Katharina Wilmes

Interneuron circuits for guiding local plasticity based on top-down signals.

Animals learn better when it matters to them. For example, they learn to discriminate sensory stimuli when they receive a reward. As a result of learning, neural responses to sensory stimuli are adjusted even in the first processing stages of sensory areas (Goltstein et al. 2013, Khan et al. 2018, Poort et al. 2015). It is thought that behaviourally relevant contexts, such as rewards, trigger an internal top-down signal available to these early sensory circuits. This could be mediated by cholinergic inputs from the basal forebrain for example (Letzkus et al. 2011). One challenge remains: contextual signals are typically present for a short time only, but synaptic changes require time to be expressed. How can these time scales be bridged? In this talk, I will present recent work on how interneuron circuits can bridge the time scales by guiding synaptic plasticity of excitatory connections. Interneuron circuits recently emerged as key players during learning and memory. We hence investigated how temporary top-down modulation by rewards can interact with local excitatory and inhibitory plasticity to induce long-lasting changes in sensory circuitry. We propose that learning can happen in two stages: 1) Unspecific top-down signals rapidly induce an inhibitory connectivity structure between different interneuron types. 2) The inhibitory structure induces changes in sensory representations by guiding excitatory plasticity between pyramidal cells. Using a computational model of layer 2/3 primary visual cortex, I will demonstrate how inhibitory microcircuits could store information about the rewarded stimulus to guide long-term changes in excitatory connectivity in the absence of further reward. Our model makes specific testable predictions in terms of activity of different neuron types.