Superior frontal gyrus

Superior frontal gyrus

The superior frontal gyrus (SFG) makes up about one-third of the frontal lobe of the human brain. It is bounded laterally by the superior frontal sulcus.

The superior frontal gyrus, like the inferior frontal gyrus and the middle frontal gyrus, is more of a region than a true gyrus.

Lateral penetration of the Superior frontal gyrus (SFG) in the left hemisphere is associated with worsening phonemic verbal fluency and has greater explanatory power than active contact location. This may be explained by lesioning of the lateral SFG-Broca area pathway, which is implicated in language function 1).

Alagapan et al. combined electrocorticography and direct cortical stimulation in three patients implanted with subdural electrodes to assess if superior frontal gyrus is indeed involved in working memory. They found left SFG exhibited task-related modulation of oscillations in the theta and alpha frequency bands specifically during the encoding epoch. Stimulation at the frequency matched to the endogenous oscillations resulted in reduced reaction times in all three participants. The results provide evidence for SFG playing a functional role in working memory and suggest that SFG may coordinate working memory through low-frequency oscillations thus bolstering the feasibility of using intracranial electric stimulation for restoring cognitive function 2).

The supplementary motor area syndrome is a characteristic neurosurgical syndrome that can occur after surgery in the superior frontal gyrus.

The superior frontal gyrus (SFG) is thought to contribute to higher cognitive functions and particularly to working memory (WM), although the nature of its involvement remains a matter of debate. To resolve this issue, methodological tools such as lesion studies are needed to complement the functional imaging approach.

du Boisgueheneuc et al have conducted the first lesion study to investigate the role of the SFG in WM and address the following questions: do lesions of the SFG impair WM and, if so, what is the nature of the WM impairment? To answer these questions, they compared the performance of eight patients with a left prefrontal lesion restricted to the SFG with that of a group of 11 healthy control subjects and two groups of patients with focal brain lesions prefrontal lesions sparing the SFG (n = 5) and right parietal lesions (n = 4)] in a series of WM tasks. The WM tasks (derived from the classical n-back paradigm) allowed us to study the impact of the SFG lesions on domain (verbal, spatial, face) and complexity (1-, 2- and 3-back) processing within WM. As expected, patients with a left SFG lesion exhibited a WM deficit when compared with all control groups, and the impairment increased with the complexity of the tasks. This complexity effect was significantly more marked for the spatial domain. Voxel-to-voxel mapping of each subject’s performance showed that the lateral and posterior portion of the SFG (mostly Brodmann area 8, rostral to the frontal eye field) was the subregion that contributed the most to the WM impairment. These data led us to conclude that (i) the lateral and posterior portion of the left SFG is a key component of the neural network of WM; (ii) the participation of this region in WM is triggered by the highest level of executive processing; (iii) the left SFG is also involved in spatially oriented processing.

The findings support a hybrid model of the anatomical and functional organization of the lateral SFG for WM, according to which this region is involved in higher levels of WM processing (monitoring and manipulation) but remains oriented towards spatial cognition, although the domain specificity is not exclusive and is overridden by an increase in executive demand, regardless of the domain being processed. From a clinical perspective, this study provides new information on the impact of left SFG lesions on cognition that will be of use to neurologists and neurosurgeons 3).

Superior frontal gyrus tumor.

The superior frontal gyrus (SFG) makes up about two thirds of the frontal lobe of the human brain


The role of the superior frontal gyrus (SFG) is not yet clear


The superior frontal gyrus (SFG) plays a functional role in working memory



Askari A, Greif TR, Lam J, Maher AC, Persad CC, Patil PG. Decline of verbal fluency with lateral superior frontal gyrus penetration in subthalamic nucleus deep brain stimulation for Parkinson disease. J Neurosurg. 2022 Jan 28:1-6. doi: 10.3171/2021.11.JNS211528. Epub ahead of print. PMID: 35090137.

