A patient demonstrated deficits in his ability to recall events in his daily life and scored poorly on the Wechsler memory scale - a specific test for declarative memory. These deficits indicated a profound loss of short-term declarative memory function or anterograde amnesia. On the other hand, the patient retained his original IQ score, as well as his ability to perform perceptual, abstract thinking, and reasoning tasks. His ability to form nondeclarative memories was thus intact. Moreover, his early memories were easily recalled, showing that the structures removed during his operation were not a permanent repository for retrograde memories. What is the most likely diagnosis for this patient?
1) Alzheimer's disease
2) Anterograde amnesia
3) Retrograde amnesia
4) Dementia