Neural synchronization is a fundamental feature of the brain at both infraslow (0.01–0.1 Hz)/fMRI and faster (1–60 Hz)/EEG/MEG frequencies. Synchrony is mediated by the phases and how they synchronize across different regions and frequencies. The present chapter focuses on the distinct kinds of phase-related processes in the brain's neural activity and how we can measure them in brain imaging (fMRI, EEG). With a strong, detailed methodological component, the more general reader may want to just glance over it. One measure of neural synchronization is functional connectivity (FC), as used in fMRI. We compare time-varying and phase-based approaches to FC; this marks FC as an instance of neural synchronization. That is followed by shedding some light on the brain's synchronization through its global activity and how its global synchronization can be measured and is viewed in current neuroscience. Turning to EEG/MEG, we show how coherence between electrodes in EEG/MEG can be calculated by the phase locking value. We also demonstrate how phase coherence or variance over different trials of the same input/stimulus can be calculated and simulated. Finally, we introduce peak frequency, which measures the power at the phase angles at each time point. Together, we conclude that there are a variety of different phase-based measures in both fMRI and EEG. This makes it clear that neural synchronization is far from homogenous and may, by itself, include and operate across different timescales. Future work is necessary to shed more light on the heterogeneity of the brain's neural synchronization in its timescales, the relationship between the different measures, and their potentially different shaping of perception and cognition.

The self is not just in the brain and or body. Rather it is closely related to its respective environmental context. This raises the question whether the self shows an analogous neuro-ecological basis in the world. We first demonstrate how environmental life shapes and impacts the neural basis of self including its topography and dynamic. That is followed by the assumption of a neuro-ecological background layer of self complementing its mental surface layer. Finally, we propose that the neuro-ecological background layer provides what philosophically has been described as the point of view, the anchoring of the self in the world from which it perceives and accesses the world in a perspectival way. This does not lay bare the neuro-ecological scale-free temporal nestedness of the self in the world but also carries major implications for our more philosophical, i.e., ontological understanding of self, brain, and world. The assumption of a deeper layer of self, a neuro-ecological background layer constituting its point of view, puts the self on a par with the iceberg: like the iceberg, the self is also exposed to various forces both from within itself and without itself by environmental context. Accordingly, here is yet another instance where even one of the key features of the mind, the self, exhibits features analogous to those characterizing the basic features of nature.

Consciousness is a fundamental feature of our mental life. While it has long been discussed in philosophy, the last 20–30 years saw a resurgence of different neuroscientific theories of consciousness. Various theories for the neural basis of consciousness have been proposed, suggesting a diversity of mechanisms, each expressed in different aspects of neural activity, either stimulus-related, preceding the stimulus (prestimulus), or spontaneous (resting state). We ask to what extent this diversity is real, or whether many theories boil down to the same basic ideas, so that there is a potential for convergence toward a more unified theory of the neural basis of consciousness. For that purpose, we review and compare the various neural signs, measures, and mechanisms proposed in different theories focusing on the currently predominating ones. Providing such comparative overview is the main goal of this chapter. As we will see, there is enormous diversity and heterogeneity just like a jungle. Providing some structure and guide to the current jungle of consciousness in neuroscience is the goal of this chapter.

The brain exhibits its own inner time as distinguished from the world's outer time. Understanding the dynamics of the brain's own inner time is the goal of this chapter. The brain's neural activity exhibits a variety of different timescales with short and longer durations, the so-called intrinsic neural timescales (INTs) (second part). The INT can be measured by correlating the neural signals with themselves over time, i.e., autocorrelation function, from which the autocorrelation window can be extracted. The findings show a hierarchy of INT in the brain with long INT in transmodal regions (like the prefrontal cortex) and short INT in unimodal regions (like primary sensory regions). Such unitransmodal hierarchy of INT can be observed during both rest and task states with both task-specific and task-unspecific modulation of INT. We conclude that the brain's inner time is characterized by a multitude of timescales as manifest in the unitransmodal hierarchy of INT. This leaves open the role or function of the INT which will be the focus in the next chapter.

We demonstrated the nested hierarchy of the three-layer topography of self in the previous chapter. That left the dynamic of the self which is the main focus in this chapter. We demonstrate that the three-layer spatial topography of interoceptive, proprioceptive, and mental self is accompanied by a corresponding temporal hierarchy from slow-longer to fast-shorter timescales. Importantly, such nested hierarchy of the dynamic of self can be shown on both neural and psychological level. This, as we tentatively hypothesize going into semantic and computation, can be related to a corresponding hierarchical gradient of semantic similarity and relatedness. Specifically, we assume that semantic similarity is shaped by the fast-shorter timescales of mainly the interoceptive self, while the higher degrees of semantic relatedness are rather related to the slow-long timescales of the mental self. We thus propose that the topographic-dynamic gradient of self (across its three layers) is manifest in a somewhat corresponding semantic gradient from similarity to relatedness. Assuming such deep temporal structuring of semantics, we propose that dynamic and topography including their convergence in a nested hierarchy are shared by both neural and psychological/semantic levels as their “common currency.” Given that (i) nested hierarchies are ubiquitous in nature, and that (ii) the brain's timescales themselves nest and are contained within the much larger repertoire of timescales of the natural world, one would assume that the self should also be deeply rooted within its respective environmental context. That shall be the focus in the next chapter.

