# Central Sulcus: Location, Function and Motor Map The central sulcus is the deep fold on the dorsolateral surface of the cerebral hemisphere that separates the frontal lobe from the parietal lobe. It divides the primary motor cortex (M1) in the precentral gyrus anterior to it from the primary somatosensory cortex (S1) in the postcentral gyrus posterior to it, and its position defines where the body's motor and sensory maps sit on the cortical surface. This single fold carries more clinical weight than any other sulcus in the mammalian brain. Neurosurgeons use it to orient before resecting tumors near the motor strip. Physiologists use it to explain why a stroke on one side of the brain weakens the opposite side of the body. Comparative anatomists use it to trace how grasping hands and skilled forelimbs evolved. It is also called the central fissure or, in standard anatomical Latin, the sulcus centralis. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Location and Surface Anatomy The central sulcus runs obliquely across the lateral surface of the hemisphere. In humans and other primates, it begins near the superomedial border of the hemisphere and travels downward and forward toward the lateral (Sylvian) fissure. Because it slants forward as it descends, the precentral gyrus is wider at the top and narrower at the bottom, while the postcentral gyrus shows the opposite taper. A frequent point of confusion is whether the central sulcus reaches the lateral fissure. In most human brains it does not. The sulcus typically stops short, leaving a small bridge of cortex, the subcentral gyrus, that connects the precentral and postcentral gyri below. The sulcus also commonly fails to reach the midline at the top, meeting the superior medial surface through a small fold. Both features mean the two gyri are physically continuous at the ends of the sulcus even though they are separated along its length. Anatomists identify the central sulcus by its shape rather than by an arbitrary line. On the superior surface it forms a characteristic hook or bend, sometimes called the genu, and its depth profile varies along its course. These morphological details matter surgically because the exact position drifts between individuals and between hemispheres. The central sulcus is one of the first cortical folds to form in development. Folding begins around the 14th week of gestation, and the central sulcus appears early in that sequence. A longitudinal MRI study of 33 typical infants followed the depth and curvature of the sulcus at 1 and 3 months of age and compared them with young adults [1]. The authors examined four regions of interest along the sulcus, including one centered on the hand knob, and tested whether the timing of morphological change matched the timetable of motor milestones across body parts. This is the kind of evidence that links a gross anatomical fold to the emerging behavior of a developing animal. ### Extent and boundaries The boundaries of the central sulcus are defined by the sulci that run parallel to it. - Anteriorly, the precentral gyrus sits between the central sulcus and the precentral sulcus. - Posteriorly, the postcentral gyrus sits between the central sulcus and the postcentral sulcus. - Inferiorly, the sulcus approaches but usually does not join the lateral fissure. - Superiorly and medially, the precentral and postcentral gyri continue onto the medial surface as the paracentral lobule. The paracentral lobule is the medial continuation of the sensorimotor strip. It wraps over the top of the hemisphere and carries the representations of the foot and the pelvic organs, which is why a lesion near the midline can produce leg weakness that spares the face and hand. ## The Precentral and Postcentral Gyri The central sulcus matters because of what sits on either side of it. Two functional strips run parallel to the sulcus, and each has a distinct job. ### Precentral gyrus and primary motor cortex The precentral gyrus contains the primary motor cortex, abbreviated M1, which corresponds to Brodmann area 4. Electrical stimulation here produces movement on the opposite side of the body. The cortex is organized topographically: different body parts occupy reproducible positions along the dorsal to ventral axis of the gyrus. The cell architecture of M1 explains its function. Layer V contains the giant Betz cells, some of the largest neurons in the mammalian brain, whose axons travel down the corticospinal tract to reach spinal motor neurons. Damage to this strip weakens or paralyzes the corresponding body part on the contralateral side. Clinical work continues to refine the map. Intraoperative electrical stimulation with laryngeal electromyography in 36 neurosurgical patients showed that the laryngeal motor cortex sits predominantly in a mid precentral gyrus region, dorsal to the face representation and near the representation of the hand [2]. Preserving that patch protects the voice. ### Postcentral gyrus and primary somatosensory cortex The postcentral gyrus holds the primary somatosensory cortex, S1, which corresponds to Brodmann areas 3, 1, and 2. This is where touch, pressure, vibration, and joint position signals from the body arrive after relaying through the thalamus. Like M1, S1 is topographic, and its map roughly mirrors the motor map on the other side of the sulcus. The deepest part of the sulcus