This study investigated the neurophysiological and affective responses elicited by nature-inspired indoor design elements, including curvilinear forms (CL), nature views (N), and wooden interiors (W), in a virtual environment, and their effects on cognitive performance. Thirty-six participants experienced one control and three experimental conditions in a within-subject design. Electroencephalography (EEG) was used to record neural activity, relaxation and valence ratings assessed affective states, and standardized tasks measured cognitive performance. The W condition elicited EEG patterns indicative of relaxed attentional engagement, including increased alpha-to-theta (ATR) and alpha-to-beta (ABR) ratios, and a decreased theta-to-beta (TBR) ratio. These neural patterns were associated with higher self-reported relaxation and positive affect, and with enhanced cognitive performance relative to the control condition. In contrast, the CL and N conditions did not improve cognitive performance, and the N condition showed elevated physiological arousal, likely due to heightened visual stimulation. Regression analysis identified ATR and relaxation as significant predictors of cognitive performance, emphasizing the role of emotional stability and neural balance in supporting task engagement. Overall, the findings highlight the potential of nature-inspired design to foster a synergy between psychological relaxation and cognitive attention, though further research is needed across diverse spatial typologies to isolate specific design parameters.