Interoception Lecture Notes

Course Logistics & Assessment Reminders

  • Lecturer began by checking audio and inviting questions on the module, seminars and assessments.

  • Seminars are:

    • “Very important for your assessment” and for learning in general.

    • Students must read the week’s paper even when not presenting; discussion improves comprehension and will make the written assignment easier.

    • You cannot write the assignment on the paper you presented; you must choose a different one.

    • Attending your own seminar group is strongly advised.

  • Core reading for this lecture:

    • Two primary papers (on Moodle) + today’s PowerPoint.

    • One additional paper listed as “suggested.”

    • References scattered throughout the slides for further study.

Overview of Today’s Lecture

  • Definitions of interoception.

  • The multi-dimensional nature of interoception.

  • Methodologies to measure it.

  • Neural correlates (brief overview).

  • Question: “Is skin an interoceptive organ?”

  • Illustrative studies linking interoception to cognition & behaviour (emotion, decision making, social cognition, self-awareness, mental health).

Senses Beyond the Classical Five

  • Traditional list: sight, hearing, smell, touch, taste.

  • Additional senses mentioned by students/lecturer:

    • Temperature (thermoception).

    • Proprioception (limb position).

    • Vestibular sense (balance & acceleration).

    • Interoceptive sensations: heart rate, respiration, hunger, thirst, core temperature, etc.

What Is Interoception?

  • Working definition: perception, processing and (sometimes) awareness of sensations originating within the body.

  • Examples: feeling your heartbeat, fullness of the stomach, need for air.

  • Core temperature is unambiguously interoceptive; skin temperature may or may not be, depending on definition.

Importance for Survival & Development

  • Life without interoception would be nearly impossible (e.g., no perception of hunger/thirst in infancy).

  • Theories propose that emotion regulation and social bonding are grounded in early caregiver-infant interoceptive tuning.

  • Only in the last ~15 years has interoception received an explosion of research attention.

Homeostasis & Allostasis

  • Homeostasis: tendency toward a relatively stable internal equilibrium maintained by physiological processes.

  • Allostasis: efficient predictive regulation—preparing the body before needs arise (e.g., feeling thirsty while eating salty food).

  • Interoception supplies the sensory information necessary for both.

Conscious vs. Unconscious Processing

  • Most interoceptive signals stay below conscious awareness to avoid sensory overload.

  • We usually become aware only during imbalance: illness, strong emotions, vigorous exercise, extreme fatigue.

  • Exteroceptive cues can overshadow interoceptive ones (e.g., chest wall stretch during breathing).

  • Referred sensations: visceral pain perceived on skin (e.g., heart attack → pain in left arm/shoulder).

Historical Definitions

Classical Definition (Sherrington legacy)

  • Interoception = signals from inside the body conveyed by visceral afferents (mechanoreceptors, chemoreceptors) via neural/humoral pathways to the brain.

  • Excludes exteroceptive senses, proprioception, vestibular input.

Extended Anatomical–Functional Definition (Craig & colleagues)

  • Interoception = all body sensations carrying homeostatic, motivational or affective relevance, regardless of receptor location.

  • Includes:

    • Thermoception (skin temperature).

    • Cutaneous pain.

    • “Affective touch.”

  • Rationale:

    • These signals travel via the Lamina I spinothalamic pathway.

    • They converge on the posterior → anterior insula—the hub of interoceptive processing.

Taxonomy / Dimensions of Interoception (bottom–up → top–down)

  1. Afferent Signalling

    • Raw physiological signals travelling to the brain.

  2. Pre-conscious Impact

    • Influence of those signals on cognition/behaviour without awareness.

  3. Interoceptive Accuracy (IA)

    • Objective ability to correctly detect internal signals.

  4. Interoceptive Sensibility (IS)

    • Subjective beliefs, confidence, attitudes toward one’s interoceptive abilities.

  5. Metacognitive Interoceptive Awareness / Insight (IAw)

    • Match–mismatch between objective IA and subjective IS.

