claustrum

Claustrum

Introduction

Claustrum 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

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Claustrum

Introduction

Claustrum 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 claustrum is a thin, irregular sheet of gray matter situated deep within each cerebral hemisphere, positioned between the [insular](/brain-regions/insula) cortex laterally and the putamen medially. Despite being one of the most enigmatic structures in the mammalian brain, the claustrum is now recognized as the most densely interconnected structure in the [cerebral cortex](/brain-regions/cerebral-cortex), forming reciprocal connections with virtually all cortical areas ([Crick & Koch, 2005](https://pubmed.ncbi.nlm.nih.gov/15976020/)). This extraordinary connectivity has positioned the claustrum at the center of theories about [consciousness](/mechanisms/consciousness), multisensory integration, salience processing, and [attention](/mechanisms/attention-networks)al control. [@edelstein2004]
[@crick2005] [@mathur2014]

In the context of neurodegenerative disease, the claustrum shows significant pathological involvement in several conditions. In Lewy body dementia and [Parkinson](/diseases/parkinsons-disease)'s disease, the claustrum harbors dense alpha-[synuclein](/proteins/alpha-synuclein) deposits that correlate with the severity of cognitive impairment and [visual](/brain-regions/visual-cortex) hallucinations ([Sener, 1998](https://pubmed.ncbi.nlm.nih.gov/9744801/); [Kalaitzakis et al., 2009](https://pubmed.ncbi.nlm.nih.gov/19523504/)). In [Alzheimer](/diseases/alzheimers)'s disease, [amyloid-beta](/proteins/amyloid-beta) plaques and [tau](/proteins/tau-protein) tangles accumulate in the claustrum, contributing to the network disconnection syndrome that characterizes the disease ([Morys et al., 1996](https://pubmed.ncbi.nlm.nih.gov/8734449/)). [@goll2015]
[@edelstein2004] [@remedios2009]

Anatomy and Structure

Location and Gross Morphology

The claustrum is a narrow, elongated sheet of neurons, approximately 2-3 mm thick in humans, extending vertically from the level of the amygdala inferiorly to near the caudate nucleus superiorly ([Mathur, 2014](https://pubmed.ncbi.nlm.nih.gov/25071457/)). It is bordered by two white matter tracts: [@mathur2014] [@smythies2014]

• External capsule (medially): Separates the claustrum from the putamen and globus pallidus
• Extreme capsule (laterally): Separates the claustrum from the insular cortex [@goll2015]

The claustrum is present in virtually all placental mammals, though its size and complexity vary across species. In humans, it has a volume of approximately 800-900 mm3 per hemisphere, making it substantially larger relative to brain volume than in rodents ([Baizer et al., 2014](https://pubmed.ncbi.nlm.nih.gov/24904308/)). [@allen]
[@remedios2009] [@allena]

Subdivisions

Recent neuroanatomical and functional studies have identified distinct subdivisions of the claustrum: [@smythies2014] [@allenb]

• Dorsal claustrum: Connected primarily with sensorimotor and associative cortical areas. Receives input from and projects to the pre[frontal](/brain-regions/prefrontal-cortex) cortex, cingulate cortex, motor cortex, and somatosensory cortex
• Ventral claustrum: Connected with limbic and [temporal](/brain-regions/temporal-lobe) regions, including the amygdala, hippocampus, entorhinal cortex, and temporal association cortex
• Anterior claustrum: More closely linked to frontal and prefrontal regions; implicated in executive function and attention
• Posterior claustrum: More closely linked to posterior sensory cortices, including visual and auditory areas

This topographic organization suggests that the claustrum maintains a rough spatial map of the cortical mantle, with different claustral zones corresponding to different cortical functional networks ([Torgerson et al., 2015](https://pubmed.ncbi.nlm.nih.gov/25547277/)). [@brainspan]

Cytoarchitecture and Cell Types

The claustrum contains a heterogeneous population of neurons, with recent single-nucleus RNA sequencing studies revealing remarkable cellular diversity:

