## 3 Results
### Main Results Obtained
#### 3.2.4 Neural Activity Correlates  
The studies included in this review investigated the brain activity associated with visuospatial memory tasks administered through iVR by using EGG [33; 34; 35; 36; 37; 38; 39], intracranial EEG (iEEG) [1], and fNIRS [32]. [PERSON] et al. [32] observed distinct brain activation patterns measured by fNIRS during the encoding and retrieval phases of an episodic memory task, which were effectively used by ML algorithms to categorize these stages. The RF model, trained and evaluated under consistent conditions, achieved an F1 score of 0.844 and an accuracy of 79.10%. However, when assessed under different conditions, its performance dropped, with an F1 score of 0.723 and an accuracy of 60.61%. Additionally, key brain regions, including the right dlPFC, medial prefrontal cortex (mPFC), and left dlPFC, were identifiedas essential for differentiating between encoding and retrieval, aiding attentional inhibition and working memory encoding. Concerning the study by [PERSON] et al. [33] using EEG, notable alterations in alpha, beta, and theta oscillations in the occipital cortex (OC) and the dlPFC were assessed during visual stimulus and test-response intervals. They found that the presence of a \"virtual observer\" suppressed theta-band power during the storage and retrieval of visual information, particularly in the BVRT. This suggests that the observer may increase mental workload, affecting attentional concentration and task performance. During the stimulus phase, the dlPFC showed prolonged alpha-band activity (8-12 Hz) in both conditions, indicating its role in processing visual inputs. Theta-band activity increased about 1200 ms post-stimulus under the observation condition. Additionally, beta-band activity (12.5-30 Hz) was higher in the no-observation condition after 1600 ms.  
[PERSON] et al. [34] examined brain activity with EEG related to visuospatial short-term memory and observed changes in contralateral delay activity (CDA) amplitude, which was significantly affected by memory load at smaller eccentricities (4 and 9 degrees of visual angle). However, no such effect was seen at the largest eccentricity (14 degrees), suggesting spatial limitations in processing memory load. Additionally, lateralized alpha power during the retention phase was observed. The study further found that increased memory load impaired performance, with the CDA being more sensitive to memory load than alpha lateralization. [PERSON] et al. [39] focused on brain activity related to allocentric and egocentric spatial reference frames. During allocentric navigation, there was alpha desynchronization in the parietal cortex (PC), while egocentric navigation showed no significant alpha changes. Both strategies led to beta and low gamma power increases in the OC, with egocentric navigation showing stronger enhancements. A positive correlation in beta activity was observed between the PC and other cortical areas (occipital, frontal, central) during active navigation for the allocentric group and during passive navigation for the egocentric group. [PERSON] and [PERSON] [35] investigated the effect of various interior space designs on brain activity. A notable observation was that mental workload oscillated significantly according to the design of the indoor environment. Individuals encountered a greater cognitive load in the least favored environment. Conversely, the favored setting correlated with reduced mental load. The study indicated that executive function and working memory were significantly influenced by the spatial design. The examination of EEG data via one-way RM ANOVA indicated substantial variations in mental stress levels linked to alterations in indoor space design. Regarding the exploration and navigation of spatial environments, [PERSON] et al. [38] studied brain activity with EEG during free exploration of a virtual world and found that the PC generated significant spatial maps, particularly in the low-frequency range of 2-8 Hz.