October 17, 2009

Alpha Oscillations, Attention and Consciousness

One way to describe brain activity measured by EEG or MEG is by its frequency content. Frequencies can be categorized into one of the following ranges: low, middle and high. The low frequencies include the delta and theta ranges, whereas the middle frequency range consists of the alpha and beta ranges. The gamma wave belongs to the high frequency group.

Different cognitive functions have been associated with these different frequency ranges. Specifically, alpha oscillations have been associated with the inhibition of brain regions that are not required to perform a given task. However, in a past paper, Palva and Palva summarized an accumulating body of evidence that suggested that alpha oscillations play a much larger role in cognition by contributing to mechanisms of attention and consciousness. Click here for full access to the paper.

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October 5, 2009

Lucid Dreaming: A State of Consciousness with Features of Both Waking and Non-Lucid Dreaming

U. Voss, R. Holzmann, I. Tuin, J.A. Hobson
Article in Sleep

Abstract
Study Objectives: The goal of the study was to seek physiological correlates of lucid dreaming. Lucid dreaming is a dissociated state with aspects of waking and dreaming combined in a way so as to suggest a specific alteration in brain physiology for which we now present preliminary but intriguing evidence. We show that the unusual combination of hallucinatory dream activity and wake-like reflective awareness and agentive control experienced in lucid dreams is paralleled by significant changes in electrophysiology.

Design: 19-channel EEG was recorded on up to 5 nights for each participant. Lucid episodes occurred as a result of pre-sleep autosuggestion.

Setting: Sleep laboratory of the Neurological Clinic, Frankfurt University.

Participants: Six student volunteers who had been trained to become lucid and to signal lucidity through a pattern of horizontal eye movements.

Measurements and Results: Results show lucid dreaming to have REM-like power in frequency bands delta and theta, and higher-than-REM activity in the gamma band, the between-states-difference peaking around 40 Hz. Power in the 40 Hz band is strongest in the frontal and frontolateral region. Overall coherence levels are similar in waking and lucid dreaming and significantly higher than in REM sleep, throughout the entire frequency spectrum analyzed. Regarding specific frequency bands, waking is characterized by high coherence in alpha, and lucid dreaming by increased delta and theta band coherence. In lucid dreaming, coherence is largest in frontolateral and frontal areas.

Conclusions: Our data show that lucid dreaming constitutes a hybrid state of consciousness with definable and measurable differences from waking and from REM sleep, particularly in frontal areas.

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April 10, 2009

Investigating the Awareness of Remembering

Ken A. Paller, Joel L.Voss, Carmen E. Westerberg
Article in Perspectives on Psychological Science

Abstract
There is a marked lack of consensus concerning the best way to learn how conscious experiences arise. In this article, we advocate for scientific approaches that attempt to bring together four types of phenomena and their corresponding theoretical accounts: behavioral acts, cognitive events, neural events, and subjective experience. We propose that the key challenge is to comprehensively specify the relationships among these four facets of the problem of understanding consciousness without excluding any facet. Although other perspectives on consciousness can also be informative, combining these four perspectives could lead to significant progress in explaining a conscious experience such as remembering. We summarize some relevant findings from cognitive neuroscience investigations of the conscious experience of memory retrieval and of memory behaviors that transpire in the absence of the awareness of remembering. These examples illustrate suitable scientific strategies for making progress in understanding consciousness by developing and testing theories that connect the behavioral expression of recall and recognition, the requisite cognitive transactions, the neural events that make remembering possible, and the awareness of remembering.

Click here for the full paper.

