State Of Brain Activity Research Articles

Differential brain activity states during the perception and nonperception of illusory motion as revealed by magnetoencephalography

We studied visual perception using an annular random-dot motion stimulus called the racetrack. We recorded neural activity using magnetoencephalography while subjects viewed variants of this stimulus that contained no inherent motion or various degrees of embedded motion. Subjects reported seeing rotary motion during viewing of all stimuli. We found that, in the absence of any motion signals, patterns of brain activity differed between states of motion perception and nonperception. Furthermore, when subjects perceived motion, activity states within the brain did not differ across stimuli of different amounts of embedded motion. In contrast, we found that during periods of nonperception brain-activity states varied with the amount of motion signal embedded in the stimulus. Taken together, these results suggest that during perception the brain may lock into a stable state in which lower-level signals are suppressed.

Cortical Activation during Clock Reading as a Quadratic Function of Dementia State

In patients with Alzheimer's disease (AD), neuroimaging studies have demonstrated decreased brain activation, while increased activation was detected in patients with mild cognitive impairment (MCI). It can be hypothesized that increased cerebral activity seen in patients with MCI reflects neural compensation at the beginning of neurodegenerative processes. Later, as patients develop AD, neural integrity is increasingly impaired. This is accompanied by decreased neural activation. In this study we examined cognitive performance and functional magnetic resonance imaging activation on a Clock Reading task (CRT) and a Spatial Control task (SCT) in healthy controls, patients with MCI, and patients with early AD. Correlations between neural-functional activation and cognitive state, measured by the Mini Mental Status Examination, were determined using rank, linear and quadratic correlation models. It could be shown that CRT, in comparison to SCT, specifically activates brain regions in the ventral visual stream and precuneus known to be involved in conceptual processing and spatial imagery. The correlation between brain activity and cognitive state followed a quadratic rather than a linear pattern in several brain regions, including the lingual gyrus, cuneus, and precuneus. The strongest brain activity was found in patients with MCI and less severely impaired early AD subjects. These findings support the hypothesis that patients in early stages of dementia compensate for neuronal loss by the recruitment of additional neural resources reflected by increased neural activation, as measured by the blood oxygen level-dependent signal.

ALTERED CONNECTIVITY IN THE AUDITORY AND ATTENTION SYSTEMS OF SCHIZOPHRENIA PATIENTS WITH AUDITORY VERBAL HALLUCINATIONS

default-mode and the salience networks in patients with schizophrenia and healthy volunteers. Methods: 20 patients with DSM-IV schizophrenia and 20 age, gender and parental socio-occupational status matched controls participated in the study after providing informed consent. The subjects performed two functional tasks (n-back memory task and auditory oddball task) and data was also acquired when the subjects were in resting state for 5 minutes, with eyes closed. Functional MR Imaging was performed on a 3 Tesla Philips MR device employing echo-planar (EPI) acquisition (TE / TR 35 / 2100 ms; 64×64 matrix, voxel size 3.25×3.25×3.25; 35 slices). Images were reoriented, realigned, coregistered, spatially normalized and smoothed using SPM5 (http://www.fil.ion.ucl.ac.uk/spm). The smoothed images from all the subjects were subjected to Independent Component Analysis (ICA) using the GIFT software (http://icatb.sourceforge.net) to decompose the data into 20 spatially independent components. The resulting components were subjected to visual inspection and correlation with apriori masks created in MRIcron. The correlation between the networks were tested using the Functional Network Connectivity software (Jafri et al., 2008). Results: Both in the two functional tasks and the resting stage, the three components correlating to the CEN, DMN and salience networks were clearly identified in the combined group ICA. Separate group ICA of the patients and controls also led to identification of the three networks in each group. The time courses of the three components showed that the CEN, and Salience components were correlated with active tasks in the functional tasks, and the DMNwas anticorrelatedwith the tasks. The functional connectivity analysis showed the complex interplay differences between patients with schizophrenia and controls. Discussion: The three networks (CEN, DMN and Salience networks) were clearly identifiable using model-free ICA analysis in both functional tasks and the resting stage for both groups, which suggests that three networks are key to information processing in both resting and active states of brain activity. The complex interplay between the three networks that is aberrant in schizophrenia may explain the 'disconnection' resulting in the diverse range of symptoms in schizophrenia.

