The numbness you mention may be a sign of a small stroke
involving the very small, deep penetrating arteries of the brain. These types of stroke
, also called lacunar strokes (from the Latin root lacuna meaning “empty space”), may be so small that they are not always apparent on an MRI. In your mother’s case, it sounds like her symptoms are purely sensory, perhaps suggesting a small “lacune” in the thalamus, which is the relay center for the brain.