Figure 3.

Thermal stimulation modulates the synchronous neural activity in the peduncle of Hydra vulgaris, see also Figures S1 and S2.

(A) Schematic of a representative thermal stimulation protocol. Gray-colored regions (I) indicate non-stimulus periods at Hydra's culture temperature (either 18°C or 25°C) lasting between 30 and 90 s. The blue-colored regions (II) indicate stimulus periods at designated temperatures for 60 s.

(B) Images of Hydra without synchronous neural firing (top) and during firing (bottom) in the peduncle (white circle). Scale bar, 1 mm.

(C) Raster plot of synchronous firing events in peduncle in (B). One black vertical line indicates one synchronous firing event. Each row represents the raster plot of spikes time-aligned with one stimulation (boxed regions) with 30 s before and after stimulation (white non-boxed region).

(D) Peristimulus time histogram (calcium firing rate) of (C), which was calculated with a 10-s sliding window.

(E) Calcium spike rate comparison between the non-stimulation (gray-colored region I in A) and stimulation (blue-colored region II in A) periods with a stimulus temperature of 18°C. (ns = not significant, Mann-Whitney U test. δ = Effect size using Cliff's delta). Box-and-whisker plots indicate Q1, median, and Q3; whisker lengths indicate the 2^nd and 98^th percentiles.

(F) Calcium spike rates from Hydra, all cultured at 18°C. N = 6 animals per stimulus temperature. (ns = not significant, ∗∗p < 0.0001, ∗∗∗p < 0.00001, Mann-Whitney U test. δ = Effect size using Cliff's delta). Box-and-whisker plots indicate Q1, median, and Q3; whisker lengths indicate the 2^nd and 98^th percentiles.

(G) Calcium spike rates from Hydra cultured at 18°C and 25°C. x axis notes the stimulation temperatures. N = 3 per culture temperature at each stimulation temperature. (ns = not significant, ∗∗∗p < 0.00001, Mann-Whitney U test. δ = Effect size using Cliff's delta). Box-and-whisker plots indicate Q1, median, and Q3; whisker lengths indicate the 2^nd and 98^th percentiles.