Evaluation of the neurotoxical effect of aluminum on the Wistar rat

Our previous investigations on an animal model of neurotoxicity show that increased power in the delta range is connected with the neurotoxic effect of aluminum exposure. In this study we used several aluminum-treated animals as a reliable model for the evaluation of the neurotoxic effects of aluminum on neurons, and compared it with a control group. We conclude that spectral analysis and the ratio between the delta and theta ranges might be reliable for a qualitative description of the neurotoxic effect of aluminum, and that the t test might be used to evaluate the change in brain activity between the treated and control groups of animals. The animal model under anesthesia was used to describe the state of brain activity with neurotoxicity with suppressed functional connectivity in the brain structure. We also performed fractal analysis to quantitatively describe neurotoxic effect in different pathophysiological states of animals treated with different doses of aluminum. A decrease in the fractal dimension is an indicator of neurodegeneration in the state of stress. This animal model is suitable for evaluation of the neurodegenerative processes in Alzheimer's dementia and Parkinson's disease. .

Differential effects of eyes open or closed in darkness on brain activation patterns in blind subjects

In functional brain imaging, specific task conditions can be compared to a reference condition which is often eyes-open or eyes-closed in darkness without the execution of a specific task. Previous fMRI studies in sighted subjects have shown that eyes-open in darkness, without visual stimulation, increases the relative activity in cortical ocular motor and attentional areas (“exteroceptive” state; contrast OPEN > CLOSED). By contrast, eyes-closed causes a relative signal increase in sensory systems (“interoceptive” state; contrast CLOSED > OPEN). In the present study we used fMRI to determine whether these differential brain activity states can also be found in congenitally blind subjects: there were intragroup differences between the OPEN and CLOSED conditions. These differences were, however, less pronounced and occurred in other areas than in sighted controls. The contrast OPEN > CLOSED revealed a relative signal increase in the left frontal eye field, the middle occipital gyrus bilaterally and in the anterior cingulum. Relative signal increases in occipital cortex areas and the anterior cingulum were also apparent for this contrast in the intergroup comparison (congenitally totally blind subjects vs. sighted controls). They reflect the increased attentional load or arousal during the eyes-open condition and could be indicative of a functional reorganization of the occipital cortex in the blind. The contrast CLOSED > OPEN in the congenitally totally blind subjects lead to relative activations in the somatosensory cortex bilaterally, the middle temporal gyrus on the left and the frontal gyri on the right. These activations are residues of the “interoceptive” state found in sighted controls.

The resting brain in blind subjects – an fMRI study with eyes open and closed in darkness

Objective: It has been shown in normal subjects that opening the eyes in darkness without external visual stimulation increases activity in the ocular motor and attentional systems. By contrast, closing the eyes causes a relative signal increase in multiple sensory areas such as the visual, somatosensory, vestibular, auditory, and gustatory cortical areas. These two states of „resting“ activity of the human brain in complete darkness, which can be imaged using fMRI, were termed the „exteroceptive“ state (contrast OPEN>CLOSED) and the „interoceptive“ state (contrast CLOSED>OPEN). In the present study we investigated whether similar brain activity states can be found in blind subjects when opening and closing their eyes. Methods: Seven congenitally, totally blind individuals participated in the study. Subjects were trained outside the scanner to perform the following tasks: eyes open (OPEN) or eyes closed (CLOSED) at rest while looking straight ahead in complete darkness. Functional images were acquired on a 1.5 T standard clinical scanner using echo-planar imaging. The data were compared to data published earlier of a matched group of healthy volunteers (Marx et al. 2003). Analysis was performed using SPM2. Results: Overall, the differences between the OPEN and CLOSED conditions were less pronounced in the blind subjects than in the controls. In congenitally, totally blind subjects the contrast OPEN>CLOSED revealed a relative increase in activity in the middle occipital gyrus bilaterally as well as in the anterior cingulate cortex. The intergroup comparison (congenitally, totally blind subjects vs. controls) for this contrast showed an activity increase in regions similar to those found in the blind subjects alone. Discussion: There are also differences in brain activity patterns between eyes-open or eyes-closed at rest in congenitally, totally blind subjects, but they are not those of the above-described „intero-“/“exteroceptive“ states. They are rather diametrically opposed to those observed in sighted controls: the activity increases in the occipital cortex for the contrast OPEN>CLOSED suggest a functional reorganization of the visual cortex. While the visual cortex has been previously shown to mediate attentional tasks in congenitally blind subjects, its activation during the eyes-open condition in conjunction with the anterior cingulate might be indicative of an increased attentional load.

