The lateral sulcus, often referred to as the Sylvian fissure, is a substantial and consistent landmark on the human brain’s surface. This deep groove marks a significant boundary across the cerebral cortex in both hemispheres. Understanding its anatomy is foundational for mapping the brain’s geography and locating major functional areas. It is a complex structural feature fundamental to the organization and functioning of the brain.
Defining the Lateral Sulcus and Its Location
The lateral sulcus is a pronounced cleft that begins near the base of the brain and extends horizontally backward and upward across the side of the cerebral hemisphere. It is also known as the Sylvian fissure. This fissure serves to physically separate the temporal lobe, located below, from the frontal and parietal lobes, which sit superiorly.
The sulcus follows a distinct trajectory, starting near the anterior perforated substance at the base of the brain before dividing into several rami, or branches, on the lateral surface. The most notable is the long posterior ramus, which continues the main course toward the back of the brain, delineating the border between the parietal and temporal lobes. Other smaller branches, such as the anterior horizontal and anterior ascending rami, are found in the frontal lobe region.
This deep fissure is formed during embryonic development. The cortical tissue that overlies the sulcus from the frontal, parietal, and temporal lobes is collectively known as the opercula, a Latin term meaning “lids.” The opercula meet and cover a hidden region of the brain, making the lateral sulcus a covering structure as well as a dividing line.
Cortical Regions and Key Functions
Pulling apart the opercula of the lateral sulcus reveals the insular cortex, a hidden lobe of the cerebrum. The insula is a multifunctional area involved in interoception, the perception of the body’s internal state, including sensations like hunger, pain, and heartbeat. It also plays a significant role in emotional processing, taste perception, and certain aspects of self-awareness and decision-making. The insula synthesizes internal bodily signals with external sensory information to contribute to conscious emotional experience.
The banks of the lateral sulcus are lined with regions functionally significant for communication. The superior temporal gyrus, which forms the lower bank of the sulcus, contains the primary auditory cortex, responsible for processing sound. Language centers are situated immediately around the sulcus, particularly in the dominant hemisphere.
Broca’s area, associated with speech production, is located in the frontal operculum. Wernicke’s area, involved in language comprehension, is found near the posterior end of the sulcus, often in the parietal and superior temporal cortex. The sulcus’s consistent anatomical position is directly linked to the brain’s ability to process and generate language.
A major blood vessel runs within the deep confines of the lateral sulcus. The Middle Cerebral Artery (MCA), one of the brain’s main arteries, travels along the floor of the sulcus, giving off branches that supply a vast territory of the lateral cerebral cortex. The artery’s M1, M2, and M3 segments are housed within the fissure, providing essential blood flow to the surrounding functional areas.
Clinical Importance in Neurology and Surgery
The Middle Cerebral Artery’s course within the lateral sulcus makes this region a frequent site for neurological events, especially ischemic stroke. An occlusion, or blockage, of the MCA is the most common type of ischemic stroke and often results in widespread deficits. Because the MCA supplies the frontal, parietal, and temporal lobes, a stroke in this vessel can cause motor weakness, sensory loss, and visual field problems on the opposite side of the body.
Damage to the MCA branches supplying the perisylvian cortex can specifically lead to aphasia, a disruption in the ability to speak or understand language. If the blockage occurs on the dominant hemisphere, it can impair Broca’s area, causing difficulty with speech articulation, or Wernicke’s area, leading to poor language comprehension. The presence of the artery also makes the sulcus a location for aneurysms, which are bulges in the vessel wall.
For neurosurgeons, the lateral sulcus serves as a reliable anatomical gateway to deeper regions of the brain. Its consistent location provides a roadmap for accessing structures like the insula, basal ganglia, and the MCA itself, often for procedures such as tumor removal or the clipping of aneurysms. Operating through the sulcus, known as a transsylvian approach, allows surgeons to reach these deep targets while minimizing disruption to the overlying functional cortex.