1983), improved detection of weak stimuli (Frens and Van Opstal 1995; Driver and Spence 1998; McDonald et al. 2000), and improved AMP-activated protein kinase pathway sensory-perception of illusory effects such as the ventriloquist or McGurk illusions (Howard and Templeton 1966; McGurk and MacDonald 1976). Human and animal studies have shown that the mere presence of additional sensory input even when it is irrelevant for performance of a task can enhance neural Inhibitors,research,lifescience,medical excitability in the attended sensory modality (Calvert et al. 1997; Macaluso
et al. 2000, 2002; Calvert 2001; Foxe et al. 2002; Kayser et al. 2005, 2007; Pekkola et al. 2006; Lehmann et al. 2006; Lakatos et al. 2007; Meehan and Staines 2009), suggesting that interactions between modality-specific cortical representations exist. By contrast, other studies have shown crossmodal enhancement in modality-specific sensory cortex only occurs when both stimuli events are relevant for behavior (Dionne et al. 2010, 2013). These findings suggest that crossmodal processing is likely governed Inhibitors,research,lifescience,medical by both bottom-up sensory-sensory interactions and top-down attentional mechanisms in order to allow for the selection, amplification, and integration of sensory input relevant for initiating goal-oriented responses. Bottom-up interactions can occur when salient
stimuli from an unattended sensory modality influence neural excitability in the attended modality, while top-down processing occurs when attention is voluntarily directed toward relevant Inhibitors,research,lifescience,medical stimuli in the presence of environmental distracters. However, while both these attentional mechanisms can modulate neural responses in modality-specific
sensory cortex, it remains unclear how these attentional mechanisms Inhibitors,research,lifescience,medical interact during sensory processing of crossmodal stimuli. Neurophysiological research in the primary auditory cortex of monkeys has provided evidence that sensory-to-sensory interactions exist. Recent studies have shown that neural responses in regionally distinct areas of the primary auditory cortex are enhanced when visual and/or tactile stimuli are paired with auditory stimuli (Kayser Inhibitors,research,lifescience,medical et al. 2005, 2007). Lakatos et al. (2007) showed that presentation of somatosensory stimuli increased auditory neural responses when the two stimuli were simultaneously combined versus when the auditory stimulus was presented in isolation. Furthermore, Bizley et al. (2007) reported a 15% neuronal increase in the ferret primary auditory cortex following simultaneous presentation of visuo-auditory nature biotechnology stimuli (Bizley et al. 2007). Neuroimaging studies in humans complement the sensory-to-sensory interactions reported in animal findings by showing that the presence of crossmodal input can modulate neural excitability in modality-specific sensory cortices. For example, several functional magnetic resonance imaging (fMRI) studies have reported increased blood oxygenation level-dependent (BOLD) responses in modality-specific cortices due to the mere presence of stimuli from another modality.