Pharmacological blockade of GABAA receptors reduces the stimulus selectivity of neurons in a variety of sensory cortices (Katzner et al., 2011; Kyriazi et al., 1996; Poo and Isaacson, 2009; Sillito, 1979; Wang et al., 2000). However, the mechanisms by which synaptic inhibition regulates cortical tuning have been a source of debate. One popular idea follows from studies of lateral inhibition in the retina, in which stimulation in the receptive field center of a photoreceptor elicits excitation and stimulation in the surround evokes inhibition (Hartline et al., 1956). In terms of the cortex, the strictest form of this lateral inhibition requires a spatial organization in which cortical neurons tuned to the same particular features of sensory stimuli are located near one another. “Lateral” inhibition could occur if adjacent domains of sensory cortex (such as orientation columns within cat visual cortex or whisker maps in rodent barrel cortex) are tuned to different stimulus features—and inhibition in one cortical subregion can be influenced by neighboring domains. While the necessary circuits for such lateral inhibitory interactions exist in cortex (Adesnik and Scanziani, 2010), determining
