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.
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/)). [1]
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: [2]
The insular cortex shows a progressive cytoarchitectonic transition from posterior to anterior (Mesulam & Mufson, 1982https://pubmed.ncbi.nlm.nih.gov/7174907/)):
The anterior insular cortex and the anterior cingulate cortex contain two specialized neuronal populations found predominantly in great apes and humans:
VENs are estimated to number approximately 193,000 in the fronto-insular cortex and 184,000 in the anterior cingulate cortex of the adult human brain (Allman et al., 2011https://pubmed.ncbi.nlm.nih.gov/21613448/)). Their selective loss in specific neurodegenerative diseases has made them a focus of research into selective neuronal vulnerability.
The insular cortex receives inputs from diverse sources (Mesulam & Mufson, 1982https://pubmed.ncbi.nlm.nih.gov/7174907/)):
The insula projects broadly to:
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.
The posterior-to-anterior axis of the insula processes interoceptive information with increasing complexity (Craig, 2009https://pubmed.ncbi.nlm.nih.gov/19096369/)):
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.
The primary gustatory cortex is located in the anterior insula and adjacent frontal operculum. This region processes taste quality, intensity, and palatability.
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/)).
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:
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:
Importantly, VENs are not significantly reduced in AD, distinguishing the pattern of insular degeneration from bvFTD (Seeley et al., 2006https://pubmed.ncbi.nlm.nih.gov/17031018/)).
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:
In MSA, insular cortex involvement contributes to the severe autonomic failure characteristic of the disease, including cardiovascular, urogenital, and thermoregulatory dysfunction.
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/)).
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.
This section links to atlas resources relevant to this brain region.
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.