Cluster analysis of resting-state fMRI time series

Functional MRI (fMRI) has become one of the leading methods for brain mapping in neuroscience. Recent advances in fMRI analysis were used to define the default state of brain activity, functional connectivity and basal activity. Basal activity measured with fMRI raised tremendous interest among neuroscientists since synchronized brain activity pattern could be retrieved while the subject rests (resting state fMRI). During recent years, a few signal processing schemes have been suggested to analyze the resting state blood oxygenation level dependent (BOLD) signal from simple correlations to spectral decomposition. In most of these analysis schemes, the question asked was which brain areas “behave” in the time domain similarly to a pre-specified ROI. In this work we applied short time frequency analysis and clustering to study the spatial signal characteristics of resting state fMRI time series. Such analysis revealed that clusters of similar BOLD fluctuations are found in the cortex but also in the white matter and sub-cortical gray matter regions (thalamus). We found high similarities between the BOLD clusters and the neuro-anatomical appearance of brain regions. Additional analysis of the BOLD time series revealed a strong correlation between head movements and clustering quality. Experiments performed with T1-weighted time series also provided similar quality of clustering. These observations led us to the conclusion that non-functional contributions to the BOLD time series can also account for symmetric appearance of signal fluctuations. These contributions may include head motions, the underling microvasculature anatomy and cellular morphology.

Information processing algorithms in the brain

If the brain is a machine that processes information, then its cognitive activity can be interpreted as a set of information processing states linking stimulus to response (i.e. as a mechanism or an algorithm). The cornerstone of this research agenda is the existence of a method to translate the measurable states of brain activity into the information processing states of a cognitive theory. Here, we contend that reverse correlation methods can provide this translation and we frame the transitions between information processing states in the context of automata theory. We illustrate, using examples from visual cognition, how this novel framework can be applied to understand the information processing algorithms of the brain in cognitive neuroscience.

Brain–computer interfaces in neurological rehabilitation

Recent advances in analysis of brain signals, training patients to control these signals, and improved computing capabilities have enabled people with severe motor disabilities to use their brain signals for communication and control of objects in their environment, thereby bypassing their impaired neuromuscular system. Non-invasive, electroencephalogram (EEG)-based brain-computer interface (BCI) technologies can be used to control a computer cursor or a limb orthosis, for word processing and accessing the internet, and for other functions such as environmental control or entertainment. By re-establishing some independence, BCI technologies can substantially improve the lives of people with devastating neurological disorders such as advanced amyotrophic lateral sclerosis. BCI technology might also restore more effective motor control to people after stroke or other traumatic brain disorders by helping to guide activity-dependent brain plasticity by use of EEG brain signals to indicate to the patient the current state of brain activity and to enable the user to subsequently lower abnormal activity. Alternatively, by use of brain signals to supplement impaired muscle control, BCIs might increase the efficacy of a rehabilitation protocol and thus improve muscle control for the patient.

Single Trial Classification of Motor Imagination Using 6 Dry EEG Electrodes

BackgroundBrain computer interfaces (BCI) based on electro-encephalography (EEG) have been shown to detect mental states accurately and non-invasively, but the equipment required so far is cumbersome and the resulting signal is difficult to analyze. BCI requires accurate classification of small amplitude brain signal components in single trials from recordings which can be compromised by currents induced by muscle activity.Methodology/Principal FindingsA novel EEG cap based on dry electrodes was developed which does not need time-consuming gel application and uses far fewer electrodes than on a standard EEG cap set-up. After optimizing the placement of the 6 dry electrodes through off-line analysis of standard cap experiments, dry cap performance was tested in the context of a well established BCI cursor control paradigm in 5 healthy subjects using analysis methods which do not necessitate user training. The resulting information transfer rate was on average about 30% slower than the standard cap. The potential contribution of involuntary muscle activity artifact to the BCI control signal was found to be inconsequential, while the detected signal was consistent with brain activity originating near the motor cortex.Conclusions/SignificanceOur study shows that a surprisingly simple and convenient method of brain activity imaging is possible, and that simple and robust analysis techniques exist which discriminate among mental states in single trials. Within 15 minutes the dry BCI device is set-up, calibrated and ready to use. Peak performance matched reported EEG BCI state of the art in one subject. The results promise a practical non-invasive BCI solution for severely paralyzed patients, without the bottleneck of setup effort and limited recording duration that hampers current EEG recording technique. The presented recording method itself, BCI not considered, could significantly widen the use of EEG for emerging applications requiring long-term brain activity and mental state monitoring.

