Fear & Anxiety

individual to collective experiences

• Individual structures - group identity and dynamics

• Collective threat perception - moral panic, prejudice and altruism

  • Has an impact on group identity and dynamics, can promote prejudice and prosocial behaviour

  • e.g. political advertising (visceral images brings attention to the message and is a message for prosocial behaviour)

(PART1) fear, anxiety and survival

fear and anxiety evolved to help organisms detect and respond to threat

• is is a survival mechanism seen in many organisms!

• key question: how should we research the neural mechanisms of fear and anxiety?

definitions of fear, anxiety and defensive behaviours

fear: response to present and immediate threat

anxiety: response to a potential or imagined threat

defensive behaviours: A range of behaviours motivated by the need to avoid or minimise harm caused from real (or imagined) threats

• Set of behaviours conserved throughout evolution (e.g. the ss)

• Other emotions also have these defensive behaviours

defensive behaviours link to predation

• predation is a key threat to survival

• adaptation for flexible defensive behaviours

• prey animals provide plenty of insight into fear

(PART2) classical fear conditioning - associative learning

associative learning: learning by forming connections between events- one stimulus or behaviour comes to predict another

• Classical conditioning (Pavlovian) - learning an association between two stimuli. A neutral stimulus comes to predict an unconditioned stimulus. Often considered passive, as responses are elicited automatically rather than controlled by the learner

• Operant conditioning (instrumental) - learning an association between behaviour and its consequences. A behaviour is strengthened by reinforcement or weakened by punishment. Considered active, as the learner’s actions directly influence the outcome

what is classical fear conditioning?

Classical fear conditioning: associative learning that occurs after the consistent pairing of (an initially neutral) conditioned stimulus (CS) with an aversive unconditioned stimulus (US).

• this CS-UCS association results in the occurrence of a conditioned response (CR; e.g., defensive behaviour) being evoked by the mere presence of the CS (i.e., CS in the absence of the US)

  • e.g. auditory fear conditioning paradigm

what are the neural mechanisms for learning fear?

these are the brain regions of interest:

• amygdala

• hippocampal formation

• insula

contemporary fear conditioning circuit

just need to be familiar with the brain regions from this

1. Information goes to the amygdala but some goes to the thalamus, UCS goes to PAG and Parabrachial nucleus (PBN) (involved in quick movement and pain)

2. Association is made influenced by the amygdala, information goes to the PAG (responsible for pain)

3. Hippocampus also involved by providing context to the response 

4. Information is sent out to the body and response occurs

fear conditioning in humans

• Administer electrical shocks to body (e.g. hands) and the US

• Pain can be unpleasant but must be bearable

• These studies have helped elucidate neural circuitry and mechanisms that may be associated with chronic clinical anxiety conditions as we can understand:

  • Fear acquisition

  • Fear extinction

examples of fear conditioning in humans = anxiety disorders

• PTSD

• specific phobias

clinical anxiety interventions for consequences of fear conditioning in humans

fear to anxiety theories

• Strong acquisition

  • Those with anxiety disorders create stronger associations between CS and US - learn fear in a stronger way

• Broad generalisations

  • Those with anxiety disorders are more likely to generalise the CR to the CS (and stimuli that are similar to the CS) (e.g. dog fear, also scared of wolves)

• Slow extinction

  • Those with anxiety disorders take longer to disassociate (or unlearn) the relationship between CS and US

• Avoidance

  • Those with anxiety disorders are more prone to avoidance defensive behaviours which make it difficult to undertake extinction processes (i.e., unlearning association between the CS and US)

but emotions are psychophysiological so need to consider the peripheral aspects such as:

• Startle reflex (humans -> eyes, rodents -> whole body)

• Heart rate variability

• Pain sensitivity (fear induced pain analgesia)

• Pupillary response (index of emotional arousal)

• Cortisol levels

• Skin conductance response

impacts of fear conditioning

• Established experimental paradigms

• Robust effects

• Valuable insights into anxiety therapies

limitations of classical and fear conditioning - how well does CC explain fear?

