, 2008). Finally, though there is little doubt that the waves propagate via synaptic excitation, it appears that synaptic inhibition is crucial to contain them. In barrel cortex in vivo, indeed, blocking GABAA receptors with bicuculline markedly increased the spread of propagating waves (London et al., 1989; Orbach et al., 1985). Similar observations were made in vitro (Chagnac-Amitai and Connors, 1989; Petersen and Sakmann, 2001; Pinto et al., 2005). These results indicate that Selleckchem Apoptosis Compound Library GABAergic inhibition controls the spatial extent of traveling waves.
GABAergic inhibition, therefore, may be involved in the marked context dependence of traveling waves in visual cortex (Figure 6). The role of GABA in traveling waves, however, is not currently understood and neither is the possible
role that might be played by long-range GABAergic projections (Higo et al., 2007; McDonald and Burkhalter, 1993; Tomioka et al., 2005). In reviewing the evidence in favor of traveling waves in primary visual cortex, we have identified multiple questions that remain unanswered. Perhaps the main one concerns the relationship between different kinds of traveling waves. Our Review has focused on concentric waves evoked by focal stimuli (Figures 2, 3, 4, and 6) and seen in ongoing activity (Figure 5), but we have also mentioned large planar waves that are seen especially during NVP-AUY922 solubility dmso non-REM sleep. What is the relationship between these kinds of waves, and do they share the same mechanisms? Also, there are other kinds of propagating activity, such as spiral waves (Huang et al., 2010), and future work needs to clarify the relationships and differences among them. In fact, while we have not hesitated in using the term “traveling wave” to describe the dynamics of activity across space and time, others might disagree with us. We have reviewed substantial evidence supporting the notion that focal visual stimuli MYO10 cause
cortical activity that spreads over time to a large region of cortex, appearing earlier in the retinotopically appropriate cortical locations and progressively later in more distal locations. We believe that it is useful to describe all this as a traveling wave. However, we have also reviewed data (Figure 7) in which some aspects of activity do not seem to show any travel (Sit et al., 2009). Based on these aspects, one might hesitate to refer to the dynamics of activity as a traveling wave. Future experiments could address these questions and ideally go beyond the representation of single waves originating in single places. By using more than one stimulus (but not too many, otherwise, as we have seen the waves disappear), one could characterize how waves interact with each other, and how they relate to the interactions between stimuli that have been extensively documented.