Psychological and physiological characteristics of a proposed object-referral/self-referral continuum of self-awareness

This research extends and confirms recent brainwave findings that distinguished an individual’s sense-of-self along an Object-referral/Self-referral Continuum of self-awareness. Subjects were interviewed and were given tests measuring inner/outer orientation, moral reasoning, anxiety, and personality. Scores on the psychological tests were factor analyzed. The first unrotated PCA component of the test scores yielded a “Consciousness Factor,” analogous to the intelligence “ g” factor, which accounted for over half of the variance among groups. Analysis of unstructured interviews of these subjects revealed fundamentally different descriptions of self-awareness. Individuals who described themselves in terms of concrete cognitive and behavioral processes (predominantly Object-referral mode) exhibited lower Consciousness Factor scores, lower frontal EEG coherence, lower alpha and higher gamma power during tasks, and less efficient cortical preparatory responses (contingent negative variation). In contrast, individuals who described themselves in terms of an abstract, independent sense-of-self underlying thought, feeling and action (predominantly Self-referral mode) exhibited higher Consciousness Factor scores, higher frontal coherence, higher alpha and lower gamma power during tasks, and more efficient cortical responses. These data suggest that definable states of brain activity and subjective experiences exist, in addition to waking, sleeping and dreaming, that may be operationally defined by psychological and physiological measures along a continuum of Object-referral/Self-referral Continuum of self-awareness.

Purpose of REM sleep: endogenous anti-epileptogenesis in man – a hypothesis

Neuro-scientists, worldwide, are endeavoring to elucidate the purpose of sleep which still remains largely elusive. There is, however, consensus on many aspects of sleep functions; one such aspect is its relationship with seizures/epilepsy. There is unequivocal agreement on increased susceptibility to epilepsy during nonrapid eye movement (NREM, slow-wave) sleep. Large number of studies have shown increased frequency of seizures and interictal epileptiform discharges in epileptic patients during NREM sleep (esp., stages I and II) which is associated with EEG synchronization. Similarly, there is widespread acceptance of de-synchronized brain-activity states being associated with rarity/total absence of epileptic potentials, one such state being rapid eye movement (REM) sleep. Certain drugs and substances which inhibit NREM sleep have been found to possess anti-convulsant properties. Not surprisingly, drugs/chemicals which enhance/promote NREM sleep or suppress/inhibit REM sleep are associated with increased susceptibility to seizures and are contraindicated in epilepsy. The manner and pattern in which REM phase occurs in sleep are also naturally programmed to exert anti-epileptogenic influence. This hypothesis-article highlights and conceptualizes the primary function of REM-sleep as endogenous anti-epileptogenic system in the body akin to the endogenous analgesia and immune systems man is born with.

NEUROPHYSIOLOGICAL BASIS OF FUNCTIONAL DE-AFFERENTATION OF THE NERVOUS SYSTEM CAUSED BY WEAK OR ABSENT MUSCLE CONTRACTIONS

In this short article we discuss putative effect of decreased ability for movement in the progressive neuromuscular disorders on the central state of brain activity. We propose possibility that such reduced activation of proprioreceptors can lead to partial ‘functional de-afferentation’. Furthermore, we briefly reviewed neurophysiological evidences of peripheral inputs to the central projections. We discussed contribution of the proprioceptive input after passive, active movements and movement induced by vibration of muscles tendons. Finally we are proposing to introduce simple vibratory protocols in daily life of people with progressive neuromuscular disorders in order to prevent central effects of reduced proprioception to endurance of brain activity of people with intact mental functions.

Vasoactive Intestinal Polypeptide and Pituitary Adenylate Cyclase-Activating Polypeptide Activate Hyperpolarization-Activated Cationic Current and Depolarize Thalamocortical NeuronsIn Vitro

