Emergence of theory of mind in young children, explored with functional MRI and Virtual Reality (VR)

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The capacity to ascribe mental states and knowledge to other people (ie, their beliefs, intentions and feelings) and thus understand and predict their behaviour (known as "theory of mind") is an essential feature of the human psyche, which emerges in early childhood between 18 months of 5 years of age (Frith et al. 2005). It is essential for everyday social interaction and community participation, with altered theory of mind found in numerous mental health disorders and is also thought to underlie neurodevelopmental conditions including autism (Senju 2012). Crucially however, the brain processing that underlies this key human skill is poorly understood partly due to the challenges inherent to designing suitable experiments that can explore this complex construct within typically rigid neuroimaging study designs which also struggle to represent real-world social interact.This is particularly problematic for methods such as functional MRI (fMRI) which can provide detailed whole-brain information about neural activity but must involve behavioural stimulation and image acquisition inside the restricted and unnatural MRI scanner environment. Despite this, recent studies have highlighted the potential of fMRI to provide insight using video stimuli and creative analysis methods showing that the related activity in the adolescent and adult brain occurs a distributed network of areas that include the medial prefrontal cortex, temporal-parietal junction (TPJ), posterior superior temporal sulcus (pSTS), posterior cingulate cortex (PCC) and precuneus (Gao et al. 2019). However, as young children often struggle to follow detailed instructions and/or find it difficult to tolerate data acquisition inside an alien environment like a MRI scanner (and so must be studied when sleeping), very little is known about how the brain and its activity changes to enable theory of mind to first emerge(Yates et al. 2021). With these factors in mind, the supervisory team has recently developed a novel MR compatible virtual reality (VR) system which provides users with an interactive simulated environment whilst lying inside the MRI scanner (Qian et al. 2021). When using the system, subjects are fully immersed in a visual environment via an MR compatible projector placed inside the scanner bore which projects directly into a VR headset and also receive auditory stimulation via active noise-cancelling headphones. A further key feature of the system is a pair of integrated MRI compatible video cameras inside the headset that provide additional real-time information about the user's visual behaviour. Using a robust gaze estimation algorithm, this not only allows precise measurementof visual attention but also allows subjects to use their gaze as an intuitive and natural means of communication as they would in their daily lives (Qian et al. 2021). By simultaneously acquiring fMRI data whilst the subject naturally explores and interacts with the VR environment, there is huge potential for this to be a transformative new platform for fMRI-based interrogation of brainactivity which at its core, overcomes the aforementioned limitations inherent to traditional rigid study designs and can enable for the first time, detailed characterisation of the brain processing underlying theory of mind in young children.