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Alpha power modulation during periods with rapid oculomotor activity in human REM sleep

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Abstract

Alpha activity attenuation (blocking) over occipital regions is an electrophysiological index of cortical activation associated with visual attention and waking mental imagery. The present work focused on exploring whether the human REM background alpha activity was modulated, attending to tonic- (without rapid oculomotor activity) and phasic-REM periods (with a prominent burst of REMs). The obtained results revealed that the background alpha activity showed a decreased spectral power over occipital brain regions during phasic-REM in comparison with tonic-REM periods. This result suggests an active visual processing caused by the complex mental imagery generated during periods of oculomotor activity in human REM sleep.

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... 6 The relationship between increased cortical arousal and dream recall has recently been disputed by a number of researchers, who have noted decreased cortical activation is conducive to higher dream recall. [20][21][22] Recall from stage 2 and REM sleep has been found to be associated with lower α power; 22 and the accepted α suppression of occipital brain regions during the engagement in visual imagery has been noted during phasic REM sleep. 20,21 Thus, research investigating the relationship between cortical arousal and dream recall has produced conflicting results. ...
... [20][21][22] Recall from stage 2 and REM sleep has been found to be associated with lower α power; 22 and the accepted α suppression of occipital brain regions during the engagement in visual imagery has been noted during phasic REM sleep. 20,21 Thus, research investigating the relationship between cortical arousal and dream recall has produced conflicting results. ...
Article
Study Objectives There is debate in dream research as to whether ponto-geniculo-occipital (PGO) waves or cortical arousal during sleep underlie the biological mechanisms of dreaming. This study comprised 2 experiments. As eye movements (EMs) are currently considered the best noninvasive indicator of PGO burst activity in humans, the aim of the first experiment was to investigate the effect of low-intensity repeated auditory stimulation on EMs (and inferred PGO burst activity) during REM sleep. It was predicted that such auditory stimuli during REM sleep would have a suppressive effect on EMs. The aim of the second experiment was to examine the effects of this auditory stimulation on subsequent dream reporting on awakening. Design Repeated measures design with counterbalanced order of experimental and control conditions across participants. Setting Sleep laboratory based polysomnography (PSG) Participants Experiment 1: 5 males and 10 females aged 18-35 years (M = 20.8, SD = 5.4). Experiment 2: 7 males and 13 females aged 18-35 years (M = 23.3, SD = 5.5). Interventions Below-waking threshold tone presentations during REM sleep compared to control REM sleep conditions without tone presentations. Measurements and Results PSG records were manually scored for sleep stages, EEG arousals, and EMs. Auditory stimulation during REM sleep was related to: (a) an increase in EEG arousal, (b) a decrease in the amplitude and frequency of EMs, and (c) a decrease in the frequency of visual imagery reports on awakening. Conclusions The results of this study provide phenomenological support for PGO-based theories of dream reporting on awakening from sleep in humans.
... One common method for improving poor EEG spectral estimates has been to average spectral power within canonical frequency bands. For example, sleep analyses may report the total power within delta (0.5-4 Hz), theta (4 -8 Hz), alpha (8 -12 Hz), sigma (12)(13)(14)(15), beta (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), or gamma (Ͼ30 Hz) bands. While averaging across frequencies reduces the variability in power over time, it greatly reduces the frequency resolution of the spectral estimate, producing a low-resolution estimate that looks like a step function (FIGURE 2, A AND D, black curves). ...
... While transient alpha power during REM has been studied in great detail by Cantero (15)(16)(17)(18)(19), this obvious feature of REM sleep microstructure is absent in R&K scoring. This is perhaps because individual bursts may not be long enough to trigger a scored arousal or epoch of Wake and would be too time consuming to score manually. ...
Article
During sleep, cortical and subcortical structures within the brain engage in highly structured oscillatory dynamics that can be observed in the electroencephalogram (EEG). The ability to accurately describe changes in sleep state from these oscillations has thus been a major goal of sleep medicine. While numerous studies over the past 50 years have shown sleep to be a continuous, multifocal, dynamic process, long-standing clinical practice categorizes sleep EEG into discrete stages through visual inspection of 30-s epochs. By representing sleep as a coarsely discretized progression of stages, vital neurophysiological information on the dynamic interplay between sleep and arousal is lost. However, by using principled timefrequency spectral analysis methods, the rich dynamics of the sleep EEG are immediately visible— elegantly depicted and quantified at time scales ranging from a full night down to individual microevents. In this paper, we review the neurophysiology of sleep through this lens of dynamic spectral analysis. We begin by reviewing spectral estimation techniques traditionally used in sleep EEG analysis and introduce multitaper spectral analysis, a method that makes EEG spectral estimates clearer and more accurate than traditional approaches. Through the lens of the multitaper spectrogram, we review the oscillations and mechanisms underlying the traditional sleep stages. In doing so, we will demonstrate how multitaper spectral analysis makes the oscillatory structure of traditional sleep states instantaneously visible, closely paralleling the traditional hypnogram, but with a richness of information that suggests novel insights into the neural mechanisms of sleep, as well as novel clinical and research applications.
