Emotion lecture 5 Flashcards
Describe a study which attempted to study emotional responses in flies
Trapped flies in a little plexiglass arena and had a paddle attached to a motor wave back and forth over the glass to simulate an overhead sweeping stimulus (aerial predator). This study quantitatively studied the behaviour of the flies after multiple presentations of the stimulus. It is remarkably effective in trigger an innate escape or avoidance response however this could reflect a reflex or something like fear- there needs to be more building blocks to establish emotion.
Describe how the building blocks were established in the fly experiment (5)
Scalability: When only a few/ single shadow passes, freezing behaviour is observed. When multiple shadows pass, hopping behaviour is observed.
Valence & Automaticity/ Priority: Shadows disperse flies from food away from the shadow
Persistence: Behavioral response persisted for seconds to minutes
Generalisation: Generalisation to different context (with or without food
This study then modelled the behaviour of the fly. Describe this
Constructed a ‘leaky integrator’ model, as if the brain integrates the shadows that pass but it leaks over time. It must reach a certain level to trigger certain behaviours. There are multiple thresholds with different behaviours (i.e freezing > Running > Hopping). The model can also predict the probability of them persisting with their behaviour depending on how many shadows have passed and how much this ‘leaky integrator’ is filled. This is more complex than a reflex.
What else does this study find possible evidence for regarding emotions?
An adaptive value of this emotion state:
Fly decision-making in real-life situations: Stay or flee is a life-and-death decision. Cost-benefit analysis through an “emotional state” leaky integrator model
Describe the conditioned and unconditioned stimuli in a study which attempted pavlovian conditioning in flies
Either an electric shock (aversive stimuli) was paired with a neutral odor or sucrose (appetitive stimuli) was paired with a neutral odour.
Name and describe a neural structure of a fly studied in this research with relevance to the study
A mushroom body cell:
- Kenyon MB cell is activated by odor synapses with MBON cells.
- The US (sucrose/ shock) activates a specific substrate of dopamine (DA) neurons
- A different subset of DA neurons for shock (γ4, γ5) vs. sucrose (γ2, γ3).
- DA facilitates synaptic transmission between kenyon MB cells and MBON (output neurons) cells in specific compartments => behaviour.
- MBONs hardwired to evoke approach (y2, y3) or avoidance (y4, y5). Odor alone too weak to evoke activity.
However if you pair it with a stimulus, then either approach or avoidance is triggered. If it is the shock, then these DA neurons trigger activity in y4 and y5 which are hardwired to trigger avoidance in the fly. The fly will then learn to avoid the odor in future. When the pairing is complete, then the synaptic transmission between the the Kenyon cell of the MB and the MBON is strengthened through this shock: Long term potentiation. At first the CS triggers activation in the specific compartment via dopamine which triggers the action, however after a while, it is facilitated so that the odor is doing it by itself.
What does the association of the CS with positive or negative valence depend on? (3)
Same general process, same neurotransmitter (DA) just depends on:
a) Sparse representation of the odor by the Kenyon MB cells (small number of highly odor-specific neurons)
b) Compartment-specific synapses with MBONs that promote either approach or avoidance
c) Strengthening of these Kenyon-MBON synapses by compartment-specific DA release from specific DA neurons activated by shock or sucrose
What implication does this pavlovian study in flies have for human neural research
It suggests that we should not associate dopamine with “reward” or a specific emotion or drive, as it has been shown to play a part in both avoidance and approaching behaviour. The circuit connectivity which is hardwired from birth plays a much bigger role in the fly.
Encoding of valence (reward/punishment) a given US (shock vs. sucrose) by DA neurons; Determined by the circuits in which specific DA neurons participate –whether these make synapses with neurons that mediate approach or avoidance. Valence is not encoded merely by the identity of a specific neurotransmitter.
Similar story regarding DA (reward AND punishment) has emerged in rodents and primates!
What is required for such an important role for these specific circuits?
An innate basis for such connectivity to ground valence (the wrong response of approach or avoid would not be evolutionarily viable)
Describe a study which investigates aggression and courtship in male flies
The structure P1 specific to males mediates both male flies’ aggressive behaviors towards other males, and courtship/mating toward females. Optogenetic stimulation of P1 leads to a persistent state in solitary flies, promoting aggression once a conspecific male is encountered, even 10 minutes later. This gives evidence that aggression/ courtship are not simply reflexes but persistent emotional states
In what other species has similar research been done on this link between aggression and courtship?