itself contains area 3a, a strip of cortex that processes proprioceptive input from muscle spindles. Researchers have implanted custom microelectrode arrays into area 3a at the bottom of the central sulcus in rhesus macaques as part of a brain-machine interface designed to restore a sense of limb position [3]. The surgical target is precisely the floor of the sulcus, which shows how functionally important the deep wall is. ### Why the two strips sit back to back The arrangement is efficient. Motor commands leave from the anterior bank, sensory feedback arrives at the posterior bank, and short connections link the two. The central sulcus is therefore a functional seam between output and input, not a barrier. ## The Motor Map and the Hand Knob The motor map, often called the homunculus, is a distorted representation of the body laid out along the precentral gyrus. Body parts that require fine control, such as the hand, lips, and tongue, occupy disproportionately large patches of cortex. The trunk and leg occupy smaller patches. The map is organized from medial to lateral. Foot and leg representations lie superiorly, near the midline and over onto the paracentral lobule. Hand and arm lie in the middle of the gyrus. Face, lips, tongue, and larynx lie inferiorly, near the lateral fissure. ### The hand knob The most recognizable landmark within the map is the hand knob, a small outward bulge or bend of the precentral gyrus that corresponds to the hand motor area. It is visible on MRI and is used to identify the sensorimotor region quickly in clinical imaging. A comparative MRI study of humans, chimpanzees, gorillas, and orangutans found that all these species show similar variation in the position of the hand knob along the dorsal to ventral axis, but the prevalence of a given knob position and the degree of left-right lateralization differ between species [4]. Humans and orangutans had the most similar and complex sulcal shapes. The authors also reported that a second ventral motor knob appears to be unique to humans, a difference they linked to divergent evolutionary pressures on hand use and locomotion rather than to a single shared lineage [4]. The hand knob also anchors the study of precentral gyrus shape in chimpanzees. In 278 MRI scans, researchers described six main variants of precentral gyrus shape and tested them against intentional communication. Vocal attention-getting sounds, but not manual gestures, were associated with the inferior precentral gyrus shape in the left hemisphere [5]. That finding does not mean the central sulcus drives vocal behavior. It shows that a nearby sulcal boundary helps define a cortical territory whose shape tracks a behavioral trait. ## Table: Nearby Sulci and Gyri | Structure | Position relative to central sulcus | Main function | |--|--|--| | Precentral sulcus | Anterior | Forms the anterior border of the precentral gyrus | | Precentral gyrus | Immediately anterior | Primary motor cortex (M1, area 4) | | Central sulcus | Reference fold | Separates frontal and parietal lobes; divides M1 from S1 | | Postcentral gyrus | Immediately posterior | Primary somatosensory cortex (S1, areas 3, 1, 2) | | Postcentral sulcus | Posterior | Forms the posterior border of the postcentral gyrus | | Paracentral lobule | Superomedial continuation | Foot and pelvic representations of M1 and S1 | | Pli de passage (bridges) | Cross the sulcus floor | Connect precentral and postcentral gyri; relate to the somato-cognitive action network | The plis de passage deserve a note. These are small gyri that bridge the precentral and postcentral gyri across the floor of the central sulcus. Microdissection of 16 human hemispheres identified a consistent chain of three such bridges with increased underlying white matter [6]. Functional MRI connectivity across 9,000 resting-state scans linked these sites to the somato-cognitive action network, a set of nodes that coordinate movement with arousal and cognitive state. Intraoperative stimulation during central sulcus surgery identified inter-effector regions at the same locations [6]. One bridge, the pli de passage fronto-pariétal moyen, is a near-universal fold in adults positioned at the level of the hand sensorimotor area [7]. These bridges help explain why stimulating the sulcus floor can produce movements that do not fit the classic single-body-part map. ## Mapping the Central Sulcus in Practice Clinicians and researchers locate the central sulcus in several ways. Each method exploits the fact that the cortex on either side of the fold has different functional properties. Somatosensory evoked potentials recorded from the cortical surface show a phase reversal across the sulcus. Sensory signals arrive at the postcentral gyrus first and are recorded as an upward deflection posterior to the sulcus, while the precentral side shows the opposite polarity. This phase reversal has long been the standard intraoperative method for locating the sulcus during surgery. A recent report used four 1,024-channel micro-electrocorticography arrays, 4,096 electrodes total, deployed around a parafalcine meningioma resection to sample the sensorimotor cortex densely, achieving a 91.3% channel yield [8]. The goal was to test whether a dense array could give a finer two-dimensional picture of the sensorimotor boundary than conventional strips. Non-invasive mapping can achieve similar