A distinguishing feature of animals is their ability to detect, internalize, and respond to

their surrounding environment. Despite the seeming simplicity of our basic sensory functions, the ability to sense requires a surprisingly complex neural architecture. Mammalian sensory systems follow several organizing principles including topography and cortical columns. The two organizing principles of topography and columns are exquisitely demonstrated in the somatosensory (touch) system of rodents. Unlike humans, rats spend most of their time in dark tunnels underground and rely on the rich tactile information provided by their whiskers. The array of whiskers on the snout project to a discrete, barrelshaped regions in the primary somatosensory cortex that match the pattern and orientation of the facial whiskers. This remarkable region is referred to as the rodent barrel cortex, and is perhaps one of the beststudied sensory cortices in the mammalian brain. However, our understanding of the rodent barrel cortex comes mostly from the anatomy and function of individual neurons, despite a general agreement that sensory function arises from large populations of neurons not single neurons. This dissertation focuses on the functional organization of barrel cortex from a mesoscopic perspective that encompasses large populations of neurons. A primary focus is the functional consequence of large, intracortical activity spreads which are ubiquitous in sensory cortex but are still poorly understood. Experimental evidence focusing on the rodent barrel cortex is presented demonstrating how large, intracortical activity spreads (point preads) underlie sensory coding and integration, provide a robust substrate for invariant sensory coding, and establish a large area of protection from ischemic attack.