Case 4.  Unsafe Driver

At recent examination, this patient had left hemiparesis, much milder in the leg than in the arm and the lower part of her face, and brisk reflexes. Two-point discrimination and pin-prick were mildly impaired on the left side of the face and arm.  When the left arm was tested alone, she accurately reported when it was touched. However, when both the left and right arm were tested simultaneously, she reported touch only on the right arm. It was not safe for her to drive, because although she saw fairly well in both left and right visual fields, she didn't pay sufficient attention to things going on in the left side of space.
Diagrams

Expert Note Case 4.
Unsafe Driver
Diagrams

Like a patient who has this lesion in the left language-dominant hemisphere (see Case 3), the patient described here also has a contralateral hemiplegia and mild sensory loss involving primarily face, hand, and arm. However instead of severe impairment of language, she has a different specific cognitive disorder which involves visuospatial perceptions of her own body and of the outside world. In her case, which is quite mild, the problem causes her to ignore stimuli delivered to the left side when the stimulus is given bilaterally. 

We really don't understand the details, but clinical evidence suggests that the right hemisphere plays an important role in attending to the entire visuospatial world while the left hemisphere has a more limited role and only attends to the right. Thus damage to the right hemisphere would be expected to particularly affect attention to and conceptualization of left personal and general space.  The anatomic basis is unclear, but there is evidence that spatial conceptualization involves systems distributed in the frontal as well as parietal and temporal lobes.  Parts of these systems are therefore nourished by the superior cortical branches of MCA, although other critical components lie in inferior MCA territory.
Clinical Note: Immediately after their strokes, patients with superior cortical branch lesions in either the left or right hemispheres may have their eyes (or their eyes and head) turned toward the side of the lesion. Impairment of eye movements contralateral to the cortical lesion usually lasts for only a few days, even when other motor deficits remain.

Question:
Do you know of some part of the gaze mechanism involving the frontal lobes?
Answer:
  • the frontal eye fields (sometimes called the frontal lobe centers for contralateral gaze).
  • each frontal eye field has a role in initiating eye movements to the opposite side. When it is damaged, the eyes are deviated to the same side (or the patient may show a gaze preference to that side).