Why Do Some People Ignore Their Left Side?

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A recent case report published to the journal BMJ Case Reports tells the story of a 75-year-old Japanese woman who was taken to Tokyo-West Tokushukai Hospital after a sudden and strange neurological episode:

"Her son spoke to her and noticed that she was staring at her right side. He approached her from her left side and talked to her, but she did not seem to notice him as if she was ignoring him. In addition, the son also noticed that only the left half of the leeks laid out on the cutting board remained uncut. The right half of the leeks had already been cut and cooked in a pot of miso soup. Besides, she seemed that she could not find a salt jar, which was located to her left. Despite the fact that she faced difficulty in paying attention to her left side, she did not ask her son for help as she did not seem to be troubled by her situation."

The son, however, was troubled, and insisted that she go to the emergency room.

"She had no fever, headache, or weakness," her doctors recalled. "On examination, she consistently turned her head and gaze to the right... When instructed to point to the middle of the stethoscope tube, she grabbed the right quarter of the tube."

Though the woman's vision seemed to be in good working order, she appeared unable to heed anything on her left side. A magnetic resonance imaging scan of her brain soon revealed the cause of her unexpected symptoms: "severe narrowing of the proximal right middle cerebral artery," in other words, a stroke.

MR angiography showed severe narrowing of the proximal right middle cerebral artery.

What the woman suffered from is a severe case of unilateral spatial neglect (UNS). Some form of UNS can occur in up to a quarter of all instances of stroke, caused by damage to the temporo-parietal junction or posterior parietal cortex of the brain, which both deal with doling out attention. Interestingly, neglect is almost exclusively of a person's left side, chiefly because the right hemisphere of the brain seems specialized for spatial perception and memory. Seeing as how brain hemispheres typically control opposite sides of the body, damage to spatial awareness centers located in the right side of the brain would trigger neglect of the opposite side of the body. Right-sided neglect does rarely occur, but there is redundant processing of the right visual fields by both brain hemispheres, so if a stroke occurs in the left side of the brain, the right side can usually pick up the slack to ensure no neglect takes place.

Treatment options for UNS are presently limited, but research in the past few years has has started to focus on transcranial magnetic and direct current stimulation, as well as virtual reality, to help sufferers rehabilitate their depleted spatial awareness. Early results are promising.

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