1. unconditioned fear

2. non-human → human research

3. experimental realism

4. ethical considerations

5. dynamic nature of the environment

first limitation

1. unconditioned fear -

• How are children getting these fears? - there are certain fears people have without having to experience

• Associative learning has a time cost

  • It takes a while and if we had to learn fear through having to experience things, we would not survive

• The trial and error nature of associative learning may increase chances of failed attempts

example of unconditioned fear

predator odour

• Odours of predators increases defensive behaviours in prey animals

• Associated with the activation of related defensive neural networks

 

Predator odour fear conditioning involves the use of a natural unconditioned stimulus (e.g. cat odour) as opposed to aversive foot shock

second limitation of classical and fear conditioning in explaining fear

2. non-human → human research

• we can translate animal research to model human brain activity but there are some methodological differences to consider

• e.g. Species-specific unconditioned stimuli

  • Natural unconditioned stimuli differs which may impact how information is processed in the brain

  • sensory modality of CS - human studies typically use a visual CS whereas rodent studies tend to use auditory CS

third limitation

3. experimental realism

• Can we truly induce emotional states in the lab with the use of certain stimuli

  • Ethical considerations (particularly with vulnerable participants)

• Can we accurately measure emotional states in real-world situations

  • Environmental confounding variables and technological limitations

fourth limitation

4. ethical considerations

• human participants, relative to rodents, are less naive to the experimental procedure for ethical reasons which may affect emotional salience in the brain

numero 5

5. dynamic nature of the environment

• The real world is more complex than lab environments - ecological validity

• The same defensive strategy demonstrated in a lab may not always work in diverse world environments

(PART3) threat imminence framework - what are the advantages and disadvantages of studying fear in lab conditions

advantages:

• greater control over extraneous variables

• easier to replicate lab environments

disadvantages:

• fear eliciting stimuli is not static on spatiotemporal dimensions - low ecological validity

why does the dynamism of the environment matter? - RECAP

need to refocus neuroscience on complex, naturalistic behaviours and functional circuitry over mental categories and individual brain regions

• emphasise HOW (context) instead of WHAT (specific brain regions)

why does the dynamism matter? - ecological validity

variance in defensive behaviours - they are not always the same and differ depending on the environment

The brain processes which may differ due to these different situations (in the ss):

• motor processing - e.g. action readiness

• executive functioning - e.g. planning

space and time

Cost-benefit decisions in dynamic environments (can i hide vs, where can i hide and is there enough time to hide)

• classic fear conditioning paradigm research can highlight key regions (e.g., hippocampus)

  • but, it can limit the ability to identify nuanced brain patterns (e.g., foraging behaviours and hippocampal place cell remapping; Kim et al., 2012)

threats in the wild - threats exist in varied space and time

• choice of defensive behaviours on spatial and temporal properties of the threat

• there isn't a single defensive behaviour strategy - why anxiety interventions don't work for everyone

• threats are dynamic not static

SPACE + TIME = DEFENSIVE BEHAVIOURS

what is the threat imminence framework?

threat imminence framework: threat and fear-based theoretical framework that explains how animals (including humans) employ defensive behaviours depending on their perception of where the threat exists in space and time

• The way animals respond to threatening situations depends on where the threat is in space and time

• Imminence of the threat determines how you respond

TIF core stages

circa strike → when you are face to face with the threat

the graded defensive responses in the TIF

• Goes from being cognitively based to physical- graded defensive responses

  • Cognitive- thinking / planning

  • Physical- narrow thinking and more limited in defensive strategies (cognitive flexibility decreases)

how do we decide to respond to threats? - the different decision based strategies

cognitive flexibility is theorised to be both

what is the model based (MB) decision strategy

Planning ways to avoid or deal with threat by building internal models of the environments dynamics (spatial configuration) - making decisions based on hypotheticals

• Internal models are used to simulate and plan future actions

• Allows for refinement of defensive strategies

• Slow process may not be helpful when threat is imminent

  • e.g. planning an alternative route home at night for safety

what is the model free (MF) decision strategy

Reliance on well-established defensive behaviours that are innate or usually learnt from direct interactions with the environment

• Defensive behaviours may not be as informed by understanding the full environment’s dynamics

• Well-established defensive behaviours may become maladaptive for varying situations

• Fast to employ when a threat is imminent as it is innate

  • e.g. avoidance behaviours

can we shift between the two decision strategies?

