Insular Lobe (Insula)

The Insular lobe (nsula) is located in depth of Sylvian fissure. The cortex of the insula is covered by frontal operculum, parietal operculum and temporal operculum. The insula has five gyri.

MRI of the brain, T1-weighted sagittal view. Level 1. Image 1. 1, Insular gyri (I-V). 2, Cerebellum. 3, Lateral sulcus.

MRI of the brain, T1-weighted sagittal view. Level 1. Image 1.
1, Insular gyri (I-V). 2, Cerebellum. 3, Lateral sulcus.

IRM cérébral, coupe axiale, Pondération T1. Level 1. Image 2. 1, Insular gyri (I-V). 2, Frontal operculum. 3, Lateral ventricle. 4, Lateral sulcus.

IRM cérébral, coupe axiale, Pondération T1. Level 1. Image 2.
1, Insular gyri (I-V). 2, Frontal operculum. 3, Lateral ventricle. 4, Lateral sulcus.

MRI of the brain, T1-weighted coronal view. Level 1 de 1. Image 3. 1, Insula. 2, Frontal operculum. 3, Temporal operculum. 4, Temporal lobe. 5, Superior frontal gyrus.

MRI of the brain, T1-weighted coronal view. Level 1 de 1. Image 3.
1, Insula. 2, Frontal operculum. 3, Temporal operculum. 4, Temporal lobe. 5, Superior frontal gyrus.

MRI of the brain, T1-weighted sagittal view. Level 1. Image 3. 1, Insular gyri (I-V). 2, Occipital lobe . 3, Cerebellum. 4, Globe.

MRI of the brain, T1-weighted sagittal view. Level 1. Image 3.
1, Insular gyri (I-V). 2, Occipital lobe . 3, Cerebellum. 4, Globe.

The Anatomy of the Insula

The insular lobe or insula is one of the least understood regions of the brain(1). It is known as the island of Reil, named after the German physician and anatomist Johann Christian Reil, who first provided a description of the insula(2). 

Since then, the insula has been a neglected part of the brain.

This structure’s limited information is mainly due to its location—deep within the brain’s lateral sulcus(3). Thus, the insula is hard to access. Moreover, the prevalence of separate insular lesions is low.

However, interest in the insula’s function has increased with recent human neuroimaging studies that provided insights into the insula’s physiological and pathological roles(4).

The insular lobe refers to a region of the cortex not visible from the surface view(5). The insular cortex was traditionally described as paralimbic or limbic integration cortex.

As it is fully covered laterally by the opercula of the parietal, frontal, and temporal lobes, the insula is not visible on the brain’s exterior view(6). 

The parietal lobe refers to the brain’s middle part(7). It helps identify objects and understand spatial relationships.

The frontal lobe is the brain’s biggest section, involved in thinking, problem-solving, movement, and memory(8).

The temporal lobe occupies the side of the brain responsible for smell, taste, and sound(9).

Meanwhile, the insular lobe plays a role in pain processing, autonomic control, and taste perception(10).

Directly medial to the insula are the claustrum and extreme capsule(11). The insula’s central sulcus is the most inferior extension of the Rolandic fissure (central sulcus) that separates the frontal and parietal lobes.

The central sulcus refers to the dividing line between the insula’s anterior and posterior sectors(12). Posterior to the central sulcus lies an area of the cortex composed of the two long posterior insular gyri (gyri longus).

Anterior to the central sulcus are shorter gyri (gyri brevis)(13). The anterior gyri converge at the ventral-oriented apex.

The human insula has posterior and anterior sections(14). The posterior regions of the insular lobe receive sensory inputs from the spinal cord and brainstems through the thalamus, in addition to those coming from the other brain lobes. Hence, these regions are involved in somatosensory, vestibular, and motor integration.

Meanwhile, the anterior regions contain reciprocal connections to limbic regions. These include the amygdala, the anterior cingulate cortex, and the dorsolateral prefrontal cortex(15). These regions play a role in integrating autonomic and visceral information into cognitive and emotional functions.

Functions of Insula in Neuropsychiatric Disorders

The insular lobe has been linked to several neuropsychiatric disorders. Neuroimaging research has detected a significant decrease in the insula’s gray matter in patients with major depressive disorder(16).

Functional magnetic resonance imaging (MRI) research also showed a significant increase in insular activity during emotional processing(17). Meanwhile, in patients with major depressive disorders, the insular activity decreased in resting-state paradigms.

