Evolutionary Advantages of Stimulus-Driven EEG Phase Transitions in the Upper Cortical Layers.

Spatio-temporal brain activity monitored by EEG recordings in humans and other mammals has identified beta/gamma oscillations (20-80 Hz), which are self-organized into spatio-temporal structures recurring at theta/alpha rates (4-12 Hz). These structures have statistically significant correlations with sensory stimuli and reinforcement contingencies perceived by the subject. The repeated collapse of self-organized structures at theta/alpha rates generates laterally propagating phase gradients (phase cones), ignited at some specific location of the cortical sheet. Phase cones have been interpreted as neural signatures of transient perceptual experiences according to the cinematic theory of brain dynamics. The rapid expansion of essentially isotropic phase cones is consistent with the propagation of perceptual broadcasts postulated by Global Workspace Theory (GWT). What is the evolutionary advantage of brains operating with repeatedly collapsing dynamics? This question is answered using thermodynamic concepts. According to neuropercolation theory, waking brains are described as non-equilibrium thermodynamic systems operating at the edge of criticality, undergoing repeated phase transitions. This work analyzes the role of long-range axonal connections and metabolic processes in the regulation of critical brain dynamics. Historically, the near 10 Hz domain has been associated with conscious sensory integration, cortical "ignitions" linked to conscious visual perception, and conscious experiences. We can therefore combine a very large body of experimental evidence and theory, including graph theory, neuropercolation, and GWT. This cortical operating style may optimize a tradeoff between rapid adaptation to novelty vs. stable and widespread self-organization, therefore resulting in significant Darwinian benefits.

The Hard Problem is Mainly Hard Work.

Doerig et al. point out that there is now a great deal of evidence bearing directly on our understanding of consciousness. However, they argue that the multiplicity of theories suggest that we have a 'lack of stringent criteria specifying how empirical data constrains ToCs.'

Global workspace dynamics: cortical "binding and propagation" enables conscious contents.

A global workspace (GW) is a functional hub of binding and propagation in a population of loosely coupled signaling elements. In computational applications, GW architectures recruit many distributed, specialized agents to cooperate in resolving focal ambiguities. In the brain, conscious experiences may reflect a GW function. For animals, the natural world is full of unpredictable dangers and opportunities, suggesting a general adaptive pressure for brains to resolve focal ambiguities quickly and accurately. GW theory aims to understand the differences between conscious and unconscious brain events. In humans and related species the cortico-thalamic (C-T) core is believed to underlie conscious aspects of perception, thinking, learning, feelings of knowing (FOK), felt emotions, visual imagery, working memory, and executive control. Alternative theoretical perspectives are also discussed. The C-T core has many anatomical hubs, but conscious percepts are unitary and internally consistent at any given moment. Over time, conscious contents constitute a very large, open set. This suggests that a brain-based GW capacity cannot be localized in a single anatomical hub. Rather, it should be sought in a functional hub - a dynamic capacity for binding and propagation of neural signals over multiple task-related networks, a kind of neuronal cloud computing. In this view, conscious contents can arise in any region of the C-T core when multiple input streams settle on a winner-take-all equilibrium. The resulting conscious gestalt may ignite an any-to-many broadcast, lasting ∼100-200 ms, and trigger widespread adaptation in previously established networks. To account for the great range of conscious contents over time, the theory suggests an open repertoire of binding coalitions that can broadcast via theta/gamma or alpha/gamma phase coupling, like radio channels competing for a narrow frequency band. Conscious moments are thought to hold only 1-4 unrelated items; this small focal capacity may be the biological price to pay for global access. Visuotopic maps in cortex specialize in features like color, retinal size, motion, object identity, and egocentric/allocentric framing, so that a binding coalition for the sight of a rolling billiard ball in nearby space may resonate among activity maps of LGN, V1-V4, MT, IT, as well as the dorsal stream. Spatiotopic activity maps can bind into coherent gestalts using adaptive resonance (reentry). Single neurons can join a dominant coalition by phase tuning to regional oscillations in the 4-12 Hz range. Sensory percepts may bind and broadcast from posterior cortex, while non-sensory FOKs may involve prefrontal and frontotemporal areas. The anatomy and physiology of the hippocampal complex suggest a GW architecture as well. In the intact brain the hippocampal complex may support conscious event organization as well as episodic memory storage.

Consciousness, biology and quantum hypotheses.

