Insular Cortex

Introduction

Insular Cortex is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

Overview

The insular cortex (also called the insula or insular lobe) is a region of cerebral cortex folded deep within the lateral sulcus (Sylvian fissure) of each cerebral hemisphere, hidden beneath the temporal, frontal, and parietal opercula. The insula is a critical hub for interoception — the sense of the internal physiological state of the body — as well as emotional processing, self-awareness, empathy, taste perception, and autonomic regulation (Craig, 2009https://pubmed.ncbi.nlm.nih.gov/19096369/)). In neurodegenerative diseases, the insular cortex shows striking and disease-specific patterns of vulnerability: it is among the earliest and most severely affected regions in the behavioral variant of Frontotemporal Dementia (bvFTD), and is also significantly impacted in Parkinson's Disease, Alzheimer's Disease, and Lewy Body Dementia (Na et al., 2019https://pubmed.ncbi.nlm.nih.gov/30851095/)). The anterior insular cortex contains a unique class of large projection neurons — von Economo neurons (VENs) — whose selective loss is a hallmark of bvFTD pathology (Kim et al., 2012https://pubmed.ncbi.nlm.nih.gov/21653712/)). [@koren2021] [@gogolla2017]

Anatomy and Organization

Location and Gross Structure

Introduction

Insular Cortex is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

Overview

The insular cortex (also called the insula or insular lobe) is a region of cerebral cortex folded deep within the lateral sulcus (Sylvian fissure) of each cerebral hemisphere, hidden beneath the temporal, frontal, and parietal opercula. The insula is a critical hub for interoception — the sense of the internal physiological state of the body — as well as emotional processing, self-awareness, empathy, taste perception, and autonomic regulation (Craig, 2009https://pubmed.ncbi.nlm.nih.gov/19096369/)). In neurodegenerative diseases, the insular cortex shows striking and disease-specific patterns of vulnerability: it is among the earliest and most severely affected regions in the behavioral variant of Frontotemporal Dementia (bvFTD), and is also significantly impacted in Parkinson's Disease, Alzheimer's Disease, and Lewy Body Dementia (Na et al., 2019https://pubmed.ncbi.nlm.nih.gov/30851095/)). The anterior insular cortex contains a unique class of large projection neurons — von Economo neurons (VENs) — whose selective loss is a hallmark of bvFTD pathology (Kim et al., 2012https://pubmed.ncbi.nlm.nih.gov/21653712/)). [@koren2021] [@gogolla2017]

Anatomy and Organization

Location and Gross Structure

The insular cortex is located deep within the lateral sulcus and can only be visualized by retracting the overlying opercula. It occupies an area of approximately 6–8 cm² in each hemisphere and is bounded by the circular sulcus of the insula (Türe et al., 1999https://pubmed.ncbi.nlm.nih.gov/10196240/)). The central insular sulcus divides the insula into two primary regions: [@gogolla2017] [@uddin2017]

• Anterior insula (AI): Contains 3–5 short insular gyri; predominantly agranular and dysgranular cortex. Extensively connected to limbic structures, the prefrontal cortex, and the amygdala.
• Posterior insula (PI): Contains 2–3 long insular gyri; predominantly granular cortex. Receives somatosensory, vestibular, and visceral afferents.

Cytoarchitecture

The insular cortex shows a progressive cytoarchitectonic transition from posterior to anterior (Mesulam & Mufson, 1982https://pubmed.ncbi.nlm.nih.gov/7174907/)): [@klein2021]

Von Economo Neurons and Fork Cells

The anterior insular cortex and the anterior cingulate cortex contain two specialized neuronal populations found predominantly in great apes and humans: [@aristizbalortiz2023]

• Von Economo neurons (VENs): Large, bipolar, spindle-shaped neurons located in cortical layer V. They have a single apical dendrite and a single basal dendrite, giving them a distinctive elongated morphology. VENs are thought to enable rapid signal transmission across the brain due to their large axon diameter (Allman et al., 2011https://pubmed.ncbi.nlm.nih.gov/21613448/)). Transcriptomic analysis has revealed that VENs are extratelencephalic-projecting excitatory neurons that express unique markers including CTIP2 and FEZF2 (Hodge et al., 2020https://pubmed.ncbi.nlm.nih.gov/32161261/)).
• Fork cells: Irregularly shaped neurons also found in layer V of the fronto-insular cortex, with a forking apical dendrite. They co-localize with VENs and may share similar functions.