YES - we can shift depending on the situation

• this shifting defines and effective animal - need to be able to use both

• the more imminent the threat, the less flexible we become so will use MF

threat imminence and behavioural flexibility

the TIF attempts to provide a neural network that describes how the brain dynamically responds to threats varying in imminence

TIF experimental realism - ways to investigate perception of imminence

TIF perspectives on neural circuitry (how different brain circuits are involved at each stage of threat) - RECAP of neuroarchitecture

• combinatorial brain connectivity - multiple routes to get from regions A to B

• neural circuits are formed in a dynamic way

• flexible neural circuits benefit survival behaviours

TIF based paradigm activation pattern

• forebrain to do with planning

• midbrain evolutionarily shared

Mobbs et al (2007) - virtual predator paradigm

shows us how cognitive flexibility is represented in the brain

phase effects

cue phase:

predator cues activated prefrontal regions linked to anticipation and regulation

• increase in activity in:

  • rostral and ventral anterior cingulate cortex

  • medial orbitofrontal cortex (mOFC)

  • ventral ACC

  • ventromedial PFC (vmPFC)

chase phase:

predator trials recruited midbrain and thalamic linked to coordination, sensory integration and defensive reactions

• increase in activity in:

  • cerebellum

  • periaqueductal grey (PAG)

  • posterior thalamus

  • pulvinar

control trials instead engaged forebrain regions

• increase in activity in:

  • medial PFC

  • right vmPFC

  • amygdala

predator distance effects

high and low intensity predators showed similar distance effects

• distal threat = increase vmPFC (including subgenual ACC)

• proximal threat = increase PAG

high intensity predators also recruited the CeA and BNST (in basal forebrain) - regions associated with emergency / high salience situations

predator intensity effects

Predator intensity modulated neural responses

• High intensity predators -> PAG, CeA, BNST activation

• Distal high intensity predators -> basolateral amygdala activation

• Low intensity predators -> vmPFC, BLA activity

so what is the overall pattern found from the virtual predator paradigm

BL amygdala only recruited for low intensity

high imminence = central amygdala

what is skin conductance

skin conductance: changes in electrical activity on the skin typically measured through sweat gland activity modulated by the sympathetic nervous system

findings of skin conductance in the virtual predator paradigm / TIF

• drops for a second - represents the body getting ready

• then increases with physiological arousal

this shows us its not just going on the the brain, but happening in the body too!

replication of the virtual predator paradigm

criticism of this study

they used a computer based predator, so could ask will brain responses to natural threats be impacted by TI (e.g. proximity effects)

are there different types of fear?

Cognitive fear - time to consider our defensive strategy (e.g. slow moving threat)

Reactive fear - little time to consider our defensive strategy (e.g. fast moving threat)

 

virtual predator based paradigm - asks how does the brain respond to fast, mid and slow attacking predators

difference in brain representations for cognitive and reactive fear

Qi et al (2018) - this study looked at virtual predator experiment

• PAG = increased activation for fast attacking

• But for slow attacking PAG almost deactivated

• Decreased activation for vmPFC fast attacking - less time to plan

• Hippocampus active when slow attacking - organise oneself in space and time

suggests the brain activates dependent on imminence!

TIF using naturalistic stimuli

again, closer = midbrain, and further = forebrain

what is the general pattern of findings?

*swap approaching and retreating and fast and slow!

TIF and anxiety disorders - difference between anxiety and anxiety disorders

do anxiety disorders affect one or more stages of the TIF

• those with high levels of anxiety are more cognitively aroused in general and when they meet the threat

• takes them longer to calm down from the threat

  • response to threat in those with anxiety disorders is more intense and takes them longer to recover than those with lower anxiety

critiques / alternatives to TIF

• The framework may oversimplify anxiety by focussing on external (rather than internal) threats

  • Feeling a certain way can induce anxiety

• How well does the TIF explain sudden panic attacks?

• Does the existence of hardwired defensive circuits challenge constructivist claims, or can they be integrated?

  • If there is a specific pattern the brain goes through, what does this mean for constructivist claims - are certain threats attenuated in certain cultures