localization. An ultra-high-density EEG system with 256 channels and an 8.6 mm inter-electrode distance used somatosensory evoked potentials and unsupervised clustering to classify individual channels as anterior or posterior to the central sulcus with 95.2% accuracy, comparable to invasive recordings [9]. Navigated transcranial magnetic stimulation has also been used to probe subdivisions of the precentral gyrus at the hand knob by delivering pulses in strips parallel to the sulcus and measuring electromyographic responses [10]. In that study, mean amplitudes were higher in the "M1 proper" strip, though the differences did not reach [statistical significance](/blog/guides/statistical-significance) in the mixed-effects model [10]. Electrocorticography during awake craniotomy adds another layer. In patients with gliomas affecting the motor cortex, finger movement areas were more dispersed and overlapped than in unaffected motor cortex, often clustering near the central sulcus and the lateral fissure [11]. This matters because a tumor can distort the functional map before surgery ever begins. ## Comparative Anatomy Across Species The central sulcus is not a universal feature of mammalian brains. Its presence, depth, and clarity vary widely, and that variation tracks the complexity of skilled limb control in each group. ### Primates The sulcus is well defined in anthropoid primates. It divides primary motor and somatosensory cortex in these species, just as it does in humans [4]. Human and great ape brains differ in the surface area and depth of the sulcus along the dorsal to ventral axis, and the hand region shows the most striking differences [4]. This is the structural signature of a lineage that evolved fine manual dexterity. ### Carnivores In dogs and cats, the cortical surface is folded, but the central sulcus is less distinct than in primates. The sensorimotor strip is present and functional, yet the sharp separation between a precentral and postcentral gyrus that a primate brain shows is muted. The boundary is a useful reference for orientation, but it does not stand out the way it does on a human MRI. ### Rodents and birds Rodents lack a central sulcus. The rat and mouse cortex is largely smooth, or lissencephalic, and the sensorimotor region sits on a flat surface without a dividing fold. Birds have a completely different forebrain architecture. The pallium of a bird contains motor and sensory territories, and the avian brain supports skilled behaviors, including tool use in corvids, but there is no central sulcus and no layered six-layer cortex in the mammalian sense. Any claim that a bird has a central sulcus is wrong. ### What the comparative pattern means The central sulcus is a fold, not a module. Its presence reflects the expansion and folding of sensorimotor cortex in a lineage, not the presence or absence of motor function. A rodent moves its limbs with a perfectly serviceable motor cortex. A bird pecks with precision using pallial circuits that never form a central sulcus. The fold is a structural landmark that helps humans and other primates organize a large cortical sheet, and its shape carries information about how that sheet evolved. ## Clinical Relevance, Limitations and Common Mistakes This section covers how clinicians use the central sulcus and where errors creep in. The central sulcus is a surgical landmark as much as an anatomical one. Preserving the precentral gyrus protects voluntary movement, and preserving the postcentral gyrus protects sensation. A 3.1 cm metastasis in the parasagittal paracentral region, straddling both primary motor and sensory cortex, was treated with five-fraction stereotactic radiosurgery rather than open resection, and the tumor showed a partial response sustained for 15.2 months, though the patient later developed adverse radiation effects that responded to medical management [12]. The choice of radiosurgery over resection reflected the difficulty of removing tissue that involves both banks of the sulcus. Structural integrity of the precentral gyrus predicts how well a brain-computer interface will work. In six people with late-stage amyotrophic lateral sclerosis, four showed more than 0.4 mm of grey matter thinning in the precentral gyrus while the postcentral gyrus was spared, and electrocorticography signal quality correlated with precentral thickness but not with functional MRI activity [13]. The practical implication is that presurgical imaging of precentral grey matter may help select candidates for implanted interfaces. Lesion studies in macaques add nuance to the motor map. After ischemic lesions of different cortical areas and electrocoagulation of the magnocellular red nucleus, reaching speed dropped most and recovered least when damage hit the posterior part of M1 on the gyrus surface, while trajectory variability was more affected by damage within the central sulcus itself and partially recovered [14]. The old idea of one uniform motor strip does not hold up. Different subdivisions of the sensorimotor region contribute different features of movement. The functional map is also not static. Brain-machine interface work aimed at restoring proprioception targets area 3a in the sulcus floor, using custom variable-length microwire arrays implanted along a trajectory planned from high-resolution MRI and CT to reach the base of the sulcus by the