g., primary auditory cortex [A1] and primary somatosensory cortex [S1]). In area V2 of macaque visual cortex, biocytin-labeled pyramidal neurons of L2/3 and L5 have been shown to provide laterally spreading axon projections that terminate in discrete patches (250–300 μm diameter), primarily in L2/3, and distributed in an elongated field orthogonal IWR-1 order to the stripe compartments (Levitt et al., 1994). There were prominent patchy connections within, as well as between, individual compartments, perhaps reflecting functional substructures within stripes. In area V4 of macaque visual cortex, pyramidal neurons of L2/3 make extensive lateral projections with oval or circular

patches of terminals in L1–L3 (Yoshioka et al., 1992). It has been reported that any small patch of tissue (∼250 μm wide) injected in the superficial layers connects reciprocally to patches scattered up to 3 mm around the injection. In contrast, small injections in L4 did not produce similar patch-like lattice connections, whereas injections in L5 gave relatively weak rising contributions compared to the superficial layer patch system. These findings indicate a functional repeat distance of 450–600 μm in area V4 with a patchy, discontinuous layout. In addition to visual cortex, other sensory cortical areas are characterized by similar

intracortical connectivity patterns. For instance, in cat primary auditory cortex (A1), it has been reported using retrograde anatomic tracing and topographic physiologic mapping of acoustic responses Luminespib research buy (Read et al., 2001) that L2/3 are characterized by long-range (>1.5 mm) connections between patches with similar acoustic properties, whereas connections in L4 are mostly local. Similarly, L3 of cat primary somatosensory about cortex (S1) is characterized by long-range horizontal axons that can travel for up to 2.5 mm (Schwark and Jones, 1989), whereas L4 connections are mostly local. Importantly, long-range horizontal connections in cat S1 are patchy and connect neurons tuned to the same whisker. Surprisingly,

we found that populations of neurons in different cortical layers may employ different coding strategies. By operating in a virtually uncorrelated state, cells in the granular layer, which receive afferents from networks in hierarchically lower cortical and subcortical areas, and have only local projections to other layers within V1, may encode incoming stimuli more accurately than cells in the supragranular and infragranular layers (based on the results of our model and using linear decoder analysis). In contrast, the output layers (supragranular and infragranular), which send projections to other cortical and subcortical areas possibly encode information less accurately by exhibiting large correlated variability.