This nasty spell "disconnects" the subject's short-term and long-term memory. While the spell is in effect, the subject is incapable of storing information in long-term memory.
Every moment is virtually an independent event for the subject; he or she can remember recent events, thoughts, and sensations for no more than a few seconds (the amount of time they remain in short-term memory).
Memories of events that happened before the onset of the spell are not affected at all; these are safely stored in long-term memory. This means that the subject can cast any spells memorized before the memory wrack took effect, but he is likely to have difficulty casting the spell as described below.
The subject of this spell has a limited ability to act. He is restricted to one action at a time and must concentrate mightily to keep the situation and any planned actions in shortterm memory. As long as the subject is able to maintain concentration, he may act normally within these limits.
If the subject is distracted (he is struck in combat, affected by a spell, startled, surprised, or a similar event occurs), he forgets everything that occurred from the onset of the spell to the moment of distraction. The subject must re-evaluate the situation as if it had just come to pass.
Consider the following example. The subject of the spell is a soldier assigned to guard the entrance to a building. The priest arrives and casts memory wrack on the guard.
The guard has no problem remembering his orders, since he received them before the onset of the spell. He also remembers the arrival of the priest. The priest now tries to convince the guard that he is authorized to enter the building. The guard refuses him entry. The priest now picks up a rock and throws it at the guard, striking him and distracting him. The guard forgets everything that happened between the onset of the spell and the moment the rock struck. He forgets that the priest has already tried to con him and that he threw a rock at him. He must reevaluate the situation as though the priest had just arrived. The priest is free to make another attempt at entering the building.
When the spell expires, the subject remembers nothing that happened while the spell was in effect, possibly leading to amusing consequences ("By the gods, how did I get here?").
The material component is a ruby of at least 200 gp value, which is crushed during the casting.