Where Bottom-up Meets Top-down: Neuronal Interactions during Perception and Imagery

• Published in: Cerebral cortex (New York, N.Y. 1991) N.Y. 1991), 2004-11, Vol.14 (11), p.1256-1265
• Main Authors: Mechelli, Andrea, Price, Cathy J., Friston, Karl J., Ishai, Alumit
• Format: Article
• Language: English
• Subjects: Adult; dynamic causal modelling; Female; functional magnetic resonance imaging; Humans; Imagination - physiology; Magnetic Resonance Imaging - methods; Male; Nerve Net - physiology; Photic Stimulation - methods; visual imagery; visual perception; Visual Perception - physiology
• ISSN: 1047-3211; 1460-2199; 1460-2199
• DOI: 10.1093/cercor/bhh087

Functional magnetic resonance imaging (fMRI) studies have identified category-selective regions in ventral occipito-temporal cortex that respond preferentially to faces and other objects. The extent to which these patterns of activation are modulated by bottom-up or top-down mechanisms is currently unknown. We combined fMRI and dynamic causal modelling to investigate neuronal interactions between occipito-temporal, parietal and frontal regions, during visual perception and visual imagery of faces, houses and chairs. Our results indicate that, during visual perception, category-selective patterns of activation in extrastriate cortex are mediated by content-sensitive forward connections from early visual areas. In contrast, during visual imagery, category-selective activation is mediated by content-sensitive backward connections from prefrontal cortex. Additionally, we report content-unrelated connectivity between parietal cortex and the category-selective regions, during both perception and imagery. Thus, our investigation revealed that neuronal interactions between occipito-temporal, parietal and frontal regions are task- and stimulus-dependent. Sensory representations of faces and objects are mediated by bottom-up mechanisms arising in early visual areas and top-down mechanisms arising in prefrontal cortex, during perception and imagery respectively. Additionally non-selective, top-down processes, originating in superior parietal areas, contribute to the generation of mental images, regardless of their content, and their maintenance in the ‘mind’s eye’.