The central sulcus is the deep groove running roughly ear-to-ear across the top of each brain hemisphere, separating the frontal lobe from the parietal lobe. It matters because the tissue immediately in front of it controls voluntary movement while the tissue immediately behind it processes touch and bodily sensation, making it the single most important anatomical landmark in the cerebral cortex for both neuroscientists and surgeons. Also known historically as the fissure of Rolando, after the Italian anatomist Luigi Rolando who first described the gyri flanking it, this groove packs an extraordinary amount of functional real estate into what looks, on the brain’s surface, like just another wrinkle.
Where It Sits and What It Looks Like
If you could look down at the top of the brain, the central sulcus runs diagonally from near the midline (where the two hemispheres meet) down and forward toward the lateral fissure on each side. It is present in both hemispheres, and its course is not perfectly straight. Instead, it takes a series of bends, or “knees,” as it descends. These bends are not random; they correspond to specific body regions mapped along the cortex.
One of the most recognizable features is the so-called omega sign, a section of the precentral gyrus (the ridge just in front of the sulcus) that looks like the Greek letter Ω on axial brain scans. The central sulcus has three characteristic bends, and the middle one creates this inverted-omega shape, which corresponds to the hand area of the motor cortex.1PubMed Central. Usefulness of the contralateral Omega sign for the topographic location of lesions in and around the central sulcus Radiologists and neurosurgeons routinely use the omega sign on MRI to quickly locate the hand-motor region before surgery.2PubMed Central. The reliability of identifying the Omega sign using axial T2-weighted magnetic resonance imaging
The name “fissure of Rolando” dates to 1839, when a naming convention honored Luigi Rolando, an anatomist born in Turin in 1773 who spent his career trying to relate brain structure to function.3Journal of Neurosurgery. Luigi Rolando and his pioneering efforts to relate structure to function in the nervous system Rolando observed the precentral and postcentral gyri flanking the groove, and that observation proved prescient: the two ridges turned out to house the brain’s primary motor and primary somatosensory cortices, respectively.4PubMed. The fissure of Rolando
The Body Map Along Its Banks
The cortex lining both walls of the central sulcus is organized as a map of the body, sometimes called the motor and sensory homunculus. Leg and foot representations sit near the top, close to the midline. Moving downward along the sulcus, you pass through the trunk, arm, hand, and face regions, with the tongue and swallowing areas near the bottom. This is not just textbook trivia; the correspondence between sulcal shape and body representation is remarkably tight. Research using functional MRI has shown that each of the central sulcus’s morphological segments houses a distinct set of body-part representations: the quadriceps and toes map onto the uppermost segment, the five fingers array across the middle segment from little finger to thumb, and blink, lip, tongue, and swallowing representations occupy the lower segments.5Cerebral Cortex. Tight Coupling between Morphological Features of the Central Sulcus and Somatomotor Body Representations: A Combined Anatomical and Functional MRI Study
This somatotopic organization even shows up before birth. Studies of preterm infants have confirmed that ankle-related brain activity sits higher on the central sulcus than wrist-related activity, and mouth stimulation lights up regions lower and more lateral, mirroring the adult layout.6Cerebral Cortex. Somatotopic Mapping of the Developing Sensorimotor Cortex in the Preterm Human Brain The map is not entirely fixed at birth, but its broad organization is already in place.
On the sensory side, behind the sulcus, the postcentral gyrus maintains a similarly precise layout. High-resolution imaging has mapped individual finger representations within the somatosensory cortex, showing that the thumb sits most lateral and the little finger most medial, with an orderly progression in between.7Oxford Academic (Cerebral Cortex). Digit Somatotopy within Cortical Areas of the Postcentral Gyrus in Humans This level of detail matters for brain-computer interfaces, where knowing exactly which patch of cortex corresponds to which fingertip can determine whether a device works or not.
