Combining transcranial magnetic stimulation and FMRI to examine the default mode network

The default mode network is a group of brain regions that are active when an individual is not focused on the outside world and the brain is at "wakeful rest." It is thought the default mode network corresponds to self-referential or "internal mentation". It has been hypothesized that, in humans, activity within the default mode network is correlated with certain pathologies (for instance, hyper-activation has been linked to schizophrenia and autism spectrum disorders whilst hypo-activation of the network has been linked to Alzheimer's and other neurodegenerative diseases. As such, noninvasive modulation of this network may represent a potential therapeutic intervention for a number of neurological and psychiatric pathologies linked to abnormal network activation. One possible tool to effect this modulation is Transcranial Magnetic Stimulation: a non-invasive neurostimulatory and neuromodulatory technique that can transiently or lastingly modulate cortical excitability (either increasing or decreasing it) via the application of localized magnetic field pulses. In order to explore the default mode network's propensity towards and tolerance of modulation, we will be combining TMS (to the left inferior parietal lobe) with functional magnetic resonance imaging (fMRI). Through this article, we will examine the protocol and considerations necessary to successfully combine these two neuroscientific tools.