Our data also support this view. Typical of CCGs, peaks are centered on zero, indicating a predominance of common input, arising either from thalamic inputs or other cortical sources. This pedestal of common input is accompanied by a prominent feedforward direction of information flow, as indicated by the strength of interareal interactions (Figure 7C) and the predominantly positive asymmetry indices (Figure 7E). In visual cortex, V1-V2 interactions are on average stronger than

V1-V1 interactions, reflecting the larger degree of spatial integration in V2 and concomitant larger network size (Hung et al., 2010; Livingstone and Hubel, 1984; Ts’o and Gilbert, 1988; Roe and Ts’o, 1999). In somatosensory cortex, greater interareal integration may also be expected due to the larger receptive field sizes in area 1 than in area 3b. Steady-state

BMS-754807 order Ulixertinib clinical trial intrinsic interactions within area 3b and within area 1 may also provide a baseline configuration upon which sensory stimuli or other active states are further elaborated (Reed et al., 2008; cf Steinmetz et al., 2000). Thus, sensory stimulation may further enhance the preexisting biases, producing in SI a strongly feedforward direction of information flow in the stimulated state. Such hypotheses have been supported by studies of macroscale networks. This study now extends these ideas to the local microscale network. Eighteen squirrel monkeys (fMRI, 11 monkeys; anatomy, 3 monkeys; electrophysiology, 4 monkeys) were anesthetized with ketamine hydrochloride (10 mg/kg)/atropine first (0.05 mg/kg) and maintained with isoflurane anesthesia (0.8%–1.1%) delivered in a 70:30 O2/N2O mixture. All procedures were in compliance with and approved

by the Institutional Animal Care and Use Committee of Vanderbilt University. All MRI scans were performed on a 9.4-T Varian Inova spectrometer (Varian Medical Systems) using a 3-cm surface coil. T2-weighted oblique structural images (echo time [TE], 16; repetition time [TR], 200 ms) at 78 × 78 × 1,000 μm3 resolution were acquired and coregistered with fMRI maps and with blood-vessel maps. Functional MRI data acquired from the same slices using a gradient echo planar sequence (TE, 16 ms; TR, 1.5 s) at voxel sizes of 575 × 575 × 2,000 μm3 (and for one case at 275 × 275 × 2,000 μm3) were reconstructed and imported into MATLAB (MathWorks) for analysis. Within each imaging session, both tactile stimulus-driven and resting-state BOLD images were acquired. Eighteen sets of resting-state fMRI data were acquired from eleven anesthetized squirrel monkeys. Determination of seed voxels in areas 3b and 3a in each animal were based on stimulus-driven fMRI activation maps and the available electrophysiology maps for each animal. Voxel-wise correlation was calculated and then thresholded at r ≥ 0.7 for display. Fingers were secured and tactile stimulation (8 Hz vibrotactile stimulation) of fingerpads was delivered with a piezoceramic device.