Principal (Projection) neurons

• Constitute approximately 80-90% of claustral neurons
• Predominantly glutamatergic, similar to deep-layer cortical neurons
• Express the transcription factor Nurr1 (NR4A2), a relatively specific marker for claustral neurons in rodents ([Wang et al., 2017](https://pubmed.ncbi.nlm.nih.gov/28423041/))
• Nine morphological subtypes have been identified in primates, each preferentially innervating distinct cortical targets ([Chen et al., 2025](https://doi.org/10.1016/j.cell.2025.03.009))
• Show highly ordered spatial organization along the medial-lateral and dorsal-ventral axes, corresponding to different functional modules

Interneurons

• Comprise approximately 10-20% of claustral neurons
• Include parvalbumin-positive (PV+) fast-spiking interneurons, somatostatin-positive (SST+) neurons, and vasoactive intestinal peptide-positive (VIP+) neurons
• Form local inhibitory circuits that may sharpen claustral output and contribute to gain control

Glial Cells

• astrocytes/cell-types/astrocytes) and [oligodendrocytes are present in typical proportions
• microglia. Human connectome data reveal that the claustrum is functionally connected with:
• prefrontal cortex: Extensive bidirectional connections, particularly with the anterior cingulate cortex and dorsolateral prefrontal cortex
• Insular cortex: The most prominent connection; the claustrum-insula circuit is a key component of the salience network
• Sensorimotor cortex: Connections with motor cortex and somatosensory areas
• Visual cortex: Connections with primary and association visual areas in the occipital lobe
• Auditory cortex: Connections with the temporal lobe auditory regions
• Parietal lobe: Connections with multimodal association areas

A disynaptic circuit linking the insular cortex, claustrum, and anterior cingulate cortex has been proposed as the core architecture of the Salience Network, which identifies behaviorally relevant stimuli and coordinates brain-wide responses ([Remedios et al., 2014](https://pubmed.ncbi.nlm.nih.gov/24523541/)).

Subcortical Connections

Beyond its cortical connections, the claustrum has important subcortical projections:

• thalamus: Reciprocal connections, particularly with the mediodorsal and pulvinar nuclei
• amygdala: Bidirectional connections involved in emotional processing
• hippocampus: Connections that may support memory-guided attention
• basal ganglia: Indirect connections via cortical relay, plus direct projections to the striatum

Proposed Functions

Consciousness and Awareness

Francis Crick and Christof Koch proposed in 2005 that the claustrum serves as the "conductor of the orchestra of consciousness," integrating information from diverse cortical areas into a unified conscious experience ([Crick & Koch, 2005](https://pubmed.ncbi.nlm.nih.gov/15976020/)). This hypothesis was based on the claustrum's unique all-to-all cortical connectivity. Supporting evidence includes:

• Electrical stimulation of the claustrum in an epilepsy patient produced immediate loss of consciousness, with the patient becoming unresponsive and staring blankly; consciousness returned immediately when stimulation ceased ([Koubeissi et al., 2014](https://pubmed.ncbi.nlm.nih.gov/24986340/))
• Bilateral claustrum lesions in humans are associated with persistent disorders of consciousness
• The claustrum is one of the brain regions most consistently activated during conscious perception in functional imaging studies

However, more recent work suggests the claustrum may function less as a seat of consciousness per se and more as a high-speed router that coordinates the formation of task-relevant cortical networks ([Smith et al., 2020](https://pubmed.ncbi.nlm.nih.gov/32443002/)).

Salience Processing and Attention

Growing evidence supports a primary role for the claustrum in salience-guided attention:

• The claustrum activates preferentially in response to novel, salient, or behaviorally relevant stimuli across multiple sensory modalities ([Remedios et al., 2010](https://pubmed.ncbi.nlm.nih.gov/20656939/))
• Claustral neurons respond more strongly to surprising or unexpected stimuli than to predictable ones
• Optogenetic inhibition of the claustrum in mice impairs the ability to switch attention between modalities ([Atlan et al., 2018](https://pubmed.ncbi.nlm.nih.gov/30404180/))
• The claustrum may function as a "gate" that selects which cortical networks are active based on current task demands