... ùÚË ‰ ‡ÌÌ˚ ÒÓ " Î ‡ÒÛ˛ÚÒfl Ò Ô‰ÎÓÊÂÌÌ˚ÏË Ì ‡ÏË Ô ‡‚ËÎ ‡ÏË ÏÓ‰ÛÎflˆËË ‚ÓÁ·Û‰ËÚÂθÌÓÈ ÔÂ‰ ‡˜Ë, ÒÓ " Î ‡ÒÌÓ ÍÓÚÓ˚Ï ‡ˆÂÚËÎıÓÎË̘ÂÂÁ‡ˆÂÚËÎıÓÎË̘ÂÂÁ Ò‚fl- Á ‡ÌÌ˚Â Ò G q/11 -·ÂÎÍ ‡ÏË ÏÛÒÍ ‡ËÌÓ‚˚ å1/å5-Â- ˆÂÔÚÓ˚ÒÔÓÒÓ·ÒÚ‚ÛÂÚˆÂÔÚÓ˚ÒÔÓÒÓ·ÒÚ‚ÛÂÚ ‰ÎËÚÂθÌÓÈ ÔÓÚÂÌˆË ‡ˆËË ‚ÓÁ·Û‰ËÚÂθÌÓÈ ÔÂ‰ ‡˜Ë Ë, ÒΉӂ ‡ÚÂθÌÓ, ÏÓ- ÊÂÚ ÔË‚Ó‰ËÚ¸ÍÔË‚Ó‰ËÚ¸Í ÔÓ‚˚¯ÂÌ˲˜ ÔÓ‚˚¯ÂÌ˲˜ ‡ÒÚÓÚ˚‡ÒÚÓÚ˚ ‡Áfl‰Ó‚ ‰ÓÙ ‡ÏËÌÂ " ˘ÂÒÍËı ÌÂÈÓÌÓ‚ [10, 11]. éëéÅÖççéëíà ÄäíàÇÄñàà áêàíÖãúçéâ äéêõ à íÄãÄåìëÄ èêà ëçéÇàÑÖçàüï ùÎÂÍÚÓÙËÁËÓÎÓ " ˘ÂÒÍËÏ ÔÓÍ ‡Á ‡ÚÂÎÂÏ ‡ÍÚË‚- ÌÓÒÚË ÁËÚÂθÌÓÈ ÍÓ˚, Ò‚flÁ ‡ÌÌÓÈ ÒÓ ÁËÚÂθÌ˚Ï ‚ÌËÏ ‡ÌËÂÏ Ë  ‡·Ó˜ËÏË Ï˚ÒÎÂÌÌ˚ÏË Ô‰ÒÚ ‡‚ÎÂ- ÌËflÏË, fl‚ÎflÂÚÒfl Á ‡ÚÛı ‡ÌË ‡Î¸Ù ‡- ‡ÍÚË‚ÌÓÒÚË ‚ Á ‡Ú˚ÎÓ˜Ì˚ı Ó·Î ‡ÒÚflı ÍÓ˚˜ÂÎÓ‚ÂÍÍÓ˚˜ÂÎÓ‚ÂÍ ‡ [17]. íÓÚ Ù ‡ÍÚ, ˜ÚÓ ‚Ó ‚ÂÏfl Ô ‡ ‡‰ÓÍÒ ‡Î¸ÌÓ " Ó ÒÌ ‡ ÒÔÂÍÚ ‡Î¸Ì ‡fl ÔÎÓÚÌÓÒÚ¸ÙÓÌÓ‚ÓÈÔÎÓÚÌÓÒÚ¸ÙÓÌÓ‚ÓÈ ‡Î¸Ù ‡- ‡ÍÚË‚ÌÓÒÚË ‚ Á ‡Ú˚ÎÓ˜Ì˚ı Ó·Î ‡ÒÚflı ÍÓ˚ÛÏÂ̸¯ÂÌÍÓ˚ÛÏÂ̸¯ÂÌ ‡ ÔÓ Ò ‡‚- ÌÂÌ˲ Ò ‰Û " ËÏË ÔÂËÓ‰ ‡ÏË ÒÌ ‡, ÛÍ ‡Á˚‚ ‡ÂÚ Ì ‡ Ì ‡- ΢ËÂ Û ˜ÂÎÓ‚ÂÍ ‡ ÔË Ô ‡ ‡‰ÓÍÒ ‡Î¸ÌÓÏ ÒÌ ‡ÍÚË‚- Ì˚ı ÍÓÍÓ‚˚ı ÁËÚÂθÌ˚ı ÔÓˆÂÒÒÓ‚, ‚˚Á‚ ‡ÌÌ˚ı ÍÓÏÔÎÂÍÒÌ˚ÏË Ï˚ÒÎÂÌÌ˚ÏË Ô‰ÒÚ ‡‚ÎÂÌËflÏË [17] . ...
