Parietal lobe

The parietal lobe is one of the four lobes of the cerebral cortex. It is located behind the central sulcus and above the lateral sulcus. Anteriorly, it is separated from the frontal lobe by the central sulcus, and beneath it is separated from the temporal lobe by the lateral sulcus. At the rear end, there is a sulcus called the parieto-occipital sulcus. This sulcus is more visible on the medial surface of the cerebral hemisphere and separates the parietal lobe from the occipital lobe.

The main function of the parietal lobe is sensory processing. It contains two important sulci: the postcentral sulcus and the intraparietal sulcus.

The postcentral sulcus runs parallel to the central sulcus, behind it, and extends downward and forward from the upper edge of the cerebral hemisphere. Together with the central sulcus, it forms the boundaries of the postcentral gyrus. This region is the primary sensory area responsible for perceiving general somatic sensations from the entire body. The postcentral gyrus also extends to the medial surface of the cerebral hemisphere, forming the posterior part of the paracentral lobule (known as the posterior paracentral gyrus). The postcentral gyrus represents our body parts in a sequential manner, known as the sensory homunculus. The face and upper body are represented on the lateral surface, while the legs are represented on the medial surface of the cerebral hemisphere. Consequently, a stroke in the middle cerebral artery would result in sensory loss in the upper limbs, whereas a stroke in the anterior cerebral artery would result in sensory loss in the lower limbs.

Behind the primary sensory area, on the lateral surface of the parietal lobe, lies the intraparietal sulcus. This sulcus is aligned horizontally and divides the parietal lobe into the superior and inferior parietal lobules or gyri. The superior parietal lobule contains the somesthetic unimodal sensory association area. The superior parietal lobule, also known as broadband's area 5 and 7, has extensive connections with other sensory areas in the cortex. Its main function is to receive and integrate sensory information from different modalities. It is also involved in a higher-order association process known as stereognosis. This allows recognition of objects in the hand without visual assistance.

Damage to the left (dominant) side of the superior parietal lobule can result in astereognosis. On the other hand, lesions on the right parietal side typically affect the body's sense of space, leading to a condition called hemineglect syndrome. People with hemineglect syndrome often lack awareness of their left side and the objects in their left visual field.