Connectivity

Afferent Connections

The insular cortex receives inputs from diverse sources (Mesulam & Mufson, 1982https://pubmed.ncbi.nlm.nih.gov/7174907/)): [@gehrlach2020]

• Thalamic nuclei: Ventral posterior medial nucleus (taste), ventral medial posterior nucleus (visceral sensation), mediodorsal nucleus (cognitive/limbic)
• Amygdala: Especially to the anterior agranular insula; conveys emotional valence
• Primary sensory cortices: Somatosensory, gustatory, olfactory, auditory inputs
• Hypothalamus and brainstem: Visceral and autonomic afferents (vagal, glossopharyngeal)

Efferent Connections

The insula projects broadly to: [@peyron2019]

• Prefrontal cortex (executive control)
• Anterior cingulate cortex (error monitoring, conflict)
• Amygdala (emotional processing)
• Striatum and nucleus accumbens (motivated behavior)
• Hypothalamus and brainstem autonomic nuclei (autonomic regulation)
• Contralateral insula (interhemispheric integration)

Connectivity Diagram

Network Membership

The anterior insula is a critical node in the Salience Network (SN), together with the anterior cingulate cortex, amygdala, and temporal pole (Menon & Uddin, 2010https://pubmed.ncbi.nlm.nih.gov/20393571/)). The Salience Network detects behaviorally relevant stimuli and coordinates switching between the default mode network and the central executive network. Disruption of the Salience Network is a core feature of bvFTD.

Normal Functions

Interoception and Body Awareness

The posterior-to-anterior axis of the insula processes interoceptive information with increasing complexity (Craig, 2009https://pubmed.ncbi.nlm.nih.gov/19096369/)):

• Posterior insula: Primary interoceptive cortex; receives direct visceral sensory signals (heartbeat, respiration, gut sensation, temperature, pain)
• Mid-insula: Integrates interoceptive information with contextual and hedonic features
• Anterior insula: Generates a unified, subjective representation of the body state — the "material me" — contributing to conscious awareness and selfhood

Emotional Processing and Empathy

The anterior insula is activated during the subjective experience of virtually all emotions — disgust, anger, fear, happiness, sadness — and is essential for empathy: the ability to understand another person's emotional state by simulating their internal state (Singer et al., 2004https://pubmed.ncbi.nlm.nih.gov/14985682/)). Lesions of the anterior insula produce profound deficits in emotional awareness, social cognition, and empathy.

Gustatory Processing

The primary gustatory cortex is located in the anterior insula and adjacent frontal operculum. This region processes taste quality, intensity, and palatability.

Autonomic Regulation

The insula exerts top-down control over the autonomic nervous system through projections to the hypothalamus and brainstem. The right anterior insula preferentially controls sympathetic function, while the left anterior insula modulates parasympathetic activity (Oppenheimer et al., 1992https://pubmed.ncbi.nlm.nih.gov/1497900/)).

Vulnerability in Neurodegenerative Disease

Behavioral Variant Frontotemporal Dementia (bvFTD)

The anterior insula is among the earliest and most severely atrophied regions in bvFTD, and its degeneration is considered a neuroanatomical signature of the disease (Seeley et al., 2008https://pubmed.ncbi.nlm.nih.gov/18341643/)). Key findings include:

• Selective VEN loss: In early bvFTD, von Economo neurons are reduced by approximately 69% in the fronto-insular cortex and 74% in the anterior cingulate cortex, far exceeding total neuronal loss in these regions (~18%). This selective targeting of VENs suggests a cell-type-specific vulnerability in bvFTD (Kim et al., 2012https://pubmed.ncbi.nlm.nih.gov/21653712/)).
• Salience Network breakdown: Progressive insular degeneration disrupts the Salience Network, producing the characteristic bvFTD symptoms: loss of empathy, social disinhibition, impaired self-awareness, and aberrant eating behavior.
• Lateralization: Right-predominant insular atrophy correlates with behavioral disinhibition and loss of empathy, while left-predominant atrophy relates more to language difficulties (overlapping with primary progressive aphasia).