... éëéÅÖççéëíà ÄäíàÇÄñàà áêàíÖãúçéâ äéêõ à íÄãÄåìëÄ èêà ëçéÇàÑÖçàüï ùÎÂÍÚÓÙËÁËÓÎÓ " ˘ÂÒÍËÏ ÔÓÍ ‡Á ‡ÚÂÎÂÏ ‡ÍÚË‚- ÌÓÒÚË ÁËÚÂθÌÓÈ ÍÓ˚, Ò‚flÁ ‡ÌÌÓÈ ÒÓ ÁËÚÂθÌ˚Ï ‚ÌËÏ ‡ÌËÂÏ Ë  ‡·Ó˜ËÏË Ï˚ÒÎÂÌÌ˚ÏË Ô‰ÒÚ ‡‚ÎÂ- ÌËflÏË, fl‚ÎflÂÚÒfl Á ‡ÚÛı ‡ÌË ‡Î¸Ù ‡- ‡ÍÚË‚ÌÓÒÚË ‚ Á ‡Ú˚ÎÓ˜Ì˚ı Ó·Î ‡ÒÚflı ÍÓ˚˜ÂÎÓ‚ÂÍÍÓ˚˜ÂÎÓ‚ÂÍ ‡ [17]. íÓÚ Ù ‡ÍÚ, ˜ÚÓ ‚Ó ‚ÂÏfl Ô ‡ ‡‰ÓÍÒ ‡Î¸ÌÓ " Ó ÒÌ ‡ ÒÔÂÍÚ ‡Î¸Ì ‡fl ÔÎÓÚÌÓÒÚ¸ÙÓÌÓ‚ÓÈÔÎÓÚÌÓÒÚ¸ÙÓÌÓ‚ÓÈ ‡Î¸Ù ‡- ‡ÍÚË‚ÌÓÒÚË ‚ Á ‡Ú˚ÎÓ˜Ì˚ı Ó·Î ‡ÒÚflı ÍÓ˚ÛÏÂ̸¯ÂÌÍÓ˚ÛÏÂ̸¯ÂÌ ‡ ÔÓ Ò ‡‚- ÌÂÌ˲ Ò ‰Û " ËÏË ÔÂËÓ‰ ‡ÏË ÒÌ ‡, ÛÍ ‡Á˚‚ ‡ÂÚ Ì ‡ Ì ‡- ΢ËÂ Û ˜ÂÎÓ‚ÂÍ ‡ ÔË Ô ‡ ‡‰ÓÍÒ ‡Î¸ÌÓÏ ÒÌ ‡ÍÚË‚- Ì˚ı ÍÓÍÓ‚˚ı ÁËÚÂθÌ˚ı ÔÓˆÂÒÒÓ‚, ‚˚Á‚ ‡ÌÌ˚ı ÍÓÏÔÎÂÍÒÌ˚ÏË Ï˚ÒÎÂÌÌ˚ÏË Ô‰ÒÚ ‡‚ÎÂÌËflÏË [17] . Ç ÔÓÚË‚Ó‚ÂÒ ÚӘ͠ÁÂÌËfl, ÒÓ " Î ‡ÒÌÓ ÍÓÚÓÓÈ ÒÓÁÌ ‡ÌË " ÂÌÂËÛÂÚÒfl ËÒÍβ˜ËÚÂθÌÓ Í ‡Í ÔÓ‰ÛÍÚ ÒÂÌÒÓÌÓ " Ó ‚ıÓ‰ ‡, ·˚ÎÓ ‚˚‰‚ËÌÛÚÓ Ô‰- ÔÓÎÓÊÂÌËÂ, ˜ÚÓ ÒÓÁÌ ‡ÌË – ˝ÚÓ ÙÛ̉ ‡ÏÂÌÚ ‡Î¸ÌÓ ҂ÓÈÒÚ‚Ó Á ‡Í˚ÚÓȈÂÔˇÍ˚ÚÓȈÂÔË, ‚ ÍÓÚÓÓȈÂÌÚÍÓÚÓÓȈÂÌÚ ‡Î¸ÌÛ˛ ÓθËÓÎ¸Ë "  ‡ÂÚ ÒÔÓÒÓ·ÌÓÒÚ¸ÍÎÂÚÓÍÒÔÓÒÓ·ÌÓÒÚ¸ÍÎÂÚÓÍ ·˚Ú¸ ·˚Ú¸ ‡ÍÚË‚ËÓ‚ ‡ÌÌ˚ÏË Á ‡ Ò˜ÂÚ ‚ÌÛÚÂÌÌËı ‚ıÓ‰Ó‚ [54] . ...
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A hypothetical mechanism of the basal ganglia involvement in the occurrence of paradoxical sleep dreams and rapid eye movements is proposed. According to this mechanism, paradoxical sleep is provided by facilitation of activation of cholinergic neurons in the pedunculopontine nucleus as a result of suppression of their inhibition from the output basal ganglia nuclei, This disinhibition is promoted by activation of dopaminergic cells by pedunculopontine neurons, subsequent rise in dopamine concentration in the input basal ganglia structure, striatum, and modulation of the efficacy of cortico-striatal inputs. In the absence of signals from retina, a disinhibition of neurons in the pedunculopontine nucleus and superior colliculus allows them to excite neurons in the lateral geniculate body and other thalamic nuclei projecting to the primary and higher visual cortical areas, prefrontal cortex and back into the striatum. Dreams as visual images and "motor hallucinations" are the result of an increase in activity of definitely selected groups of thalamic and neocortical neurons. This selection is caused by modifiable action of dopamine on long-term changes in the efficacy of synaptic transmission during circulation of signals in closed interconnected loops, each of which includes one of the visual cortical areas (motor cortex), one of the thalamic nuclei, limbic and one of the visual areas (motor area) of the basal ganglia, pedunculopontine nucleus, and superior colliculus. Simultaneous modification and modulation of synapses in diverse units of neuronal loops is provided by PGO waves. Disinhibition of superioir colliculus neurons and their excitation by pedunculopontine nucleus lead to an appearance of rapid eye movements during paradoxical sleep.
... Известно, что состояние человека (бодр ствование, сон, усталость) и восприятие им сенсорной информации находят отражение в спектре ЭЭГ [1,2,4,10,15,26,27]. Если пред лагаемая нами гипотеза о роли спонтанных PGO волн в ухудшении зрительного воспри ятия при микросне верна, то это должно про явиться в изменении спектра ЭЭГ в затылоч ных областях, под которыми располагаются первичные зрительные области. ...
... Альфа ритм достигает максимальной ампли туды, когда испытуемый находится в состоя нии покоя с закрытыми глазами. В состоянии бодрствования затухание альфа ритма в за тылочных областях является электрофизио логическим показателем корковой актива ции, ассоциированной со зрительным вни манием и воображением [10]. Усиление мощности в тета и альфа диапазонах ЭЭГ наблюдаются и при монотонной деятельно сти, что ассоциируют с изменением функци онального состояния мозга в сторону сниже ния активации [1]. ...