A Surprise in the Depths
The central sulcus is not just a passive border between “motor” and “sensory” territories. Recent work using depth electrodes implanted directly into the brain has revealed something unexpected: buried at the bottom of the sulcus, roughly at its midpoint along the lateral face, there is a motor association area that does not fit the classic body map at all. Unlike the neatly organized motor strip on the surface, this deep region activates during many different types of movements and responds to activity from both sides of the body.8bioRxiv. Homunculus Interruptus: A motor association area in the depth of the central sulcus Researchers have described it as an “interruption” of the classic homunculus, a zone that coordinates across body regions rather than controlling any single one. The finding is still being validated, but it suggests the textbook picture of the motor cortex as a tidy body map is oversimplified.
How Handedness Shapes the Sulcus
Your dominant hand leaves a visible mark on the central sulcus. MRI measurements have shown that in right-handed people, the left central sulcus (the hemisphere controlling the right hand) is deeper than the right, and vice versa in left-handers.9PubMed. Asymmetry in the human motor cortex and handedness A deeper sulcus means more cortical surface area tucked into the fold, and tissue analysis has confirmed that the dominant hemisphere also has a larger volume of neuropil, the mesh of dendrites, axons, and synapses that supports neural communication, in the primary motor area. In practical terms, the hemisphere that does more fine motor work physically expands its wiring.
The pattern of asymmetry is not identical in men and women. Studies characterizing sulcal depth profiles have found that males tend to show leftward depth asymmetry in the upper portion of the central sulcus, while females show it closer to the sulcus’s midpoint.10PubMed Central. The central sulcus: an observer-independent characterization of sulcal landmarks and depth asymmetry Why the asymmetry peak shifts location between sexes is not well understood, but the finding reinforces that the central sulcus is not just a fixed anatomical groove; it reflects an individual’s history of brain use and development.
When It First Appears and How It Ages
The central sulcus is one of the earliest grooves to form on the fetal brain. Using high-field MRI on fetal specimens, researchers have tracked its emergence between roughly the 11th and 22nd weeks of gestational age, measuring both its depth and length as markers of early cortical development.11PubMed. Early development of the fetal central sulcus on 7.0T magnetic resonance imaging The fact that the central sulcus appears so early, before most other cortical folds, underscores how fundamental this boundary is to brain organization. The fetal brain essentially lays down its motor-sensory dividing line first and then builds the rest of its folding pattern around it.
At the other end of life, the central sulcus shows measurable age-related changes. Surface area along both walls decreases with age, and the gap between the anterior and posterior walls widens, meaning the sulcus effectively opens up. These changes are not symmetrical: the posterior wall, which houses somatosensory cortex, degrades more rapidly than the anterior (motor) wall.12NeuroImage. Age-related changes in the surface morphology of the central sulcus That posterior-faster-than-anterior decline aligns loosely with the common clinical observation that sensory discrimination can dull with age even when motor strength is relatively preserved, though many other factors contribute to both.
The Evolutionary Story
All primates have a central sulcus, but its shape differs in ways that track with manual dexterity and locomotion. In humans and great apes, the middle portion of the central sulcus is relatively shallow compared to the dorsal and ventral ends, a pattern absent in gibbons and Old World monkeys. This shallowing reflects the enlargement of a structure called the pons pontis frontomesialis (PPFM), a buried fold at the hand-knob area, which is much more pronounced in species with sophisticated hand use.13PubMed Central. Evolution of the Central Sulcus Morphology in Primates
More recent comparative work has found that while all great ape species show a hand knob in roughly the same spot, its exact position along the sulcus and the degree of left-right asymmetry vary between species. Humans appear to be unique in possessing a second, ventral motor knob, which may relate to our fine control of facial and vocal muscles. Interestingly, humans and orangutans exhibit the most complex and similar central sulcus shapes among the great apes, though this resemblance likely reflects different evolutionary pressures since orangutans are arboreal and their hand demands are very different from ours.14PubMed Central. Phylogenetic differences in the morphology and shape of the central sulcus in great apes and humans: implications for the evolution of motor functions
Why Surgeons Obsess Over Finding It
If a tumor, blood vessel malformation, or epileptic focus sits near the central sulcus, the surgeon needs to know exactly where the groove is. Cut into the precentral gyrus and you risk paralysis. Damage the postcentral gyrus and you may leave the patient unable to feel part of their body. This makes precise localization of the central sulcus a critical step in presurgical planning.
