Fig. 7: High-frequency bursting upon whisker stimulation is observed in L5tts projecting to different subcortical targets.

a Injections of retrograde tracers into the major subcortical targets of L5tts in rat primary somatosensory cortex (S1), allowing back-labeling and projection-specific identification. Panel adapted from ref. ¹¹. b Loose-patch recording and biocytin labeling leads to identification of cell-type-specific morphology and projection target. Here, biocytin labeling of exemplary neuron in L5, after retrograde tracer injections into the SC (FG), Pons (CTB-594), and POm (CTB-647). Slices were stained with Alexa-405 and Alexa-488 to reveal retrogradely and biocytin-labeled neurons (white arrow), respectively. Right panel: 3D morphological reconstruction of the exemplary L5tt. c Cartoon of recording configuration with loose-patch, single-unit recording in primary somatosensory cortex in combination with passive, multi-whisker stimulation (air-puff). Example voltage trace illustrates a stimulus-evoked high-frequency burst of the POm-projecting L5tt pyramid shown in Fig. 7b. d Raster plot with AP spiking aligned to consecutive touches. APs at instantaneous frequency of ≥100 Hz are indicated by red bullets. e Peri-stimulus-time-histogram (PSTH) aligned to touch start. f Examples of L5tt reconstructions projecting to different subcortical targets and high-frequency bursts (bottom trace) observed in these neurons. Scale bar biocytin-filled cell bodies: 50 μm. g, h High-frequency bursts are observed during g spontaneous and h stimulus-evoked windows in L5tts with different project-targets (individual ratios not significant relative to general population, Chi-Square p > 0.05). i Burst rate for individual L5tt neurons across conditions with color code representing projecting target (legend in a). j–l Fraction of supracritical burst events upon whisker stimulus is generalizable across L5tts with different projection targets (Kruskal–Wallis, p > 0.05) as shown for spontaneous spiking (j), the onset of evoked activity (k), and in the window representing sustained activity (l), respectively. Boxplots show median as central mark, the edges of the box the 25th and 75th percentiles, the whiskers extend to the most extreme data points, and the outliers are plotted individually.