Carnegie Mellon University and University of Pittsburgh scientists gave people material to memorize — once after being injected with a placebo and once after an injection of midazolam, a drug that causes short-term anterograde amnesia, in which the ability to form new memories is inhibited, while leaving old memories unaffected.

The drug prevents people linking a studied item with the experiment — a linkage necessary for a process known as recollection, in which people retrieve contextual details involved in the experience of studying information.

People sometimes recognize something as having been studied without using recollection — in this case, without remembering details of the study event — if the item seems sufficiently familiar. That’s a process called familiarity.

Although the drug affected the recollection process, the familiarity process was not.

This helps us understand the general functions of memory, said Carnegie Mellon psychology Professor Lynne Reder, the study’s lead author. It helps us to relate, for example, the memory declines seen in old age to those seen in patients with hippocampal damage.

The research appears in the journal Psychological Science.