Posterior parietal cortex

Clinic

• Posterior parietal cortex is the portion of parietal neocortex posterior to the primary somatosensory cortex
• It plays an important role in planned movements, spatial reasoning, and attention.
• Its damage can produce a variety of sensorimotor deficits, including deficits in the
  • Perception and memory of spatial relationships
  • Inaccurate reaching and grasping
  • Control of eye movement, and
  • Inattention

• The two most striking consequences of PPC damage are apraxia and hemispatial neglect.

• PPC is an ‘associative’ cortical region because it is neither strictly sensory nor motor, but combines inputs from a brain areas including somatosensory, auditory, visual, motor, cingulate and prefrontal cortices, and it integrates proprioceptive and vestibular signals from subcortical areas.

Anatomy

• PPC receives input from the three sensory systems that play roles in the localization of the body and external objects in space: Visual / Auditory / Somatosensory system.
• Much of the output goes to areas of frontal motor cortex: the dorsolateral prefrontal cortex, various areas of the secondary motor cortex, and the frontal eye field.

Functions

• PPC has been understood to have separate representations for different motor effectors (e.g. arm vs. eye).
• In addition to separation based on effector type, some regions are activated during both decision and execution, while other regions are only active during execution.

• Learning motor skills
• Coordination of different effectors
• PPC encode various aspects of the planned action simultaneously.
• PPC encode not only the planned physical movement, but also the anticipated visual consequence of the intended movement during the planning period.

• Self-directed switches in attention.
• Sustained spatial attention.

• Episodic retrieval memory, Connection between attention and episodic recall.

• Damage to posterior parietal cortex results in deficits in visual working memory. Patients could name objects that they had previously seen, but were impaired at recognizing previously presented objects, even if these objects had a familiar name.

• PPC is also activated during reasoning tasks, and some of the areas activated for reasoning tend to also show activation for mathematics or calculation.

• It plays a role in perception of pain.

• Feelings of "free will" at least partially originate in this area.

• PPC clearly participates in a manifold of cognitive function
• While the present discussion was centered around the theme of body schema and neural coding in first-person
• It also plays a major role in shaping how we see the world ‘out there’. For example, the deficiencies in spatial attention seen after parietal damage extend well beyond corporeal awareness, and include features and images in the outside world.

• Selective attention
• Evidence accumulation
• Decision making
• Working memory