Visual cognition and awareness: Projects
Neural basis of visual awareness
The role of the pimary visual cortex in visual awareness has been the subject of much debate. We use transcranial magnetic stimulation in normal participants as well as in patients to understand the contribution of this region to awareness. Our studies have shown that visual qualia can be experienced without V1 in specific circumstances (Silvanto et al, 2008 Current Biology). Our work with normal subjects explores the functional significance of cortico-cortical interactions in the visual cortex (Koivisto et al, 2010 Neuroimage; Silvanto et al, 2005, Nature Neurosci).
Koivisto M, Mäntylä T, Silvanto J (2010). The role of early visual cortex (V1/V2) in conscious and unconscious visual perception. Neuroimage. 51:828-34.
Silvanto J. (2008). A re-evaluation of blindsight and the role of striate cortex (V1) in visual awareness. Neuropsychologia 46(12):2869-71.
Silvanto J, Cowey A, Walsh V. (2008). Inducing conscious perception of colour in blindsight. Current Biology. 18:950-951.
Silvanto J, Cowey A, Lavie N, Walsh V. (2005). Striate cortex (V1) activity gates awareness of motion. Nature Neuroscience 8(2):143-4.
TMS methodology: state-dependent TMS paradigms
Most transcranial magnetic stimulation (TMS) studies in cognitive neuroscience use the “virtual lesion” approach developed by Amassian more than twenty years ago. Although this approach has been useful in demonstrating the necessity of cortical regions in cognitive functions, it says very little about how information is processed in the region of interest. Furthermore, effects can be variable, with stimulation leading sometimes to paradoxical facilitations, an effect which does not fit well with the virtual lesion conceptualisation of TMS effects.
To overcome these problems, we have developed a novel TMS approach, state-dependent TMS, which enables one to explore the selectivity and information content of specific neuronal populations within a cortical area (see Silvanto & Muggleton, 2008, Neuroimage). Furthermore, this state-dependency approach can explain why TMS sometimes impairs behavioral while in other circumstances a facilitation is observed.
Schwarzkopf DS, Silvanto J, Rees G. (2011). Stochastic resonance effects reveal the neural mechanisms of transcranial magnetic stimulation. Journal of Neuroscience.
Cattaneo Z, Rota F, Vecchi T, Silvanto J. (2008). Using state-dependency of transcranial magnetic stimulation (TMS) to investigate letter selectivity in the left posterior parietal cortex: a comparison of TMS-priming and TMS-adaptation paradigms. Eur J Neurosci. 28(9):1924-9.
Silvanto J, Muggleton NG. (2008). New light through old windows: moving beyond the "virtual lesion" approach to transcranial magnetic stimulation. Neuroimage 39(2):549-52.
Silvanto J, Muggleton NG. (2008). Testing the validity of the TMS state-dependency approach: targeting functionally distinct motion-selective neural populations in visual areas V1/V2 and V5/MT+. Neuroimage 40(4):1841-8.
Silvanto J, Muggleton NG, Walsh, V. (2008). State dependency in brain stimulation studies of perception and cognition. Trends in Cognitive Sciences. 12: 447-454
Mental imagery and visual short-term memory Visual cortical areas are believed to be involved in the imagery and short-term maintanance of visual attributes. We use TMS to investigate the visual cortical activation states associated with these cognitive processes, and to explore the information content in specific visual areas during working memory maintanance. Our results have shown that that information in short-term memory can modulate the pattern of visual activation reaching awareness, providing evidence for the view that overlapping neuronal populations are involved in conscious visual perception and VSTM. (Silvanto & Cattaneo, 2010, Neuroimage).
Silvanto J, Cattaneo Z. (2010). Transcranial magnetic stimulation reveals the content of visual short-term memory in the visual cortex. Neuroimage. 50(4):1683-9
Cattaneo Z, Vecchi T, Pascual-Leone A, Silvanto J (2009).Contrasting early visual cortical activation states causally involved in visual imagery and short-term memory. Eur J Neurosci. 2009 Oct;30(7):1393-400.