Figure 2. A, Schematic architecture of the olfactory bulb. Filled circles on the intersection of processes denote bidirectional synaptic connections; filled circles that abut neurons indicate polarized axo-dendritic synapses. Open circles indicate connections that are suspected but not directly confirmed or are mediated by diffuse extrasynaptic signaling. ET, External tufted; G, granule; M, mitral; PG, periglomerular; SA, short-axon; T, tufted. B, Top, Response time course of three glomeruli (see arrows with corresponding colors below) to ethyl butyrate (1% saturated vapor). Bottom, Patterns of fluorescence signals in 154 ms time windows centered on the time points indicated by lines (modified from Spors et al., 2006). C, Respiration (measured as intranasal pressure) in an awake, freely moving rat, showing changes in frequency, amplitude and duration of individual “sniffs”—as well as pauses in breathing—within a ∼15 s span. Arrow indicates direction of inspiration (modified from Wachowiak, 2011). D, Spike trains from two sister MT cells (red and blue) and respiration (top). Sister cell responses to different odors have similar firing rates, but can have different phases (modified from Dhawale et al., 2010).