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November 24, 2008

Gamma oscillations mediate stimulus competition and attentional selection in a cortical network model

Christoph Börgers, Steven Epstein, and Nancy J. Kopell
Article in Proceedings of the National Academy of Science, USA

Abstract
Simultaneous presentation of multiple stimuli can reduce the firing rates of neurons in extrastriate visual cortex below the rate elicited by a single preferred stimulus. We describe computational results suggesting how this remarkable effect may arise from strong excitatory drive to a substantial local population of fast-spiking inhibitory interneurons, which can lead to a loss of coherence in that population and thereby raise the effectiveness of inhibition. We propose that in attentional states fast-spiking interneurons may be subject to a bath of inhibition resulting from cholinergic activation of a second class of inhibitory interneurons, restoring conditions needed for gamma rhythmicity. Oscillations and coherence are emergent features, not assumptions, in our model. The gamma oscillations in turn support stimulus competition. The mechanism is a form of “oscillatory selection,” in which neural interactions change phase relationships that regulate firing rates, and attention shapes those neural interactions.

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November 2, 2008

Theta phase synchrony and conscious target perception: Impact of intensive mental training

Heleen A. Slagter, Antoine Lutz, Lawrence L. Greischar, Sander Nieuwenhuis, and Richard J. Davidson.
Article in Journal of Cognitive Neuroscience

Abstract
The information processing capacity of the human mind is limited, as is evidenced by the attentional blink-a deficit in identifying the second of two targets (T1 and T2) presented in close succession. This deficit is thought to result from an overinvestment of limited resources in T1 processing. We previously reported that intensive mental training in a style of meditation aimed at reducing elaborate object processing, reduced brain resource allocation to T1, and improved T2 accuracy [Slagter, H. A., Lutz, A., Greisschar, L. L., Frances, A. D., Nieuwenhuis, S., Davis, J., et al. Mental training affects distribution of limited brain resources. PloS Biology, 5, e138, 2007]. Here we report EEG spectral analyses to examine the possibility that this reduction in elaborate T1 processing rendered the system more available to process new target information, as indexed by T2-locked phase variability. Intensive mental training was associated with decreased cross-trial variability in the phase of oscillatory theta activity after successfully detected T2s, in particular, for those individuals who showed the greatest reduction in brain resource allocation to T1. These data implicate theta phase locking in conscious target perception, and suggest that after mental training the cognitive system is more rapidly available to process new target information. Mental training was not associated with changes in the amplitude of T2-induced responses or oscillatory activity before task onset. In combination, these findings illustrate the usefulness of systematic mental training in the study of the human mind by revealing the neural mechanisms that enable the brain to successfully represent target information.

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October 26, 2008

New vistas for alpha-frequency band oscillations

EEG,attention,brain networks,memory — alice @ 3:50 am

Palva S, Palva JM.
Article in Trends in Neurosciences

Abstract
The amplitude of alpha-frequency band (8-14 Hz) activity in the human electroencephalogram is suppressed by eye opening, visual stimuli and visual scanning, whereas it is enhanced during internal tasks, such as mental calculation and working memory. Alpha-frequency band oscillations have hence been thought to reflect idling or inhibition of task-irrelevant cortical areas. However, recent data on alpha-amplitude and, in particular, alpha-phase dynamics posit a direct and active role for alpha-frequency band rhythmicity in the mechanisms of attention and consciousness. We propose that simultaneous alpha-, beta- (14-30 Hz) and gamma- (30-70 Hz) frequency band oscillations are required for unified cognitive operations, and hypothesize that cross-frequency phase synchrony between alpha, beta and gamma oscillations coordinates the selection and maintenance of neuronal object representations during working memory, perception and consciousness.

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October 13, 2008

Theta synchronization during episodic retrieval: Neural correlates of conscious awareness

EEG,conscious states,memory — alice @ 2:04 am

In a past study, Klimesch and colleagues examined whether the conscious experience of remembering and knowing are associated with neural synchronization in the theta bandwidth.  These investigators first presented participants with a series of words (through both auditory and visual means) and then tested participants’ memory for these words using a recognition test and the “Remember-Know” task. 

During the recognition test, participants were shown a series of words (the participants saw some of these words earlier during the experiment, whereas other words were not seen before) and were asked to judge whether these same words were presented to them earlier.  For those words that were judged as “old” (previously presented), participants also performed the Remember-Know task. 

