One of the outstanding problems in the cognitive sciences is to understand how ongoing conscious experience is related to the workings of the brain and nervous system. Neurodynamics offers a powerful approach to this problem because it provides a coherent framework for investigating change, variability, complex spatiotemporal patterns of activity, and multiscale processes (among others). In this chapter, we advocate a neurodynamical approach to consciousness that integrates mathematical tools of analysis and modeling, sophisticated physiological data recordings, and detailed phenomenological descriptions. We begin by stating the basic intuition: Consciousness is an intrinsically dynamic phenomenon and must therefore be studied within a framework that is capable of rendering its dynamics intelligible. We then discuss some of the formal, analytical features of dynamical systems theory, with particular reference to neurodynamics. We then review several neuroscientific proposals that make use of dynamical systems theory in characterizing the neurophysiological basis of consciousness. We continue by discussing the relation between spatiotemporal patterns of brain activity and consciousness, with particular attention to processes in the gamma frequency band. We then adopt a critical perspective and highlight a number of issues demanding further treatment. Finally, we close the chapter by discussing how phenomenological data can relate to and ultimately constrain neurodynamical descriptions, with the long-term aim being to go beyond a purely correlational strategy of research.

Key words: Consciousness, neurodynamics, dynamical system theory, complex brain patterns, large-scale integration, gamma band, phase synchrony, phenomenological descriptions.

This article presents, for the first time, a practical method for the direct quantification of frequency-specific synchronization (i.e., transient phase-locking) between two neuroelectric signals. The motivation for its development is to be able to examine the role of neural synchronies as a putative mechanism for long-range neural integration during cognitive tasks. The method, called phase-locking statistics (PLS), measures the significance of the phase covariance between two signals with a reasonable time-resolution (<100 ms). Unlike the more traditional method of spectral coherence, PLS separates the phase and amplitude components and can be directly interpreted in the framework of neural integration. To validate synchrony values against background fluctuations, PLS uses surrogate data and thus makes no a priori assumptions on the nature of the experimental data. We also apply PLS to investigate intracortical recordings from an epileptic patient performing a visual discrimination task. We find large-scale synchronies in the gamma band (45 Hz), e.g., between hippocampus and frontal gyrus, and local synchronies, within a limbic region, a few cm apart. We argue that whereas long-scale effects do reflect cognitive processing, short-scale synchronies are likely to be due to volume conduction. We discuss ways to separate such conduction effects from true signal synchrony.

Key words: neural synchrony, phase-locking, coherence, EEG, EcoG, epilepsy, gamma-band, deblurring

This paper studies gamma-band responses from two implanted epileptic patients during a simple visual discrimination task. Our main aim was to ascertain, in a reliable manner, whether evoked (stimulus-locked) and induced (triggered by, but not locked to, stimuli) responses are present in intracranial recordings. For this purpose, we introduce new methods adapted to detect the presence of gamma responses at this level of recording, intermediary between EEG-scalp and unicellular responses. The analysis relies on a trial-by-trial time–frequency analysis and on the use of surrogate data for statistical testing. We report that visual stimulation reliably elicits evoked and induced responses in human intracranial recordings. Induced intracranial gamma activity is significantly present in short oscillatory bursts (a few cycles) following visual stimulation. These responses are highly variable from trial to trial, beginning after 200 ms and lasting up to 500 ms. In contrast, intracranial-evoked gamma responses concentrate around 100 ms latencies corresponding to evoked responses observed on the scalp. We discuss our results in relation to scalp gamma response in a similar protocol [Tallon-Baudry et al. (1996) J. Neurosci., 16, 4240–4249] and draw some conclusions for bridging the gap between gamma oscillations observed on the scalp surface and their possible cortical sources.

Key words: human, gamma-band activity, intracortical recordings, phase synchronization, surrogate data, time-frequency analysis, visual discrimination

The contents of consciousness are complex and dynamic and are embedded in perception and cognition. The study of consciousness and subjective experience has been central to philosophy for centuries. However, despite its relevance for understanding cognition and behaviour, the empirical study of consciousness is relatively new, embroiled by the seemingly opposing subjective and objective sources of data. Francisco Varela (1946–2001) pioneered the empirical study of consciousness by developing novel, naturalised and rich approaches in a non-reductive and comprehensive manner. In this article, we review the main conceptual distinctions and philosophical challenges of consciousness research and highlight the main contributions of Varela and his associates: the development of neurophenomenology as a methodological framework that builds a bridge between subjective and objective sources of data and the discovery of gamma-band phase synchronisation as a neural marker of perceptual awareness. Finally, we describe the work of Varela on time consciousness, his philosophical approach and the implementation of his neurophenomenological framework for its study by integrating subjective reports with neural measures.

Key words: consciousness, perception, neurophenomenology, philosophy of mind, francisco varela

We studied subdural recordings from a patient with an unusually focal and stable occipito-temporal epileptic discharge under four experimental conditions. The series of time intervals between successive spike discharges displayed a few (3–5) clusters of periodic values representing statistically significant short-term periodicities when tested against surrogate data. This short-term predictability was modulated during the different experimental conditions by periodicity shifts of the order of 15–30 ms. Correspondingly, there was an increased gamma-band (30–70 Hz) coherence between the epileptic focus and surrounding recording sites. We conclude that the focal epileptic activity is part of an extended network of neural activities which exert a fast modulation reflected in changes of transiently periodic activities.

Neurophenomenology, as an attempt to combine and mutually enlighten neural and experiential descriptions of cognitive processes, has met practical difficulties which have limited its implementation into actual research projects. The main difficulty seems to be the disparity of the levels of description: while neurophenomenology strongly emphasizes the micro-dynamics of experience, at the level of brief mental events with very specific content, most neural measures have much coarser functional selectivity, because they mix functionally heterogeneous neural processes either in space or in time. We propose a new starting point for this neurophenomenology, based on (a) the recent development of human intra-cerebral EEG (iEEG) research to highlight the neural micro-dynamics of human cognition, with millimetric and millisecond precision and (b) a disciplined access to the experiential micro-dynamics, through specific elicitation techniques. This lays the foundation for a microcognitive science, the practical implementation of neurophenomenology to combine the neural and experiential investigations of human cognition at the subsecond level. This twofold microdynamic approach opens a line of investigation into the very cognitive acts in which the scission between the objective and the subjective worlds originates, and a means to verify and refine the dynamic epistemology of enaction. Relevance: The twofold microdynamic approach that we are advocating in this article not only provides a methodological solution to the problems of correlation between experiential and neuronal, first-person and third-person descriptions of our cognitive processes. It also opens a line of investigation into the very cognitive acts in which the scission between the objective and the subjective worlds originates, and a means to verify and refine the dynamic epistemology of enaction.

Key words: Elicitation, neuro-phenomenology, microcognition, microdynamics, neurofeedback, enaction, microgenesis, gamma band

This paper presents a novel reading of ideas on temporal binding as a key for cognitive operations by means of fast (gamma band) phase synchrony. We advocate a view of binding of widely distributed cell assemblies transiently locked in a neural hypergraph which serves as a reference point to incorporate or interpret other less coherent concurrent neural events. The paper traces in some detail the empirical evidence concerning the gamma binding process and presents some implications for the constitution of a unified cognitive-mental space. Relevance: 

Key words: Cell assemblies, cognitive operations, gamma binding, neural hypergraph, phase synchrony.