Alagapan S, Lustenberger C, Hadar E, Shin HW, Frӧhlich F. Low-frequency direct cortical stimulation of left superior frontal gyrus enhances working memory performance. Neuroimage. 2019 Jan 1;184:697-706. doi: 10.1016/j.neuroimage.2018.09.064. Epub 2018 Sep 27. PubMed PMID: 30268847; PubMed Central PMCID: PMC6240347.

du Boisgueheneuc F, Levy R, Volle E, Seassau M, Duffau H, Kinkingnehun S, Samson Y, Zhang S, Dubois B. Functions of the left superior frontal gyrus in humans: a lesion study. Brain. 2006 Dec;129(Pt 12):3315-28. Epub 2006 Sep 19. PubMed PMID: 16984899.

Inferior frontal gyrus

Inferior frontal gyrus

Broca’s area is located in the inferior frontal gyrus

Its superior border is the inferior frontal sulcus (which divides it from the middle frontal gyrus).

Its inferior border the lateral fissure (which divides it from the superior temporal gyrus), and its posterior border is the inferior precentral sulcus.

Above it is the middle frontal gyrus (the gyrus frontalis medius), behind it the precentral gyrus (the gyrus praecentralis).

The inferior frontal gyrus, like the middle frontal gyrus and the superior frontal gyrus, is more of a region than a true gyrus.

The middle frontal gyrus is usually more sinous than the inferior frontal gyrus (IFG) or superior frontal gyrus (SFG).

The uncinate fasciculus: connects the anterior temporal lobe to the inferior frontal gyrus. Damage can cause language dysfunction.


Pars opercularis

Pars triangularis

Pars orbitalis

The bone flap has been removed and the dura mater has been opened as a flap pediculated towards the greater sphenoid wing previously roungered to improve parasellar visualization. Sylvian fissureInferior frontal gyrusSuperior temporal gyrus and Middle temporal gyrus are exposed. Three pars of parasylvian inferior frontal gyrus must be distinguished: pars orbitalis (pOr) in relation to the orbital roofpars triangularis(pT) the widest area of sylvian fissure (good place for start opening of sylvian fissure); pars opercularis (pOp) where Broca’s Area is located.

Connections and Functions

Briggs et al. identified a callosal fiber bundle connecting the inferior frontal gyri bilaterally was also identified. The IFG is an important region implicated in a variety of tasks including language processing, speech production, motor control, interoceptive awareness, and semantic processing 1).

In 7 of the 14 patients, we identified nine sites where cortical stimulation interfered with syntactic encoding but did not interfere with single-word processing. All nine sites were localized to the inferior frontal gyrus, mostly to the pars triangularis and opercularis. Interference with syntactic encoding took several different forms, including misassignment of arguments to grammatical roles, misassignment of nouns to verb slots, omission of function words and inflectional morphology, and various paragrammatic constructions. The findings suggest that the left inferior frontal gyrus plays an important role in the encoding of syntactic structure during sentence production 2).


Removal of glioma from the dominant side of the inferior frontal gyrus (IFG) is associated with a risk of permanent language dysfunction. While intraoperative cortical and subcortical electrical stimulations can be used for functional language mapping in an effort to reduce the risk of postoperative neurological impairment, the extent of resection is limited by the functional boundaries. Recent reports proposed that a two-stage surgical approach for low-grade glioma in eloquent areas could avoid permanent deficits via the functional plasticity that occurs between the two operations.

In a patient with World Health Organization (WHO) grade II oligoastrocytoma in the left inferior frontal gyrus, in functional plasticity of language occurred in the interval between two consecutive surgeries. Intraoperative electrical stimulations suggested that a language area and related subcortical fiber crossed the pre-central sulcus during tumor progression owing to functional plasticity. In the present case, the authors integrated neurophysiological data into the intraoperative neuronavigation system. They also confirmed the peri-lesional shift of language area and related subcortical fiber on image findings. Consequently, the tumor was sub-totally removed with two separate resections. Permanent language disturbance did not occur, and this favorable outcome was attributed to functional plasticity. The present experience sustains the multistage approach for low-grade gliomas in the language area. A combination of intraoperative electrical stimulations and updated neuronavigation may facilitate the characterization of brain functional plasticity 3).

