Inter-regional interactions uncouple within-region inhibition stabilization and paradoxical responses

Paradoxical responses, in which excitatory perturbations of inhibitory neurons reduce their firing rates, are widely regarded as a hallmark of inhibition-stabilized networks (ISNs) and have been observed in multiple brain regions. However, because brain regions are interconnected by long-range projections, it remains unclear whether a paradoxical response observed in a given region reflects inhibition stabilization within that region or instead arises from distributed interactions among regions. Here, using analytically tractable multi-region population models and numerical simulations, we show that inter-regional connections can dissociate local inhibition stabilization from paradoxical responses. The condition for a paradoxical response in a given region is jointly determined by recurrent excitation within that region, feedback mediated through other regions, and the dynamics of those other regions. Consequently, inter-regional coupling can generate a paradoxical response in a region that is not locally inhibition-stabilized or abolish it in a region that is. Thus, in an interconnected network, a paradoxical response is neither necessary nor sufficient for local inhibition stabilization. These findings demonstrate that local perturbation responses cannot generally be interpreted solely in terms of local circuit dynamics and highlight the importance of accounting for inter-regional connections when inferring the local circuit properties of individual brain regions.