Stimulation of brain has a long history dating back to the 18th century, using transcranial electrical stimulation. In the era, people did not have enough knowledge about neurophysiology such that they shocked their own brain regardless of irreversible permanent brain damage.
Thanks to advances of neuroscience, we can see through brain and its activity with MRI and now seek to modulate brain functions.
Transcranial magnetic stimulation (TMS) is considered to be a promising tool to induce reliable functional changes of human brains (see figure above). The principle of TMS is based on electromanetic theory of inducing electrical current as magnetic field changing in time. With current TMS technology, only cortical brain regions near the skull could be stimulated (but see dTMS). A research group in Northwestern University led by Prof. Joel Voss demonstrated that repetitive high frequency TMS (rTMS) could enhance associative memory function by targeted stimulation of hippocampus. They showed stimulating left parietal region showing the maximum correlation with hippocampus target in resting-state could significantly enhance hippocampal-cortical connectivity.
I recently found targeted rTMS to the hippocampus also could enhance evoked activity of hippocampal-cortical network, especially in posterior-medial network involved in processing of item-context memory and associative memory recognition performance (see figures below, Kim et al., Science Advances, 2018).
In the future, I continue this line of research to further understand distinct neural mechanism for various types of context-dependent declarative memory. Additionally, I will investigate on how TMS can modulate interaction between different memory systems, such as procedural memory (e.g., motor memory) and declarative memory.