Post-sauna recovery enhances brain neural network relaxation and improves cognitive economy in oddball tasks

Figures & data

Figure 1. Schematic representation of the experimental protocol. Temperature in the sauna was 80–90 °C; the ambient temperature (T_a) during rest was 23 °C.

Figure 2. Mean absolute powers presented using a base 10 logarithmic scale for the Fz, Cz, and Pz electrodes (top). The mean absolute powers for the theta (4–8 Hz), alpha (8–12 Hz) and beta (12–30 Hz) frequency bands at three EEG sites (Fz, Cz, and Pz) before and 90 min after the sauna for the control (CON) vs experimental (EXP) trials are shown on the lower panel. Values are shown as the mean ± SEM; *p <.05 compared with before.

Figure 3. Grand-averaged event-related potential (ERP) waveforms at three EEG sites (Fz, Cz, and Pz) before and 90 min after the sauna for the control (CON) vs experimental (EXP) trials for visual tasks are shown on the left. The mean N1, N2, and P3 amplitudes at three sites (Fz, Cz, Pz) before and after rest for the CON vs EXP trials for visual tasks are shown on the right. Values are shown as the mean ± SD; *p <.05 compared with before. Note. N.D: Not Detected; the response of ERPs P3 component in the 80% non-target (standard) condition was too small to compute a reliable mean response for amplitude and latency.

Figure 4. Grand-averaged event-related potential (ERP) waveforms at three EEG sites (Fz, Cz, and Pz) before and 90 min after the sauna for the control (CON) vs experimental (EXP) trials for auditory tasks are shown on the left. The mean N1, N2, and P3 amplitudes at three sites (Fz, Cz, and Pz) before and after rest for the CON vs EXP trials for auditory tasks are shown on the right. Values are shown as the mean ± SD; *p <.05 compared with before. Note. N.D: Not Detected; the response of ERPs P3 component in the 80% non-target (standard) condition was too small to compute a reliable mean response for amplitude and latency.

Table 1. Mean response time (ms) and mean percentage (%) of correct responses in the target condition.

	Visual task			Auditory task
	CON		EXP	CON		EXP
Response time, ms
Before	376.49 ± 43.27		358.76 ± 36.35	351.79 ± 55.39		346.77 ± 57.85
After	360.99 ± 40.01		360.15 ± 36.68	355.18 ± 57.69		349.68 ± 65.64
Accuracy, %
Before	86.79 ± 22.88		87.14 ± 19.96	87.51 ± 22.20		91.07 ± 18.28
After	85.89 ± 22.46		83.93 ± 21.88	88.21 ± 20.57		83.39 ± 28.04

Values are shown as the mean ± SD.

Table 2. Generalized overview of 90-min post-sauna effect on neural network arousal, information processing and cognitive behavior.

	Fz			Cz			Pz
Pre-test EEG power	Theta	Alfa	Beta	Theta	Alfa	Beta	Theta	Alfa	Beta
	−	↑	−	−	↑	−	−	↑	−
	Event-related potential amplitude
Auditory	Target	Standard		Target	Standard		Target	Standard
N1 – sensory to stimulus	−	−		−	−		−	−
N2 – stimulus discrimination	−	−		−	↑		−	↑
P3 – stimulus categorization	↓	N.D.		↓	N.D.		↓	N.D.
Visual
N1 – sensory to stimulus	−	−		−	−		−	−
N2 – stimulus discrimination	−	−		↑	−		↑	−
P3 – stimulus categorization	↓	N.D.		↓	N.D.		↓	N.D.
	Cognitive performance in the ‘Target’ condition
	Auditory task				Visual task
Response time	−				−
Accuracy	−				−

Arrows indicates significant (p < .05) change (increase ↑; decrease ↓) from before to 90-min post-sauna. N.D.: Not Detected; the response of ERPs P3 component in the 80% non-target (Standard) condition was too small to compute a reliable mean response amplitude and latency.