetamorphosis* – excessive attention to visual stimuli and tendency to touch every stimulus, visual agnosia (not recognize visual information), amnesia.
- likely due to due to the visual agnosia
Flat affect - lack of sensory processing so they need to be hyperstimulated to feel anything.
Cannot use perception in order to behave adequately.
- Kluver and Bucy (1937) originally described changes in behaviour of monkeys who had undergone bilateral temporal lobe lesions → like if they have blindness cannot see things but can actually.
- no perception of fear
- “Complete Klüver-Bucy syndrome in man” - Marlowe et al. 1975.
What is the underlying cause of Kluver-Bucy Syndrome
- Underlying cause? In patients, damage (e.g., due to stroke, encephalitis) is large…
- Weiskranzt (1956) performed bilateral amygdala lesions PLUS overlaying cortex in monkeys and demonstrated many of the described symptoms
Fear conditioning
- Pavlovian fear conditioning has become the main model for the study of emotional learning (rats or mice)
- Studies in rodents have mapped the inputs to, and outputs of, amygdala nuclei and subnuclei that mediate fear conditioning.
➢ Single-cell recordings in rodents have shown that the cells in the dorsal subnucleus of the lateral amygdala respond to a CS (e.g., sound of a bell) and the same cells receive input about the US (e.g., foot shock).
➢ After the CS and US have been paired, the cellular response to the CS is greatly enhanced (i.e. more action potentials are elicited). Fear conditioning will happen when the animal or human learns to associate these 2 types of stimulus. - What is the mechanism of this plasticity?
CS= not associated with any emotional response
US = associated with emotional response
* A lot of responses associated with fear conditioning (hormones, freezing and other types of behaviours).
Dorsal subnucleus of the lateral amygdala responds to the CS and the same cell will receive information from the US
* activation of the lateral amygdala will be enhanced (increase in action potentials) every time these two simulus are associated together.
* The lateral nucleus is involved in associating conditioned and unconditioned stimuli
How does fear conditioning work? What is going on at the cellular level?
Hebb: Neurons that fire together wire together
Memory - need the brain to get activated when the info is no longer there. Needs to create AP - possible by the fact that it has enhance sensitivity to a type of stimulus.
Associate neutral stimulus with emotional stimulus → will be associated with increased AP. Neurons associated with emotional stimulus will be activated at the same time ass neurons with neutral stimulus. Neurons that fire together wire together. Lots of AP that will occur. Will create modification in gene expression and protein synthesis.
- In vitro studies of long-term potentiation (LTP) have allowed a detailed analysis of the molecular mechanisms underlying what is going on at the cellular level (ignore Figure 5 in LeDoux 2007):
- Glutamate released from sensory fibers (e.g., auditory tone) in the lateral amygdala binds to NMDA and AMPA receptors. Binding to AMPA receptors leads to depolarizations that are inhibited with repetition. Binding to NMDA receptors is inconsequential because there is a magnesium ion that blocks these receptors.
- If the cell is strongly depolarized by additional input (e.g., foot shock) this Mg2+ ion is removed from NMDA receptors and Ca2+ can enter cell for much more depolarization.
- If enough depolarization occurs, Ca2+ voltage-gated channels open to allow further Ca2+ influx.
- This great increase in Ca 2+ activates a series of steps that eventually lead to gene expression and protein synthesis.
- These proteins are shuttled back to the synapse to stabilize the connection to presynaptic neurons (e.g., additional AMPA receptors) → now same level of response to CS alone. Addition of receptors (more receptors on both sides) will create a new reaction.
* The stabilization of memory via protein synthesis after learning is called consolidation.
* Protein synthesis can also be triggered from memory retrieval → reconsolidation. Therefore, efforts are being studied to block such reconsolidation for treatment of PTSD.
Memory and fear response associated with LTP.
Amydala circuit for auditory fear conditioning
The amygdala in humans
- A - activation of the amygdala (fMRI) to a CS after pairing with an US
- C- activation of the amygdala to a CS after observation of someone else underdoing fear conditioning to that CS (happens when we see someone else – associated with emotional perception of others)
- Structural and/or functional changes in the amygdala are associated with a wide variety of psychiatric conditions in humans: PTSD, phobia and panic disorder, depression, schizophrenia, and autism
- stimulating or inhibiting amygdala used as treatment
The amygdala – fear perception
Neuroimaging has shown that the amygdala is activated during recognition and the interpretation of emotions conveyed by facial expressions, especially those regarded as fearful or happy.
Specific lesion to amygdala = difficulty recognizing faces??
Don’t feel fear so they can’t recognize it
The amygdala – fear and aversive responses
- Activation of certain regions of the amygdala in rodent models in response to odours of predators (e.g., cat) or the predator itself
- Same for trimethylthiazoline (TMT), an odorous substance found in fox feces
= Elicit unconditioned fear responses (e.g., freezing)
Role of the medial nucleus of the amygdala
Aversive responses to odors.
The amygdala – conditioned taste aversion
- In this behavioral paradigm, a particular food item or liquid (conditioned stimulus, CS) is paired with an agent that induces nausea (LiCl, unconditioned stimulus, US). This protocol elicits in the animals a subsequent avoidance of the CS.
- Seems to involve the basolateral nucleus, the lateral nucleus, and perhaps the central nucleus (lesions show attenuated conditioned taste aversion).
- tested on rodents
amygdala – reward and motivation
- Not necessary for simple reward feedback itself (e.g., in a typical visual discrimination task). It is rather about the formation of stimulus-value associations between discrete stimuli and their intrinsic reward coded in amygdala.
- For example, forming an association between a visual appearance of a new food item with its incentive value (how it tastes). Next time you see this food you will have an emotion towards the food.
- Reciprocal connections with OFC for updating value of stimulus-reward associations → reinforcer devaluation task (do not need to know this task). Update stimulus-reward association
- not only about visual discrimination but rather about the assosciation of the stimulus witht the reward and its value. → enhancement of the activation of the amygdala. Anything that reminds you about this traumatic event will cause the amygdala to respond in a specific manner.
