The species dependence is further evidenced by differences in cortical organization between cat and mouse V1. First, in the cat V1, simple cells are found in thalamocortical recipient layers (layer 4 and 6; Hirsch and

Martinez, 2006) and the spatial arrangement of feed-forward thalamic inputs is important for the establishment of OS. In the mouse V1, neurons in layer 4 are mostly monocontrast and simple cells primarily appear in layer 2/3 (Liu et al., 2009). OS of simple cells we recorded likely results from BTK inhibitor ic50 integrating recurrent inputs from layer 2/3 and feed-forward inputs from layer 4 (Dantzker and Callaway, 2000 and Mooser et al., 2004), some of which may already be orientation tuned (Niell and Stryker, 2008 and Ma et al., 2010). Second, there is a columnar organization of OS in the cat V1, whereas in the mouse V1 neurons preferring different orientations are intermingled in a “salt-and-pepper” fashion (Ohki et al., 2005). It has been shown that patterns of synaptic inputs to cat V1 neurons Epacadostat mouse vary depending on the cell’s location in the orientation map (Schummers et al., 2002 and Mariño et al., 2005). Within the orientation domain, the neuron receives intracortical inputs from other cells sharing the same orientation preference, whereas at pinwheel centers the intracortical inputs are from cells with a wide range of different orientation preferences. Therefore, both excitation

and inhibition are much more broadly tuned at pinwheel centers than within orientation domains (Mariño et al., Florfenicol 2005; note that the simple or complex cell type was not explicitly identified in this study). In comparison, synaptic inputs to our recorded cells exhibited less selectivity than those to cat cells within orientation

domains. This observation is consistent with a lack of orientation maps in the mouse V1 and the result that local synaptic inputs to the layer 2/3 neuron have a wide variety of orientation preferences (Jia et al., 2010). A more careful comparison indicates that excitatory inputs to mouse simple cells are more selective than those to cat cells at pinwheel centers, implying that synaptic connections to mouse simple cells might be slightly more selective than cat cells at pinwheel centers. Our study demonstrates two effects that significantly impact OS. The first one is the membrane blurring of selectivity when PSP responses are generated from excitatory inputs alone. This is due to a saturation of PSP response with increasing excitatory input strength, caused by a rapid reduction in the excitatory driving force as the depolarizing potential approaches the reversal potential for excitatory currents. For relatively small excitatory conductances, the membrane blurring would be less a problem, since the initial phase of the input-output curve can be approximated by a linear function crossing the origin, i.e., f(x) = ax.