Ascending pathways mediated by monoamine neurotransmitters regulate the firing mode of thalamocortical neurons and modulate the state of brain activity. We hypothesized that specific neuropeptides might have similar actions. The effects of vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) were tested on thalamocortical neurons using whole-cell patch-clamp techniques applied to visualized neurons in rat brain slices. VIP (2 microm) and PACAP (100 nm) reversibly depolarized thalamocortical neurons (7.8 +/- 0.6 mV; n = 16), reduced the membrane resistance by 33 +/- 3%, and could convert the firing mode from bursting to tonic. These effects on resting membrane potential and membrane resistance persisted in the presence of TTX. Morphologically diverse thalamocortical neurons located in widespread regions of thalamus were all depolarized by VIP and PACAP38. In voltage-clamp mode, we found that VIP and PACAP38 reversibly activated a hyperpolarization-activated cationic current (I(H)) in thalamocortical neurons and altered voltage- and time-dependent activation properties of the current. The effects of VIP on membrane conductance were abolished by the hyperpolarization-activated cyclic-nucleotide-gated channel (HCN)-specific antagonist ZD7288, showing that HCN channels are the major target of VIP modulation. The effects of VIP and PACAP38 on HCN channels were mediated by PAC(1) receptors and cAMP. The actions of PACAP-related peptides on thalamocortical neurons suggest an additional and novel endogenous neurophysiological pathway that may influence both normal and pathophysiological thalamocortical rhythm generation and have important behavioral effects on sensory processing and sleep-wake cycles.

Spatiotemporal Brain Imaging of Visual-Evoked Activity Using Interleaved EEG and fMRI Recordings

Combined analysis of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) has the potential to provide higher spatiotemporal resolution than either method alone. In some situations, in which the activity of interest cannot be reliably reproduced (e.g., epilepsy, learning, sleep states), accurate combined analysis requires simultaneous acquisition of EEG and fMRI. Simultaneous measurements ensure that the EEG and fMRI recordings reflect the exact same brain activity state. We took advantage of the spatial filtering properties of the bipolar montage to allow recording of very short (125–250 ms) visual-evoked potentials (VEPs) during fMRI. These EEG and fMRI measurements are of sufficient quality to allow source localization of the cortical generators. In addition, our source localization approach provides a combined EEG/fMRI analysis that does not require any manual selection of fMRI activations or placement of source dipoles. The source of the VEP was found to be located in the occipital cortex. Separate analysis of EEG and fMRI data demonstrated good spatial overlap of the observed activated sites. As expected, the combined EEG/fMRI analysis provided better spatiotemporal resolution than either approach alone. The resulting spatiotemporal movie allows for the millisecond-to-millisecond display of changes in cortical activity caused by visual stimulation. These data reveal two peaks in activity corresponding to the N75 and the P100 components. This type of simultaneous acquisition and analysis allows for the accurate characterization of the location and timing of neurophysiological activity in the human brain.

Spectral and Topographic Microstructure of Brain Alpha Activity During Drowsiness at Sleep Onset and REM Sleep

Abstract High-resolution frequency methods were used to describe the spectral and topographic microstructure of human spontaneous alpha activity in the drowsiness (DR) period at sleep onset and during REM sleep. Electroencephalographic (EEG), electrooculographic (EOG), and electromyographic (EMG) measurements were obtained during sleep in 10 healthy volunteer subjects. Spectral microstructure of alpha activity during DR showed a significant maximum power with respect to REM-alpha bursts for the components in the 9.7-10.9 Hz range, whereas REM-alpha bursts reached their maximum statistical differentiation from the sleep onset alpha activity at the components between 7.8 and 8.6 Hz. Furthermore, the maximum energy over occipital regions appeared in a different spectral component in each brain activation state, namely, 10.1 Hz in drowsiness and 8.6 Hz in REM sleep. These results provide quantitative information for differentiating the drowsiness alpha activity and REM-alpha by studying their microstructural properties. On the other hand, these data suggest that the spectral microstructure of alpha activity during sleep onset and REM sleep could be a useful index to implement in automatic classification algorithms in order to improve the differentiation between the two brain states.

Correlation of high-frequency oscillations with the sleep–wake cycle and cognitive activity in humans

