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The most characteristic field pattern of the waking, activated neocortex is gamma oscillation. Its generation depends on the time decay of GABA_A-receptor-mediated Laurent inhibition and/or shunting. These receptors are uniformly distributed in the cerebral cortex and other brain regions. Because inhibitory postsynaptic potentials mediated by these neurons are reliable, they provide a more efficient means for timing than excitatory postsynaptic potentials. Due to the localized axon arbors of basket and chandelier cells and the local gap junctions, gamma oscillations in the cortex are often confined to a small piece of tissue. Coupling of distant gamma oscillators requires fast-conducting conduits, provided by the widespread axon collaterals of long-range interneurons and possibly by the long axons of some pyramidal cells. The physiological importance of the gamma rhythm is supported by the observation that neuronal assemblies in the waking brain self-organize themselves into temporal packages of 15 to 30 milliseconds.

In a previous monograph, the authors described an experimental model of the 40 Hz oscillations produced in vivo by visual stimulation. The model involved tetanic stimulation of one or two sites in a hippocampal slice, and was able to produce synchronized oscillations in the presence of axonal conduction delays. The monograph showed how network simulations and in vitro studies complement each other, for example in elucidating the cellular mechanisms by such long-range synchrony could occur. The present monograph continues this type of research, but focuses on additional sorts of oscillations, many of which depend on gap junctions.

Chapters 3 and 4 defend a theory according to which conscious states are attended intermediate-level representations, or AIRs. When expressed this way, the AIR theory described the psychological correlated of consciousness, but not the neural correlates. This chapter asks how consciousness arises in the brain, and thus seeks the neural correlates of AIRs. Intermediate-level representations are hypothesized to be realized by temporal patterns in populations of neurons, or vectorwaves. Vectorwaves, it is argued, are important for distinguishing states with different qualitative character. Attention is said to be realized by neural oscillations within the gamma band. This confirms older theories that relate consciousness to gamma activity, but this theories differs from some others by relating gamma to attention rather than binding. Putting these two elements together, the neural correlates of AIRs are gamma vectorwaves.

Sleep is a fundamental behavior that affects cognition, mood, health, and consciousness, but the mechanisms mediating the interplay between sleep and cognition remain unclear. Microelectrode sleep studies offer a unique opportunity to bridge the gap between human behavioral studies and rodent electrophysiology, especially given the technical challenges associated with functional imaging of human sleep. Sleep studies are well tolerated by patients, and allow prolonged recordings from multiple brain regions that play a pivotal role in sleep oscillations such as slow waves, sleep spindles, and hippocampal ripples. Indeed, single-unit sleep studies have revealed important discoveries, highlighting the regional diversity in the occurrence, spectral, and temporal aspects of these sleep oscillations. Sleep and epilepsy are intimately related, providing rare opportunities for understanding epileptogenesis, but special care must be exerted when making inferences about normal sleep physiology. Exciting future directions await the field of microelectrode studies of human sleep.

How are neuronal mechanisms related to the phenomenal unity as manifested in phenomenal consciousness? The book proposes a “continuity-based hypothesis of phenomenal unity.” The continuity-based hypothesis of phenomenal unity proposes that the phenomenal unity is based on and supersedes the already constituted spatial and temporal continuity in the ongoing resting state activity. More specifically, the stimulus may be linked to the resting state’s ongoing spatial and temporal continuity.

This chapter begins to explain many of our most important perceptual and cognitive abilities, including how we rapidly learn to categorize and recognize so many objects and events in the world, how we remember and anticipate events that may occur in familiar situations, how we pay attention to events that particularly interest us, and how we become conscious of these events. These abilities enable us to engage in fantasy activities such as visual imagery, internalized speech, and planning. They support our ability to learn language quickly and to complete and consciously hear speech sounds in noise. The chapter begins to explain key differences between perception and recognition, and introduces Adaptive Resonance Theory, or ART, which is now the most advanced cognitive and neural theory of how our brains learn to attend, recognize, and predict objects and events in a changing world. ART cycles of resonance and reset solve the stability-plasticity dilemma so that we can learn quickly without new learning forcing catastrophic forgetting of previously learned memories. ART can learn quickly or slowly, with supervision and without it, and both many-to-one maps and one-to-many maps. It uses learned top-down expectations, attentional focusing, and mismatch-mediated hypothesis testing to do so, and is thus a self-organizing production system. ART can be derived from a simple thought experiment, and explains and predicts many psychological and neurobiological data about normal behavior. When these processes break down in specific ways, they cause symptoms of mental disorders such as schizophrenia, autism, amnesia, and Alzheimer’s disease.

Brain oscillations are present in the same form in all mammals and represent a fundamental aspect of neuronal computation, including the generation of movement patterns, speech, and music production. Neuronal oscillators readily entrain each other, making the exchange of messages between brain areas effective. Because all neuronal oscillations are based on inhibition, they can parse and concatenate neuronal messages, a prerequisite for any coding mechanism. This chapter discusses how the hierarchical nature of cross-frequency–coupled rhythms can serve as a scaffold for combining neuronal letters into words and words into sentences, thus providing a syntactic structure for information exchange.

Synchronization of oscillatory responses in the beta- and gamma-band is involved in a variety of cognitive functions, such as perceptual grouping, attention-dependent stimulus selection, working memory, and perceptual awareness. Here, we review evidence that autism (ASD), schizophrenia and epilepsy show temporal processing deficits that are associated with abnormal neural synchronization. There are close correlations between abnormalities in neuronal synchronization and cognitive dysfunctions, emphasizing the importance of temporal coordination. ASD is a developmental disability that affects social behavior and language acquisition. Current theories and experimental data converge on the notion that dysfunctional integrative mechanisms in autism may be the result of reduced neural synchronization. There is also consistent evidence that neural synchrony in the β‎- and γ‎-frequency ranges is impaired in patients with schizophrenia. The cognitive abnormalities in schizophrenic patients include fragmented perception, erroneous binding of features, deficits in attention, impaired working memory, delusions, and hallucinations. Synchronization of oscillatory activity in the beta- and gamma-band frequency range is associated with cognitive functions that are disturbed in schizophrenia patients. Epilepsy is a common and diverse set of chronic neurological disorders characterized by seizures. Seizures may not only be a consequence of heightened neuronal excitability such as results from an imbalance between excitatory and inhibitory mechanisms. Alterations of the mechanisms that support the oscillatory patterning and the synchronization of neuronal activity appear to be equally important. Both the reduced synchronization preceding some forms of epileptic activity and the enhanced synchronization associated with seizures proper go along with the disturbance of cognitive functions. There are suggestive genetic links between schizophrenia and epilepsy, between schizophrenia and dyslexia via magnocellular deficits, and between autism and SLI through impaired language.

To effectively send a message, a single neuron must cooperate with its peers. Such cooperation can be achieved by synchronizing their spikes together within the time window limited by the ability of the downstream reader neuron to integrate the incoming signals. Therefore, the cell assembly, defined from the point of view of the reader neuron, can be considered as a unit of neuronal communication, a “neuronal letter.” Acting in assemblies has several advantages. A cooperative assembly partnership tolerates spike rate variation in individual cells effectively because the total excitatory effect of the assembly is what matters to the reader mechanism. Interacting assembly members can compute probabilities rather than convey deterministic information and can robustly tolerate noise even if the individual members respond probabilistically.