femme Neuroscience Notes

Some Topics

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