Summary

The posterior parietal cortex (PPC) is involved in planning movements. To do this, it combines information from different sensory areas to get an idea of the position of the body relative to other objects in the environment.

Function

This area plays an important role in planning movements. In order to properly execute a movement, the body must have knowledge of its own position, and of the objects in the space it is in. Without this knowledge, it is difficult to maintain balance, or to not run into any objects.

The PPC is divided into small areas, with each area specializing in a specific movement.

• The lateral part of the PPC contains a map of all areas of the visual field. This information is used to control eye movements. When you see a relevant stimulus, you move your eyes toward it to better study it.
• The ventral part of the PPC receives information from the different senses (visual, auditory, somatosensory and from the balance organ).
• The medial part of the PPC has neurons that provide coding for the location of a movement. In order to properly execute a movement and grab an object from the table, you need to know exactly where on the table the object is, and therefore where the movement should go.
• The anterior part of the PPC processes information about the shape, size and orientation of objects. This information is then used to control the fine movements of the hand. This makes the distance between your fingers precisely large enough to pick up the object.

Location

This area is part of Brodmann Area 7, and is located directly behind the primary somatosensory cortex.

Fact

This area receives input from three different sensory systems, the visual system, the auditory system, and the somatosensory system. These different systems are combined to get a good idea of how the body relates to the other objects in the room. Most of the output from the PPC goes to areas of the motor cortex. The motor cortex is responsible for carrying out planned movements.

Patients

Damage to this area can lead to many different problems, such as difficulty picking up objects or controlling eye movements. In very severe cases, damage to this brain area can cause apraxia or hemispheric neglect. Apraxia is a disorder in which it is difficult to perform planned movements. This can occur in different forms, with different types of movements. An example is ideational apraxia, in which the execution of various tasks in the correct order is difficult. For example, some patients would put on their pajamas before taking off their clothes. Hemispheric neglect is a disorder in which attention is paid only to one part of the visual field. These people can perceive all visual stimuli, but this is not further processed and remembered. Hemispheric neglect is manifested so that, for example, when drawing a house, people who suffer from this only draw one half of the house.

Author: Myrthe Princen (translated by Melanie Smekal)