Alzheimer's Disease

In Alzheimer's Disease, the insular cortex is affected in the moderate-to-severe stages. Both amyloid plaques and neurofibrillary tangles accumulate in the insula, though less prominently than in the hippocampus and entorhinal cortex (Braak & Braak, 1991https://pubmed.ncbi.nlm.nih.gov/1759558/)). Insular atrophy in AD contributes to:

• Anosognosia (impaired awareness of cognitive deficits)
• Autonomic dysregulation
• Emotional blunting in later stages

Parkinson's Disease and Lewy Body Dementia

In Parkinson's Disease and Lewy Body Dementia, alpha-synuclein Lewy pathology affects the insular cortex. A 2022 study found that axonal degeneration in the anterior insular cortex is associated with Alzheimer's co-pathology (co-occurring amyloid-beta and phosphorylated tau] in addition to alpha in both PD and DLB (Dijkstra et al., 2022https://pubmed.ncbi.nlm.nih.gov/36474289/)). Insular involvement contributes to:

• Autonomic dysfunction (orthostatic hypotension, constipation)
• Impaired interoception and pain processing
• Cognitive decline and dementia

Multiple System Atrophy

In MSA, insular cortex involvement contributes to the severe autonomic failure characteristic of the disease, including cardiovascular, urogenital, and thermoregulatory dysfunction.

Clinical Significance

Insular Cortex as a Biomarker

Structural MRI measurements of insular cortex volume and shape can help differentiate between neurodegenerative diseases. Anterior insular atrophy disproportionate to overall cortical atrophy is a strong indicator of bvFTD over AD (Rabinovici et al., 2007https://pubmed.ncbi.nlm.nih.gov/17898333/)). A systematic review and meta-analysis of differential insular cortex sub-regional atrophy confirmed disease-specific patterns across AD, bvFTD, PD, and semantic dementia (Defined et al., 2019https://pubmed.ncbi.nlm.nih.gov/31218597/)).

Surgical Considerations

The deep location of the insular cortex makes it surgically challenging. Insular gliomas and epileptic foci require specialized approaches, and resection carries risks of hemiparesis, aphasia, and autonomic complications.

External Links

• [Allen Human Brain Atlas](/datasets/allen-human-brain-atlas) — Insula Expression Datahttps://human.brain-map.org/microarray/search/show?search_term=insula
• [Insular cortex](/brain-regions/insular-cortex) — ScienceDirect Topicshttps://www.sciencedirect.com/topics/neuroscience/insular-cortex
• BrainFacts.org — The Insulahttps://www.brainfacts.org/)

Brain Atlas Resources

• Allen Human Brain Atlas: [Insular Cortex expression search](https://human.brain-map.org/microarray/search/show?search_term=Insular+Cortex)
• Allen Mouse Brain Atlas: [Insular Cortex search](https://mouse.brain-map.org/search/index.html?query=Insular+Cortex)
• Allen Cell Type Atlas: [Transcriptomic cell type reference](https://portal.brain-map.org/atlases-and-data/rnaseq)
• BrainSpan Developmental Transcriptome: [Insular Cortex developmental expression](https://www.brainspan.org/rnaseq/search/index.html?search_term=Insular+Cortex)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Amyloid-Beta Aggregation](/proteins/amyloid-beta)
• [Tau Pathology](/mechanisms/tau-pathology)
• [Parkinson's Disease](/genes/ar)
• [ALS](/diseases/amyotrophic-lateral-sclerosis)
• [Frontotemporal Dementia](/diseases/frontotemporal-dementia)
• [Hippocampus](/brain-regions/hippocampus)
• [Cerebral Cortex](/brain-regions/cerebral-cortex)
• [Lewy Body Dementia](/diseases/lewy-body-dementia)
• [Vascular Dementia](/diseases/vascular-dementia)

See Also

• [Alzheimer's Disease](/diseases/alzheimer-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Frontotemporal Dementia](/diseases/frontotemporal-dementia)
• [Lewy Body Dementia](/diseases/lewy-body-disease)
• [Multiple System Atrophy](/diseases/multiple-system-atrophy)
• [Cingulate Cortex](/brain-regions/cingulate-cortex)
• [Hippocampus](/brain-regions/hippocampus)
• [Cerebral Cortex](/brain-regions/cerebral-cortex)

Background

The study of Insular Cortex has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

References

Pathway Diagram

The following diagram shows the key molecular relationships involving Insular Cortex discovered through SciDEX knowledge graph analysis: