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  Home : Other Subjects : Psychology Study Guides : Neuro : Brain Anatomy : Parietal and Occipital Lobes
Brain Anatomy
  
 
Parietal and Occipital Lobes
Parietal Lobe
The parietal lobe is located posterior to the central sulcus and superior to the lateral fissure (see figure. The major function of the parietal lobe is to mediate attention, but it is also involved in long-term memory and somatic sensory perception. The association cortex of the parietal lobe, together with a section of the temporal lobe, is responsible for long-term storage of vocabulary words.
Somatic Sensory Cortex
The somatic sensory area, located adjacent to the central sulcus, receives input from nerves that travel from sensory receptors in all parts of the body, through the spinal cord and brainstem, and into the cortex. The somatic sensory area, like the primary motor area, is organized as a map of the body; nerves projecting from adjacent locations in the body tend to terminate near to each other in the cortex. Damage to the somatic sensory area results in loss of perception of bodily sensations, namely the sense of touch.
Attention and Neglect
The parietal lobe is best known for its importance in attention. PET scans show high activity in the parietal lobe during tasks that require concentrated attention to one or more aspects of a stimulus. For example, if subjects are required to specifically attend to the color, velocity, or shape of an object in their view, blood flow to the parietal lobe increases, indicating that they are using that area of the brain to carry out the task. Damage to the parietal lobe results in a syndrome called neglect, in which patients treat parts of their body or objects in part of their visual field as though they did not exist. This effect is contralateral: if the right parietal lobe is damaged, people will neglect their left side; if the left parietal lobe is damaged, they will neglect their right side. For example, a woman with damage to the right parietal lobe might put makeup on only the right side of her face and eat the food on only the right side of her plate. The visual system remains intact; they can see the neglected side just fine. But because the parietal lobe is damaged, they cannot direct their attention to it, so they fail to notice that it is there. Neglect syndrome is more likely to occur as a result of damage to the right side of the parietal lobe than the left. This is because the right parietal lobe mediates attention to both the left and right fields, while the left controls attention to the right only. Thus, when the left parietal lobe is damaged, the right can compensate, but the converse is not true.
Occipital Lobe
The occipital lobe comprises the most posterior section of the brain, situated posterior to the parieto-occipital sulcus and directly above the cerebellum (see figure). The most important feature of the occipital lobe is the primary visual cortex, also called the striate cortex. The primary visual cortex receives and interprets information from the retina of the eye. Signals from receptors in the eye travel through optic nerves to the lateral geniculate nucleus, a small structure near the center of the brain, where the information is organized and relayed to the primary visual cortex. Like the primary motor cortex and the somatic sensory cortex, the primary visual cortex is organized into a topographic map, with the size of receptor fields in the cortex corresponding to the density of receptors at each location on the retina. Also like the primary motor and somatic sensory areas, the primary visual cortex is contralateral; the signals from the left side of each retina are received by the right side of the visual cortex, and vice versa. Damage to the visual cortex results in loss of vision in the contralateral visual field (the visual field is only the left or right side of each eye, not the entire contralateral eye). In addition to the primary visual cortex, overlapping areas in the occipital and parietal lobes work together to control eye movements following a moving target.
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