While several authors have suggested that high-frequency electroencephalogram activity (gamma, >30 Hz) correlates with conscious thought, others have suggested that electroencephalogram activity >30 Hz shows the same relationships to cognitive activity and sleep as activity in the conventional beta frequency band. The existence of coherence of gamma over large distances also remains controversial. We studied quantitatively the relationship of gamma activity to the sleep–wake cycle and cognitive tasks during wakefulness in humans using intracranial electroencephalogram. Gamma activity made up less than 1% of the total power spectrum. A significant relationship was observed between gamma activity and the sleep–wake cycle such that gamma was highest during wakefulness, intermediate during light and rapid eye movement sleep, and lowest during slow-wave sleep. As well, gamma was higher during rapid eye movement sleep with eye movements than during rapid eye movement sleep without eye movements. During a cognitive task experiment, while lower frequencies, including beta, showed a stepwise reduction with increasing task difficulty, gamma was observed to increase during cognitive tasks as compared to the resting state. The relationship between gamma and the sleep–wake cycle and cognitive tasks was independent of brain region and hemisphere. Coherence of gamma activity at distances of 5 mm and greater was not observed. Our data support previously reported findings that gamma activity has a significant relationship to the sleep–wake cycle. The findings of differences in gamma during REM sleep with and without eye movements suggest that the presence or absence of eye movements may reflect two different states of brain activity. Our findings of differences in the relationships of the beta and gamma bands to both the sleep–wake cycle and cognitive tasks demonstrate that various components of the high-frequency spectrum behave differently in some situations.

Brain spatial microstates of human spontaneous alpha activity in relaxed wakefulness, drowsiness period, and REM sleep.

Spontaneous alpha activity clearly present in relaxed wakefulness with closed eyes, drowsiness period at sleep onset, and REM sleep was studied with spatial segmentation methods in order to determine if the brain activation state would be modulating the alpha spatial microstates composition and duration. These methods of spatial segmentation show some advantages: i) they extract topographic descriptors independent of the chosen reference (reference-free methods), and ii) they achieve spatial data reduction that are more data-driven than dipole source analysis. The results obtained with this study revealed that alpha activity presented a different spatio-temporal pattern of brain electric fields in each arousal state used in this study. These differences were reflected in a) the mean duration of alpha microstates (longer in relaxed wakefulness than in drowsy period and REM sleep), b) the number of brain microstates contained in one second (drowsiness showed more different microstates than did relaxed wakefulness and REM state), and c) the number of different classes (more abundant in drowsiness than in the rest of brain states). If we assume that longer segments of stable brain activity imply a lesser amount of different information to process (as reflected by a higher stability of the brain generator), whereas shorter segments imply a higher number of brain microstates caused by more different steps of information processing, it is possible that the alpha activity appearing in the sleep onset period could be indexing the hypnagogic imagery self-generated by the sleeping brain, and a phasic event in the case of REM sleep. Probably, REM-alpha bursts are associated with a brain microstate change (such as sleep spindles), as demonstrated by its phasic intrusion in a desynchronized background of brain activity. On the other hand, alpha rhythm could be the "baseline" of brain activity when the sensory inputs are minimum and the state is relaxed wakefulness.

Cortical activation states in sleep and anesthesia. II: Respiratory reflexes

Under urethane anesthesia, animals exhibit patterns of cortical activity similar to those seen in wake, drowsiness and slow-wave sleep in unanesthetized animals. In the present study, hypoxic and hypercapnic ventilatory reflexes were examined in unanesthetized and urethane-anesthetized golden mantled ground squirrels in states with similar EEG profiles. Synchronized EEG patterns occurred less frequently in both unanesthetized and anesthetized animals during hypoxic (10% O 2) and hypercapnic (5% CO 2) exposure. Breathing frequency fell significantly during sleep in animals breathing all gas mixtures, while the relative ventilatory sensitivity to hypoxia and hypercapnia increased during sleep. Urethane-anesthetized animals also showed significant falls in breathing frequency and ventilation and increases in relative ventilatory sensitivity to hypoxia and hypercapnia as they moved into states with synchronized EEG patterns. These data suggest that the brain activity states observed under urethane anesthesia mimic sleep/wake in terms of their effect on respiratory function and that changes in breathing pattern and the enhancement of ventilatory responses in states with a synchronized EEG is not due solely to changes in levels of behavioural stimuli.

Visualization of EEG Using Time-Frequency Distributions

The EEG is a time-varying or nonstationary signal. Frequency and amplitude are two of its significant characteristics, and are valuable clues to different states of brain activity. Detection of these temporal features is important in understanding EEGs. Commonly, spectrograms and AR models are used for EEG analysis. However, their accuracy is limited by their inherent assumption of stationarity and their trade-off between time and frequency resolution. We investigate EEG signal processing using existing compound kernel time-frequency distributions (TFDs). By providing a joint distribution of signal intensity at any frequency along time, TFDs preserve details of the temporal structure of the EEG waveform, and can extract its time-varying frequency and amplitude features. We expect that this will have significant implications for EEG analysis and medical diagnosis.