Multiple techniques compete for this job. Functional MRI, magnetoencephalography (MEG), and somatosensory-evoked potential dipole localization can all estimate where the central sulcus sits before the patient reaches the operating room. A study comparing these methods against direct intraoperative mapping found that MEG correctly identified the central sulcus in all patients tested, while functional MRI gave the right answer in most but mislocalized the sulcus in about a quarter of cases, placing the primary activation in the postcentral sulcus instead of the precentral gyrus.15PubMed. Sensorimotor cortex localization: comparison of magnetoencephalography, functional MR imaging, and intraoperative cortical mapping Another comparison reported that the mean discrepancy between noninvasive functional imaging methods and direct cortical stimulation ranged from about 6 to 26 millimeters, and that expert judgments based on anatomy alone were less reliable than combining structural and functional imaging.16PubMed. Noninvasive identification of human central sulcus: a comparison of gyral morphology, functional MRI, dipole localization, and direct cortical mapping The upshot for patients: surgeons who use multiple imaging techniques before operating near the central sulcus are more likely to avoid critical tissue.
Clinical Conditions That Involve the Central Sulcus
Because the central sulcus separates motor from sensory cortex, damage anywhere along it tends to produce very specific deficits depending on exactly where the injury lands. A small stroke in the postcentral gyrus at the level of the hand area, for example, can produce a pure sensory deficit affecting the hand and foot without any weakness, a pattern that was historically associated only with deeper brain lesions.17PubMed. Pure sensory stroke caused by a small cortical infarct in the middle cerebral artery territory The tight body-part mapping along the sulcus means a surgeon or neurologist can often predict where a lesion sits just from asking which body part lost function.
Neurodegenerative diseases can also target the central sulcus region selectively. In amyotrophic lateral sclerosis (ALS), grey matter volume reductions are concentrated in the pre- and postcentral gyri on both sides and extend into surrounding premotor and parietal regions.18PubMed Central. Widespread sensorimotor and frontal cortical atrophy in Amyotrophic Lateral Sclerosis This pattern fits with what ALS does clinically: progressive motor neuron loss that starts with weakness and atrophy in the limbs or bulbar muscles.
Epilepsy provides another example. A particular type of structural brain abnormality called bottom-of-sulcus dysplasia, a small area of disordered cortex sitting at the very base of a sulcus, has been recognized as a surgically treatable cause of epilepsy. These lesions can be extremely subtle on standard imaging. One case report described a focal cortical dysplasia at the bottom of a sulcus near the left precentral gyrus that was only spotted on ultrahigh-field (7 Tesla) MRI after conventional scans missed it.19PubMed. Bottom-of-sulcus focal cortical dysplasia presenting as epilepsia partialis continua multimodality characterization including 7T MRI The central sulcus is one of the more common locations for these dysplasias, and identifying them precisely matters because surgical removal can be curative for the patient’s seizures.20PubMed Central. The surgically remediable syndrome of epilepsy associated with bottom-of-sulcus dysplasia
Brain-Computer Interfaces and the Challenge of Reaching the Depths
The central sulcus poses a practical problem for brain-computer interfaces. Most BCI electrodes sit on the brain’s surface or penetrate just the top of a gyrus, which gives them good access to the crowns of the pre- and postcentral gyri. But the representation of fingertips and other distal body parts extends deep into the sulcal walls, well beyond the reach of surface electrodes. Researchers working on sensory restoration have found that stimulating only the gyral surface tends to produce broad, poorly localized sensations, whereas targeting the sulcal walls of the primary somatosensory cortex can evoke highly focal percepts that feel like they come from individual fingertips.21Brain Stimulation. Evoking highly focal percepts in the fingertips through targeted stimulation of sulcal regions of the brain for sensory restoration
This is a significant technical hurdle. Getting electrodes safely into a deep, narrow groove without damaging the motor or sensory cortex on either side requires new device designs and surgical approaches. But the payoff would be substantial: prosthetic hands that let the user feel objects at the fingertips rather than just vaguely sensing that something was touched. The central sulcus, in other words, is not just a landmark neuroscientists study for its own sake. Its depth and geometry directly constrain what today’s neuroprosthetics can and cannot do, and overcoming those constraints is one of the active frontiers in the field.