An Unexpected Dependence of Cortical Depth in Shaping Neural Responsiveness and Selectivity in Mouse Visual Cortex

Abstract

Two-photon imaging studies in mouse primary visual cortex (V1) consistently report that around half of the neurons respond to oriented grating stimuli. However, in cats and primates, nearly all neurons respond to such stimuli. Here we show that mouse V1 responsiveness and selectivity strongly depends on neuronal depth. Moving from superficial layer 2 down to layer 4, the percentage of visually responsive neurons nearly doubled, ultimately reaching levels similar to what is seen in other species. Over this span, the amplitude of neuronal responses also doubled. Moreover, stimulus selectivity was also modulated, not only with depth but also with response amplitude. Specifically, we found that orientation and direction selectivity were greater in stronger responding neurons, but orientation selectivity decreased with depth whereas direction selectivity increased. Importantly, these depth-dependent trends were found not just between layer 2/3 and layer 4 but at different depths within layer 2/3 itself. Thus, neuronal depth is an important factor to consider when pooling neurons for population analyses. Furthermore, the inability to drive the majority of cells in superficial layer 2/3 of mouse V1 with grating stimuli indicates that there may be fundamental differences in the micro-circuitry and role of V1 between rodents and other mammals.

Keywords: calcium; laminae; multi-photon; neocortex; selectivity; two-photon.

Figure 1.

Increased neural responsiveness with cortical depth in mouse V1. Left, Anatomical images of five different depth planes from one mouse. Center, Time courses of responses from two example cells from each depth plane as indicated by yellow numbers/arrows in left column. Right, Neuronal cell masks are color coded by the p value from the ANOVA for responsiveness. With increasing depth there are more cell masks colored in redder hues, indicating increased responsiveness. See Extended Data Figure 1-1 for pixel-based direction maps across cortical depth. Also see Extended Data Figure 1-2 for cortical responses to pharmacological stimuli.

Figure 2.

Population summary of cortical depth dependence on neural responsiveness and response amplitude. A, Percentage of responding neurons as a function of imaging depth. In this and subsequent panels/figures, colored lines and circles correspond to individual mice and black squares correspond to the population average at each depth. Error bars indicate SD. The thick gray line is the linear fit to the individual runs. B, Change in response amplitude with depth. C, Histogram of the distribution of response amplitude across the neuronal population at each depth plane. Blue arrows correspond to the median and red arrows to the mean.

Figure 3.

Cortical depth dependence of the OSI. A, Average of OSI values for each mouse and imaging depth. B, Average after dividing neurons into three groups based on response amplitude. Conventions as in previous figure. Also see Extended Data Figure 3-1 for the OSI of every responsive neuron in the population grouped by response amplitude and depth.

Figure 4.

Cortical depth dependence of orientation tuning width. A, At each imaging depth, the population average response is shown and fit with a tuning curve. Averages were computed for each run (five depth planes, seven animals) after aligning preferred orientations and normalizing to the maximum response for each neuron. The responses at each depth plane were then averaged across animals to obtain the population average (circles) and SD (error bars). B, Population averages grouped by response amplitude. C, The bandwidth of the tuning curves for each animal/depth plane (colored circles) and the population average (black squares) and SD (black bars). The gray line is the linear fit to the individual animal data. D, Similar to panel C but for neurons grouped by response amplitude. E, F, Similar to C, D but for the baseline amplitude of the tuning curves.

Figure 5.

Cortical depth dependence of the OMI. A, Average of OMI values for each mouse and imaging depth. B, Average grouped by neuronal response amplitude. Conventions as in previous figures.

Figure 6.

Cortical depth dependence of direction selectivity. A, Population average responses across all 16 directions at each depth were fit with a dual peak tuning curve (one peak for each of the two orthogonal directions; see Materials and Methods). B, Same as A, but for populations grouped by response amplitude. C, DMI computed from the fits. D, Same as C but for neurons grouped by response amplitude. Conventions as in Figure 4.