Neurophysiological correlates of mental imagery in different sensory modalities

Mental Imagery is supposed to be a basic phenomenon of conscious mental operations, which is exerted in any sensory modality. The aim of the present study was to investigate neurophysiological correlates of mental imagery in the visual, the acoustic and tactile modality. For that purpose, word lists were created based on their power to evoke mental imagery in these modalities. Nine young healthy volunteers were included. Words were presented on a computer screen with 3-s intervals. Evoked electrical activity was recorded simultaneously with a 21-channel system. After inspection for artifacts and off-line averaging, further analysis was performed in a time range of 250-450 ms, corresponding to the P300 component. Within this range, six topographically stable segments were found. A repeated measures ANOVA was significant for the left-right directions of the positive and of the negative centroid, but not for the anterior-posterior directions. The posterior centroid was most right-located in the visual sensory modality and most left-located for tactile imagery; in the acoustic modality it had a midline-position. These differences in centroid locations during mental imagery in different sensory modalities can be explained by the underlying activity of different neural generator ensembles, possibly involving modality specific primary cortical areas.