Short communicationInferior central sulcus: variations of anatomy and function on the example of the motor tongue area
Introduction
The primary somatomotor and somatosensory cortices of the brain form a pericentral region composed of the precentral gyrus (preCG), postcentral gyrus (postCG), subcentral gyrus (subCG) and paracentral lobule, arrayed around the central sulcus (CS) (Yousry, 1998). Classically, the CS is divided into three genua (knees) Broca, 1878, Déjérine, 1895, Yousry, 1998. The superior genu lies along the medial segment of the central sulcus, and has its convexity directed anteriorly. The middle genu lies lateral to the superior genu, has its convexity directed posteriorly, and corresponds to the motor hand knob Yousry, 1998, Yousry et al., 1997. The inferior genu of the CS is the next curve found along the lateral surface, and has its convexity directed anteriorly. The segment of the CS situated inferolateral to the inferior genu has been stated to be nearly straight and devoid of curves (Sastre Janer et al., 1998), but its precise course has not yet been analyzed in detail.
Functionally, the primary motor and primary somatosensory areas exhibit somatotopic organization, which is classically summarized as the motor and sensory homunculi Boling et al., 2002, Foerster, 1936a, Foerster, 1936b; Penfield and Rasmussen, 1950). Recent work using electrical microstimulation of primary motor and premotor cortex in monkeys (Graziano et al., 2002) however indicates that these regions have a further, more complex organization that directs muscle groups to assume complex body postures, and that the motor homunculus is actually a map of the positions in space at which movements terminate, not a map of which body part is moved.
The locations of the somatotopic regions have been well demonstrated with respect to each other (relative position), but poorly defined in absolute position. Thus far, only the hand motor area has been shown to map to a characteristic protuberance of the posterior face of the precentral gyrus (the motor hand knob at the middle genu of the CS) (Yousry et al., 1997). The motor tongue area (MTA) is known to lie close to the sylvian fissure, but cortical mapping studies have shown that the MTA may be situated either near to Corfield et al., 1999, Woolsey et al., 1979 or up to 4 cm superior to (Urasaki et al., 1994) the sylvian fissure.
This study was undertaken to evaluate the topography of the inferior portion of the CS in greater detail, to evaluate the position of the MTA on fMRI, and to correlate the two to determine whether any specific anatomic feature along the CS could serve as a surrogate landmark for the MTA.
Section snippets
(1) study material
This study was conducted in accordance with the Declaration of Helsinki. All subjects who participated in this study gave written informed consent prior to the beginning of the study.
The anatomy of the central sulcus was evaluated in 24 healthy subjects (12 men and 12 women ranging in age from 24 to 36 years, mean age: 28 years). The site(s) of the motor tongue area was evaluated by fMRI in 11 healthy right-handed subjects (five men and six women ranging in age from 24 to 30 years, mean age: 27
(1) anatomy
The middle genu was present in all 48 hemispheres, and corresponded to the motor hand knob in each case (100%). The inferior genu was also present in all 48 hemispheres (100%). The contour of the CS inferolateral to the inferior genu was straight with no additional curves in 1 (2%) of the hemispheres examined, exhibited two additional curves in 33 (69%), three curves in 3 (6%), and four curves in 11 (23% hemispheres). Because the literature provides names for only the three genua of the CS,
Anatomy
Classically, the CS is divided into three curves or genua Broca, 1878, Cunningham, 1892, Déjérine, 1895, Déjérine, 1895, Sastre Janer et al., 1998, Testut, 1911, Yousry, 1998, Yousry et al., 1997. Of these, the middle (posterior convex) and the inferior (anterior convex) genua are constant Cunningham, 1892, Eberstaller, 1890, Horsley, 1887, Yousry, 1998. The superior (anterior convex) genu (Yousry, 1998) is less constant, probably accounting for those studies that report the existence of only
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