The parietal lobe sits above the occipital lobe and behind the central sulcus. It does two related jobs: it maps the body, and it maps space. Both are essential for navigating the world.
The primary somatosensory cortex sits just behind the central sulcus. It receives touch, pressure, temperature, and proprioception from the body, organized in a famous map called the homunculus. The body is represented in proportion not to its physical size but to its sensory innervation. The hands and lips are huge in the homunculus; the trunk is small. This reflects the density of sensory innervation: your fingertips can discriminate tiny features, while your back can barely tell whether one or two pencil points are touching it.
Behind the primary somatosensory cortex, the rest of the parietal lobe handles higher-order spatial cognition. It integrates information from vision, touch, and proprioception to build a coherent model of where your body is in space and where objects are relative to you. It guides reaching, grasping, navigation, and attention.
Damage to the parietal lobe produces strikingly specific syndromes. Lesions on the dominant (usually left) parietal cortex can produce Gerstmann syndrome — finger agnosia, left-right disorientation, agraphia, acalculia. Lesions on the non-dominant (usually right) parietal cortex produce hemispatial neglect, which is perhaps the most clinically dramatic deficit in neurology.
In hemispatial neglect, the patient ignores the left side of space — not because they cannot see it (their visual fields may be intact) but because they cannot attend to it. They will eat only the right side of their plate. They will dress only the right side of their body. They will draw only the right half of a clock face. They may not recognize their own left arm as belonging to them. The deficit is in spatial attention, not in primary sensation.
The asymmetry — left neglect is much more common than right neglect — reflects functional specialization. The right parietal lobe handles attention to both sides of space. The left parietal lobe handles attention primarily to the right. If the right parietal lobe is damaged, the left side of space loses its only champion. If the left parietal lobe is damaged, the right parietal can still attend to the right side.
Hold the architecture. The parietal lobe is the brain's body map and space map. When it fails, the patient's relationship to their body and to the surrounding world becomes incoherent in specific, localizable ways.