In an event-related fMRI study of overt speech production, Pützer et al. investigated the relationship between gestural complexity and underlying brain activity within the bilateral inferior frontal gyrus (IFG). They operationalized gestural complexity as the number of active articulatory tiers (glottal, oral, nasal) and the degree of fine-grained temporal coordination between tiers (low, high). Forty-three neurotypical participants produced three types of highly-frequent non-word CV-syllable sequences, which differ systematically in gestural complexity (simple: [‘dadada], intermediate: [‘tatata], complex: [‘nanana]). Comparing blood oxygen level-dependent (BOLD) responses across complexity conditions revealed that syllables with greater gestural complexity elicited increased activation patterns. Moreover, when durational parameters were included as covariates in the analyses, significant effects of articulatory effort were found over and above the effects of complexity. The results suggest that these differences in BOLD-response reflect the differential contribution of articulatory mechanisms that are required to produce phonologically distinct speech sounds4).



Briggs RG, Chakraborty AR, Anderson CD, Abraham CJ, Palejwala AH, Conner AK, Pelargos PE, O’Donoghue DL, Glenn CA, Sughrue ME. Anatomy and white matter connections of the inferior frontal gyrus. Clin Anat. 2019 May;32(4):546-556. doi: 10.1002/ca.23349. Epub 2019 Feb 28. PubMed PMID: 30719769.

Chang EF, Kurteff G, Wilson SM. Selective Interference with Syntactic Encoding during Sentence Production by Direct Electrocortical Stimulation of the Inferior Frontal Gyrus. J Cogn Neurosci. 2018 Mar;30(3):411-420. doi: 10.1162/jocn_a_01215. Epub 2017 Dec 6. PubMed PMID: 29211650; PubMed Central PMCID: PMC5819756.

Saito T, Muragaki Y, Miura I, Tamura M, Maruyama T, Nitta M, Kurisu K, Iseki H, Okada Y. Functional Plasticity of Language Confirmed with Intraoperative Electrical Stimulations and Updated Neuronavigation: Case Report of Low-Grade Glioma of the Left Inferior Frontal Gyrus. Neurol Med Chir (Tokyo). 2014 Feb 28. [Epub ahead of print] PubMed PMID: 24584281.

Pützer M, Moringlane JR, Sikos L, Reith W, Krick CM. fMRI and acoustic analyses reveal neural correlates of gestural complexity and articulatory effort within bilateral inferior frontal gyrus during speech production. Neuropsychologia. 2019 Jun 22;132:107129. doi: 10.1016/j.neuropsychologia.2019.107129. [Epub ahead of print] PubMed PMID: 31238044.

Subcentral gyrus

Subcentral gyrus

The central sulcus joins the Sylvian Fissure in only 2 % of cases .

In 98 % there is a subcentral gyrus.

The precentral gyrus and postcentral gyrus are consistently united inferiorly by the subcentral gyrus (Broca’s inferior frontoparietal pli de passage, or rolandic operculum).


A single axial DWI image – obtained in the anterior commissureposterior commissure plane – was selected from each scan just above the subcentral gyrus such that it included the most inferolateral portion of the central sulcus. These single images were given to 10 readers (neuroradiologists, a neuroradiology fellow and radiology trainees) who marked the central sulcus based on the presence of the ‘invisible cortex sign’. Their accuracy in identifying the central sulcus was compared with that of the principal investigators, who used tri-planar T1 volumetric MRI sequences.

One hundred and eight consecutive patients (55 female, 53 male) were selected, ranging from 18 to 81 years old (mean = 40.5, σ = 18.2). The central sulcus was correctly identified in 95.5% of cases (σ = 3.7%; range 89.4-99.1%).

The ‘invisible cortex sign’ is a highly accurate method of identifying the inferolateral central sulcus on a single axial DWI slice without relying on the more superior aspects of the sulcus 1).

