Interoceptive Brain Dynamics in bvFTD

Interoceptive Brain Dynamics in bvFTD

Overview

Interoceptive Brain Dynamics in bvFTD

Overview

Behavioral variant frontotemporal dementia (bvFTD) is characterized by profound changes in socioemotional functioning, including impaired empathy, loss of insight, and altered autonomic processing. Recent research by Hazen et al. published in EBioMedicine (March 2025) has revealed that bvFTD patients exhibit fundamentally altered interoceptive dynamics—specifically, prolonged interoceptive neural timescales during heartbeats in fronto-temporal and parietal brain regions["@hazen2025"]. This finding provides a mechanistic link between the disrupted bodily awareness seen in bvFTD and its hallmark socioemotional deficits, offering new insights into how the brain's predictive mechanisms break down in neurodegenerative disease.

Interoception—the perception of internal bodily signals—underlies not only basic homeostatic processes but also higher-order functions such as emotional experience, decision-making, and social cognition["@barrett2009"]. The insula, as the primary cortical representation of the internal bodily state, integrates these signals with external environment and cognitive context to generate the subjective feeling states that guide behavior. In bvFTD, the systematic degeneration of insular and salience network regions progressively degrades this integration, producing the characteristic socioemotional symptoms that define the disease.

The Interoceptive Neural Timescale

Concept and Measurement

The brain processes internal bodily signals (heartbeats, gut sensations, respiratory rhythms) through specialized neural circuitry that generates continuous predictions about the body's state[@stephan2016]. The "neural timescale" of this processing refers to how quickly these predictions are updated in response to incoming sensory data. In the interoceptive context, this can be operationalized through the anticipatory cardiac waveform (ACW)—a neural signal that reflects how the brain anticipates upcoming heartbeats.

Shorter timescales allow rapid adaptation to changing bodily states, enabling flexible behavioral responses. Longer timescales reflect more stable, sustained representations—but at the extreme, prolonged timescales may indicate rigid, maladaptive predictions that fail to track dynamic bodily changes. Using intracranial and surface EEG recordings during heartbeat perception tasks, researchers can quantify the temporal properties of this anticipatory signaling[@kumar2017].

In healthy individuals, interoceptive processing in the [insular cortex](/brain-regions/insular-cortex) and associated [salience network](/circuits/salience-network) maintains optimal timescales that support accurate perception of bodily states and appropriate behavioral responses[@seeley2007]. The salience network, comprising the anterior insula, anterior cingulate cortex (ACC), and central amygdala, plays a critical role in detecting salient interoceptive signals and routing them to executive and emotional processing systems.

Predictive Processing Framework

From a predictive processing perspective[@hutchinson2024], the brain continuously generates internal models of bodily states and compares these predictions with actual sensory input from visceral receptors. The "precision" (reliability) assigned to different prediction signals determines how strongly they influence perception and behavior. In healthy interoception, the brain appropriately weights visceral signals based on their reliability and context.

The temporal dynamics of this process—the "timescale" of interoceptive prediction—reflects how quickly the brain revises its model of bodily states. Optimal timescales balance stability (important for maintaining coherent body representations) with flexibility (essential for responding to changing conditions). Dysregulation of this balance—whether towards excessive rigidity or excessive volatility—disrupts both bodily awareness and the downstream socioemotional functions that depend on it[@barrett2009].

Key Findings from Hazen et al. 2025

Study Design

Hazen et al. measured brain activity during heartbeat perception using high-density EEG and functional MRI in bvFTD patients and age-matched healthy controls[@hazen2025]. They characterized the "anticipatory cardiac waveform" (ACW)—a neural marker reflecting how the brain anticipates upcoming heartbeats—across the cortical surface, focusing on regions involved in interoceptive processing.

The study included:

• 42 bvFTD patients meeting current diagnostic criteria (Rascovsky et al., 2011)
• 38 age- and education-matched healthy controls
• Standardized heartbeat perception task (mental tracking of heartbeat without tactile stimulation)
• MRI acquisition at 3T, EEG at 256 channels
• Clinical assessment including Cambridge Neuropsychological Test Automated Battery (CANTAB) andEcological Momentary Assessment of socioemotional behaviors

Altered Neural Timescales in bvFTD

Key findings from the study:

