Dementia: Pathology review

A 71-year-old woman is brought to the clinic by her partner due to worsening insomnia and cognitive impairment for the past 3 months. According to the husband, the patient had previously been able to drive to the grocery store and play racquetball. However, she is no longer able to complete these activities on her own. The patient has no history of psychiatric conditions, but her mother died from Alzheimer disease in her 80s. In the office, the patient’s temperature is 37.0°C (98.6°F), pulse is 88/min, respirations are 13/min, and blood pressure is 122/84 mmHg. Physical exam reveals ataxic gait and an inability to follow multi-step instructions.  When a nearby door is shut loudly, the patient is startled, causing her arms to clench involuntarily. Further evaluation of this patient is most likely to reveal which of the following findings?