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The pars opercularis refers to the vertically oriented fold of the inferior frontal gyrus in the frontal lobe of the brain. It is the most caudal of the three cortical segments that form the inferior frontal gyrus along with the pars triangularis and the pars orbitalis in a caudorostral direction. It is most commonly affiliated with Broca’s area when paired with the pars triangularis which plays a significant role in the production of speech 4-7.
The pars opercularis is delimited rostrally by the ascending ramus of the lateral sulcus separating it from the pars triangularis. It is delimited caudally by the inferior precentral sulcus separating it from the precentral gyrus. The inferior frontal sulcus which originates close to the inferior precentral sulcus makes up the dorsal boundary of the pars opercularis delineating it from the middle frontal gyrus 4-7.
It is supplied by the frontal branches of the middle cerebral artery.
An additional sulcus called the diagonal sulcus which subdivides the pars opercularis into rostral and caudal segments may be identified in some brains. It may be distinguishable as a separate sulcus or blend with any of the surrounding sulci depending on the variable curvature of the pars opercularis and how much of it remains on the surface of the brain. A variable extent of the caudal segment submerges into the inferior precentral sulcus 4,5.
Radiographically the pars opercularis can be identified as the most caudal vertically oriented portion of the inferior frontal gyrus which takes on a characteristic “M” configuration. This is also referred to as the M sign when identifying the inferior frontal gyrus3.
The pars opercularis corresponds to the area of cortex that is associated with Brodmann’s area 44 in the dominant hemisphere. Traditionally, together with Brodmann’s area 45 (a.k.a. pars triangularis), it is considered to constitute the classical Broca’s area. There is no clear functional segregation between areas 44 and 45. Broca’s area is well documented in its involvement in aspects of language and comprehension. Brodmann’s area 44 has also demonstrated some motor functions due to its interactions with neighboring premotor areas. The same cortical region in the non-dominant hemisphere is involved in non-verbal communication such as gesticulation, facial expression and modulation of timing and intonation of speech 1,2,7.
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- 2. Tomaiuolo F, MacDonald JD, Caramanos Z, Posner G, Chiavaras M, Evans AC, Petrides M. Morphology, morphometry and probability mapping of the pars opercularis of the inferior frontal gyrus: an in vivo MRI analysis. The European journal of neuroscience. 11 (9): 3033-46. Pubmed
- 3. M. Wagner, A. Jurcoane, E. Hattingen. The U Sign: Tenth Landmark to the Central Region on Brain Surface Reformatted MR Imaging. American Journal of Neuroradiology. 34 (2): 323. doi:10.3174/ajnr.A3205 - Pubmed
- 4. Michael Petrides. Neuroanatomy of Language Regions of the Human Brain.(2014) ISBN: 9780124059313
- 5. Juergen K. Mai, George Paxinos. The Human Nervous System.(2012) ISBN: 9780080921303
- 6. Stephan Ulmer, Olav Jansen. fMRI. ISBN: 9783642343421
- 7. Paul Johns. Clinical Neuroscience. ISBN: 9780443103216