In male mice mating and aggression controlled by colocalised and anatomically intermingled neurons in the ventrolateral subdivision of the ventromedial hypothalamus (VMHvl) (although flies and mice are separated by 500 million years of evolution!)
How well is the amygdala conserved across evolution
Pretty darn well:
Non-mammalian species (reptiles, birds, fish, but not flies) have an amygdala-like brain region with similar circuits and function as the mammalian amygdala
What amygdala nuclei are involved in fear conditioning?
Only 3–5 of of 12 amygdala nuclei involved in fear conditioning: Basolateral complex (BLA, including the lateral [LA], cell group), and central nucleus (CeA, containing lateral [CeL] and medial [CeM] subdivisions)
What were these two nuclei thought to be involved in traditionally?
Basolateral complex: Aquisition of conditioned fear
Central nucleus: Expression of conditioned fear
To what extent is the amydala required/ sufficient for fear?
Amygdala is necessary for acquisition and expression of conditioned fear (but not sufficient for conscious experience of fear)
Is the amygdala involved in defensive or appetitive behaviours?
Distinct amygdala sub-populations control defensive vs appetitive behaviors (not visible on fMRIs)
To what extent is the amydala required/ sufficient for defensive behaviour?
Not all amygdala: Hypothalamus necessary and sufficient for innate defensive behaviors (freeze, escape, avoidance)
Amygdala is more involved in learned fear, not innate responses.
How may the amydala elicit behaviour?
The amygdala is important for the emotion state in fear conditioning and has output to pre-motor areas such as the the Peri-aqueductal grey which then initiates freezing behaviour for example. It has similar connections with other anatomical targets for other behaviour and bodily responses. This is know as the:
Global organismal response: Coordinated behavioral, autonomic, and endocrine response.
Describe the classical view of how acquisition and expression of fear conditioning occurs
- Acquisition: Pathways conveying CS (cue) and US (shock) converge in the BLA (or LA), where they strengthen synaptic responses to the CS
- Expression: This information is then relayed to CeA(CE) as the final common pathway for output from the amygdala
However what has more recent work indicated regarding the central nucleus?
Indicates distinct functions of CeAsubdivisions and cell types:
- CeL also plays a role in acquisition
- CeM coordinates output via inhibitory projection neurons (by disinhibiting target cells in downstream structures such as PAG) –global coordination
- Distinct CeA neuronal sub-populations controlling defensive vs. appetitive behaviors
What evidence led to the claim that the amygdala is involved in both defensive and appetitive behaviour?
Progress thanks to novel neurotechnology (e.g. optogenetics) has revealed seven distinct cell types within different subdivision of CeA: Some involved in appetitive behavior, some in defensive behavior. Complexity of amygdala circuits: Cell-type specific techniques are necessary to identify and manipulate brain function so as not to mix circuit functions
What has more recent research found to be true about the inner workings of the Basolateral complex?
There are distinct neuronal subtypes in the BLA:
- BLA neurons activated by aversive stimuli (e.g. foot shock) project to the CeA, and are necessary and sufficient for fear conditioning
- BLA neurons activated by rewarding stimuli (e.g. nicotine) project to the NAc and support positive reinforcement
These different types of neurons are interspersed in BLA without any anatomical demarcation (found through marking genetically defined neurons, engaging them in reward/ fear conditioning for hour then killing the mouse and slicing the brain (?)).
Has this finding regarding the BLA been found in other species?
Similarly interspersed neurons found in monkeys
This research has obvious implications for debates about the role of amygdala in emotion. How does it explain some previous research and what issue does it exemplify?
Some meta analyses found evidence for activation in the amygdala for both negative and positive emotions. This research has some implications for applications of neuroimaging because while it can show activation in this general region, there would be no way to discern from fMRI why there was activation shown in that area for both valences (cannot detect the influence of different cell types.)
This ambiguity in the stimuli in which the amygdala is sensitive to led to the theory that there is a general role of the amygdala in ‘relevance detection.’ But human neuroimaging does not have sufficient cell-type/circuit-level resolution to pick up the fear and reward specific circuits in the amygdala.