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We tested our earlier suggested hypothesis that one of mechanisms for failures of performance of behav ioural tasks during microsleep is a spontaneous generation of ponto geniculo occipital (PGO) waves that suppress transmission of visual information from the retina via lateral geniculate nucleus to primary visual cortical areas and the striatum, and therefore significantly impair visual perception and attention. Experiments were done during the nighttime. Monotonic testing during performance of the two alter native psychomotor test invoked participants into a state defined as a microsleep with open eyes. For each participant we made a comparative analysis of intensity of EEG spectrum during state of micros leep with open eyes when failure in test performance occurred and during accurate performance in wak ing state. Following trends in changes of EEG spectrum were found: increase in intensity of low alpha range, and decrease in intensity of high alpha and beta ranges. Changes in theta , low beta and gam ma ranges were differently directed. Taking into account the known from the literature data these changes specify decrease in activation of primary visual cortical areas. Revealed data could support our hypothesis concerning mechanism of visual motor disturbances during microsleep with open eyes.
... espiration (a pause in diaphragm activity that lasts ∼20–100 ms), rapid eye movements, and muscle twitches (Hunt et al., 1998; Nelson et al., 1983). According to Hong et al. (1995), the same cortical areas are involved in eye movements in REM sleep and wakefulness, suggesting that REM eye movements are saccadic scans of targets in the dream scenes. Cantero et al. (1999) hypothesized that REM and waking brain states use the same general mechanisms to produce mental images.Serotonin, histamine and norepinephrine neurotransmitters that are used during waking hours, are decreased during non-REM sleep and stop altogether in REM (McCarley, 2007). This neurotransmitter shutdown causes REM atonia, a state in w ...
... Braun et al. (1998) suggested that the brain mechanisms underlying REM sleep are visual association cortices and their paralimbic projections, operating as a closed system dissociated from the regions of the visual hierarchy, which mediate interactions with the external world. Visual imagery during REM sleep, in comparison to wakefulness, can occur through the inverse pathway of visual information processing (Cantero et al., 1999; Ogawa et al., 2006). ...
Article
A novel molecular hypothesis about visual perception and imagery has recently been proposed (Bókkon, 2009; BioSystems). Namely, external electromagnetic visible photons are converted into electrical signals in the retina and are then conveyed to V1. Next, these retinotopic electrical signals (spike-related electrical signals along classical axonal-dendritic pathways) can be converted into synchronized bioluminescent biophoton signals (inside the neurons) by neurocellular radical reactions (redox processes) in retinotopically organized V1 mitochondrial cytochrome oxidase-rich visual areas. The bioluminescent photonic signals (inside the neurons) generated by neurocellular redox/radical reactions in synchronized V1 neurons make it possible to produce computational biophysical pictures during visual perception and imagery. Our hypothesis is in line with the functional roles of reactive oxygen and nitrogen species in living cells and states that this is not a random process, but rather a strict mechanism used in signaling pathways. Here, we suggest that intrinsic biophysical pictures can also emerge during REM dreams.
... EEG recording conditions across all subjects. In the case of the a band, the statistical analysis revealed that attention was statisti-The EEG was recorded from 13 scalp sites (Fz, Cz, Pz, cally significant as a main factor (F (1,19)58.01, P50.011) cally, this late effect showed the maximum activity in 0.06260.022 mV). ...
... [16] during the planning of movement: there was a visual processing is needed, such as attention [5], visual decrease of mu rhythm and a generation of 40-Hz oscillaimagery [11], and during the phasic phase of REM sleep tions, occurring both synchronously in time and overlap- [1]. ping in space. ...
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Event-related potentials (ERPs) are an electrophysiological index of various cognitive processes such as attention. However, this kind of analysis does not allow observation of differences in the spectral content taking place during a sensory, cognitive or motor task. The goal of the present work was to compute the temporal dynamics of EEG oscillations using a technique called temporal spectral evolution (TSE). The electroencephalogram (EEG) was recorded during the presentation of flashed stimuli that were randomly presented to the left or right visual field. Subjects were asked to pay attention, alternately in different blocks of trials, to the left or to the right to detect an infrequent target. The results showed a decrease in the alpha band in a time window of 375-500 ms and an increase in the beta band at 500-875 ms after stimulus onset, for both attended and unattended stimuli. Statistical analysis showed that the decrease in alpha and the increase in beta were more marked during the attentional condition. In conclusion, these results demonstrate that the decrease in alpha band and the increase in beta band are electrophysiological markers of visual spatial attention.
... In keeping with this, significant negative correlations between the visual activity index (defined by performing a quantitative analysis of dream content, also see [42]) and occipital alpha power have been demonstrated during REM's dream mentation in congenitally blind subjects [43]. This is largely in line with reduced or blocked alpha power over the occipital cortex, commonly associated with visual imagery in normally sighted people [44][45][46]. Strikingly, some congenitally blind subjects have also been able to represent the visual content of their dreams in accurate drawings, if somewhat less detailed and slightly more symbolic and archetypal, similar to those of sighted controls [42]. ...
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It is unclear to what extent the absence of vision affects the sensory sensitivity for oneiric construction. Similarly, the presence of visual imagery in the mentation of dreams of congenitally blind people has been largely disputed. We investigate the presence and nature of oneiric visuo-spatial impressions by analysing 180 dreams of seven congenitally blind people identified from the online database DreamBank. A higher presence of auditory, haptic, olfactory, and gustatory sensation in dreams of congenitally blind people was demonstrated, when compared to normally sighted individuals. Nonetheless, oneiric visual imagery in reports of congenitally blind subjects was also noted, in opposition to some previous studies, and raising questions about the possible underlying neuro-mechanisms.
... In keeping with this, signi cant negative correlations between the visual activity index and occipital alpha power has been demonstrated during REM's dream mentation in congenitally blind subjects 40 . This is largely in line to reduced or blocked alpha power over the occipital cortex, commonly associated with visual imagery in the normally sighted people [41][42][43] . Strikingly, some congenitally blind subjects have also been able to represent the visual content of their dreams in drawings similarly accurate, if somewhat less detailed and slightly more symbolic and archetypal, as those of sighted controls 39 . ...
