Here, have a look. And that's just measuring a surrogate parameter, blood flow. Anything with a neuron-level resolution requires electrodes stuck into the brain.

As for memory interference being measured just from timings, can you elaborate on that? The question is on the role of certain genetic factors, do you mean a study with a large number of genetically screened subjects? That may work. I'm still waiting for the sequencing cost to come down further ... it's the great medical bottleneck of our time.