  6. Execution & Attribution

    • Higher-order interpretation of causes and action plans (e.g. “I’m hungry → eat”).

(Garfinkel et al., 2015 introduced the IA–IS–IAw triad; older papers often mix terminology.)

Measuring Interoceptive Accuracy

Cardiac Domain

Heartbeat Counting Task (Schandry)

  • Procedure: “Start” & “Stop” tones (e.g., 20 s). Count felt heartbeats without palpating pulse.

  • Score = 1−∣Recorded HB−Counted HB∣Recorded HB1 - \frac{|\text{Recorded HB} - \text{Counted HB}|}{\text{Recorded HB}} (ranges 0–1).

  • Observations:

    • People vary widely; many under-estimate at rest.

    • Average resting HR ≈ 74 bpm74\,\text{bpm}.

  • Limitations:

    • Prior knowledge/beliefs or wearable data contaminate estimates.

    • Can “cheat” by counting seconds if HR is low.

    • Conducted at rest—arguably interoceptively unchallenging.

Heartbeat Discrimination (Whitehead)

  • Ten auditory tones per trial, either on-beat (0 ms delay) or off-beat (shifted). Participant judges synchrony.

  • Strength: Immune to HR knowledge—sequence always matches actual rhythm.

  • Weakness: Very difficult; only sensitive in high-IA individuals.

Pharmacological / Arousal Manipulation

  • Infuse adrenaline/isoproterenol; participant tracks moment-to-moment cardiopulmonary arousal.

  • Strength: Measures detection during physiological change (ecological).

  • Weakness: Invasive; limited contexts.

Respiratory Domain

  • Participants breathe through a circuit where inspiratory resistances are inserted (manually or digitally).

  • Tasks: detection (“change vs no-change”), threshold tracking, or graded resistance rating.

Measuring Interoceptive Sensibility

  • Add confidence ratings after each IA trial (“How sure are you?”).

  • Self-report questionnaires:

    • MAIA (Multidimensional Assessment of Interoceptive Awareness) – 8 subscales (Noticing, Attention Regulation, Emotional Awareness, etc.).

    • BPQ (Body Perception Questionnaire) – frequency of bodily sensations.

  • Related construct: Alexithymia (difficulty identifying/expressing emotions). Highly correlated with poor interoception but conceptually distinct.

Metacognitive Interoceptive Awareness / Insight

  • Good IA + correct high confidence → high insight.

  • Good IA + low confidence, or poor IA + high confidence → poor insight.

  • Case example: participant objectively excellent yet insists “I’m just guessing” (low insight).

Relationships Among Dimensions

  • Empirical findings mixed:

    • Some studies: IA, IS, IAw largely independent.

    • Others: correlation emerges only above a threshold of IA.

Neural Correlates

  • Brainstem nuclei: first relay & reflexive regulation.

  • Posterior → Anterior Insula: primary cortical hub; integrates interoceptive, exteroceptive, social & contextual information.

  • Anterior Cingulate Cortex (ACC): motivational/affective aspects, autonomic control.

  • Primary & Secondary Somatosensory Cortices (S1/S2): tactile & body-mapping contributions.

  • fMRI evidence:

    • Heartbeat discrimination vs control → right anterior insula activation; better performers show higher BOLD and greater grey-matter volume in that region.

    • Respiratory arousal tracking → similar insula & ACC engagement proportional to task accuracy.

Is Skin an Interoceptive Organ? – CT Afferents & Affective Touch

  • C-Tactile (CT) Afferents:

    • Unmyelinated, low-threshold mechanoreceptors in hairy skin.

    • Optimal firing at 1–10 cm⋅s−11–10\,\text{cm·s}^{-1} (peak 2–3 cm⋅s−12–3\,\text{cm·s}^{-1}) — the natural caressing speed.

    • Convey slow, pleasant touch → project via Lamina I to posterior insula.

  • Functional roles:

    • Emotion regulation, social bonding, caregiver–infant attachment.

