Parietal Lobes
Each parietal lobe sits between the visual brain
(occipital lobe) behind, and the frontal lobes in front and the temporal lobe
below. In the simplest terms, there two functional regions. The postcentral
gyrus is the sensor cortex that receives data from the body and face via the
thalamus (see somatosensation). The remainder of the parietal lobe has been
considered an associative device that integrates body sensory input with visual
information to create awareness of a moving body in space.
Damage to the parietal lobes can often be recognized as loss of motor skills and abnormalities
in body image and spatial relations. Damage on the left side may cause
right-left confusion, verbal memory deficits, difficulty with writing (agraphia),
difficulty with mathematics (acalculia), other disorders of language (aphasia)
and the inability to identify and use objects (agnosia). Right parietal lobe
damage causes neglect of part of the body, difficulty making things
(constructional apraxia), and denial of deficits (anosagnosia). Bilateral
parietal lobe disease may be recognized by the inability to control eye
movements (ocular apraxia), inability to resolve visual information into
recognizable objects (simultanagnosia), and inability to reach for an object
with visual guidance (optic ataxia).
On the medial side, the precuneus remain relatively undefined but appears to
be continuous to with the cingulate gyrus. Margulies et al used functional MRI
to investigate precuneus function in humans and macaque monkeys. They
described: Three distinct patterns of functional connectivity were demonstrated
within the precuneus of both species:
(i) the anterior precuneus, functionally
connected with the superior parietal cortex, paracentral lobule, and motor
cortex, suggesting a sensorimotor region.
(ii) the central precuneus,
functionally connected to the dorsolateral prefrontal, dorsomedial prefrontal,
and multimodal lateral inferior parietal cortex, suggesting a
cognitive/associative region.
(iii) the posterior precuneus, displaying functional connectivity with
adjacent visual cortical regions. These functional connectivity patterns were
differentiated from the more ventral networks associated with the posterior
cingulate, which connected with limbic structures such as the medial temporal
cortex, dorsal and ventromedial prefrontal regions, posterior lateral inferior
parietal regions, and the lateral temporal cortex
Daniel S. et al. Precuneus shares intrinsic functional architecture in humans and monkeys. PNAS November 24, 2009 vol. 106 no. 47
