In this article, we examine the methodology and considerations relevant to the combination of TMS and fMRI to examine the effects of brain stimulation on the default network.
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Method Article
Combining Transcranial Magnetic Stimulation and fMRI to Examine the Default Mode Network
In This Article
Summary
Abstract
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."1,2,3 It is thought the default mode network corresponds to self-referential or "internal mentation".2,3
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 4,5,6 and autism spectrum disorders 7 whilst hypo-activation of the network has been linked to Alzheimer's and other neurodegenerative diseases 8). 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.9
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.
Protocol
1. Preparation
- To begin, obtain a baseline anatomical scan of your subject. This should be done several days before the actual experiment.
- Next, load the scan into your frameless stereotactic software package.
- Finally, locate and target your stimulation coordinates. In this case, we will be targeting the left inferior parietal lobule.
2. The Initial Scan
- On the day of the experiment, your subject will, once again, start in the MRI machine.
- Begin with an anatomical scan.
- Next, conduct three functional experimentation runs. For this exp....
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Discussion
When conducting an offline TMS/MRI experiment, arguably the most important consideration involves the swift and effortless transition from the site of stimulation to the MRI bay. As such, it would be worth revisiting several of the aforementioned ideas suggested to aid in this transition. First: use a portable TMS machine set up in a location as close to the MRI bay as possible. Two: circumvent any automatic stand-by or equivalent mechanism programmed into the MRI equipment. Three: ensure the platform is raised an.......
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Disclosures
No conflicts of interest declared.
Materials
| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| MRI Equipped for fMRI (pictured in video is a Philips) | |||
| TMS Device Capable of Repetitive Stimulation (pictured in video is a Magstim) | |||
| Frameless Stereotaxy Equipment (pictured in video is Brainsight) | |||
| Ear Plugs | |||
| Chair for Subject during Stimulation | |||
| Back Projection Screen or MRI Compatible Goggles | |||
| Blank Stimuli Screen |
References
- Raichle, M. E., MacLeod, A. M., Snyder, A. Z., Powers, W. J., Gusnard, D. A., Shulman, G. L. A default mode of brain function. Proc. Nat. Acad. Sciences. 98 (2), 676-682 (2001).
- Buckner, R. L., Andrews-Hanna, J. R., Schacter, D. L. The brain's default network: anatomy, function and relev....
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