Natural phenomena are reducible to quantum events in principle, but quantum mechanics does not always provide the best level of analysis. The many-body problem, chaotic avalanches, materials properties, biological organisms, and weather systems are better addressed at higher levels. Animals are highly organized, goal-directed, adaptive, selectionist, information-preserving, functionally redundant, multicellular, quasi-autonomous, highly mobile, reproducing, dissipative systems that conserve many fundamental features over remarkably long periods of time at the species level. Animal brains consist of massive, layered networks of specialized signaling cells with 10,000 communication points per cell, and interacting up to 1000 Hz. Neurons begin to divide and differentiate very early in gestation, and continue to develop until middle age. Waking brains operate far from thermodynamic equilibrium under delicate homeostatic control, making them extremely sensitive to a range of physical and chemical stimuli, highly adaptive, and able to produce a remarkable range of goal-relevant actions. Consciousness is "a difference that makes a difference" at the level of massive neuronal interactions in the most parallel-interactive anatomical structure of the mammalian brain, the cortico-thalamic (C-T) system. Other brain structures are not established to result in direct conscious experiences, at least in humans. However, indirect extra-cortical influences on the C-T system are pervasive. Learning, brain plasticity and major life adaptations may require conscious cognition. While brains evolved over hundreds of millions of years, and individual brains grow over months, years and decades, conscious events appear to have a duty cycle of ∼100 ms, fading after a few seconds. They can of course be refreshed by inner rehearsal, re-visualization, or attending to recurrent stimulus sources. These very distinctive brain events are needed when animals seek out and cope with new, unpredictable and highly valued life events, such as evading predators, gathering critical information, seeking mates and hunting prey. Attentional selection of conscious events can be observed behaviorally in animals showing coordinated receptor orienting, flexible responding, alertness, emotional reactions, seeking, motivation and curiosity, as well as behavioral surprise and cortical and autonomic arousal. Brain events corresponding to attentional selection are prominent and widespread. Attention generally results in conscious experiences, which may be needed to recruit widespread processing resources in the brain. Many neuronal processes never become conscious, such as the balance system of the inner ear. An air traveler may "see" the passenger cabin tilt downward as the plane tilts to descend for a landing. That visual experience occurs even at night, when the traveler has no external frame of spatial reference. The passenger's body tilt with respect to gravity is detected unconsciously via the hair cells of the vestibular canals, which act as liquid accelerometers. However, that sensory activity is not experienced directly. It only becomes conscious via vision and the body senses. The vestibular sense is therefore quite different from visual perception, which "reports" accurately to a conscious field of experience, so that we can point accurately to a bright star on a dark night. Vestibular input is also precise but unconscious. Conscious cognition is therefore a distinct kind of brain event. Many of its features are well established, and must be accounted for by any adequate theory. No non-biological examples are known. Penrose and Hameroff have proposed that consciousness may be viewed as a fundamental problem in quantum physics. Specifically, their 'orchestrated objective reduction' (Orch-OR) hypothesis posits that conscious states arise from quantum computations in the microtubules of neurons. However, a number of microtubule-associated proteins are found in both plant and animal cells (like neurons) and plants are not generally considered to be conscious. Current quantum-level proposals do not explain the prominent empirical features of consciousness. Notably, they do not distinguish between closely matched conscious and unconscious brain events, as cognitive-biological theories must. About half of the human brain does not support conscious contents directly, yet neurons in these "unconscious" brain regions contain large numbers of microtubules. QM phenomena are famously observer-dependent, but to the best of our knowledge it has not been shown that they require a conscious observer, as opposed to a particle detector. Conscious humans cannot detect quantum events "as such" without the aid of special instrumentation. Instead, we categorize the wavelengths of light into conscious sensory events that neglect their quantum mechanical properties. In science the burden of proof is on the proposer, and this burden has not yet been met by quantum-level proposals. While in the future we may discover quantum effects that bear distinctively on conscious cognition 'as such,' we do not have such evidence today.

Not full reductions, but better explanations: Comment on "Neuroontology, neurobiological naturalism, and consciousness: a challenge to scientific reduction and a solution" by Todd E. Feinberg.

Feinberg (2012) [8] suggests that science so far cannot "reduce critical features of consciousness to neural processes." But this poses an unrealistic standard. If science required full reductive explanations, neither Newton nor Darwin would be remembered today, since neither gave a reductive account of gravity or heredity. Indeed, we do not have such full reductions today. Useful theories, like Darwin's, are often not reductionistic to biological cells like neurons, though they can offer explanations of basic puzzles. Even theoretical physics cannot explain mountain avalanches and oak trees at the level of fundamental particles. Yet physics is a widely admired model of scientific theory. Judging by more modest historical standards we are making steady progress on Feinberg's four basic questions.

Biology of consciousness.

The Dynamic Core and Global Workspace hypotheses were independently put forward to provide mechanistic and biologically plausible accounts of how brains generate conscious mental content. The Dynamic Core proposes that reentrant neural activity in the thalamocortical system gives rise to conscious experience. Global Workspace reconciles the limited capacity of momentary conscious content with the vast repertoire of long-term memory. In this paper we show the close relationship between the two hypotheses. This relationship allows for a strictly biological account of phenomenal experience and subjectivity that is consistent with mounting experimental evidence. We examine the constraints on causal analyses of consciousness and suggest that there is now sufficient evidence to consider the design and construction of a conscious artifact.

