# Physiological Responses Related to Sitting Comfort Due to Changes in Seat Parameters
## 4 Discussion  
The current study examined the relationship between seat pressure characteristics and physiological indices representing the reaction of the human nervous system in response to changes in several seat parameters. Indices calculated from EEGs and ECGs were used to investigate the activity of the central and autonomic nervous system in response to the influences of Reclining, Ottoman, and Slab as target conditions. Significant differences in brain activity and heart rate variability indices were found when comparing the control and target conditions. Although subjective ratings of relaxation were significantly higher in all target conditions compared to the base conditions, the specific physiological indices with significant differences varied for each condition. In terms of seat pressure distribution, significant differences were observed in peak pressure and contact area for all conditions tested in this study. Specifically, reclining increased the contact area of the backrest while decreasing peak pressure on the seat pan. This similar trend of reduced peak pressure on the seat pan due to reclining aligns with the findings of [PERSON] et al. [30]. Using the Ottoman reduced peak pressure on the front side of the seat pan, and the slab increased the contact area of the backrest while also reducing peak pressure. These relationships, combined with changes in joint angles, are believed to have triggered psychological and physiological responses, leading to changes in various indices. As for the central nervous system response, the results from the reference data (Supine-Standing) indicated a significant increase in the values of \((\theta+\alpha)/\beta\) in the central and parietal lobes during the supine position. This suggests that the supine position may induce a relaxation response in the central nervous activity across various brain regions. Similar brain responses were observed during the use of the slab, as demonstrated in Part 3 (Slab-Neutral). Conversely, reclining had no discernible effect on the differences in the value of \((\theta+\alpha)/\beta\) in the central and parietal lobes, as shown in Part 1 (Reclining-Neutral). Moreover, the values of \((\theta+\alpha)/\beta\) in the central and parietal lobes decreased due to the ottonan. This indicates that the ottonan led to an activation of brain activity, contrary to the effects observed in the supine position and with the slab. Among the various brain activities, central and parietal lobe activity is associated with motor function and somatosensory processing [31, 32]. Therefore, the activation of brain response by the ottonan was likely attributed to pressure on the lower extremities, especially the calves. Furthermore, it can be inferred that the slab increased the contact area of the user's back region and distributed the pressure, resulting in reduced peak pressure on the back and a subsequent decrease in central brain activity. As for the autonomic nervous system response, the results from the reference data (Supine-Standing) indicated a significant increase in RRI and HF content, along with a significant decrease in LF/HF during the supine position, which aligns with findings from related studies [33, 34]. This suggests that the supine position may elicit parasympathetic