Romei et al. (2009) measured visual cortical excitability in humans by using transcranial magnetic stimulation (TMS) to induce visual phosphenes, and they found stronger visual phosphene perception following the presentation of sounds—hence demonstrating sound-induced enhancement of visual perception. However, whether V1 is really the key area critically affected Abiraterone supplier by TMS in that study remains uncertain, and perception ultimately

depends on multiple sensory areas and their collective interplay. Hence, the specific contributions of crossmodal activations in individual areas and their causal relation to behavior remain to be elucidated. In addition, it remains to be seen whether the reported SH in V1 can support some of the functional specificity of crossmodal interactions reported in previous studies. For example, in the TMS study, certain sounds (for example, looming) caused stronger excitability than simple noises (Romei et al., 2009), revealing specificity with regard to the acoustic input. And in a visual perceptual learning experiment, sounds were found to enhance learning in a spatially restricted region of the visual field, pointing to specificity locally within visual retinotopic maps (Beer and Watanabe, 2009). Ongoing work suggests that rodents can display similar behavioral crossmodal benefits as humans.

Rats trained and tested by using operant conditioning on an audio-visual detection task that uses food reward Resminostat (rather than aversive conditioning) show better and faster detection as found in corresponding human psychophysical studies (Gleiss et al., 2012, Cosyne, abstract). This suggests that Sirolimus manufacturer the

behavioral findings of Iurilli et al. (2012) do not result from a species-specific stereotype but are better interpreted in the context of crossmodal competition induced and emphasized by the behavioral paradigm of aversive conditioning. Recent work shows that aversive conditioning engages neuromodulatory feedback on primary sensory cortices through the translaminar activation of layer 2/3 pyramidal neurons by reducing the tonic inhibition of local interneurons (Letzkus et al., 2011). Hence, whereas aversive learning seems to enhance neuronal responses to the aversive-associated stimulus (here, visual), crossmodal activations (here, auditory) can reduce these. The new findings therefore also predict that the acquisition of aversive-associative learning should be slowed in a multisensory context. Still, additional studies would be required to elucidate in detail how the behavioral task context affects the behavioral and neural patterns of crossmodal interactions. Anatomical studies have highlighted the direct connectivity between early sensory cortices of different modalities (Falchier et al., 2002). The new study in mice not only reveals the prominence of sound-induced changes in V1, but also reports that visual stimulation has a weaker effect on auditory or somatosensory cortex than vice versa.