The ratio between synaptic excitation and inhibition is a fundamental determinant of circuit function. Inhibition was long thought to operate in proportionality to excitation in neocortex, leaving the E/I ratio largely unperturbed. However, more recent results have revealed the central role of short-term modulation and long-term plasticity of inhibitory transmission for adjusting pyramidal neuron function to the current computational requirements of the animal. The emerging picture is thus that the rich diversity of inhibitory interneuron types endows the circuit with a set of distinct control units that are critical for tuning pyramidal cell computations for brain functions ranging from contextual control of stimulus processing to learning, memory and cortical map plasticity. Moreover, aberrant regulation and plasticity of neocortical inhibition is firmly linked to a range of brain disorders.

Here, we will present recent insights into these mechanisms, and discuss the emerging computational concepts with a focus on sensory neocortex. Jochen Staiger (Göttingen) will elucidate local and long-range circuit motifs formed by disinhibitory interneurons expressing the marker VIP. Julia Veit (Freiburg) will discuss the emerging role of VIP interneurons in controlling gamma band synchronization in a stimulus- and behavioral-state dependent way. Simon Renner (young investigator, Munich) will take a theory-based approach to infer functional connectivity between inhibitory and excitatory cortical populations from sensory response properties. Johannes Letzkus (Freiburg) will cover the role of inhibition during active behaviors, and present recent insights into plasticity of inhibition in layer 1 in the context of learning, focusing both on established and novel interneuron types that supply inhibition to this major association site. Jastyn Pöpplau (young investigator, Hamburg) will elucidate the developmental role of prefrontal cortex PV interneurons for oscillatory activity, network function and cognition. Tania Rinaldi Barkat (Basel) will finally illustrate the central contribution of PV interneurons to critical period plasticity during auditory cortex development.

Start Symposium