2.3. Tactile stimulation

The tactile skin stimulation was performed with a Dual-Mode Lever System (300C-l, Aurora Scientific, Canada) with a tip size of 0.79 mm². We stimulated the skin in the third annulus of the segment of interest (Figure 1B). Within this third annulus, the ventral midline was defined as 0° and the lateral edges as −180° and +180°, respectively (Pirschel and Kretzberg, 2016). The default starting position was ±90° (filled white circles), on the ipsilateral side of the recorded cell. Even though predominantly the lateral T cell has its receptive field at this position, usually more than one T cell at the ipsilateral side of the ganglion reliably responded to touch with spikes that could be measured with the recording electrode at the soma (see Supplementary Figure S1 for an example of all three ipsilateral T cells responding to touch at the same position). If no spikes were elicited by the standard tactile stimulus, we changed the stimulus location along the third annulus to either ±135°, ±45°, or 0° (empty circles in Figure 1B). Hence, we did not aim for one of the three ipsilateral T cells specifically, even though their anatomy and spiking behavior were shown to differ in isolated ganglia (Meiser et al., 2023).