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It is unclear to what extent the absence of vision affects the sensory sensitivity for oneiric construction. Similarly, the presence of visual imagery in the mentation of dreams of congenitally blind people has been largely disputed. We investigate the presence and nature of oneiric visuo-spatial impressions by analysing the dreams of the congenitally blind people identified from the online database DreamBank. A higher presence of auditory, haptic, olfactory and gustatory sensation in dreams of congenitally blind was demonstrated, by comparison to normally sighted individuals. Nonetheless, oneiric visual imagery in reports of congenitally blind subjects was also noted, in opposition to some previous studies and raising the questions about the possible underlying neuromechanisms.
... 51 Of note, occipital alpha power decreased during phasic periods was interpreted as visual-cortex activation associated with mental imagery processing. 52,53 Thus, iRBD patients with more pronounced visual-cortex activation are more susceptible to conversion into neurodegenerative diseases. Furthermore, the iRBD-C group showed an increment in delta power during phasic REM periods in this study. ...
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Purpose Idiopathic rapid eye movement sleep behavior disorder (iRBD) is the prodromal marker of α-synuclein degeneration with markedly high predictive value. We aim to evaluate the value of electroencephalography (EEG) data during rapid eye movement (REM) sleep and subjective RBD severity in predicting the conversion to neurodegenerative diseases in iRBD patients. Methods At the baseline, iRBD patients underwent clinical assessment and video-polysomnography (PSG). Relative spectral power for nine frequency bands during phasic and tonic REM sleep in three regions of interest, slow-to-fast ratios, clinical and PSG variables were estimated and compared between iRBD patients who converted to neurodegenerative diseases (iRBD-C) and iRBD patients who remained disease-free (iRBD-NC). Receiver operating characteristic (ROC) curves evaluated the predictive performance of slow-to-fast ratios, and subjective RBD severity as assessed with RBD Questionnaire-Hong Kong. Results Twenty-two (33.8%) patients eventually developed neurodegenerative diseases. The iRBD-C group showed shorter total sleep time (p < 0.001), lower stage 2 sleep percentage (p = 0.044), more periodic leg-movement-related arousal index (p = 0.004), increased tonic chin electromyelographic activity (p = 0.040) and higher REM density in the third REM episode (p = 0.034) than the iRBD-NC group. EEG spectral power analyses revealed that iRBD phenoconverters showed significantly higher delta and lower alpha power, especially in central and occipital regions during the phasic REM state compared to the iRBD-NC group. Significantly higher slow-to-fast ratios were observed in a more generalized way during the phasic state in the iRBD-C group compared to the iRBD-NC group. ROC analyses of the slowing ratio in occipital areas during phasic REM sleep yielded an area under the curve of 0.749 (p = 0.001), while no significant predictive value of subjective RBD severity was observed. Conclusion Our study shows that EEG slowing, especially in a more generalized manner during the phasic period, may be a promising marker in predicting phenoconversion in iRBD, rather than subjective RBD severity.
... Before speculating on the mechanism in which alpha suppression relates to psychedelic imagery, it is important to note other conditions in which alpha power decreases. These are: visual stimulus with eyes open (Hanslmayr, et al., 2007;Klimesch, 2011) or closed (Pfurtscheller and Aranibar, 1977), increased attention (Foxe, et al., 1998;Kelly, et al., 2006;Worden, et al., 2000), increased anticipatory attention (Bastiaansen and Brunia, 2001), mental imagery (Salenius, et al., 1995;Schupp, et al., 1994;Slatter, 1960), increased attention to details of mental imagery (Salenius, et al., 1995), phasic-REM (with eye movements) compared to tonic-REM 1. BACKGROUND (without eye movements) (Cantero, et al., 1999), and with stimulants such as amphetamine, cocaine and caffeine (Deslandes, et al., 2005;Fink, 1969;Monnier, 1957;Pfeiffer, et al., 1965;Siepmann and Kirch, 2002). ...
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Psychedelics can induce eyes-closed imagery in which various visions can be experienced. These visions vary from simple geometrical patterns, to more complex imagery, to full immersion within “other realms”. Past studies suggest that the visual cortex is involved in processing these visions, yet these studies were limited into investigation of activity. In this thesis, the aim was to expand on the involvement of the visual cortex by investigating processes that are beyond simple activation maps, such as functional connectivity and dynamics. In study 1, it was hypothesized that the visual cortex will show increased functional connectivity with many cortical and subcortical regions. This was investigated with 15 subjects that were scanned using fMRI under the influence of 75 µg of LSD or placebo. The results of this study showed increased resting state functional connectivity (RSFC) between the primary visual cortex and many cortical and subcortical regions. This result correlated with subjective ratings of psychedelic imagery and with occipital alpha power suppression measured with MEG, which is a reliable neural correlate of the intensity of the psychedelic state. It study 2, it was hypothesized that connectivity within the visual cortex would match its retinotopic architecture. Retinotopic mapping is the representation of the visual field (the world we observe) in the visual cortex – e.g. areas which are near to each other in the visual field will be near each other in the visual cortex. In this study, it was found that under LSD (same procedure as study 1), with eyes closed, connectivity patterns between different subregions of the visual cortex matched the retinotopic mapping of these regions, suggesting that the visual system behaves as if it is seeing spatially localized input, with eyes-closed under LSD. In study 3, it was hypothesized that during the onset phase of psychedelic imagery, the activation of subregions of the visual cortex will be from low level to high level areas, which is according to the subjective dynamics of the experience – i.e. from simple to complex. This was tested in 9 subjects that were scanned in the fMRI during the onset or “come-up” phase - i.e. 3 minutes post (1 min) infusion of 2mg psilocybin IV - which has a particularly fast onset. Results in this study revealed that during the onset phase the BOLD dynamics of regions within the ventral stream are organized by the hierarchy of regions. Overall, study 1 and 2 revealed that, with eyes closed, under LSD, communication patterns between visual cortex and the rest of the brain and within the visual cortex match the kind of processing known to occur during regular vision. This adds to a body of knowledge supporting the view that the visual cortex is particularly engaged under the influence of psychedelics, and by measuring patterns of connectivity, we were able to provide strong support for the view that abnormal activity in the visual cortex underlies psychedelic imagery.
