The history of the neurophysiology and neurology of the parietal lobe.

The development and change of knowledge on the function of the parietal lobe from the second half of the 19th century to the early 1970s are reviewed. Motor and somatosensory functions were initially localized in a broad frontoparietal region. At the beginning of the 20th century the motor cortex was restricted to the posterior frontal lobe. The separate attribution of somatosensory functions to the parietal lobe was initially based on anatomic considerations, but mostly on localized bodily sensations elicited by electric stimulation in awake patients. Patients and nonhuman primates with anterior parietal damage showed deficits in somatic sensation (tactile discrimination and position sense, less markedly pain and thermal sensitivity). Somatosensory evoked potentials demonstrated in all mammals that the body is orderly and multiply represented in the anterior parietal cortex. The parietal lobe was divided into an anterior and a posterior cortex (PPC). The PPC is particularly developed in primates, where it includes a superior and an inferior parietal lobule. The PPC was initially thought to be a higher-order region for somatosensory information processing, but its functional specialization proved soon to be greater and more complex. PPC damage in humans gives rise to a variety of neuropsychologic disorders: pain asymbolia, sensory extinction, spatial neglect, optic ataxia and limb apraxia, alexia and agraphia. Single-neuron recordings in freely behaving monkeys furnished the complementary information that the PPC is involved in body-environment interactions, for visual exploration and hand use as a sensor and a tool. The PPC is now believed to underpin higher-order processes of sensory inputs, multisensory and sensorimotor integration, spatial attention, intention, and the conjoint representation of external space and the body. The symptoms in which disorders of these processes manifest after PPC damage are considerably different in humans and nonhuman primates.