We demonstrated various features of thought dynamic in the previous chapter. How does the dynamic contribute to the constitution or formation of thoughts? Thought dynamic refers to the constant flux, change, or dynamic of thought as emphasized in recent models like the dynamic framework of thought (Christoff et al., 2016) and the spatiotemporal theory of task-unrelated thought (Northoff, 2018). Following the findings on thought dynamic in the previous chapter, we propose a baseline model of thought (BMT). The BMT states that the dynamic dimensions of especially spontaneous thought provide the reference or standard for shaping the other dimensions of thought namely contents, constraints, and structure. This is supposedly mediated through three dynamic mechanisms including intrinsic neural timescales, temporal integration-segregation, and phase-related synchronization. We conclude that dynamic is the most basic and fundamental dimension of thought which may be shared by both brain and thought as their “common currency” (Northoff et al., 2019).

We introduced the dynamic layer model of brain (DLB) in the previous part. This left open how such layer-based organization is related to cognition; that is the focus in this chapter. How is the brain's spontaneous or ongoing activity with its various dynamic layers related to cognition? The currently predominant dual model of cognition (DMC) model associates ongoing brain activity with (i) resting state, (ii) the default-mode network (DMN), and (iii) internally oriented cognition. This triad, in existing literature, stands in contrast to task states, non-DMN and externally oriented cognition—for that reason, we speak of a ‘dual model.’ Extending Marcus Raichle's original search for the default-mode of brain function beyond the canonical DMN regions, we propose that ongoing brain activity with its different dynamic layers serves as a neuronal baseline. This entails what we refer to as ‘Baseline model of cognition’ (BMC). Akin to an internal biological clock for the rest of the organism, the ongoing activity with its different dynamic layers may serve as an internal point of reference or standard: the different dynamic layers provide a neural code for the brain's rest and task states including their associated cognition. We conclude that recent empirical evidence supports a Baseline model of cognition (BMC) over the currently prevailing DMC. The BMC, in turn, is based on the DLB: the various dynamic layers provide the dynamic capacities and thereby a global neural and specifically temporal code that serves as baseline or reference for any form of cognition including both internally- and externally oriented.

What is the self? This has originally long been discussed in philosophy and, more recently, also in neuroscience. There has been an enormous diversity and multiplicity of self on psychological, conceptual, and neural levels. How can we reconcile similarity and difference across our self and its distinct aspects? Recent studies show a three-layer topography of self in the brain in terms of its anatomical structures. Interoceptive self is mediated more by subcortical and cortical regions like thalamus and insula, proprioceptive self is related to cortical regions like temporo-parietal junction, and mental self is associated with typical cortical midline default mode network regions like anterior and posterior cingulate cortex. Importantly, the regions of the interoceptive layer of self are recapitulated within the ones of the proprioceptive and the mental layers of self (and the same applies for the regions of the proprioceptive layers with respect to the mental layer). Together, this amounts to the topography of a nested hierarchy of self which can be supported on anatomical, functional, processing, and phenomenal grounds. Such nested hierarchy of self can be compared to the Russian dolls where, analogously, similarity and difference are combined by nesting similar dolls of different sizes within each other.

We showed the topography and dynamic of self. This left open the role or function of the self for both brain and cognition, though. Addressing that gap is the goal of this chapter. The self has often been conceived as form of internally oriented cognition as distinguished from externally oriented cognition. More dualities are set in terms of resting state versus task-related activity, lower-order sensory/bodily self and higher-order cognitive self, and, most basic, of self vs nonself. However, the empirical findings do not follow these dichotomies but suggest a more basic and foundational characterization of self beyond these dichotomies. The self itself can be featured by a gradient of self-non-self-specificity which, neuronally, is mediated by a spatial gradient of different degrees of subcortical cortical topographic extension and a temporal gradient of slow/long-fast/short dynamic. This highlights the key role of the topographic and dynamic characterization of self for which reason we speak of a spatiotemporal self. We propose that such spatiotemporal self, through its mental topography and mental dynamic, provides a psychological baseline for perception, emotion, and cognition including both internally- and externally oriented. For that reason, we propose what we describe as “baseline model of self-specificity” (BMSS). The BMSS characterizes the role or function of self as psychological baseline which conceives the self as a reference point for all cognitive function and its capacity for adapting to changing environmental contexts.

Consciousness is not only an empirical subject matter in neuroscience but is also extensively discussed on more theoretical grounds in philosophy of mind. We here want to point out one important theoretical presupposition in the current neuroscience of consciousness. Originating and carried over from philosophy, most neuroscientific theories assume that consciousness is special by itself for which reason we need to assume an analogously special neuronal mechanism. This is indeed the case as special neuronal mechanisms like information integration and global neuronal workspace (and others) are for instance assume in both IIT and GNWT. In contrast, one may also assume that consciousness is nonspecial which entails the search for some most basic features shared by brain and consciousness. This leads us to temporospatial dynamic as nonspecial mechanism of consciousness as it is explicated in the four temporospatial mechanisms of the temporospatial theory of consciousness (TTC). Being mediated by nonspecial neuronal mechanisms, the TTC entails that spatial-topographic and temporal-dynamic features are shared by both brain and consciousness as their “common currency.” We subsequently develop the “common currency hypothesis” (CCH) of brain and consciousness. Together, we here propose an alternative view of consciousness, namely that it and its underlying neuronal mechanisms are nonspecial compared to and thus shared by both nonconsciousness and brain in general as their “common currency.”