Feedback is a ubiquitous anatomical feature of sensory processing in vertebrates. In this issue of Neuron, two papers (Boyd et al., 2012, and Markopoulos et al., 2012) analyze the features of feedback from olfactory cortex to olfactory bulb.

This paper concludes the Focus Serial assembled of invited papers in key areas of nonlinear optics (Editors: J.M. Dudley and R.W. Boyd), and it discusses new directions for future research in this field.

OBJECTIVE To evaluate the reproducibility of the calculation of breast density with DM-Scan software, which is based on the semiautomatic segmentation of fibroglandular tissue, and to compare it with the reproducibility of estimation by visual inspection. MATERIAL AND METHODS The study included 655 direct digital mammograms acquired using craniocaudal projections. Three experienced radiologis...

A multilinear version of the Boyd interpolation theorem is proved in the context of quasi-normed rearrangement-invariant spaces. A multilinear Marcinkiewicz interpolation theorem is obtained as a corollary. Several applications are given, including estimates for bilinear fractional integrals.