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

Abstract

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'.

Exploring commonalities across participants in the neural representation of objects

“…There are multiple brain regions, besides classical object-selective cortex that contain information about the object category. These results are consistent with previous findings of the distributed patterns of activation evoked by objects [Ishai et al, 1999[Ishai et al, , 2000Mechelli et al, 2004].…”

Stimulus onset asynchrony and the timeline of word recognition: Event-related potentials during sentence reading

“…Instead, active predictions about upcoming sensory events continuously influence the incoming signal and interact as top-down projections with earliest perceptual processes (Bar, 2007;Carlsson, Petrovic, Skare, Petersson, & Ingvar, 2000;Churchland et al, 1994;Corbetta & Shulman, 2002;Engel, Fries, & Singer, 2001;Enns & Lleras, 2008;Gilbert & Sigman, 2007;Kastner, Pinsk, De Weerd, Desimone, & Ungerleider, 1999;Kutas, 2006;Kveraga, Ghuman, & Bar, 2007;McClelland & Rumelhart, 1981;Mechelli, Price, Friston, & Ishai, 2004;O'Connor, Fukui, Pinsk, & Kastner, 2002;Somers, Dale, Seiffert, & Tootell, 1999;Williams, Baker, Op de Beeck, Mok Shim, Dang, Triantafyllou et al, 2008).…”

Dynamic causal modelling for fMRI: A two-state model

“…The neuronal dynamics are described by the differential equations describing the dynamics of a single state that summarizes the neuronal or synaptic activity of each area; this activity then induces a hemodynamic response as described by an extended Balloon model (Buxton et al, 1998). Examples of DCM for fMRI can be found in Mechelli et al (2004), Noppeney et al (2006), Stephan et al (2005), and Griffiths et al (2007) (for a review on the conceptual basis of DCM and its implementation for functional magnetic resonance imaging data and event-related potentials, see Stephan et al, 2007).…”