The Remember-Know task is widely used in memory research to study one’s state of consciousness during a recognition decision.  ”Remember” judgments are made when an “old” decision on the recognition test is accompanied by awareness of details of the previous occurrence of the stimulus in question.  “Know” judgments are made when an “old” decision is not accompanied by such awareness.

Among other interesting results, Klimesch and colleagues found that theta power was larger for Know judgments early during the recognition period of a word (300 – 450 ms) and larger for Remember judgments during a later period (450 – 625 ms). The investigators concluded that these patterns of theta associated with Remember and Know judgments demonstrate that the temporal dynamics of the neural synchronization plays an important role in the experiential characteristics associated with memory retrieval.

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October 11, 2008

Comparison of event-related potentials in attentional blink and repetition blindess

EEG,attention — alice @ 4:44 pm

In a recent study, Mika Koivisto and Antti Revonsuo compared the timing and mechanisms of attentional blink (AB) and repetition blindness (RB) directly during the same rapid serial visual presentation stream to examine the relation between the two phenomena.  To do so, they recorded electrophysiological responses over the scalp (EEG, ERP) to repeated and unrepeated targets.

The authors report the following findings:

Comparable to earlier ERP studies on visual awareness, the results showed for both types of targets a negative amplitude difference between ERPs to consciously recognized and unrecognized targets during 250-350 ms from stimulus onset, suggesting that both AB and RB are associated with deficits of conscious perception, occurring at earlier stages than access to working memory. However, the perceptual deficit in RB is more severe, which may be related to higher overall negativity in response to repeated targets observed 150-300 ms after stimulus onset, suggesting stronger cortical baseline activation and higher perceptual threshold for repeated targets as compared with unrepeated ones.

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October 5, 2008

EEG activity in Carmelite nuns during a mystical experience

EEG,mystical experience — alice @ 5:20 am

In a recent article, Beauregard and Paquette examined EEG spectral power and coherence in 14 Carmelite nuns during a mystical experience, which is characterized by a sense of union with God and is reported across all cultures.

EEG data were recorded for three conditions: Mystical, Control and Baseline. During the Mystical conditions, the nuns were asked to remember and relive the most intense mystical experience felt in their lives as a member of the Carmelite Order. In the Control condition, the nuns were instructed to remember and relive the most intense state of union with another human ever felt in their lives while being affiliated with the Carmelite Order. The Baseline condition was a normal restful state.

The phenomenological data that were collected indicate that the nuns actually experienced genuine mystical experiences, instead of vivid memories of a mystical state, during the Mystical condition. The experiences reported during this condition were multidimensional, implicating changes in perception (e.g., visual mental imagery), cognition (e.g., representations about the self), and emotion (e.g., peace, joy, and unconditional love).

In the Mystical, compared to Control, condition, greater theta power was observed over the left and central fronto-parietal region, whereas greater gamma1 power was observed over the right temporal and parietal regions. Additionally, greater coherence for the theta and alpha bands were displayed over different pairs of electrodes

Beauregard and Paquette concluded that the results of this study demonstrate that mystical experiences are mediated by marked changes in EEG power and coherence and that these changes implicate several cortical areas of the brain in both hemispheres.

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October 31, 2007

Dynamic neural correlates of consciousness

EEG,fMRI,neuroimaging,perception — thomasr @ 3:27 am

PLOS Biology has a most interesting article from Stanislas Dehaene‘s group on the neurodynamics of conscious experience. The researchers studied brain activation using EEG, while subjects rated visually presented stimuli on a scale from unseen to clearly seen. It was found that conscious experience of a stimulus was related to the engagement of a widespread network involving the frontal, parietal and temporal cortices.

SCR note: It is mentioning a recent study using fMRI (Christensen et al. 2006) provided comparable results, and adding two factors; (1) the conscious experience of a visual stimulus involved activation of both thalami, and (2) subjects consistently rated some experiences as vague, i.e., as “detected but not identified”. This experience was associated with both lower activation in those regions involved in conscious experience, and unique activation of additional regions, including some prefrontal regions.

