Question: What Are the Effects of a Parietal Lobe Stroke?
Answer: The parietal lobe is one of the richest areas in the brain. In it, and around it, our brains create our perception of the world based on what we feel, hear, and see. Consequently, parietal lobe strokes cause a myriad of symptoms which can be separated into the four categories delineated below.
- Homonimous quadrantanopsia: These are nerve fibers that carry information from the lower parts of our visual field travel through the parietal lobes on their way to the occipital lobe (where vision is processed). These fibers can be damaged by parietal strokes, causing vision in the lower quarter of the side opposite the stroke to be lost.
- Spatial Dysperception: Difficulty interpreting visual information in our surroundings, such as the length, depth, and size of objects.
- Hand-Eye Incoordination: Difficulty bringing one’s hand to a spot where one is looking. An example is a stroke survivor who looks at an object which lies on a table with the intention of picking it up, but his hand overshoots the target and he is unable to grab it.
- Inability to visually scan one’s surroundings, in spite of having full eye movements. This prevents the stroke survivor from seeing objects, people, and other visual stimuli presented in his peripheral vision.
- Sensory loss: The parietal lobe harbors the sensory cortex, which let us feel sensations such as touch, temperature and vibratory sense. Strokes in the sensory cortex can cause profound numbness.
Abnormalities of Self-Perception
- Hemineglect: People with parietal strokes in the non-dominant language side of their brain have a tendency to completely ignore the opposite side of their body. The deficit can be extremely striking and is best exemplified by people who are left with hemiplegia after a stroke that affected both the motor and sensory cortices. Not only do these people ignore the fact that one side of their body is completely paralyzed, but they can't even recognize their own body parts on that side of their body. Consequently, they fail to shave or wear lipstick on the side affected by stroke.
- Finger agnosia: Selective inability to name fingers. For instance a stroke survivor might not be able to say that his thumb is a thumb.
- Right-left confusion: Profound inability to differentiate right from left.
- Difficulty with reading, writing, and math
Allan Ropper and Robert Brown, Adam's and Victor's Principles of Neurology, 8th Edition McGraw-Hill Companies Inc, United States of America, 2005, pp 417-430.