Volume 27, Issue 13, Pages 3733-3740.e3 (June 2019) Activation of a Visual Cortical Column by a Directionally Selective Thalamocortical Neuron  Yulia Bereshpolova, Carl R. Stoelzel, Chuyi Su, Jose-Manuel Alonso, Harvey A. Swadlow  Cell Reports  Volume 27, Issue 13, Pages 3733-3740.e3 (June 2019) DOI: 10.1016/j.celrep.2019.05.094 Copyright © 2019 The Authors Terms and Conditions

Cell Reports 2019 27, 3733-3740.e3DOI: (10.1016/j.celrep.2019.05.094) Copyright © 2019 The Authors Terms and Conditions

Figure 1 Postsynaptic Impact of LGN DS Neurons (A) We recorded from one or more LGN neurons in awake rabbits using an array of independently movable microelectrodes. Spike-triggered field potentials, generated from spontaneous spikes of the LGN neuron, were recorded from the retinotopically aligned region of V1 using a 16-channel silicone probe (vertical spacing, 100 μm) or single electrodes. (B) RFs of an LGN DS neuron and the multiunit cortical RFs from the aligned region of V1 were mapped with sparse noise and plotted using reverse correlation. Retinotopic alignment of the LGN DS cell’s ON responses (red) and OFF responses (blue) with a L4 cortical site (black) was very good, with the RF centers of the LGN and cortical fields separated by less than half the diameter of the LGN RF. (C) Polar plot of the directional selectivity of this LGN DS neuron showing a strong preference for motion from posterior to anterior visual field. (D) Distribution of preferred directions of all LGN DS neurons studied. Numbers of cells that fall into directions of cardinal axes are indicated by numbers. (E and F) Spike-triggered average field potentials (for this cell, generated by 9,947 LGN spikes) were plotted on all cortical probe sites (E), and the spike-triggered CSD depth profile of these averages was derived (F). Downward and upward responses in (F) represent current sinks (inward currents) and sources, respectively. (G) Color map of the spike-triggered CSD depth profile shown in (F). Here and in Figures 2 and 3, the solid horizontal arrow in colorized CSD profiles (on the left) indicates the cortical channel that corresponded to the reversal point of the field potential generated by a diffuse flash stimulus, brackets indicate estimate of the upper and lower boundaries of L4 (STAR Methods), and red and blue represent current sinks and sources, respectively. (H) A spike-triggered average LFP elicited from the cortical site with the peak postsynaptic response (channel 5 in E), showing a strong presynaptic (left oblique arrow) and postsynaptic (right oblique arrow) response. Vertical dashed line indicates time of the LGN spike. Cell Reports 2019 27, 3733-3740.e3DOI: (10.1016/j.celrep.2019.05.094) Copyright © 2019 The Authors Terms and Conditions

Figure 2 Comparing the Impact Generated in V1 by LGN DS Neurons and Concentric Neurons: Depth and Strength of Impact, Thalamocortical Conduction Times, and Spontaneous Impulse Activity (A) RFs of a pair of simultaneously recorded LGN DS and LGN concentric neurons and the RF of the retinotopically aligned recording site in L4 (mapped and plotted as in Figure 1B). (B and C) Depth profiles, recorded simultaneously and on the same probe in V1, of the spike-triggered presynaptic (axonal, left oblique arrows) and postsynaptic (right oblique arrows) currents generated by this LGN DS neuron (B) and concentric neuron (C). Although these two LGN neurons have a similar depth profile, the DS neuron has a somewhat longer latency. (D) The frequency distribution of depths for the maximum amplitude postsynaptic responses generated by well-aligned LGN DS neurons (n = 20 cells, n = 2 rabbits) and concentric neurons (n = 38 cells, n = 3 rabbits) (the same cells were used for analysis in F–I), normalized to the flash reversal point (depth of “0”; STAR Methods). Four of the DS neurons and 7 of the concentric neurons also generated a postsynaptic response near the L5/L6 border. Asterisks show the depth of V1 SINs (n = 10 cells, n = 1 rabbit) that, on the basis of cross-correlation analysis, received a synaptic drive from an LGN DS neuron (Figure 4). (E) For comparative purposes, the depth distributions of the cell bodies of corticotectal neurons, antidromically activated from the superior colliculus (green bars, taken from Bereshpolova et al., 2007), and the depth distribution of the most superficial L6 corticogeniculate neurons (antidromically activated via LGN stimulation) found in similarly studied penetrations (Stoelzel et al., 2017) are shown. (F) The distribution of thalamocortical presynaptic (axonal) latencies for LGN DS neurons and LGN concentric neurons. The inset shows the mean latencies for LGN DS and LGN concentric neurons (p < 0.001, Mann-Whitney U test). (G–I) Comparison of average amplitude (G; p = 0.606, Mann-Whitney U test) and rise time (H; p = 0.2415, t test) of the peak postsynaptic responses generated by well-aligned LGN DS and concentric neurons. The spontaneous firing rates of these LGN populations were also compared (I; p = 0.729, t test). Error bars indicate SEM. Cell Reports 2019 27, 3733-3740.e3DOI: (10.1016/j.celrep.2019.05.094) Copyright © 2019 The Authors Terms and Conditions