Patients with bipolar disorder showed structural and functional abnormalities of the insula(18). Structural neuroimaging research indicated a consistent decrease in the insula’s gray matter in patients with bipolar disorder, including altered developmental trajectories of the insular volume.

Structural and functional deficits in the insular lobe have been associated with anxiety disorders, schizophrenia for disturbed affective processing, and anorexia nervosa for distorted subjective feelings of a person’s body(19).

Moreover, the insula is reportedly involved in multiple sclerosis and Huntington’s disease for impaired processing of facial emotions in individuals with these conditions(20).   

The insular lobe has also been linked to desires, cravings, and addiction(21). Research showed that drug-associated cues may elicit insular activity in individuals with substance abuse(22).

Insular Epilepsy

Insular epilepsy is usually misdiagnosed and undertreated because of its similar features with temporal lobe epilepsy(23). Moreover, the insula is located deep within the brain, making it challenging to get electroencephalography (EEG) from the scalp surface.

The stimulation of the insular lobe includes the following symptoms(24). 

  • A sensory symptom before the seizure happens: often manifested as a sensation of burning heat restricted in the perioral area
  • Consciousness during the seizure
  • An abnormal sensation of retrosternal pain, nausea and vomiting, dyspnea, and abdominal elongation and distension
  • Movement symptoms in the facial or upper limb spasm and rotating head or eyes
  • Paroxysm (sudden attack or spasm) sensations, along with contralateral hands of the discharge side, and extending to the cervix, to grab and scratch

A 2019 study published in Cureus presented a case of insular epilepsy discovered through intracranial electroencephalography (iEEG)(25).

Early identification of insular involvement may limit epilepsy morbidity and prompt action to eliminate further seizure activity(26). 

Thus, the insular lobe is an underestimated brain area. However, its study is essential to understand further and evaluate various neuropsychiatric disorders.

References

  1. Uddin, L. Q., Nomi, J. S., Hébert-Seropian, B., Ghaziri, J., & Boucher, O. (2017). Structure and Function of the Human Insula. Journal of clinical neurophysiology: official publication of the American Electroencephalographic Society, 34(4), 300–306. doi.org/10.1097/WNP.0000000000000377. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6032992/ 
  2. Namkung, H., Kim, S. H., & Sawa, A. (2017). The Insula: An Underestimated Brain Area in Clinical Neuroscience, Psychiatry, and Neurology. Trends in neurosciences, 40(4), 200–207. doi.org/10.1016/j.tins.2017.02.002. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5538352/ 
  3. Uddin, L. (2017). Op Cit.
  4. Ibid. 
  5. Ibid. 
  6. Shura, R. D., Hurley, R. A., & Taber, K. H. (2014). Insular cortex: structural and functional neuroanatomy. The Journal of neuropsychiatry and clinical neurosciences, 26(4), 276–282. doi.org/10.1176/appi.neuropsych.260401. https://pubmed.ncbi.nlm.nih.gov/26037887/ 
  7. Johns Hopkins Medicine. Magnetic Resonance Imaging (MRI) of the Spine and Brain. Retrieved from https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/magnetic-resonance-imaging-mri-of-the-spine-and-brain 
  8. Ibid.
  9. Ibid. 
  10. Ibid. 
  11. Shura, R. D., Hurley, R. A., & Taber, K. H. (2014). Insular cortex: structural and functional neuroanatomy. The Journal of neuropsychiatry and clinical neurosciences, 26(4), 276–282. doi.org/10.1176/appi.neuropsych.260401. https://neuro.psychiatryonline.org/doi/full/10.1176/appi.neuropsych.260401 
  12. Ibid. 
  13. Ibid. 
  14. Namkung, H. (2017). Op Cit.
  15. Ibid.
  16. Ibid.
  17. Ibid.
  18. Ibid.
  19. Ibid.
  20. Ibid.
  21. Vasković, J. (2020, Oct. 29). Insula. Retrieved from https://www.kenhub.com/en/library/anatomy/insula-en 
  22.  Uddin, L. (2017). Op Cit.
  23. Kurukumbi, M., Leiphart, J., & Singer, L. (2019). A Rare Case of Insular Epilepsy: Not To Be Missed in Refractory Epilepsy Patients. Cureus, 11(8), e5434. doi.org/10.7759/cureus.5434. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6701894/#:~:text=Insular%20epilepsy%20is%20a%20rare,misdiagnosed%20and%20undertreated%20%5B1%5D 
  24. Vasković, J. (2020). Op Cit.
  25. Kurukumbi, M. (2019). Op Cit. 
  26. Ibid.
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