    • Candidate for inclusion in “extended” interoception.

Empirical Links Between Interoception & Other Domains

Emotion Perception & Memory

  • High-IA participants show larger initial HR deceleration to emotional pictures and superior recall of them vs low-IA.

  • High-IA group demonstrates tighter coupling between subjective and physiological arousal.

Intuitive Decision Making

  • Iowa-style gambling task with ambiguous decks: higher IA → better implicit learning of advantageous decks (“gut feelings”).

  • Real-world extension: London financial traders with higher IA outperform peers and remain longer in the job.

Unconscious Conditioning / “Gut” Predictions

  • Subliminal spider/snake images, some followed by shock.

  • Participants rate shock expectancy despite no conscious cue awareness.

  • Higher IA → more accurate expectancy ratings (heart-driven somatic marker guides decision).

Social Cognition

  • Theory of Mind: IA correlates with affective ToM (inferring others’ feelings), not with cognitive ToM (beliefs, intentions).

  • Focal Insula Lesions: patients impaired in IA and in tasks of emotional prosody, facial emotion morphing & Eyes-Test → causal role of insula.

  • Social Exclusion & Touch: Cyberball ostracism paradigm:

    • CT-optimal stroking (slow, gentle) after exclusion reduces negative affect & feelings of ostracism versus fast stroking.

  • Perceived Intentions in Touch: Slow stroking on forearm increases reported love, arousal & intimacy intentions. Interestingly, slow stroking on palm (glabrous skin) still boosts love & intimacy (mechanism unclear; may reflect learned pleasantness).

Body Ownership & Self-Awareness

  • Classic Rubber Hand Illusion (RHI): synchronous visuo-tactile stimulation → ownership of fake hand. High IA = less illusion (stronger internal body model).

  • Cardio-Visual RHI (VR hand pulsing): hand colour pulses in synchrony vs asynchrony with heartbeat. High IA = more illusion under synchrony (superior cross-modal integration of cardiac signals).

  • Affective Touch & RHI: slow CT-optimal stroking produces stronger ownership than fast stroking.

  • Infant Study (5 months): animated shapes bounce in sync vs async with infants’ heartbeats. Infants look longer at asynchronous stimuli, indicating sensitivity to heartbeat–visual contingencies. Heartbeat-evoked cortical potentials modulated by emotional faces correlate with this sensitivity.

Key Numbers & Facts for Revision

  • Average adult resting HR: ≈74 bpm\approx 74\,\text{bpm} (range 50–90).

  • Heartbeat counting practice demo: 20-s interval ≈ 25 beats at average HR.

  • CT-optimal stroking speed: 2–3 cm⋅s−12–3\,\text{cm·s}^{-1} (effective range 1–101–10).

  • IA tasks often classify “good” vs “poor” performers by median split or accuracy thresholds (>0.85 Schandry score in some studies).

Practical & Ethical Considerations

  • Choice of IA task must align with research question; each has specific confounds (knowledge, difficulty, invasiveness).

  • Researchers must state clearly which dimension of interoception they examine (accuracy, sensibility, etc.) to avoid terminological confusion.

  • Affective touch may have therapeutic potential (e.g., mitigating loneliness), but requires sensitivity to consent and cultural norms.

Connections to Previous & Future Content

  • Links to earlier lectures on proprioception, vestibular sense and psychophysiology.

  • Foreshadows Year-3 module “Neuroscience of Cognitive Disorders” (interoception & mental health).

Take-Home Messages

  • Interoception extends beyond visceral signals; definitions dictate inclusion of skin-based “affective touch.”

  • It is multi-dimensional: objective accuracy, subjective sensibility and metacognitive insight are separable.

  • Measurement is non-trivial; understand strengths/limitations of each paradigm.

  • Insula is the cortical nexus integrating bodily, emotional and social information.

  • Individual differences in interoception shape emotion, decision making, social cognition and self-representation from infancy onward.

  • Continued clarity of terminology and methodology is essential as the field rapidly expands.