The application of TMS in the Study of Consciousness
Consciousness is being increasingly studied via TMS. TMS enables the examination of the effects of reversible visual cortex disruption on visual information processing for brain functions requiring visual awareness, which allows the elucidation of the contributions of different cortical regions to visual awareness. Studies (Matthews et al 2001 and Kammer 2007) demonstrate that TMS can be used systematically to produce unawareness of visual events.
Ongoing research
Several recent TMS studies have elucidated the mechanisms through which the primary visual cortex leads to visual awareness. A single-pulse TMS study by Silvanto et al (2007) suggested a key role of the feedback projections of interhemispheric connections to the primary visual cortex. It has been shown that the application of TMS over the primary cortex can induce visual unawareness and suppression, providing strong evidence that visual information can be processed without true awareness. In addition, studies by Bar (2003) and Ganis et al (2007) demonstrated a role of the prefrontal cortex, with its strong connections to the inferior temporal cortex, in the cortical network that mediates visual object identification.
TMS provided the first neurophysiological evidence that motor programs are facilitated by observing other people’s actions (Fadiga et al 1995).
Repetitive TMS (rTMS) can induce short-term functional reorganization in the human cortex. Using rTMS in healthy individuals has shown that the premotor cortex is crucial for visual discriminations of actions, whereas the extrastriate body area mainly processes an actor’s body identity (Urgesi et al 2006).
In addition, there is preliminary evidence suggesting that TMS represents a promising tool by which to determine pathophysiological sequelae of impaired consciousness, e.g. coma, vegetative state and minimally conscious state, and potentially direct future therapeutic interventions (Lapitskaya et al 2009).
References
- Kammer, Psychol Res. 2007
- Matthews et al. Exp Brain Res. 2001
- Fadiga al. J Neurophysiol. 1995
- Silvanto et al., Eur J Neurosci. 2007
- Bar, J Cogn Neurosci. 2003
- Ganis et al., Neuroimage. 2007
- Urgesi et al., J Neurosci. 2006
- Lapitskaya N et al., Chapter 13. Coma science: clinical and ethical implications Vol 177. 2009