... Some authors regard alpha activity attenuation (i.e. decreasing of the power) or blocking as an indicator of visual imagery in general 37,38,39,40,41,42 . Alpha power attenuation with visual content was also confirmed in sighted subjects during visual exploration by Goldie 43 . ...
Conference Paper
The question regarding visual imagery and visual perception remain an open issue. Many studies have tried to understand if the two processes share the same mechanisms or if they are independent, using different neural substrates. Most research has been directed towards the need of activation of primary visual areas during imagery. Here we review some of the works providing evidence for both claims. It seems that studying visual imagery in blind subjects can be used as a way of answering some of those questions, namely if it is possible to have visual imagery without visual perception. We present results from the work of our group using visual activation in dreams and its relation with EEG’s spectral components, showing that congenitally blind have visual contents in their dreams and are able to draw them; furthermore their Visual Activation Index is negatively correlated with EEG alpha power. This study supports the hypothesis that it is possible to have visual imagery without visual experience.
... Recently, we argued (Bókkon and Mallick, 2012) that activation of the retinotopic visual areas is central to REMS associated dreams and that REMS associated dreaming and visual imagery may have co-evolved in homeothermic animals during evolution. In addition, visual imagery during REMS utilizes a common visual neural pathway similar to that used in wakefulness and during dreams expressed during REMS (Braun et al., 1998;Cantero et al., 1999;Gottesmann and Gottesman, 2007;Miyauchi et al., 2009;Horikawa et al., 2013). This pathway subserves visual processes accompanied by auditory experiences and intrinsic feelings. ...
Article
Full-text available
Recently, we proposed a novel biophysical concept regarding on the appearance of brilliant lights during near death experiences (NDEs) (Bókkon and Salari, 2012). Specifically, perceiving brilliant light in NDEs has been proposed to arise due to the reperfusion that produces unregulated overproduction of free radicals and energetically excited molecules that can generate a transient enhancement of bioluminescent biophotons in different areas of the brain, including retinotopic visual areas. If this excess of bioluminescent photon emission exceeds a threshold in retinotopic visual areas, this can appear as (phosphene) lights because the brain interprets these intrinsic retinotopic bioluminescent photons as if they originated from the external physical world. Here, we review relevant literature that reported experimental studies (Imaizumi et al., 1984; Suzuki et al., 1985) that essentially support our previously published conception, i.e., that seeing lights in NDEs may be due to the transient enhancement of bioluminescent biophotons. Next, we briefly describe our biophysical visual representation model that may explain brilliant lights experienced during NDEs (by phosphenes as biophotons) and REM sleep associated dream-like intrinsic visual imageries through biophotons in NDEs. Finally, we link our biophysical visual representation notion to self-consciousness that may involve extremely low-energy quantum entanglements. This article is intended to introduce novel concepts for discussion and does not pretend to give the ultimate explanation for the currently unanswerable questions about matter, life and soul; their creation and their interrelationship.
... To our knowledge, the present study is the first report of a microstructural and topographic description of REMalpha bursts without clear signs of awakenings, although some specific dreaming correlates linked to the REMbackground alpha activity have already been observed (Cantero et al., 1999c). However, the REM alpha activity studied in this work was not extracted from EEG background, but rather appeared highly synchronized in bursts without any association to other prominent phasic activities typical of this sleep stage and without a simultaneous change in the submental EMG amplitude. ...
Article
Full-text available
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. EEG, electrooculograph (EOGH), and EMG/H measurements were obtained during sleep in 10 healthy volunteer Ss (aged 19–25 yrs). 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 2 brain states. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
... Alpha coherence between homologous frontal sites has been shown to be state dependent in some studies. For example, alpha coherence between frontal sites was found to become weaker from wakefulness to drowsiness to REM sleep (Cantero et al., 1999), and to be reduced during a cognitive task vs. resting state (Nunez, 2000). The here observed EM-related decrease in alpha-band coherence over frontal sites might thus reflect changes in brain state related to decreased arousal or cognitive processing. ...
Article
Full-text available
Series of horizontal saccadic eye movements (EMs) are known to improve episodic memory retrieval in healthy adults and to facilitate the processing of traumatic memories in eye movement desensitization and reprocessing (EMDR) therapy. Several authors have proposed that EMs achieve these effects by increasing the functional connectivity of the two brain hemispheres, but direct evidence for this proposal is lacking. The aim of this study was to investigate whether memory enhancement following bilateral EMs is associated with increased interhemispheric coherence in the electroencephalogram (EEG). Fourteen healthy young adults were asked to freely recall lists of studied neutral and emotional words after a series of bilateral EMs and a control procedure. Baseline EEG activity was recorded before and after the EM and control procedures. Phase and amplitude coherence between bilaterally homologous brain areas were calculated for six frequency bands and electrode pairs across the entire scalp. Behavioral analyses showed that participants recalled more emotional (but not neutral) words following the EM procedure than following the control procedure. However, the EEG analyses indicated no evidence that the EMs altered participants’ interhemispheric coherence or that improvements in recall were correlated with such changes in coherence. These findings cast doubt on the interhemispheric interaction hypothesis, and therefore may have important implications for future research on the neurobiological mechanism underlying EMDR.
