L5tt cells cause the brain to notice a stimulus. To do so, they burst, triggering detection via thalamus, SC, and striatum.
L5tt cells can burst upon touch.
This study just measured spiking while the rat whisked and touched an object.
Many L5tt cells were capable of responding to touch by bursting. Most of this paper addresses possible complications, so it’s fairly safe to take that result as-is. For example, they can burst upon touch regardless of their long-range projections.
Bursting might overcome the generally depressed corticothalamic synapses, causing thalamocortical cells to fire.
I’m mentioning this study because the other study is a bit ambiguous. It uses calcium imaging, for example.
Bursts are required to notice stimuli, at least very weak ones. (Or at least apical calcium events are required.)
This study measured the perceptual threshold, meaning the stimulus strength which the mouse noticed half the time. You can imagine trying to notice a very weak stimulus.
If the mouse notices the stimulus, the L5tt cells burst (or at least have an apical calcium signal closely associated with bursting). Otherwise, they don’t. Activating their apical dendrites reduces the perceptual threshold.
The L5tt cells in this study project to thalamus, superior colliculus, striatum, pons, and medulla. Silencing their synapses in thalamus or superior colliculus strongly impaired the mouse’s detection performance. The same goes for the striatum, but the effect was smaller. There was no effect for pons or medulla.
They repeated the experiment without the behavioral task or reward. This reduced the average calcium signal a lot.
That contradicts the other study, where they burst without a behavioral task or reward. However, the stimuli in this study were very weak, so I think the mice just didn’t notice them. There are other possible explanations, though.