The timing of the cognitive cycle.

We propose that human cognition consists of cascading cycles of recurring brain events. Each cognitive cycle senses the current situation, interprets it with reference to ongoing goals, and then selects an internal or external action in response. While most aspects of the cognitive cycle are unconscious, each cycle also yields a momentary "ignition" of conscious broadcasting. Neuroscientists have independently proposed ideas similar to the cognitive cycle, the fundamental hypothesis of the LIDA model of cognition. High-level cognition, such as deliberation, planning, etc., is typically enabled by multiple cognitive cycles. In this paper we describe a timing model LIDA's cognitive cycle. Based on empirical and simulation data we propose that an initial phase of perception (stimulus recognition) occurs 80-100 ms from stimulus onset under optimal conditions. It is followed by a conscious episode (broadcast) 200-280 ms after stimulus onset, and an action selection phase 60-110 ms from the start of the conscious phase. One cognitive cycle would therefore take 260-390 ms. The LIDA timing model is consistent with brain evidence indicating a fundamental role for a theta-gamma wave, spreading forward from sensory cortices to rostral corticothalamic regions. This posteriofrontal theta-gamma wave may be experienced as a conscious perceptual event starting at 200-280 ms post stimulus. The action selection component of the cycle is proposed to involve frontal, striatal and cerebellar regions. Thus the cycle is inherently recurrent, as the anatomy of the thalamocortical system suggests. The LIDA model fits a large body of cognitive and neuroscientific evidence. Finally, we describe two LIDA-based software agents: the LIDA Reaction Time agent that simulates human performance in a simple reaction time task, and the LIDA Allport agent which models phenomenal simultaneity within timeframes comparable to human subjects. While there are many models of reaction time performance, these results fall naturally out of a biologically and computationally plausible cognitive architecture.

Spontaneous repetitive thoughts can be adaptive: postscript on "mind wandering".

When researchers use the term mind wandering for task-unrelated thoughts in signal detection tasks, we may fall into the trap of believing that spontaneous thoughts are task unrelated in a deeper sense. Similar negative connotations are attached to common terms like cognitive failures, resting state, rumination, distraction, attentional failures, absent-mindedness, repetitiveness, mind lapses, going AWOL in the brain, cortical idling, and the like. Nevertheless, it seems obvious that mathematicians and scientists often engage in spontaneous repetitive thoughts and that the results of those thoughts are by no means maladaptive. Yet that seems to be implied by the standard use of common terms in the research literature. As humans, we know that spontaneous ideation goes on during all of our waking hours, during dreams and even in slow-wave sleep. It is unlikely that such a great allocation of mental resources has no useful adaptive function. This view of the spontaneous stream is consistent with the perspective of global workspace theory on conscious contents, which suggests that conscious events are not like unconscious cognitive representations. Rather, conscious events trigger widespread adaptive changes in the brain, far beyond their cortical origins. The brain evidence for such "global broadcasting" triggered by conscious (but not matched unconscious) events throughout the cortex is now quite compelling. Spontaneous conscious thoughts, even if they appear to be arbitrary, irrelevant, unwanted, or intrusive, may still play an important adaptive role in life-relevant problem solving and learning.

An architectural model of conscious and unconscious brain functions: Global Workspace Theory and IDA.

While neural net models have been developed to a high degree of sophistication, they have some drawbacks at a more integrative, "architectural" level of analysis. We describe a "hybrid" cognitive architecture that is implementable in neuronal nets, and which has uniform brainlike features, including activation-passing and highly distributed "codelets," implementable as small-scale neural nets. Empirically, this cognitive architecture accounts qualitatively for the data described by Baars' Global Workspace Theory (GWT), and Franklin's LIDA architecture, including state-of-the-art models of conscious contents in action-planning, Baddeley-style Working Memory, and working models of episodic and semantic longterm memory. These terms are defined both conceptually and empirically for the current theoretical domain. The resulting architecture meets four desirable goals for a unified theory of cognition: practical workability, autonomous agency, a plausible role for conscious cognition, and translatability into plausible neural terms. It also generates testable predictions, both empirical and computational.

Global workspace theory of consciousness: toward a cognitive neuroscience of human experience.

