My quick suggestions:

• In vivo two photon spine imaging
• Immediate early genes mapping

Thank you very much for your answer.

Rafal's suggestions are right on the mark. You also might consider the following approaches if the right molecular, physiology and imaging tools are available to you.:

1) activity dependent dye imaging (Fura2, Fluo-4, etc) to assess neural activity across many cells at once or imaging of genetically-encoded reporters of activity (GCaMPs, synaptopHluorin, etc) to assess activity changes in specific populations of synapses or neurons.

2) Similarly, one might apply multi-electrode array approaches to slices to assess changes in activity as well.

Thank you David for your answer. I will check it...