Introduction to Interoception

What is interoception and what are it’s key aspects?

• our ability to feel sensation from our body

• is distinct from the five senses

• homeostasis is key

• is the foundation of our sense of the physical self

• self-awareness/emotion

What is restrictive interoception?

• how it was defined historically as purely visceral (Sherrington 1948)

• only information concerning the functional state of the internal organs

How is the contemporary view of interoception more inclusive than the historical view?

• regards general homeostatic sensory capacity (Craig 2002, 2003, 2008)

• information concerning the broader physiological state and motivational needs of the body

• including pain, temperature and touch which all activate the same pathway

What is homeostasis?

physiological equilibrium

How does interoception relate to an anatomical pathway?

• Information about the physiological state of the body follows a similar (parallel) pathway to the brain

• similar categories of afferent nerves

• signals that follow this pathway are classed as interoception

What are afferents?

• sensory information from the body to the brain

• sensory neurons

What are efferents?

• regulatory signals from the brain to the body

• motor neurons

Which direction does the interoception neural anatomical pathway travel?

• ascending pathway

What are afferent neurons?

nerve fibres that carry information towards the brain

How do different afferent neurons differ?

• different types of fibres carry different types of information and follow different pathways

• but afferent nerves that carry information about the physical state of the body (interoception) follow a similar pathway.

Which afferent neurons carry the signals of interoception?

• small diameter A-delta and C afferent nerves

• including nociceptors (pain)

• thermoreceptors (temperature)

• osmoreceptors (thirst)

• baroreceptors (heart rate)

What is the difference between C afferents and other fibres?

• C afferents are unmyelinated nerve fibres

• they carry signals slower

What is Myelination and how does it cause different afferents to differ?

• myelination is a layer of insulation (fatty sheath) surrounding a neuron

• increases efficiency of electrical transmission (nerve signals travel faster)

• unmyelinated neurons are comparatively slow

• mylinated nerves = nociceptors (pain)

• unmylinated nerves = CT afferents (affective touch) - less urgent

How are the cells in the dorsal horn divided?

• divided into physiologically distinct layers called laminae

What are the characteristics of Lamina I in the dorsal horn?

• lamina I is the most superficial layer (marginal layer) of the dorsal horn

• all introceptive signals come into this layer (a delta and C fibres)

What is the neural anatomic pathway of interoception from Lamina I to the cortex?

• small-diameter afferent nerves project to Lamina I of the dorsal horn of the spinal chord

• projects contralaterally to the lateral spinothalamic tract

• Lamina I projects to the brain stem (info regarding breathing etc doesn’t go further)

• then thalamus, hypothalamus and amygdala

• cortex (anterior cingulate and insula - interoceptive cortex)

What are the functions of the interoceptive neural anatomical pathway?

• afferent projections from the dorsal horn provide the somato-autonomic reflexes crucial for maintaining homeostasis

• these are not emergency mechanisms, but provide continuous feedback

• Lamina I also receives decending (efferent) modulation for interoceptive signals

What is the cortical terminus of the neuroanatomical pathway?

the insular cortex (the interoceptive cortex)

Why do we scratch to alleviate an itch?

• scratching inhibits itch via inhibitory interneurons in the dorsal horn of the spinal cord

• the pain signals from scratch take priority - activates inhibitory neurons which dull down the itch sensation

What are the 4 parts of the itch scratch cycle?

• scratching the skin to alleviate itch

• damage skin, release inflammatory chemicals

• stimulate nerve endings of itch afferents

• feelings of itch lead to the urge to scratch

What is the basic idea of interoception and emotion?

• intrinsic link between the physiological state of the body and emotion

• understanding our emotions involves interpreting internal bodily signals

• emotions can be felt in the body

• e.g panic or excitement - heart rate

• fear or surprise - muscle tension

What is alexithymia?

• having no words for emotions

• linked to interoception deficits

What relates to the interconnection between the gut and the brain?

• deeply rooted in our language e.g. hangry

• neural network communicates with the brain about gastrointestinal homeostasis. Also emotion motivation and decision making

• bidirectional - emotions can influence digestive system

What is the historical development of our understanding of where the self is?