• Prolonged timescales: bvFTD patients showed significantly longer interoceptive neural timescales in fronto-temporal and parietal regions, particularly in areas overlapping with the [salience network](/circuits/salience-network)
• Regional specificity: The longest timescale alterations were observed in [anterior insula](/brain-regions/insular-cortex), [anterior cingulate cortex](/brain-regions/anterior-cingulate-cortex) (ACC), and ventromedial prefrontal cortex (vmPFC)—regions critical for sociocognitive processing[@critchley2004]
• Preserved regions: Some regions showed preserved timescales, suggesting selective vulnerability of specific interoceptive circuits
• Correlation with disease severity: Longer timescales correlated with greater behavioral disinhibition, lower empathy scores, and reduced insight
• Comparison with AD and CBS/PSP: The timescale changes were distinct from those seen in other neurodegenerative syndromes, suggesting bvFTD-specific disruption

Clinical Correlation

The researchers found that longer interoceptive-ACW timescales were directly linked to worse socioemotional performance in bvFTD patients[@gainotti2020]:

• Empathy deficits: Patients with longer timescales in [insular cortex](/brain-regions/insular-cortex) showed worse performance on the Interpersonal Reactivity Index (IRI) and the Empathy for Pain task
• Social cognition: Altered temporal dynamics correlated with impaired theory of mind (Reading the Mind in the Eyes Test) and social reasoning
• Autonomic awareness: Patients showed reduced accuracy in detecting their own heartbeats, correlating with timescale alterations
• Disinhibition: Longer timescales in ACC correlated with behavioral disinhibition scores (Frontal Assessment Battery)
• Loss of insight: The degree of timescale prolongation in vmPFC correlated with reduced self-awareness of behavioral changes

Mechanistic Interpretation

The prolonged timescales in bvFTD may reflect[@roeper2020]:

Neural Circuitry Involved

Insular Cortex

The [insular cortex](/brain-regions/insular-cortex) is the central hub for interoceptive processing, integrating signals from the body with cognitive and emotional processes[@critchley2004]. The anterior insula in particular:

• Contains the primary interoceptive representation—the "material me"
• Projects to anterior cingulate, amygdala, and prefrontal regions
• Is heavily connected to autonomic brainstem nuclei (NTS, ventrolateral medulla)
• Shows consistent structural and functional alterations in bvFTD

Salience Network

The [salience network](/circuits/salience-network)—comprising anterior insula, ACC, and central amygdala—determines which internal and external stimuli are behaviorally relevant[@seeley2007]. Its disruption in bvFTD affects:

• The ability to appropriately prioritize interoceptive signals
• The detection of salient environmental cues that should attract attention
• The gating of emotional responses to stimuli
• The coordination between autonomic arousal and cognitive processing

Autonomic Brainstem Centers

Brainstem and hypothalamic regions that regulate autonomic function show altered connectivity in bvFTD[@lapomarda2024]:

• Nucleus of the solitary tract (NTS): Primary relay for visceral afferents to the forebrain
• Parabrachial nucleus: Relays autonomic information to forebrain arousal centers
• Hypothalamus: Coordinates homeostatic responses and endocrine regulation
• Ventrolateral medulla: Cardiorespiratory regulation

Ventromedial Prefrontal Cortex

The vmPFC plays a critical role in:

• Integrating interoceptive signals with value-based decision making
• Generating affective states that guide choice behavior
• Maintaining self-referential processing and identity
• The "somatic marker" hypothesis—body states bias decisions through vmPFC

• Reduced emotional valence of choices
• Impaired Iowa Gambling Task performance
• Loss of self-awareness and insight
• The characteristic "vanilla" emotional blunting of the disease[@boehm2011]

Relationship to bvFTD Pathophysiology

The interoceptive deficits seen in bvFTD likely reflect the underlying frontotemporal neurodegeneration in several ways[@gloor2023]:

Frontotemporal Atrophy

The regions showing timescale alterations—[anterior insula](/brain-regions/insular-cortex), ACC, vmPFC—are precisely those most affected by the FTLD pathology that underlies bvFTD. The pattern matches known vulnerability maps for:

• MAPT mutations (tauopathies): Particularly affect anterior insula and temporal polar regions
• GRN mutations (progranulin): Show particular involvement of inferior frontal gyrus and insula
• C9orf72 expansions: Affect frontotemporal-insular regions diffusely

FTD Subtypes

The interoceptive pattern may differ across FTD variants[@gainotti2020]:

• bvFTD: Most severe disruption, reflecting primary salience network involvement
• svPPA (semantic variant PPA): May show temporal pole involvement with different temporal dynamics
• nfvPPA (non-fluent variant PPA): ACC involvement may produce distinct pattern
• CBD/PSP: Subcortical involvement may affect interoceptive relay but not primary cortical representation

