A patient needs a drug causing short-term anterograde amnesia (a diazepam-family drug). Which property is responsible?

GABA-A receptor potentiation Benzodiazepines (midazolam is the classic choice for dental sedation because of its marked amnestic effect) cause anterograde amnesia by potentiating GABA-A-mediated inhibition in limbic structures. This is why midazolam is used for conscious sedation.