Congratulations! Your answer was correct.
It's D. Loss of neurons in the nucleus basalis of Meynert and septal nuclei, reducing the cholinergic input to the forebrain.

Explanation: Loss of neurons in the nucleus basalis of Meynert and septal nuclei reduces cholinergic input to the forebrain and increases (option D), rather than decreases (option B), the likelihood of delirium from anticholinergic drugs such as bladder or gastrointestinal relaxants. Loss of pigmented substantia nigra cells, another normal, age-related change, increases the sensitivity of D2 receptors and thus sensitivity to extrapyramidal effects of antipsychotic agents (options A, C, E).

Muskin PR and Dickerman AL, eds. Study Guide for the Psychiatry Board Examination. Arlington, VA: American Psychiatric Association Publishing; 2016: 52, 264. Click here to purchase. Members can purchase at a discount.