Do early sensory cortices integrate cross-modal information?

Abstract

Our different senses provide complementary evidence about the environment and their interaction often aids behavioral performance or alters the quality of the sensory percept. A traditional view defers the merging of sensory information to higher association cortices, and posits that a large part of the brain can be reduced into a collection of unisensory systems that can be studied in isolation. Recent studies, however, challenge this view and suggest that cross-modal interactions can already occur in areas hitherto regarded as unisensory. We review results from functional imaging and electrophysiology exemplifying cross-modal interactions that occur early during the evoked response, and at the earliest stages of sensory cortical processing. Although anatomical studies revealed several potential origins of these cross-modal influences, there is yet no clear relation between particular functional observations and specific anatomical connections. In addition, our view on sensory integration at the neuronal level is coined by many studies on subcortical model systems of sensory integration; yet, the patterns of cross-modal interaction in cortex deviate from these model systems in several ways. Consequently, future studies on cortical sensory integration need to leave the descriptive level and need to incorporate cross-modal influences into models of the organization of sensory processing. Only then will we be able to determine whether early cross-modal interactions truly merit the label sensory integration, and how they increase a sensory system's ability to scrutinize its environment and finally aid behavior.

Developing Synaesthesia

“…Upon viewing achromatic numbers or letters, grapheme-color synesthetes show co-activation of grapheme regions in the posterior temporal lobe and color area V4, which has been suggested to give rise to the concurrent sensation of color Sperling et al, 2006). This pattern of activation in synesthetes is consistent with research on crossmodal integration in the normal population revealing the engagement of early sensory regions in multimodal processes (Driver and Spence, 2000;Kayser and Logothetis, 2007). proposed that this cross-activation is driven by an excess of neural connections in synesthetes, possibly due to decreases in neural pruning between typically interconnected areas, with a recent update of this model introduced by .…”

Functional gradients through the cortex, multisensory integration and scaling laws in brain dynamics

“…This scheme, mere abstraction of the observed facts, offers a dynamic conception of quantitative localizations which permits an ordering and an interpretation of multiple phenomena and syndromes. Also, this scheme is in relation to recent works suggesting that traditional specific cortical domains are separated from one another by transitional multisensory zones [15], and that multisensory interactions occur even in the primary sensory cortices [1,3,13]. …”

Multisensory Congruency as a Mechanism for Attentional Control over Perceptual Selection

“…Recently, neurophysiologists were able to demonstrate that an attended rhythm in a task enforced the entrainment of low-level neuronal excitability oscillations across different sensory modalities (Lakatos et al, 2008). The fact that oscillations in V1 entrain to attended auditory stimuli just as well as to attended visual stimuli rein-forces the view that the primary cortices are not the exclusive domain of a single modality input (Foxe and Schroeder, 2005;Macaluso and Driver, 2005;Ghazanfar and Schroeder, 2006;Kayser and Logothetis, 2007;Lakatos et al, 2007) and confirms the role of attention in coordinating heteromodal stimuli in the primary cortices (Brosch et al, 2005;Budinger et al, 2006;Lakatos et al, 2007Lakatos et al, , 2008Shinn-Cunningham, 2008). We suggest that the same populations of neurons may control multimodal sensory integration and attentional control, suggesting that the neural network that creates multimodal sensory integration may also provide the interface for top-down perceptual selection.…”