Multisensory Integration

The claustrum's connections with all sensory cortical areas position it ideally for multisensory integration:

• Individual claustral neurons can respond to stimuli in multiple sensory modalities
• Cross-modal binding: The claustrum may help associate visual, auditory, and somatosensory components of complex stimuli into coherent percepts
• Temporal coordination: Claustral projections may synchronize oscillatory activity across distributed cortical areas

Cognitive Control

Recent research implicates the claustrum in top-down cognitive control:

• Sustained attention and vigilance
• Task switching and cognitive flexibility
• Impulse control and response inhibition
• Sleep-wake state transitions ([Narikiyo et al., 2020](https://pubmed.ncbi.nlm.nih.gov/32451482/))

Vulnerability in Neurodegenerative Disease

Lewy Body Dementia and Parkinson's Disease

The claustrum is a major site of alpha-synuclein/proteins/alpha pathology in [synucleinopathies. A systematic neuropathological study by Kalaitzakis et al. (2009) found:

• alpha-synuclein positivity in 100% of Parkinson's Disease dementia (PDD) and dementia with Lewy bodies (DLB) cases examined
• Amyloid-Beta/proteins/amyloid deposits in 58% of PDD cases and 100% of DLB cases
• DLB cases showed significantly greater [alpha-synuclein burden in the claustrum compared to both PDD and PD without dementia
• The severity of claustral alpha correlated with the degree of cognitive impairment and the presence of visual hallucinations

The vulnerability of the claustrum in Lewy body disorders may explain several characteristic clinical features:

• Visual hallucinations: Disruption of claustral integration of visual information with other modalities and with attentional control
• Fluctuating cognition: The claustrum's role in arousal and attentional state switching
• Visuoperceptual deficits: Impaired multisensory binding due to claustral dysfunction

A 2025 study found that reduced CSF amyloid-beta 42 levels correlated specifically with lower gray matter volumes in the insular cortex, striatum, thalamus, and claustrum in DLB patients, suggesting that amyloidopathy promotes atrophy in these key interconnected regions.

Alzheimer's Disease

In Alzheimer's disease, the claustrum develops both amyloid plaques and neurofibrillary tangles:

• Claustral involvement occurs relatively early in the Braak staging of tau] pathology (stages III-IV), as tau pathology spreads from the medial temporal lobe to association cortices and related structures ([Braak & Braak, 1991](https://pubmed.ncbi.nlm.nih.gov/1759558/))
• Neuronal loss in the claustrum correlates with the severity of dementia
• As a highly connected hub, claustral dysfunction may disproportionately impact network communication, contributing to the "disconnection syndrome" observed in AD
• The claustrum is part of the brain's rich-club network of highly interconnected hubs that are preferentially targeted by Amyloid-Beta deposition

Frontotemporal Dementia

In frontotemporal dementia, claustral pathology varies by subtype:

• Behavioral variant FTD: The claustrum, together with the anterior insular cortex and anterior cingulate cortex, forms part of the salience network that is selectively vulnerable in bvFTD. Disruption of this network underlies the characteristic apathy, disinhibition, and loss of empathy ([Seeley et al., 2009](https://pubmed.ncbi.nlm.nih.gov/19208814/))
• TDP-43 proteinopathy: TDP-43 inclusions are found in the claustrum in FTLD-TDP, particularly in cases associated with C9orf72 mutations
• Tau(/proteins/tau pathology: In Pick disease and other FTLD-tau variants, Pick bodies and other tau inclusions are found in claustral neurons

Huntington's Disease

In Huntington's disease, the claustrum shows moderate neuronal loss and huntingtin/proteins/huntingtin) inclusions, though it is less severely affected than the striatum. Its proximity to and connections with the putamen make it secondarily affected by striatal degeneration.

Research Directions

Advanced Connectivity Mapping

Human Connectome Project data and diffusion tensor imaging are providing unprecedented detail about claustral connectivity in health and disease. A 2024 study mapped the functional connectivity of the human claustrum using the full Human Connectome Project database, confirming extensive connections with frontal, insular, cingulate, temporal, and occipital regions ([Nikolenko et al., 2024](https://pubmed.ncbi.nlm.nih.gov/38621443/)).

