http://download.neurosky.com/docs/papers/bcq/Klimesch_1999_EEG_alpha_and_theta_oscillations_reflect_cognitive_and_memory_performance.pdf

EEG alpha and theta oscillations reflect cognitive and memory performance: a review and analysis

EEG alpha oscillations: The inhibition–timing hypothesis

Converging evidence from electrophysiological, physiological and anatomical studies suggests that abnormalities in the synchronized oscillatory activity of neurons may have a central role in the pathophysiology of schizophrenia. Neural oscillations are a fundamental mechanism for the establishment of precise temporal relationships between neuronal responses that are in turn relevant for memory, perception and consciousness. In patients with schizophrenia, the synchronization of beta- and gamma-band activity is abnormal, suggesting a crucial role for dysfunctional oscillations in the generation of the cognitive deficits and other symptoms of the disorder. Dysfunctional oscillations may arise owing to anomalies in the brain's rhythm-generating networks of GABA (gamma-aminobutyric acid) interneurons and in cortico-cortical connections.

Abnormal neural oscillations and synchrony in schizophrenia

The human AIDS viruses human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2) represent cross-species (zoonotic) infections. Although the primate reservoir of HIV-2 has been clearly identified as the sooty mangabey (Cercocebus atys), the origin of HIV-1 remains uncertain. Viruses related to HIV-1 have been isolated from the common chimpanzee (Pan troglodytes), but only three such SIVcpz infections have been documented, one of which involved a virus so divergent that it might represent a different primate lentiviral lineage. In a search for the HIV-1 reservoir, we have now sequenced the genome of a new SIVcpzstrain (SIVcpzUS) and have determined, by mitochondrial DNA analysis, the subspecies identity of all known SIVcpz-infected chimpanzees. We find that two chimpanzee subspecies in Africa, the central P. t. troglodytes and the eastern P. t. schweinfurthii, harbour SIVcpz and that their respective viruses form two highly divergent (but subspecies-specific) phylogenetic lineages. All HIV-1 strains known to infect man, including HIV-1 groups M, N and O, are closely related to just one of these SIVcpz lineages, that found in P. t. troglodytes. Moreover, we find that HIV-1 group N is a mosaic of SIVcpzUS- and HIV-1-related sequences, indicating an ancestral recombination event in a chimpanzee host. These results, together with the observation that the natural range of P. t. troglodytes coincides uniquely with areas of HIV-1 group M, N and O endemicity, indicate that P. t. troglodytes is the primary reservoir for HIV-1 and has been the source of at least three independent introductions of SIVcpz into the human population.

Origin of HIV-1 in the chimpanzee Pan troglodytes troglodytes

Neuroelectric and imaging studies of meditation are reviewed. Electroencephalographic measures indicate an overall slowing subsequent to meditation, with theta and alpha activation related to proficiency of practice. Sensory evoked potential assessment of concentrative meditation yields amplitude and latency changes for some components and practices. Cognitive event-related potential evaluation of meditation implies that practice changes attentional allocation. Neuroimaging studies indicate increased regional cerebral blood flow measures during meditation. Taken together, meditation appears to reflect changes in anterior cingulate cortex and dorsolateral prefrontal areas. Neurophysiological meditative state and trait effects are variable but are beginning to demonstrate consistent outcomes for research and clinical applications. Psychological and clinical effects of meditation are summarized, integrated, and discussed with respect to neuroimaging data.

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Meditation States and Traits: EEG, ERP, and Neuroimaging Studies.

Alpha oscillations in brain functioning: an integrative theory.

During the "Decade of the Brain", brain science is coming to terms with its ultimate problem: understanding the mechanisms by which the immense number of neurons in the human brain interact to produce the higher cognitive functions. The analysis of the brain's natural frequencies opens a new window toward a combined analysis of sensory and cognitive functions at the level of single neurons and the field potentials. In the last decade, our research group has been strongly involved in the development of nonlinear brain dynamics and with the oscillatory processes of neural assemblies. Recently, three new volumes extensively described this new evolution in neuroscience by concluding that a new integrative neurophysiology and a new "brain theory" is needed in order to confront the problems recognized in this decade of the brain. This article provides a brief outline of how the findings in the last 20 years of research have led to such a development.

Oscillatory brain theory: a new trend in neuroscience

Several paradigms or strategies-some of them introduced here-were applied to point out that the EEG serves as a functionally relevant signal (or operator) in various frequency channels. These can be brought to resonant behavior depending on functional brain states. The authors emphasize that the EEG-operators are functionally significant if 1-4 Hz, 4-7 Hz, 8-13 Hz, or 40 Hz activities can be brought to a resonant state with a high degree of synchrony. The time-locking of an internally induced EEG fragment may depend on the specific behavior (for example induced alpha templates prior to a cognitive target, 40 Hz induced rhythmicities with 300 ms latency in hippocampus during cognitive tasks). For topographic aspects see, e.g., Schurmann & Basar (1994) and Basar & Schurmann (1994). The authors assume that the analysis of evoked potentials (EPs) performed within the scope of resonance phenomena and/or induced rhythmicities can be developed into a most important tool to understand and to inter-relate sensory and cognitive functions of the brain. Once the physiological significance of 10 Hz and 40 Hz resonance phenomena is established, the type of component analysis here presented provides, the authors believe, an excellent possibility to describe functional states of the intact brain during consciousness. The authors assume that by using such methods, the analysis of EEG, sensory EPs, and event-related potentials will experience a renaissance in functional brain research. >

Time and frequency analysis of the brain's distributed gamma-band system

We performed an analysis of topographic and modality-dependent responsiveness of auditory and visual cortex in 5 cats and of vertex and occipital derivations in 12 human subjects. The evoked potentials were studied in the frequency domain by means of the Fourier transform.Furthermore, digital filtering was applied to confirm and extend the analysis. Preliminary results indicate that resonances were observed mainly in the 5, 10, 20 and 40 Hz frequency bands. The frequency of resonance maxima depended on the sites of measurement electrodes and stimulus modality. It is concluded that the analysis of resonance phenomena in the brain is a useful approach to understanding the relation between evoked potentials, evoked magnetic fields and single-cell recordings.

Sensory and Cognitive Components of Brain Resonance Responses: An Analysis of Responsiveness in Human and Cat Brain upon Visual and Auditory Stimulation

M. Schürmann

Papers

Alpha oscillations in brain functioning: an integrative theory.

Oscillatory brain theory: a new trend in neuroscience

Time and frequency analysis of the brain's distributed gamma-band system

Sensory and Cognitive Components of Brain Resonance Responses: An Analysis of Responsiveness in Human and Cat Brain upon Visual and Auditory Stimulation

A possible role of evoked alpha in primary sensory processing: common properties of cat intracranial recordings and human EEG and MEG.