• Aristotle (greek philosopher) believed the self was in the heart

• Limanowski + Hecht (2011) - both head and heart

• Alsmith + Longo (2014) - between the head and the torso

What is the relationship between interoception and behaviour?

• emotional behaviours evolved to produce goal-directed action that fulfil homeostatic needs of the body

• how you feel can be moderated by physiological state of the body

• how you feel can influence your behaviour

• e.g. cold shower when you’re hot

What are the aspects of physiological motivations?

• cognition takes place within the context of the body that needs to stay alive, and be healthy

• brains evolved to regulate bodies within a social context

What is the Attentional Blink paradigm used in procedure by Garfinkel et al (2014)

• tests temporal capacity of the limits of attention

• identification of an initial tarted (T1) during a rapid serial visual presentation (RSVP) of stimuli impairs the ability to detect a second target

• stimuli in the RSVP presented in different phases of the heartbeart

What are the different phases of the heartbeat?

systole - when the heart contracts

diastole - when the heart relaxes

What do baroreceptors from the heart convey?

• information about the strength and timing of the heart beat which facilitates modulation of blood pressure through vasodilation

• these signals also communicate to the brain and regions associated with emotion and cognition (insular, amygdala)

• brain knows which phase the heart is in at any time

What did Garfinkel et al present during their procedure and then what were ppts asked?

• presented a house at T1

• T2 was a face (disgust, fear, sad, happy, neutral)

• the rest of the stimuli were scrambled images

• second task examined recognition of T1 and T2 stimuli presented in preceding RSVP

• participants given three options of facial expressions and asked to identify

What did Garfinkel et al find regarding systole presentation of stimuli at T2?

• timing of stimuli facilitated detection of T2 for fear faces only

• systole presentation led to greater proportion of fear faces detected

• heart contracting/ in stress bias to threat detection

What did Garfinkel’s experiments show when either neutral or fear faces were briefly presented, time locked to heartbeat and emotional intensity ratings were given of the presented face?

• same face showed in different conditions, only difference was when it was presented with heartbeat

• timing of the stimuli related to intensity judgements

• systole stimuli led to greater intensity for fear faces

• diastole stimuli trend for greater intensity for neutral faces

• greater alertness to fearful stimuli with contraction of heartbeat

Which variable causes a difference in Garfinkel’s found effect of the interaction between cardiac cycle and emotion intensity?

the effect is exacerbated in individuals with higher state anxiety

What did Garfinkel’s MRI experiments show in the brain?

• main effect of the stimulus timing associated with activity in the anterior insula

• interaction between cardiac timing and emotion (of faces) associated with amygdala activity

What would greater arousal mean?

• greater arousal (more and stronger heartbeats) would mean more time in systole compared to diastole

• in systole the heart is working hardest

• perception of threat is dependent on the level of physiological arousal

Garfinkel conclusions (screenshot)

What was Azevedo et al (2017) procedure studying more complex human behaviour - the effect of cardiac cycle on racial stereotyping?

• compared stimulus presentation when the muscle is contracting vs relaxing

• had to identify targets (tool or a weapon)

• primed by either black or white males faces

• all sample were white - trying to prime potential black stereotypes using this paradigm

• stimuli were presented at systole or diastole

What did Azevedo et al (2017) find studying more complex human behaviour - the effect of cardiac cycle on racial stereotyping?

• systole exacerbated racially stereotyped responses

• e.g. less accurate identifying tools when primed to face of a balck man than to white

What were the results of Azevedo’s first person shooter task in which ppts had to decide whether to shoot or not exposed to different stimuli with racial differences. Presentation was timed with phase of the cardiac cycle

ppts chose to shoot unarmed black men more often than unarmed white men

What can be concluded from Azevedo’s research?

• in the context of potential threatening stimuli heaightened representation of cardiac signals in the brain may enhance salience of social cues and promote negative racial stereotypes

• important brain-body mechanism influencing processing of salient social cues and subsequent actions

• prediction-based on previous social association moderated by current body state