Complementary networks of cortical somatostatin interneurons enforce layer specific control

Abstract

The neocortex is functionally organized into layers. Layer four receives the densest bottom up sensory inputs, while layers 2/3 and 5 receive top down inputs that may convey predictive information. A subset of cortical somatostatin (SST) neurons, the Martinotti cells, gate top down input by inhibiting the apical dendrites of pyramidal cells in layers 2/3 and 5, but it is unknown whether an analogous inhibitory mechanism controls activity in layer 4. Using high precision circuit mapping, in vivo optogenetic perturbations, and single cell transcriptional profiling, we reveal complementary circuits in the mouse barrel cortex involving genetically distinct SST subtypes that specifically and reciprocally interconnect with excitatory cells in different layers: Martinotti cells connect with layers 2/3 and 5, whereas non-Martinotti cells connect with layer 4. By enforcing layer-specific inhibition, these parallel SST subnetworks could independently regulate the balance between bottom up and top down input.

Taxonomy of neural oscillation events in primate auditory cortex

“…Detailed computational modeling of neural circuits has shown how interactions between different classes of interneurons contribute to fast and slow rhythms, via short and long GABA A synaptic time constants [39][40][41][42] . In vivo , we expect that interactions between different interneuron sub-populations and pyramidal neurons will result in a mix of oscillations in the recorded signals [43][44][45][46][47] , making it unlikely to observe a constant frequency/amplitude oscillation. Some of these interactions, which could lead to shifts in peak oscillation frequency over time or variability in waveform shapes in different nearly simultaneous oscillation events, could be explored through detailed computational modeling.…”

Head Movements Control the Activity of Primary Visual Cortex in a Luminance Dependent Manner

“…In fact, by comparing the activity of SOM cells across layers, only SOM cells in deep layers were excited in response to head movements in the dark, no longer so in light, and increased their basal activity in light. These SOM cells are likely deep layer Martinotti cells, because of their location and spike shape [22][23][24] (see methods). Therefore, we propose that deep layer Martinotti cells integrate vestibular and luminance signals in V1.…”

“…For our analysis, we included only SOM cells with regular spike shape (see section: Definition of RS and FS cells). We excluded from our analysis five putative SOM cells that had fast spiking shape because they are non-Martinotti cells [22][23][24] (see Discussion).…”

ALK4 coordinates extracellular and intrinsic signals to regulate development of cortical somatostatin interneurons

“…Chondrolectin (encoded by Chodl) has been found to mark a distinct class of deep layer SST + cells (Tasic et al, 2018(Tasic et al, , 2016 with long-range projections that cross to the contralateral hemisphere (Taniguchi et al, 2011;Kubota et al, 1994;Tomioka et al, 2005). Finally, Hpse mRNA (encoding Heparanase) was also recently found to specifically label a subpopulation of SST + cells in cortical layer IV that targets PV + fast-spiking interneurons in the same layer (Naka et al, 2019). This subpopulation is sometimes referred to as X94 cells, since a large fraction of these cells is labeled in the X94 Gad67 eGFP mouse transgenic line (Ma et al, 2006).…”

“…This could have been due to a stochastic requirement for ALK4 signaling across different SST + interneuron subtypes, or else reflect the existence of subpopulations of SST + cells with distinct requirements. Recent studies have leveraged single-cell RNA-Seq methods to molecularly define distinct populations of cortical GABAergic interneurons, including several subtypes of SST + cells (Mayer et al, 2018;Mi et al, 2018;Tasic et al, 2018;Naka et al, 2019). Although much remains to be learned about the functional features of many of those subpopulations, a few of the molecular markers identified do label cortical GABAergic neurons with known functional properties.…”