Abstract
Recent studies using functional imaging and electrophysiology demonstrate that processes related to sensory integration are not restricted to higher association cortices but already occur in early sensory cortices, such as primary auditory cortex. While anatomical studies suggest the superior temporal sulcus (STS) as likely source of visual input to auditory cortex, little evidence exists to support this notion at the functional level. Here we tested this hypothesis by simultaneously recording from sites in auditory cortex and STS in alert animals stimulated with dynamic naturalistic audio–visual scenes. Using Granger causality and directed transfer functions we first quantified causal interactions at the level of field potentials, and subsequently determined those frequency bands that show effective interactions, i.e. interactions that are relevant for influencing neuronal firing at the target site. We found that effective interactions from auditory cortex to STS prevail below 20 Hz, while interactions from STS to auditory cortex prevail above 20 Hz. In addition, we found that directed interactions from STS to auditory cortex make a significant contribution to multisensory influences in auditory cortex: Sites in auditory cortex showing multisensory enhancement received stronger feed-back from STS during audio–visual than during auditory stimulation, while sites with multisensory suppression received weaker feed-back. These findings suggest that beta frequencies might be important for inter-areal coupling in the temporal lobe and demonstrate that superior temporal regions indeed provide one major source of visual influences to auditory cortex.
Highlights
Our brain integrates the information registered through the different sensory modalities into a coherent percept, based upon which we interact with our environment (Stein and Meredith, 1993)
While anatomical studies suggest regions in the superior temporal sulcus (STS) as a likely source of visual input to auditory cortex (Bizley et al, 2006; Budinger et al, 2006; Cappe and Barone, 2005; Hackett et al, 1998; Padberg et al, 2003; Smiley et al, 2007), little evidence exists at the functional level to support this notion (Ghazanfar et al, 2008)
We tested this hypothesis by performing simultaneous recordings from auditory cortex and STS in alert animals stimulated with naturalistic audio–visual scenes and using advanced methods of causal time series analysis
Summary
Our brain integrates the information registered through the different sensory modalities into a coherent percept, based upon which we interact with our environment (Stein and Meredith, 1993). For example, functional imaging studies revealed activation patterns conforming to the principles of sensory integration (Calvert et al, 1997; Foxe et al, 2000, 2002; Kayser et al, 2005, 2007b; van Atteveldt et al, 2004), and electrophysiological recordings revealed that neuronal responses to sounds can be modulated by visual or somatosensory stimuli (Bizley et al, 2006; Ghazanfar et al, 2005; Kayser et al, 2008; Lakatos et al, 2007; Schroeder and Foxe, 2002) These findings of multisensory influences in primary and secondary auditory cortex naturally beg the question of whether they reflect multisensory feed-back from association areas such as the STS, or whether they constitute processes related to sensory integration occurring independently from those in association cortices (Driver and Noesselt, 2008)
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