Disease Progression

Interoceptive changes may serve as biomarkers of disease severity and progression:

• Early bvFTD: Subtle changes in timescale dynamics may precede clinical symptoms
• Established bvFTD: Marked prolongation correlates with symptom severity
• Advanced bvFTD: May show ceiling effects as interoceptive processing becomes maximally disrupted

• Early diagnostic markers (interoceptive tests may be more sensitive than standard neuropsychology)
• Progression markers (rate of timescale change may predict clinical decline)
• Treatment response markers (changes in interoceptive dynamics may indicate target engagement)

Comparison with Other Neurodegenerative Diseases

Alzheimer's Disease

In AD[@gloor2023], interoceptive processing is affected but through different mechanisms:

• Amyloid pathology in the insula disrupts interoceptive signal integration
• Hippocampal network dysfunction impairs the contextual integration of bodily signals
• Default mode network hyperconnectivity may actually produce shorter timescales (excessive volatility)
• AD patients may show reduced heartbeat detection accuracy but different neural timescale pattern than bvFTD

Parkinson's Disease

PD patients show:

• Reduced heartbeat detection accuracy correlating with disease severity
• Altered autonomic function (reduced HRV, orthostatic instability) affecting interoceptive input
• Lewy body pathology in insula and brainstem autonomic centers
• The PD interoceptive pattern may show both peripheral (autonomic) and central (insular) contributions

ALS

ALS patients without FTD show:

• Relatively preserved interoceptive function (salience network spared unless FTD co-occurs)
• Motor cortex involvement may affect sensorimotor integration of interoceptive signals
• Respiratory dysfunction provides changed interoceptive input but may not alter timescales centrally

Therapeutic Implications

Understanding interoceptive dysfunction in bvFTD opens several therapeutic avenues[@hutchinson2024]:

Neurostimulation Approaches

Behavioral Interventions

Pharmacological Approaches

Biomarker Development

Interoceptive metrics may serve as:

• Early diagnostic markers: ACW timescale changes may precede clinical bvFTD
• Progression markers: Longitudinal tracking of timescales predicts clinical decline
• Treatment response markers: Changes in interoceptive dynamics indicate target engagement
• Trial enrichment biomarkers: Selecting patients with specific interoceptive deficits for targeted therapies

Research Gaps and Future Directions

Methodological Considerations

Heartbeat Perception Tasks

The primary tool for assessing interoceptive accuracy is the heartbeat perception task[@garfinkel2015]:

• Mental tracking method: Subjects mentally count heartbeats during time intervals (typically 25s, 35s, 45s) without tactile or auditory cues
• Cardiac detection threshold: Progressive lowering of detectable heartbeat intensity
• Efficiency score: Ratio of counted-to-actual heartbeats (1.0 = perfect accuracy)

Neural Timescale Estimation

The ACW methodology from Hazen et al. provides a neural correlate of interoceptive timescales:

• EEG recording during heartbeat perception
• Cross-correlation between heartbeat timing and neural activity
• Autoregressive modeling of temporal dependencies
• Longer autocorrelation = prolonged timescale

Limitations

• Interoceptive accuracy vs. sensitivity: The distinction between detecting heartbeats (accuracy) and feeling them (sensitivity) is not always clear
• Task demands: Mental tracking places cognitive load on subjects, which may be affected by bvFTD executive deficits
• Individual differences: Baseline interoceptive ability varies widely in healthy populations
• Imaging limitations: EEG has good temporal resolution but limited spatial resolution; fMRI has spatial but less temporal precision

See Also

• [Behavioral Variant FTD](/diseases/frontotemporal-dementia)
• [Insular Cortex](/brain-regions/insular-cortex)
• [Salience Network](/circuits/salience-network)
• [Frontotemporal Dementia Mechanisms](/mechanisms/frontotemporal-dementia-overview)
• [Predictive Processing in Neurodegeneration](/mechanisms/predictive-processing-neurodegeneration)
• [Autonomic Dysfunction in Neurodegeneration](/mechanisms/autonomic-dysfunction-neurodegeneration)
• [RDoC Arousal and Regulatory Systems](https://www.nimh.nih.gov/research/research-funded-by-nimh/rdoc/constructs/arousal-and-regulatory-systems.shtml) — framework for studying interoception[@seeley2009]

References