Fig. 5.
Proximal and distal modulation of neural activity in anesthetized animals. A: spike raster plot of a significantly activated unit (unit 2; blue square) recorded in the second TT from the probe tip at 10, 20, or 50 Hz or with a continuous wave (CW). B: mean spontaneous (black) and light-induced (blue) spiking of examples of 4 highly responsive units (cross-correlation ~99%), labeled units 1–4, respectively, and marked with orange, blue, purple, and brown squares, respectively, throughout the figure. C: spike raster plot and peristimulus time histograms of a significantly inhibited example unit. D: median baseline-normalized firing rate (ΔFr) of all units (n = 60) recorded in anesthetized animals (n = 6) during different light stimulation paradigms. Significantly activated or inhibited units are marked by closed circles (Kruskal Wallis and Dunn’s post hoc test, P < 0.05, Benjamini-Hochberg correction for multiple testing). All other units are marked by open circles. CW results in greater spread of significantly activated neurons but also increases the number of significantly inhibited neurons. E: mean latency of all significantly activated units relative to their respective distance from the light outlet. Shortest latencies are observed close to the light outlet. F: mean latency of all significantly activated units vs. spike fidelity. Units 1–4 are characterized by a spike fidelity >50% and a latency <15 ms. These units are presumed directly activated neurons. G: presumed directly activated units spike reliably in response to optical stimulation across stimulation frequencies. Values are mean spike fidelity(±SD) of all presumed directly activated units (gray) and all other units (black; 2-way ANOVA and Bonferroni post hoc, dflatency = 1, dffrequency = 2, P < 0.0). ***P < 0.0001. H: quality metrics of all significantly activated units as measured by likelihood ratio (LRO) and isolation distance (IsoD). I: correlation between mean latency of all significantly activated units and the inhibiting effect of CW (calculated as the difference of the normalized firing rate during CW and 50-Hz stimulation, rFrCW−rFr50Hz).