Neuroscience, being the science and theory of how the brain works, is traditionally studied via lesions or brain damage, measuring blood flow or electrical activity and using animal preparations.

However, problems with studying damaged brains include reorganisation issues and the inability to use the patient as their own control. In a more controlled fashion Transcranial Magnetic Stimulation (TMS) can interfere with cortical activity for varying lengths of time and in a specific site, eliminating many problems previously seen when studying lesions. TMS has therefore become a very valuable tool in neuroscience. TMS can be used on its own, single pulse or repetitively (in rTMS), or combined with brain mapping PET, MRI (or fMRI) and EEG in order to: Localise the target of stimulation; measure local and distal response of the brain to the stimulation; and to assess long-term effects of rTMS (Oxford Handbook).

In summary, there are three methods available with which to examine the effects of TMS on brain function:

• Measure the effects on distinct aspects of cortical excitability eg. in the motor cortex, where motor-evoked responses are recordable.
• Examine the behavioural outcomes when applying TMS during a specific task.
• Examine the effects of TMS on regional activity using imaging techniques such as PET, fMRI and EEG. These approaches offer complementary information and have different strengths and weaknesses. (Oxford Handbook)

When considering the use of imaging along with TMS to evaluate cognitive processes, PET and fMRI are less useful compared to EEG as they offer low temporal resolution. However they can still be useful when using neuronavigation of TMS towards active regions already detected by PET or fMRI when scanning the same subject in the same experimental context as they have greater spatial resolution (Herwig et al. 2003).

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