... Some authors regard alpha activity attenuation (i.e. decreasing of the power) or blocking as an indicator of visual imagery in general (Barrett & Ehrlichman, 1982;Cantero, Atienza, Salas & Gómez, 1999;Goodman, Beatty & Mulholland, 1980;Schupp, Lutzenberger, Birbaumer, Miltner & Braun, 1994;Williamson & Kaufman, 1989;Williamson, Kaufman, Lu, Wang & Karron, 1997). Alpha power attenuation with visual content was also confirmed in sighted subjects during visual exploration by Goldie (Goldie & Green, 1960). ...
Article
Full-text available
The question regarding visual imagery and visual perception remain an open issue. Many studies have tried to understand if the two processes share the same mechanisms or if they are independent, using different neural substrates. Most research has been directed towards the need of activation of primary visual areas during imagery. Here we review some of the works providing evidence for both claims. It seems that studying visual imagery in blind subjects can be used as a way of answering some of those questions, namely if it is possible to have visual imagery without visual perception. We present results from the work of our group using visual activation in dreams and its relation with EEG’s spectral components, showing that congenitally blind have visual contents in their dreams and are able to draw them; furthermore their Visual Activation Index is negatively correlated with EEG alpha power. This study supports the hypothesis that it is possible to have visual imagery without visual experience.
... To our knowledge, there is no information available in the literature on the generation mechanisms of the REM-alpha bursts. However, this activity has shown different properties of brain microstates [4] and seems to be functionally different from the alpha activity contained in the REM-EEG background [5]. The functional relationships between different brain areas supposedly involved in the generation of an EEG activity can be studied by means of the coherence technique [1] [6]. ...
Article
The functional relationships between the brain areas supposedly involved in the generation of the alpha activity were quantified by means of INTRA- and INTER-hemispheric coherences during different arousal states (relaxed wakefulness, drowsiness at sleep onset, and rapid eye movement sleep) where such an activity can be clearly detectable in the human EEG. A significant decrease in the fronto-occipital as well as in the inter-frontal coherence values in the alpha range was observed with the falling of the vigilance level, which suggests that the brain mechanisms underlying these coherences are state dependent. Making fronto-frontal coherence values in the alpha frequency band useful indexes to discern between brain functional states characterized by a different arousal level.
... Taken together, these results indicate that REM-alpha bursts might be indexing brain processes different from those in waking and/or drowsiness at sleep onset. REM-alpha bursts could even have a functional role different from REM background alpha activity , since the latter alpha activity variant showed a power modulation (blocking) over occipital scalp regions simultaneously to the presence of prominent oculomotor activity as compared with tonic REM periods (Cantero et al., 1999d). Micro-arousals not associated with awakenings (Kcomplexes ) during NREM sleep stages are well-known electrophysiological phenomena, being able to be evoked by endogenous (Johnson and Karpan, 1968; Niiyama et al., 1996) or exogenous stimulation (Davis et al., 1939). ...
Article
Spectral power contribution in the range of alpha activity is a well-known electrophysiological feature of human REM sleep, which could be caused by the spontaneous bursts of alpha activity not associated with arousals that usually appear during this brain state. The present study was undertaken to determine the density of alpha bursts during tonic and phasic (oculomotor) REM periods for each REM cycle. In addition, this phasic brain event was also described from a spectral and topographical point of view. Ten healthy right-handed subjects (5 females) aged 19-25 years (mean 22.9 years, SD 2.6) participated in the present study. Each selected subject filled in a daily sleep log for 2 weeks before the experimental night to provide information on all 3 salient aspects of sleep pattern, sleep experience and sleep effects. The results revealed that transient REM-alpha bursts, which lasted about 3 s and were accompanied by no increase in the EMG amplitude, appeared in all subjects who participated in this study, showing a higher density in the third and fourth REM cycle during phasic in comparison with tonic periods. The bandpass filtered signals showed the highest spectral contribution for the slower alpha components (8-9 Hz), the occipital scalp regions being the main generator source of this brain activity. The authors hypothesize that REM-alpha bursts may work as micro-arousals (or incomplete arousals) facilitating the brain connection with the external world in this cerebral state, whereas REM-alpha arousals - usually longer and accompanied by changes in the EMG amplitude - generate a shift of brain state associated with sleep fragmentation (complete arousal).
... En los últimos años se han realizado numerosos trabajos que han tratado de relacionar las distintas bandas que componen el EEG (alfa, beta, theta, etc.) con diversos procesos sensoriales, motores y cognitivos. Así, el decremento en la banda alfa se ha relacionado, entre otros, con el desarrollo de un movimiento voluntario [5], con tareas de memoria [6], con tareas de rotación mental [7] y con procesos oníricos durante el sueño REM [8]. Relacionado directamente con el proceso de atención visuoespacial, se ha observado mediante el empleo de la transformada rápida de Fourier (FFT) que se produce un decremento de la banda alfa (9-11 Hz) y un incremento de la banda beta (15)(16)(17), asociado a una selección atencional del espacio visual [9,10]. ...
Article
The event related potentials (ERPs) allow to study the evolution of the cerebral electric activity related with the diverse sensorial, motors and cognitive processes. However, the ERPs and the spectral analyses based in Fast Fourier Transform, are not able to show the variations along the time of the spectral content of the electroencephalogram (EEG). The present work will show the necessary methodology to obtain the temporal dynamics of the frequency (TSE) in the EEG, a technique described by Salmelin and Hari (1994) that allows the analysis of the modulations of any spectral band along the time. The presented data correspond to the electroencephalographic registration of 20 human subjects during an experiment of visual spatial attention. The modulations of the ERPs differ of the observed by the spectral techniques in latency and topography. Likewise, comparing different spectral techniques is proven that the TSE allows to define with more temporal precision the variations on the spectral content. The application of the TSE technique to the same EEG signal that is used for obtaining the ERPs, allows the inclusion of the variable time in the spectral analysis of the EEG, what can be crucial to understand the physiological bases of some neuropathologies.