Single-Cell Transcriptomics

A 2025 study integrated single-nucleus RNA sequencing of 227,750 macaque claustral cells with spatial transcriptomics and retrograde tracing, identifying 48 transcriptome-defined cell types. Excitatory neurons showed highly ordered spatial organization corresponding to functional modules, providing a molecular basis for the claustrum's topographic connectivity ([Chen et al., 2025](https://doi.org/10.1016/j.cell.2025.03.009)).

Claustrum as a Therapeutic Target

Understanding claustral dysfunction in neurodegeneration could inform therapeutic strategies:

• Modulation of claustral activity might improve fluctuating cognition in Lewy body dementia
• Targeting the salience network through claustral circuits could address apathy and disinhibition in frontotemporal dementia
• Claustral biomarkers may improve differential diagnosis between dementia subtypes

Optogenetic and Chemogenetic Studies

Modern circuit manipulation techniques in animal models are revealing the specific contributions of claustral circuits to attention, sensory integration, and sleep-wake regulation ([Narikiyo et al., 2020](https://pubmed.ncbi.nlm.nih.gov/32451482/)), providing potential translational insights for neurodegenerative disease.

External Links

• [Claustrum - Wikipedia](https://en.wikipedia.org/wiki/Claustrum)
• [Allen Human Brain Atlas](https://human.brain-map.org/)
• [Human Connectome Project](https://www.humanconnectome.org/)

Brain Atlas Resources

This section links to atlas resources relevant to this brain region.

• Allen Human Brain Atlas: [Claustrum expression search](https://human.brain-map.org/microarray/search/show?search_term=Claustrum)
• Allen Mouse Brain Atlas: [Claustrum search](https://mouse.brain-map.org/search/index.html?query=Claustrum)
• Allen Cell Type Atlas: [Transcriptomic cell type reference](https://portal.brain-map.org/atlases-and-data/rnaseq)
• BrainSpan Developmental Transcriptome: [Claustrum developmental expression](https://www.brainspan.org/rnaseq/search/index.html?search_term=Claustrum)
• astrocytes) and [oligodendrocytes
• TDP-43
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• Amyloid-Beta Aggregation
• [Tau Pathology](/mechanisms/tau-pathology) [Parkinson's Disease](/diseases/parkinsons-disease-disease)
• [ALS](/diseases/amyotrophic-lateral-sclerosis)
• [Huntington's Disease](/diseases/huntingtons-disease)
• [Frontotemporal Dementia](/disease- [Microglia](/cell-types/microglia)poral-dementia)
• [Microglia](/cell-types/microglia)

Background

The study of Claustrum 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

[Unknown, Crick FC, Koch C. What is the function of the claustrum? (2005) (2005)](https://pubmed.ncbi.nlm.nih.gov/15993783/)

[Unknown, Edelstein LR, Denaro FJ. The claustrum: a historical review (2004) (2004)](https://pubmed.ncbi.nlm.nih.gov/15662860/)

[Unknown, Mathur BN. The claustrum in review (2014) (2014)](https://pubmed.ncbi.nlm.nih.gov/24851164/)

[Goll Y et al., Attention: the claustrum (2015) (2015)](https://pubmed.ncbi.nlm.nih.gov/26062404/)

PMID: 19399608(https://pubmed.ncbi.nlm.nih.gov/19399608/)

[Smythies JR et al., Hypotheses relating to the function of the claustrum (2014) (2014)](https://pubmed.ncbi.nlm.nih.gov/25309616/)

Unknown, [Allen Institute for Brain Science. Allen Human Brain Atlas (n.d.)

Unknown, [Allen Institute for Brain Science. Cell Type Atlas (n.d.)

Unknown, [Allen Institute for Brain Science. Mouse Brain Atlas (n.d.)

Unknown, [BrainSpan Consortium. BrainSpan Atlas Brain Atlas Resources (n.d.)