The parietal lobe is one of the four major divisions of the cerebral cortex. It is situated near the top and rear of the skull, positioned directly behind the frontal lobe and above the temporal lobe. This region is a primary hub for integrating data received from various sensory inputs across the body. Its fundamental role is to take raw sensory signals and organize them into a cohesive, understandable experience of the world. The parietal lobe is thus instrumental in transforming simple sensations into meaningful perception and awareness.
Processing Touch and Physical Sensation
The anterior strip of the parietal lobe, known as the primary somatosensory cortex (S1), is the brain’s main receiving station for all physical sensations. This area is located immediately behind the central sulcus, which separates it from the frontal lobe. It processes incoming signals related to touch, pressure, vibration, temperature, and pain from the entire surface of the body. These sensory inputs travel through the thalamus before reaching S1 for conscious interpretation.
The somatosensory cortex features a unique, distorted representation of the body, often conceptualized as a sensory homunculus. This map shows that the amount of brain tissue dedicated to a specific body part is proportional not to its physical size, but to its sensory sensitivity. Highly sensitive areas like the lips, tongue, and fingertips occupy a disproportionately large area of the cortex. This specialized organization allows for fine-grained discrimination.
Spatial Mapping and Navigation
A separate but related function of the parietal lobe is managing the body’s spatial sense, which allows for smooth interaction with the physical environment. This involves processing proprioception, the unconscious sense of where individual body parts are located in relation to each other. Proprioception is what allows a person to touch their nose with their eyes closed or know the precise bend of their elbow without looking. It constantly provides updates on muscle stretch and joint position to the brain.
The posterior parietal cortex integrates this internal sense of self with external visual and auditory information to create a comprehensive spatial map. This integrated mapping is necessary for complex actions like reaching out to grasp a moving object or accurately judging the distance to a doorway. It allows for visuomotor coordination, which is the ability to guide movements, such as a hand, based on visual input. The parietal lobe is the neural system responsible for everyday navigation and coordinating fine motor skills in three-dimensional space.
Integrating Information for Calculation and Language
The posterior parietal lobe integrates diverse sensory and symbolic information. This area is heavily involved in numerical cognition, particularly the understanding of quantity and the mental manipulation of numbers. The intraparietal sulcus, a groove within the lobe, is considered a core region for representing numerical magnitude and performing arithmetic. The functions are lateralized, with the left parietal lobe playing a larger role in the verbal aspects of mathematics, such as the retrieval of memorized facts like multiplication tables. Conversely, the right parietal lobe often contributes more to the spatial representation of numbers, which is employed in tasks like subtraction and estimation based on a mental number line.
The lobe contributes to language by processing symbolic representations, aiding in reading and understanding the abstract relationships between letters and words. This function is especially concentrated in the angular gyrus of the left hemisphere, which helps translate visual information into a meaningful linguistic form.
What Happens When the Parietal Lobe is Injured
Damage to the parietal lobe can result in specific neurological deficits. One striking consequence of injury, typically to the right parietal lobe, is neglect syndrome, where a person fails to attend to or acknowledge the contralateral side of space. Individuals with neglect might only eat food on the right side of a plate or draw only the right half of an image, acting as if the left side of the world does not exist.
Lesions to the left parietal lobe, particularly involving the angular gyrus, can lead to a collection of symptoms known as Gerstmann’s syndrome. This condition is characterized by acalculia, which is a difficulty with performing mathematical calculations, and agraphia, which is the inability to write despite intact motor function. Patients also experience finger agnosia, the inability to identify or recognize their own fingers, and left-right disorientation.