Visual stimuli modulate frontal oscillatory rhythms in a cortically blind patient: Evidence for top-down visual processing.
OBJECTIVE
We investigated neuronal correlates of faces versus non-faces processing in a cortically blind patient (TN) and a group of healthy age-matched controls in order to test electrophysiological correlates of the processing of pertinent stimuli in this patient.


METHODS
An EEG paradigm was used, in which intact and scrambled faces were displayed on a screen. First, time-frequency transforms were conducted on the patients' data alone. These oscillations were then compared to the frontal activity of six control participants.


RESULTS
Post stimulus oscillatory modulations (synchronisation in theta and alpha frequency bands) of both intact and scrambled faces at frontal scalp sites were observed in TN. These modulations were different for correct and incorrect responses. A more important increase in the theta band for incorrect responses was observed. The oscillatory rhythms highlighted in blindsight and in frontal regions differ from the ones observed in control participants.


CONCLUSIONS
Despite the destruction of the visual cortex, oscillatory rhythms are not cancelled out but are shifted to anterior regions, revealing the activity of an alternate pathway for residual visual function.


CONCLUSIONS
The results provide evidence for a top-down cognitive control process in blindsight.
Methodology and Data Analysis, Department of Psychology, University of Geneva, Switzerland; Distance Learning University, Sierre, Switzerland. Electronic address: eda.tipura@unige.ch.
Eda
E
Tipura
School of Psychology, The University of Queensland, Brisbane, Australia; Laboratory of Experimental Neuropsychology, Department of Psychology, University of Geneva, Switzerland.
Alan J
AJ
Pegna
Cognitive and Affective Neuroscience Laboratory, University of Maastricht, The Netherlands.
Beatrice
B
de Gelder
Methodology and Data Analysis, Department of Psychology, University of Geneva, Switzerland.
Olivier
O
Renaud
D019575:Blindness, Cortical / Q000175:diagnosis / Q000503:physiopathology*; D016022:Case-Control Studies; D005625:Frontal Lobe / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D013826:Theta Rhythm; D014795:Visual Pathways / Q000503:physiopathology; D014796:Visual Perception
Blindsight; EEG; Event-related spectral perturbation; Frontal cortex; Frontal midline theta rhythm; Vision