Brain surface reformatted images (Mercator view) map the frontoparietal brain surface in 1 view and provide a synopsis of the most important landmarks. In this view, the U-shaped subcentral gyrus appears as a distinct anatomic structure enclosing the Sylvian end of the central sulcus. The purpose of a study was to add the subcentral gyrus as a new landmark to the central region (U sign) and to compare its frequency and applicability with common landmarks in healthy hemispheres.

Mercator views of 178 hemispheres in 100 patients were generated from 3D MR imaging datasets. The hemispheres were evaluated on Mercator views for the presence or absence of each of the 9 common landmarks and the new U sign identifying the central region.

The landmark U sign was most common (96.6%), followed by the thin postcentral gyrus sign (95.5%). The least common landmark was the Ω-shaped handknob (54.5%). None of the landmarks could be identified in all hemispheres. All landmarks could be identified bilaterally in only 1.3% of patients.

On the Mercator view, the U sign is an applicable and even the most frequent landmark to identify the central region. Considering the variability of the anatomic structures of the brain, including the motor hand area, the synopsis of all 10 landmarks on this surface-reformatting projection is a helpful adjunct to standard MR imaging projections to identify the central region 2).

Subcentral gyrus approach

Maesawa et al. reported on a patient presenting with secondary somatosensory cortex epilepsy with a tumor in the left deep parietal operculum. The patient was a 24-year-old man who suffered daily partial seizures with extremely uncomfortable dysesthesia and/or occasional pain on his right side. MRI revealed a tumor in the medial aspect of the anterior transverse parietal gyrus, surrounding the posterior insular point. Long-term video electroencephalography monitoring with scalp electrodes failed to show relevant changes to seizures. Resection with cortical and subcortical mapping under awake conditions was performed. A negative response to stimulation was observed at the subcentral gyrus during language and somatosensory tasks; thus, the transcortical approach (specifically, a transsubcentral gyral approach) was used through this region. Subcortical stimulation at the medial aspect of the anterior parietal gyrus and the posterior insula around the posterior insular point elicited strong dysesthesia and pain in his right side, similar to manifestation of his seizure. The tumor was completely removed and pathologically diagnosed as pleomorphic xanthoastrocytoma. His epilepsy disappeared without neurological deterioration postoperatively. In this case study, 3 points are clinically significant. First, the clinical manifestation of this case was quite rare, although still representative of secondary somatosensory cortex epilepsy. Second, the location of the lesion made surgical removal challenging, and the transsubcentral gyral approach was useful when intraoperative mapping was performed during awake surgery. Third, intraoperative mapping demonstrated that the patient experienced pain with electrical stimulation around the posterior insular point. Thus, this report demonstrated the safe and effective use of the transsubcentral gyral approach during awake surgery to resect deep parietal opercular lesions, clarified electrophysiological characteristics in the secondary somatosensory cortex area, and achieved successful tumor resection with good control of epilepsy 3).



Su S, Yang N, Gaillard F. Invisible cortex sign: A highly accurate feature to localize the inferolateral central sulcus. J Med Imaging Radiat Oncol. 2019 Aug;63(4):439-445. doi: 10.1111/1754-9485.12875. Epub 2019 Mar 15. PubMed PMID: 30874376.

Wagner M, Jurcoane A, Hattingen E. The U sign: tenth landmark to the central region on brain surface reformatted MR imaging. AJNR Am J Neuroradiol. 2013 Feb;34(2):323-6. doi: 10.3174/ajnr.A3205. Epub 2012 Jul 19. PubMed PMID: 22821920.

Maesawa S, Fujii M, Futamura M, Hayashi Y, Iijima K, Wakabayashi T. A case of secondary somatosensory epilepsy with a left deep parietal opercular lesion: successful tumor resection using a transsubcentral gyral approach during awake surgery. J Neurosurg. 2016 Mar;124(3):791-8. doi: 10.3171/2015.2.JNS142737. Epub 2015 Aug 21. PubMed PMID: 26295917.
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