## 2 Why the Electroencephalogram (EEG)?
### qEEG and Experiential Sellhood  
Indeed, in various neuropsychological conditions, _self-consciousness_ alterations dominate the patient's phenomenological experiences and have either a long-term or permanent presence [277, 278, 279]. Even though _experiential Sellhood_ (also referred to as self-consciousness or self-awareness) is a multi-layered concept that is often conceptualized in different ways by various disciplines [280], the currently emerging consensus is that self-referential processing constitutes the core of Selfhood [281,282]. Empirical evidence from neuroscience [281,283,284,285,286] indicates that such self-referential processing is instantiated by a specific _self-referential network_ (SRN) within the brain, sometimes also referred to as the default mode network (DMN) [283, 284, 285, 286, 287]. Further, it has been documented that specific qEEG oscillations have a significant positive correlation with the SRN [288, 289, 290, 291, 292]. Recently, a _three-dimensional_ neurophysiological model of the complex experiential Sellhood (which is based on the qEEG analysis) was proposed [286,293,294] (for a detailed description, see [295]). This triad model of Selfhood considers the neurophysiological evidence that _three_ major spatially separate yet functionally interacting brain subnets constitute the SRN and account for the phenomenological distinctions between three major aspects of Selfhood, namely, (i) first-person agency (conceptualized as the 'witnessing observer' or simply the '_Self_'), (ii) embodiment (conceptualized as'representational-emotional agency' or simply '_Me_'), and (iii) reflection/narration (conceptualized as'reflective agency' or simply '_I_' ), all of which commensurate with one another [296] and, together, form a unified sense of Selfhood [286] (see also [297]). Each aspect of the triad can be enhanced or weakened depending on the current physiologic and mental state [286,298], voluntary training [293,294], and neuropsychopathology [299, 300, 301]. Since aspects of Selfhood rarely fall under the purview of clinical practice, we present below a few examples of the potential application of qEEGs in the assessment of experiential Selfhood for different neuropsychopathologies. For example, in its 'pure' unmedicated form, major depressive disorder is associated with functional enhancement (measured by qEEG) of all three aspects ('Self', 'Me', and 'T') [300], thus reflecting the well-documented excessive self-focus, increased running, and increased embodiment in patients with depression [302; 303; 304; 305; 306; 307]. One could speculate that \"these three components of complex Selfhood (indexed by (qEEG)) synergize with one another in a maladaptive loop and, over time, become habitual, leading to a vicious circle that maintains a disordered affective state that clinically manifests as depression\" [300] (p. 34). It has been further proposed that the \"Self' plays a chief role here as it organizes, represents, and appraises the salience of interoceptive/emotional/bodily information presented by 'Me' and the narrative and semantic-conceptual information presented by 'T' [300]. PTSD is characterized by rather different Self-Me-I dynamics [301]. Increased activity (measured by qEEG) of the \"Self' aspect was found to be significantly associated with the increased vigilance of PTSD sufferers to their surroundings, with a concurrent shift of their first-person perspective from the current moment in time to the moment of the traumatic event (criterion E, according to DSM-5 [308]). We have speculated [301] that such constant hypervigilance coupled with profound emotional arousal leads to sensory overload and further exacerbates alienation of the Self in such patients [309].