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The brain's mysterious guardian: How does the parietal lobe influence our sensory perception?
The parietal lobe is one of the four major lobes in the mammalian cerebral cortex, located above the temporal lobe and behind the prefrontal lobe and central sulcus. This specialized area integrates information from a variety of senses, including spatial awareness and navigation (proprioception), as well as the primary receptor for touch, the somatosensory cortex, located behind the central sulcus. Earlier studies showed that the major sensory inputs from the skin (touch, temperature, and pain receptors) are transmitted to the parietal lobe via the thalamus. Appropriate neural structures are closely associated with the integration of these sensory perceptions.
The parietal lobe is not only a center for sensory processing, it also plays an important role in language processing.
Anatomically, the parietal lobe is defined by three boundaries: the central sulcus separates the parietal lobe from the prefrontal lobe; the parieto-occipital sulcus separates the parietal lobe from the occipital lobe; and the lateral sulcus (Silvian sulcus) is the most lateral border, separating it from the temporal lobe. The cortex of each hemisphere in the parietal lobe represents an area of skin on the opposite side of the body.
The parietal lobe has a wide range of functions, including:
- Two-point discrimination: based on touch alone without the aid of other senses.
- Pattern perception: Recognizing letters or numbers on the skin by touch.
- Tactile localization: the ability to localize under simultaneous bilateral stimulation.
These functions demonstrate the critical role the parietal lobe plays in integrating sensory information from across the body.
The parietal lobe also plays an important role in visual-spatial processing. Although it is multisensory, the posterior parietal cortex is often referred to by vision scientists as the “where” pathway (i.e., vision in space) and the “how” pathway (i.e., vision for action), as the names suggest. This posterior parietal cortex receives input from touch and vision, and then controls the movements of the hands, arms, and eyes based on motor signals. Several studies in the 1990s showed that different areas of the posterior parietal cortex of monkeys represent different parts of space.
Clinically, parietal lobe lesions are characterized by contralateral hemibody sensory loss due to unilateral parietal lobe lesions and "stereotactile impairment", which is the inability to determine three-dimensional shapes by touch. These symptoms further affect daily life; for example, left-right agnosia can interfere with a patient's spatial cognition and cause difficulties with mathematics and reading.
Right-sided lesions often result in loss of imagery, visualization of spatial relationships, and neglect of the left side of the body, while left-sided lesions affect the ability to do math, read long passages, write, and understand symbols.
Damage to the parietal lobe is not limited to sensory loss. Damage to the right side often results in agnosia, or a lack of awareness of one's disability, which means the brain's ability to process spatial information is severely affected and can cause significant challenges in daily life.
As the mysterious guardian of the brain, how does the parietal lobe integrate multiple sensory information and influence our daily behavior and cognition?
