Functional response properties of VIP-expressing inhibitory neurons in mouse visual and auditory cortex

Abstract

Despite accounting for about 20% of all the layer 2/3 inhibitory interneurons, the vasoactive intestinal polypeptide (VIP) expressing neurons remain the least thoroughly studied of the major inhibitory subtypes. In recent studies, VIP neurons have been shown to be activated by a variety of cortico-cortical and neuromodulatory inputs, but their basic sensory response properties remain poorly characterized. We set out to explore the functional properties of layer 2/3 VIP neurons in the primary visual (V1) and primary auditory cortex (A1), using two-photon imaging guided patch recordings. We found that in the V1, VIP neurons were generally broadly tuned, with their sensory response properties resembling those of parvalbumin (PV) expressing neurons. With the exception of response latency, they did not exhibit a significant difference from PV neurons across any of the properties tested, including overlap index, response modulation, orientation selectivity, and direction selectivity. In the A1, on the other hand, VIP neurons had a strong tendency to be intensity selective, which is a property associated with a subset of putative pyramidal cells and virtually absent in PV neurons. VIP neurons had a best intensity that was significantly lower than that of PV and putative pyramidal neurons. Finally, sensory evoked spike responses of VIP neurons were delayed relative to pyramidal and PV neurons in both the V1 and A1. Combined, these results demonstrate that the sensory response properties of VIP neurons do not fit a simple model of being either PV-like broadly tuned or pyramidal-like narrowly tuned. Instead, the selectivity pattern varies with sensory area and can even be, as in the case of low sound intensity responsiveness, distinct from both PV and pyramidal neurons.

Response reversal during top-down modulation in cortical circuits with multiple interneuron types

“…Furthermore it could be extended to explain similar phenomena observed in A1 [12,29]. In addition it is in line with experimental results that show that VIP interneurons play an important role in cortical activity modulation [7,8,20].…”

VIP interneurons in mouse primary visual cortex selectively enhance responses to weak but specific stimuli

“…This complementary size tuning parallels the complementary contrast tuning observed here, suggesting that VIP and SST neurons in V1 are tuned for weak and strong inputs, respectively, across multiple stimulus dimensions. Indeed, this relationship appears to hold across sensory modalities as VIP neurons in mouse primary auditory cortex are selective for lower sound intensities than SST or PV neurons ( Mesik et al, 2015 ). Taken together, a parsimonious explanation of these results is that VIP neuron activity supports a high gain regime that increases sensitivity to weak inputs, whereas SST neuron activity promotes a low gain regime that decreases sensitivity to strong inputs and maintains network stability.…”

Inhibitory Units: An Organizing Nidus for Feature-Selective SubNetworks in Area V1

“…This procedure likely discriminates in favor of VIP-negative and PV-negative interneurons, such as SOMϩ cells, which are more likely to be tuned for orientation and direction than PVϩ and VIPϩ cells (Kerlin et al, 2010;Ma et al, 2010). PVϩ and VIPϩ cells are typically broadly tuned and not selective for these features (Kerlin et al, 2010;Ma et al, 2010;Mesik et al, 2015, but see Runyan et al, 2010 for examples of oriented PVϩ cells). Figure 5, A and B, illustrates an example of three direction tuned pyramidal IPP-cluster members linked to their tuned interneuron partner.…”