SummaryGABAergic activity is thought to influence developing neocortical sensory circuits. Yet the late postnatal maturation of local layer (L)4 circuits suggests alternate sources of GABAergic control in nascent thalamocortical networks. We show that a population of L5b, somatostatin (SST)-positive interneuron receives early thalamic synaptic input and, using laser-scanning photostimulation, identify an early transient circuit between these cells and L4 spiny stellates (SSNs) that disappears by the end of the L4 critical period. Sensory perturbation disrupts the transition to a local GABAergic circuit, suggesting a link between translaminar and local control of SSNs. Conditional silencing of SST+ interneurons or conversely biasing the circuit toward local inhibition by overexpression of neuregulin-1 type 1 results in an absence of early L5b GABAergic input in mutants and delayed thalamic innervation of SSNs. These data identify a role for L5b SST+ interneurons in the control of SSNs in the early postnatal neocortex.

Attention allows animals to respond selectively to competing stimuli, enabling some stimuli to evoke a behavioral response while others are ignored. How the brain does this remains mysterious, although it is increasingly evident that even animals with the smallest brains display this capacity. For example, insects respond selectively to salient visual stimuli, but it is unknown where such selectivity occurs in the insect brain, or whether neural correlates of attention might predict the visual choices made by an insect. Here, we investigate neural correlates of visual attention in behaving honeybees (Apis mellifera). Using a closed-loop paradigm that allows tethered, walking bees to actively control visual objects in a virtual reality arena, we show that behavioral fixation increases neuronal responses to flickering, frequency-tagged stimuli. Attention-like effects were reduced in the optic lobes during replay of the same visual sequences, when bees were not able to control the visual displays. When bees were presented with competing frequency-tagged visual stimuli, selectivity in the medulla (an optic ganglion) preceded behavioral selection of a stimulus, suggesting that modulation of early visual processing centers precedes eventual behavioral choices made by these insects.invertebrate | vision | electrophysiology | local field potential A ttention allows animals to respond selectively to competing stimuli (1, 2). Stimulus-selective responses in the human brain can be endogenously driven, and this volitional form of attention has been referred to as a "top-down" process, to distinguish it from salience-driven or "bottom-up" attention (3). Although even insects display bottom-up attention (4-10), it is unclear whether attention-like selection in the insect brain might also precede or predict behavioral choices. The case for top-down attention is especially compelling for honeybees, which have welldemonstrated visual discrimination and cognitive capabilities (11)(12)(13)(14). To effectively relate attention processes to behavior, however, requires sophisticated behavioral tracking or recording brain activity from behaving insects selecting distinct objects (15). Previous psychophysical studies in insects have measured whole body movements using tethered, closed-loop flight paradigms (4-8, 15). However, most studies of visual perception and memory in the bee have involved free flight (11, 13, 14; but see ref. 16). To address the neural mechanisms subserving these behaviors, researchers have traditionally recorded brain activity from immobilized bees performing elemental associative learning (e.g., refs. 17 and 18). Animal immobilization, however, is not ideal for gaining a better understanding of the relationship between the complex cognitive behaviors seen in freely moving bees and the underlying neural activity (13,14). To this end, we developed a closed-loop paradigm for walking honey bees (19), allowing them to select and fixate visual cues by rotating an air-supported ball. To simultaneously examine attentio...

GABAergic interneurons are a highly heterogeneous group of cells that are critical for the mature function and development of the neocortex. In terms of the latter, much attention has focused on the well-established role of parvalbumin (PV+)-expressing, fast spiking, basket cells in determining the critical period plasticity. However recent endeavours have started to shed the light on the contribution of other interneuron subtypes to early circuit formation and plasticity. Data suggests that there are significant interactions between PV+ cells and other interneuron subtypes that regulate circuit development in rodents in the first postnatal week. Moreover, a number of these early interactions are transient which points to an important, distinct role for interneuron diversity in setting up emergent neocortical processing.