## 4 Common/Unifying Theoretical-Conceptual Framework
### qEEG Phenotype and Neuropsychophysiological Type  
_qEEG phenotypes_ are the clusters of commonly occurring qEEG characteristics within qEEG oscillatory patterns found in the general population that are believed to be the net result of genetics, pre- and post-natal individual development, and significant life events such as brain traumas or neuro-diseases (see above). In contrast to the classical view, which sees qEEG phenotypes as classes of qEEG _abnormalities_, where, usually, one qEEG characteristic defines a qEEG phenotype and each phenotype is static [451], we believe that qEEG phenotypes characterize all variabilities of the population, covering the whole _spectrum_, from health to pathology, and, further, that such phenotypes are dynamic. In this view, some of the qEEG phenotypes are characteristic of healthy conditions, while others are typical for different degrees of deviation from the healthy state up to the situation where the qEEG phenotype is pathological. Additionally, every phenotype is defined by the combination of qEEG features (qEEG oscillatory pattern--a _coherent functional whole_) and is dynamic, meaning that every qEEG phenotype may exhibit changes, to some extent, within its own qEEG oscillatory pattern due to dysfunction or development of pathology (Figure 3). This is so because the type of qEEG oscillatory pattern is a phenotypic expression (qEEG phenotype) of (a) cellular and biochemical (dys)function; (b) mutational processes (or delaying factors), partially genetically and epigenetically determined; (c) neurotransmitter (im)balance; (d) regulatory systems (and their disturbances); (e) early subclinical organic brain damage; or (f) morpho-functional disturbances that may be present in neuropsychiatric disorders. Such conceptualization underwent theoretical development and empirical verification in the work of Zhirmunskaya and colleagues [452; 453; 454; 455; 456] and was successfully applied to several clinical neuropsychophathologies as well as various modes of pharmacological influence [156; 457; 458; 459; 460; 459; 461; 462]. In this context, a given qEEG phenotype reflects a _neuropsychophysiological type_ (neurodynamic constitution) of the individual. Indeed, numerous studies have demonstrated that qEEG characteristics can encompass functionally different psychophysiological determinants [1; 463]. On one hand, a qEEG phenotype reflects the inherent brain functional organization and dynamic structure of brain activity, which are intra-individually stable traits, as evidenced by test-retest reliability (Section 2.2) and genetic studies (Section 2.3). On the other hand, since intrinsic brain activity supports and conditions individual cognitive and information processing, self-regulatory functions, decision-making, behavior, and consciousness, a qEEG phenotype reflects the neurophysiological predispositions of the underlying cognition and personality, temperament, and character factors thus reflecting the individual's psychological and behavioral traits. Indeed, it was found that individual differences in qEEG variability relate strongly to stable indicators of subject identity [464]. Hence, both an individual's neurophysiological and psychological differences can be neuropsychophysiologically interpreted under the same unified notion of the qEEG phenotype [1; 465; 466; 467; 468; 469; 470]. This brings us to the idea that a qEEG phenotype is not just a concept but a _real phenomenon_. This is supported by the observations that qEEG phenotypes reliably predict the effectiveness of drug interventions, while nosological or behavioral groupings do not [451]: for example, effective treatment of ADHD [366; 471], refractory depression [472], and major depressive disorder [369] was achieved when it was based on prospectively identified qEEG phenotypes related to different sub-types within the diagnostic group, thus suggesting that nosological heterogeneity is well-reflected in the multiplicity of spatial-temporal parameters of qEEG oscillatory patterns.