, 1979, Sillito et al., 1980,

Sato et al., 1996 and Ringach et al., 2003). In theoretical studies, inhibition that is more broadly tuned than excitation has been employed to effectively sharpen OS (Somers et al., 1995, Ben-Yishai et al., 1995, Troyer et al., 1998 and McLaughlin et al., 2000). However, except for a few cases (Wu et al., 2008 and Poo and Isaacson, 2009), a match of excitatory and inhibitory tunings is widely observed in the sensory cortex (in cat visual cortex, Anderson et al., 2000, Monier et al., 2003, Mariño et al., 2005 and Priebe and Ferster, 2005; in rodent auditory and somatosensory cortex, Wehr and Zador, 2003, Zhang et al., 2003, Tan et al., 2004, Okun and Lampl, 2008 and Tan and Wehr, 2009). While previous mechanistic studies were mostly carried out in cats, mouse visual cortex has recently emerged as an important Y-27632 research buy experimental model for

RO4929097 supplier visual research. Recent recordings in the mouse V1 have shown that similarly as in the cat V1, spiking responses of simple cells can be strongly orientation tuned (Mangini and Pearlman, 1980, Niell and Stryker, 2008 and Liu et al., 2009). However, the spatial distribution of excitatory and inhibitory synaptic inputs largely differs from that proposed for cat simple cells (Liu et al., 2010), implying that the mouse circuits for OS might be different from those in cats. First, each synaptic subfield (On or Off, excitatory or inhibitory) often possesses a rather round shape with small aspect ratios, which suggests that the spatial arrangement of synaptic inputs may not sufficiently account for OS. Second, while excitation

and inhibition are organized in a spatially opponent manner in cat simple MTMR9 cells (Ferster, 1988, Hirsch et al., 1998 and Anderson et al., 2000), in mouse simple cells the excitatory and inhibitory subfields for the same contrast display a large spatial overlap, suggesting that excitation and inhibition evoked by oriented stimuli may temporally overlap significantly at whichever stimulus orientation. These properties of synaptic inputs to mouse simple cells suggest that inhibition can play a significant role in determining orientation tuning properties of their spike responses. To investigate the synaptic mechanisms underlying OS in the mouse V1, we carried out in vivo whole-cell voltage-clamp recordings from simple cells in layer 2/3. We dissected excitatory and inhibitory synaptic inputs evoked by oriented stimuli and characterized the spatiotemporal interplay between these inputs. We found that excitatory conductances are broadly tuned with only a moderate bias for a preferred orientation. Inhibition exhibits the same preferred orientation, but the tuning is significantly broader than that of excitation.