Passage Summary: Brain healing only happens if new cells turn into the most common type of cell in the injured spot, but in one specific part of the brain, they never do that.

Reasoning: Healing an injured brain requires new neurons to become the most common type in that area; however, in the striatum, new neurons never become the most common type (midsized spiny neurons).

Analysis: This stimulus sets up a conditional requirement for healing: if healing occurs, then the new neurons must have become the most common type. The researcher then provides a fact that contradicts the 'then' part of that rule for the striatum: the new neurons never become the most common type there. Using the contrapositive, we can conclude with certainty that new neurons do not heal the striatum. Look for an answer that reflects this deduction, as it is the only logical outcome when the necessary condition for healing is impossible to meet.