Figure 3 Thalamocortical Synapses of LGN DS Neurons Display Short-Term Depression LGN DS spikes with long preceding interspike intervals generate more powerful postsynaptic potentials than spikes with short preceding intervals. (A1 and B1) Individual action potentials were selected from spontaneous spike trains of LGN DS neurons, on the basis of their preceding interspike interval. Arrows indicate selected spikes. New spike trains were generated using only those spikes with preceding interspike intervals within a specific range. Short-interval spikes (A1) were those with preceding interspike intervals between 5 and 20 ms, while long-interval spikes (B1) were those with intervals of 500–3,000 ms. (A2 and B2) Spike-triggered LFP and CSD profiles were generated using only these selected spikes (short, n = 3,348 spikes; long, n = 405 spikes). Gain settings and color intensities for both spike-triggered CSD (stCSD) profiles are identical. (C) Spike-triggered field potentials generated in L4 by this LGN DS neuron. The spike-triggered average responses based on differing preceding interspike intervals are shown. As in Figure 1H, the dashed vertical line indicates the onset of a thalamic spike. (D) Postsynaptic amplitude reductions generated by thalamic spikes with short versus long preceding intervals for 16 LGN DS neurons (left) compared with those seen in LGN concentric transient (middle) and concentric sustained (right) neurons (data from concentric sustained versus transient neurons from Stoelzel et al., 2008). LGN DS neurons generated a postsynaptic response that was reduced at the short preceding interspike intervals to a similar extent to what was seen in concentric transient neurons (p = 0.817, t test) but significantly less reduced than the reduction seen in concentric sustained cells (p < 0.001, t test). Cell Reports 2019 27, 3733-3740.e3DOI: (10.1016/j.celrep.2019.05.094) Copyright © 2019 The Authors Terms and Conditions

Figure 4 LGN DS Neurons Drive V1 Neurons (A) Cross-correlation of spontaneous spike trains of an LGN DS neuron and a retinotopically aligned SIN in L4 of V1. The LGN DS neuron (red and blue contours) shows overlapping ON/OFF responses) and the V1 SIN (black contours) also shows overlapping ON/OFF responses. The orientation-directional tuning curves show that the LGN DS neuron (left) has a very strong preference for downward movement, but the SIN (right) responds similarly to all directions of movement. The black contour plot shows the F0 responses, and the red contour shows F1 responses (which are minimal in both neurons). The sharp, short-latency peak in the cross-correlogram (onset at ∼1.8 ms) shows a brief increase in L4 SIN’s spike probability following the LGN DS spike, indicative of monosynaptic connectivity (Swadlow and Gusev, 2001, 2002; Zhuang et al., 2013). (B) Another LGN DS neuron making a functional contact with a V1 SIN. In this case the SIN was located near the L5/L6 border. Cell Reports 2019 27, 3733-3740.e3DOI: (10.1016/j.celrep.2019.05.094) Copyright © 2019 The Authors Terms and Conditions