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October 22, 2007

Empathy for Pain and Touch in the Human Somatosensory Cortex

empathicpain.jpegAlthough feeling pain and touch has long been considered inherently private, recent neuroimaging and neurophysiological studies hint at the social implications of this experience. Here we used somatosensory-evoked potentials (SEPs) to investigate whether mere observation of painful and tactile stimuli delivered to a model would modulate neural activity in the somatic system of an onlooker.

Viewing video clips showing pain and tactile stimuli delivered to others, respectively, increased and decreased the amplitude of the P45 SEP component that reflects the activity of the primary somatosensory cortex (S1). These modulations correlated with the intensity but not with the unpleasantness of the pain and touch ascribed to the model or the aversion induced in the onlooker by the video clips. Thus, modulation of S1 activity contingent upon observation of others’ pain and touch may reflect the mapping of sensory qualities of observed painful and tactile stimuli.

Results indicate that the S1 is not only involved in the actual perception of pain and touch but also plays an important role in extracting somatic features from social interactions.

Bufalari et al. in Cerebral Cortex

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August 31, 2007

Final proof of role of neural coherence in consciousness?

neuralsynchrony.jpgMelloni et al. have recently demonstrated, in the Journal of Neuroscience, that neural synchrony in the gamma range between distal rain regions is important for conscious perception. The authors say about their work that “the access to conscious perception is the early transient global increase of phase synchrony of oscillatory activity in the gamma frequency range”

Here we link to the article and some related works.

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June 15, 2007

Learning to pay attention

EEG,altered states,attention — thomasr @ 3:20 am

attention_plos.jpgBy Rachel Jones

Our sensory system is constantly bombarded with inputs, but owing to the brain’s finite processing power, we are forced to pay attention to only a tiny proportion of these inputs at any given time. In a new study, Richard Davidson and colleagues report [in PLoS Biology] that intensive training in meditation can alter the way in which the brain allocates attentional resources to important stimuli, allowing people to improve their performance on a demanding visual task.

In the “attentional blink” task, volunteers were asked to identify two “target” stimuli—for example, two particular numbers—in a stream of rapidly presented “non-target” stimuli—for example, letters—which are irrelevant to the task. When the first target number appears on the screen, it captures the attention of the subject, and this can prevent the person from spotting the second target if it appears within around half a second of the first (the attentional blink). It is as if the brain is so busy processing the first target that it can’t also process the second, and therefore the second target goes unnoticed. However, the attentional blink does not represent a structural processing bottleneck. Most subjects are able to spot the second target on at least a small proportion of trials. Since this task gauges the ability of subjects to allocate cognitive resources efficiently when multiple stimuli compete for attention, it is perfectly suited for investigations of the effects of mental training on attention.

Read full story at PLoS Biology

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February 8, 2007

Pain in the brain

EEG,brain imaging,fMRI,pain,perception — thomasr @ 5:21 am

index_pain.gifPain is one of the most prominent examples of the problem of consciousness: from a subjective point of view we know the experience of pain all too well. Seen from the objective side of pain, the neural processes related to pain are becoming unravelled. But the essential relationship between neural processes going on from the sensation to the experience are much less known.

In a study by Christmann and colleagues, a combination of EEG and fMRI demonstrates how regional brain areas make different contributions — and at different times — to the experience of pain.

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December 30, 2006

Visuo-spatial consciousness and parieto-occipital EEGs

Which brain areas are involved in visuospatial consciousness? In a recent study by Babiloni and colleagues, subjects performed a visual perception task. Interestingly, these scientists found that visual-evoked potentials at parieto-occipital areas had the same peak latencies for cases of conscious, as well as unconscious, perception. These visual-evoked potentials were located to the occipital (BA 19) and parietal (BA 7) cortices.

Source strength was significantly stronger in consciously, compared to unconsciously, perceived cases at about +300 ms poststimulus. Babiloni and colleagues concluded that these features of the observed parieto-occipital activation might be connected to visuospatial consciousness.

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