shortest perpendicular path [3]. The fact that the target sits at the bottom of the fold, not on the surface, is a reminder that the sulcus wall is functional tissue. Several mistakes recur. The first is treating the central sulcus as a complete divider. The precentral and postcentral gyri connect through the subcentral gyrus and through plis de passage, so function can cross the fold. The second is assuming the map is fixed. Tumors distort it, lesions shift the balance between subdivisions, and individual variation in the hand knob position is real [4][11]. The third is applying a human or primate motor map directly to a dog, cat, or rodent. The general topographic principle holds, but the sharp precentral and postcentral separation does not. The fourth is confusing the central sulcus with the lateral fissure or the precentral sulcus. The central sulcus runs obliquely from superomedial to inferolateral and typically stops short of the lateral fissure, which is the key discriminator on imaging. Structural connectivity at the sulcus also has behavioral relevance beyond movement. In 88 patients with mild cognitive impairment and subsyndromal depression, carriers of the APOE ε4 allele showed reduced functional connectivity between the ventral hippocampus and the left postcentral gyrus in a gene dose-dependent pattern, and this connectivity mediated the link between depressive symptoms and cognitive function [15]. The postcentral gyrus is not only a sensory waypoint. It participates in wider networks. The central sulcus also appears on a short list of alternative targets for speech brain-computer interfaces. A brain-wide intracranial EEG study of 30 participants found significant speech detection accuracy in both gray and white matter, with no significant difference between gyri and sulci, and identified the (sub)central sulcus as one potential target alongside the transverse temporal gyrus, supramarginal cortex, and parts of the insula [16]. Speech prostheses have focused on motor cortex, and this work suggests that the sulcal depth may hold useful signal too. These findings are still developing. Individual anatomy, disease state, and technique all affect how well any mapping method works. Any clinical decision about a specific animal or patient requires a veterinarian or physician who can interpret imaging and examination together. ## Frequently Asked Questions ### What is the central sulcus? It is the fold on the lateral surface of the cerebral hemisphere that separates the frontal and parietal lobes. The primary motor cortex lies in front of it and the primary somatosensory cortex lies behind it. ### Is the central sulcus the same as the central fissure? Yes. Central fissure is an older synonym for the same structure. The standard Latin term is sulcus centralis. ### Does the central sulcus reach the lateral fissure? Usually not. It typically stops short, leaving a small bridge of cortex called the subcentral gyrus that connects the precentral and postcentral gyri. ### What is the hand knob? It is a small bulge or bend in the precentral gyrus that marks the hand motor area. It is visible on MRI and is used to locate the sensorimotor region. ### Do dogs and cats have a central sulcus? They have folded cortex with a sensorimotor region, but the central sulcus is far less distinct than in primates. The boundary between precentral and postcentral cortex is not as sharply defined. ### Do rodents have a central sulcus? No. The rodent cortex is largely smooth and lacks the fold. The sensorimotor area is present but sits on a flat surface. ### What happens if the central sulcus area is damaged? Damage to the precentral gyrus weakens or paralyzes the opposite side of the body. Damage to the postcentral gyrus impairs sensation on the opposite side. Specific effects depend on which part of the strip is involved. ### How do surgeons find the central sulcus during an operation? They record somatosensory evoked potentials from the cortical surface and look for a phase reversal across the fold, or they use high-density electrode arrays and imaging to map the boundary. ## Related Articles - [RNA Location: Types, Functions, and Cellular Distribution](/knowledge/molecular-biology/rna-location) - [Z-DNA Found in Biology: Location, Function, and Detection](/knowledge/molecular-biology/z-dna-found) - [Prokaryotic DNA: Location, Structure, and Function](/knowledge/diagnostics/molecular/prokaryotic-dna-location-structure-and-function) - [Bioinformatics Salary by Location](/blog/careers/bioinformatics-salary-by-location-cost-of-living-adjusted-pay-in-major-us-and-global-hubs) - [Nucleotide to Protein: The Central Dogma Explained](/knowledge/molecular-biology/nucleotide-protein) - [Feline Neuromuscular Physiology: Reflexes and Motor Control](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/feline-neuromuscular-physiology-reflexes-motor-control) - [Central Fovea (Fovea Centralis): Structure and Function](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/central-fovea-fovea-centralis-structure-and-function) - [Lateral Sulcus (Sylvian Fissure): Anatomy and Borders](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/lateral-sulcus-sylvian-fissure-anatomy-and-borders) - [MAP and TAU in Bayesian Statistics](/blog/research-skills/map-and-tau-in-bayesian-statistics) ## Sources 1. 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