Fig. 5
The stimulus–response functions (SRFs) of noxious-excitatory units to contact heat stimuli. a An example response of a MD thalamic nuclear unit to 40, 45, and 50 °C contact heat applied to the fore paw. The baseline temperature of the probe was held at 35 °C. Bin = 6 s. b The responses of all MD/IL thalamic nuclear units (n = 36) plotted against time. Each row represents data from a single unit, and units’ activities are represented by the color-coded Z score. Note that there was a sudden increase in activity for most heat-responsive units (arrows). c The firing histograms of two example units responding to 50 °C contact heat applied to the fore paw. The upper and lower units, respectively, show coding and non-coding properties. The two units were recorded at the same time in the same rat. The baseline temperature was held at 35 °C. At 10 s, the Peltier thermal probe was turned on, and it had reached 50 °C by the end of the 30-s heating period. The 50 °C stimulation-response data were used to construct the SRFs. d Averaged SRF (mean ± SE) of 22 units with step-function-like features showed the responses significantly increased from 46 to 50 °C. e Averaged SRF (mean ± SE) of 7 units with coding property showed the responses significantly increased from 49 to 50 °C. *p < 0.05, compared to the baseline activity at 35 °C (Kruskal–Wallis one-way ANOVA on ranks, post hoc analysis: Dunn’s test)