Global workspace (GW) theory emerged from the cognitive architecture tradition in cognitive science. Newell and co-workers were the first to show the utility of a GW or "blackboard" architecture in a distributed set of knowledge sources, which could cooperatively solve problems that no single constituent could solve alone. The empirical connection with conscious cognition was made by Baars (1988, 2002). GW theory generates explicit predictions for conscious aspects of perception, emotion, motivation, learning, working memory, voluntary control, and self systems in the brain. It has similarities to biological theories such as Neural Darwinism and dynamical theories of brain functioning. Functional brain imaging now shows that conscious cognition is distinctively associated with wide spread of cortical activity, notably toward frontoparietal and medial temporal regions. Unconscious comparison conditions tend to activate only local regions, such as visual projection areas. Frontoparietal hypometabolism is also implicated in unconscious states, including deep sleep, coma, vegetative states, epileptic loss of consciousness, and general anesthesia. These findings are consistent with the GW hypothesis, which is now favored by a number of scientists and philosophers.

Subjective experience is probably not limited to humans: the evidence from neurobiology and behavior.

In humans, conscious perception and cognition depends upon the thalamocortical (T-C) complex, which supports perception, explicit cognition, memory, language, planning, and strategic control. When parts of the T-C system are damaged or stimulated, corresponding effects are found on conscious contents and state, as assessed by reliable reports. In contrast, large regions like cerebellum and basal ganglia can be damaged without affecting conscious cognition directly. Functional brain recordings also show robust activity differences in cortex between experimentally matched conscious and unconscious events. This basic anatomy and physiology is highly conserved in mammals and perhaps ancestral reptiles. While language is absent in other species, homologies in perception, memory, and motor cortex suggest that consciousness of one kind or another may be biologically fundamental and phylogenetically ancient. In humans we infer subjective experiences from behavioral and brain evidence. This evidence is quite similar in other mammals and perhaps some non-mammalian species. On the weight of the biological evidence, therefore, subjectivity may be conserved in species with human-like brains and behavior.

Criteria for consciousness in humans and other mammals.

The standard behavioral index for human consciousness is the ability to report events with accuracy. While this method is routinely used for scientific and medical applications in humans, it is not easy to generalize to other species. Brain evidence may lend itself more easily to comparative testing. Human consciousness involves widespread, relatively fast low-amplitude interactions in the thalamocortical core of the brain, driven by current tasks and conditions. These features have also been found in other mammals, which suggests that consciousness is a major biological adaptation in mammals. We suggest more than a dozen additional properties of human consciousness that may be used to test comparative predictions. Such homologies are necessarily more remote in non-mammals, which do not share the thalamocortical complex. However, as we learn more we may be able to make "deeper" predictions that apply to some birds, reptiles, large-brained invertebrates, and perhaps other species.

Neural Darwinism and consciousness.

Neural Darwinism (ND) is a large scale selectionist theory of brain development and function that has been hypothesized to relate to consciousness. According to ND, consciousness is entailed by reentrant interactions among neuronal populations in the thalamocortical system (the 'dynamic core'). These interactions, which permit high-order discriminations among possible core states, confer selective advantages on organisms possessing them by linking current perceptual events to a past history of value-dependent learning. Here, we assess the consistency of ND with 16 widely recognized properties of consciousness, both physiological (for example, consciousness is associated with widespread, relatively fast, low amplitude interactions in the thalamocortical system), and phenomenal (for example, consciousness involves the existence of a private flow of events available only to the experiencing subject). While no theory accounts fully for all of these properties at present, we find that ND and its recent extensions fare well.

Identifying hallmarks of consciousness in non-mammalian species.

Most early studies of consciousness have focused on human subjects. This is understandable, given that humans are capable of reporting accurately the events they experience through language or by way of other kinds of voluntary response. As researchers turn their attention to other animals, "accurate report" methodologies become increasingly difficult to apply. Alternative strategies for amassing evidence for consciousness in non-human species include searching for evolutionary homologies in anatomical substrates and measurement of physiological correlates of conscious states. In addition, creative means must be developed for eliciting behaviors consistent with consciousness. In this paper, we explore whether necessary conditions for consciousness can be established for species as disparate as birds and cephalopods. We conclude that a strong case can be made for avian species and that the case for cephalopods remains open. Nonetheless, a consistent effort should yield new means for interpreting animal behavior.

Consciousness eclipsed: Jacques Loeb, Ivan P. Pavlov, and the rise of reductionistic biology after 1900.

The life sciences in the 20th century were guided to a large extent by a reductionist program seeking to explain biological phenomena in terms of physics and chemistry. Two scientists who figured prominently in the establishment and dissemination of this program were Jacques Loeb in biology and Ivan P. Pavlov in psychological behaviorism. While neither succeeded in accounting for higher mental functions in physical-chemical terms, both adopted positions that reduced the problem of consciousness to the level of reflexes and associations. The intellectual origins of this view and the impediment to the study of consciousness as an object of inquiry in its own right that it may have imposed on peers, students, and those who followed is explored.