The entire story is here, but this is the money quote:
learning can occur via two distinct systems – an explicit, hippocampus-based system, and an implicit, intuitive system, more dependent on the brain’s reward pathways. And they believe that by knocking out hippocampus-based explicit memory, Midazolam actually enhances memory based on intuition.
Here’s their experiment:
Michael Frank and colleagues tested the ability of 23 participants to learn the relative value of different abstract symbols…. Later on, they were tested on their ability to recall the outcome of many of these specific pairings, and also on their ability to work out the more valuable of two symbols not previously compared.
I haven’t grabbed the article yet, but I think this is what they did. They showed the subjects two symbols, say :-0 and :-), and then told them that :-) is worth more than :-0. Then they were shown another pair, say :-) and :-}, and were told that :-} is worth more than :-). If subjects were presented with a novel pair, say :-} and :-0 and asked which was more valuable, they would be able to answer, because it follows logically given the earlier pairs that :-} is worth more than :-0. Now, that’s a pretty simple example, and the researchers used arbitrary symbols, not emoticons, which have intrinsic meaning. But I think they did something like that. Anyway, back to our show:
After taking the tranquiliser Midazolam, participants became worse at remembering the outcome of previously encountered pairings, but they actually became better at solving the outcome of novel pairs….
The researchers believe Midazolam interfered with explicit memory for previous pairs, but enhanced participants’ ability to use their gut feeling to solve novel pairs.
And here is the authors’ abstract:
People often make logically sound decisions using explicit reasoning strategies, but sometimes it pays to rely on more implicit “gut-level” intuition. The transitive inference paradigm has been widely used as a test of explicit logical reasoning in animals and humans, but it can also be solved in a more implicit manner. Some researchers have argued that the hippocampus supports relational memories required for making logical inferences. Here we show that the benzodiazepene midazolam, which inactivates the hippocampus, causes profound explicit memory deficits in healthy participants, but enhances their ability in making implicit transitive inferences. These results are consistent with neurocomputational models of the basal ganglia–dopamine system that learn to make decisions through positive and negative reinforcement. We suggest that disengaging the hippocampal explicit memory system can be advantageous for this more implicit form of learning.
Cite: Frank, M.J., O’Reilly, R.C. & Curran, T. (2006). When memory fails, intuition reigns. Midazolam enhances implicit inference in humans. Psychological Science, 17, 700-707.