... In this regard, registration of topographic properties of EEG sleep signals could provide additional information that could complement rCBF data. It has been shown that sleep EEG activity is not a homogenous global phenomenon and that regional differences of EEG frequency band depend on sleep stage and cortical area [3][4][5][6][7][8][9][10]. More recently, magnetoencephalography (MEG) signals have been used for source localisation during sleep [11,12]. ...
Article
Full-text available
This article deals with a new approach in sleep characterization that combines EEG source localisation methods with standard frequency analysis of multielectrode EEGs. First, we describe the theoretical methodology and the benefits that we get from a three-dimensional image (LORETA) of the cerebral activity related to a frequency band. Then, this new application is used as signal-processing technique on sleep EEG recordings obtained from young male adults using four frequency bands (delta 0.5-3.5 Hz, theta 4.0-7.5 Hz, alpha 8.0-12.5 Hz and beta 13.0-32.0 Hz) in different sleep stages. Finally, we show that the obtained results are highly consistent with other physiological assessments (standard EEG mapping, functional magnetic resonance imaging, etc.), but give us more realistic additional information on the generators of electromagnetic cerebral activity.
... Average of all pairs of derivations is shown (main effect of stage). Bottom: Mean and standard error of absolute power, log transformed, for REM sleep and Stage 2. Maquet et al., 1996), with increased power of fast frequencies, decreased power of slow frequencies (Borb e ely, Baumann, Brandeis, Strauch, and a attenuation (Cantero, Atienza, Salas, & G o omez, 1999), and agree with the postulated role of fast activity for greater recall, complexity and variety of content of REM sleep dreaming (Moffit et al., 1982) and also with the postulated role of coherent activity for perception (Srinivasan et al., 1999). ...
Article
EEG coherent activity is involved in the binding of spatially separated but temporally correlated stimuli into whole events. Cognitive features of rapid eye movement sleep (REM) dreaming resemble frontal lobe dysfunction. Therefore, temporal coupling of EEG activity between frontal and perceptual regions was analyzed from 10 min prior to dream reports (8 adults) from stage-2 and REM sleep. EEG correlation between frontal and perceptual regions decreased and, among perceptual regions increased during REM. The temporal dissociation of EEG activity between executive and perceptual regions supplies an inadequate mechanism for the binding and interpretation of ongoing perceptual activity resulting in dream bizarreness.
... In the present experiment, a decrease in alpha was obtained, but it must be remarked that as the subjects do not know the location of the next target, it would be more convenientfor the processing of the next visual stimulusto decrease alpha power in left and right visual cortices. In this sense, decreasing alpha activity has already been reported during different kinds of cognitive operations on visual images, such as attention (Gómez et al. 1998, visual imagination (Michel et al. 1994), and the phasic REM period (Cantero et al. 1999). The decrease of alpha during the pre-target period obtained in the present experiment could be interpreted as an active preparation of the visual cortex to process the next incoming stimulus. ...
Article
Full-text available
The contingent negative variation (CNV), and the associated event-related desynchronization (ERD) on motor areas and sensory areas, and increase of alpha in the ipsilateral to the cued stimulus side, are different brain signals that reflect motor, sensory, and cognitive activations related to the expectancy of the next stimulus. However, the possibility of an overall change in EEG oscillatory activity during expectancy periods has not been directly addressed. The present report tests whether the background oscillatory activity is modulated by a warning signal. During the expectancy period, the power spectral density (PSD) between 0 and 42.9 Hz--including delta, theta, alpha, beta, and gamma--decreased with respect to the baseline. These results suggest that during expectancy periods there is a generalised decrease in the oscillatory activity, and that reduction of the EEG power would facilitate the phasic and oscillatory neural activities triggered by the next target stimulus.
Article
The study of cerebral rhythms is possible by analyzing its electrophysiological features with quantitative EEG techniques. In the cases in which the same activity appears spontaneously in different brain states, the study of its electrophysiological features would help to establish functional differences associated to each of these states. The present work reviews those studies that determined the electrophysiological features of the different normal variants of alpha activity appearing in the wake-sleep continuous, more specifically, during relaxed wakefulness, drowsiness and REM sleep. The results indicate that each normal variant of alpha activity, in spite of showing a similar topographical distribution in each of the brain states, shows different features in relation to its spectral composition, functional relationships among cortical regions, and underlying brain micro-states. According to these experimental findings, each alpha variant would play a different brain function. Thus, the wakefulness alpha rhythm seems to reflect a maximum neuronal synchronization due to the absence of visual processing, whereas alpha activity during the drowsiness period would be associated with the brain processing of hypnagogic imagery happening at sleep onset. However, spontaneous alpha bursts of REM sleep would reflect the contact between the sleeping brain and the environment. This electrophysiological characterization has its most direct applied field in the design of algorithms to stage sleep automatically, as well as in the diagnosis and evaluation of clinical entities in which the brain generator mechanisms of this activity could be affected through the wake-sleep continuous.
Article
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The latest experimental results support that multiple retinotopic visual systems play a central role not only in the processing of visual signals but also in the integration and processing of internally represented auditory and tactile information. These retinotopic maps have access to higher levels of cognitive processing, performed by the frontal lobes, for example. The occipital cortex may have a special role in multisensory integration. There is a functional basis for the development and maturation of visual memory in association of rapid eye movement sleep (REMS) which is linked to dreams and visual imagery. Physiological and psychological processes of REMS are similar to waking visual imagery. Furthermore, visual imagery during REMS utilize a common visual neural pathway similar to that used in wakefulness. This pathway subserves visual processes accompanied with auditory experiences and intrinsic feelings. We argue that the activation of the retinotopic visual areas is central to REM sleep associated dreams and that REMS associated dreaming and visual imagery may have co-evolved in homeothermic animals during evolution. We also suggest that protoconscious state during REM sleep, as introduced by Hobson many years ago, may be a basic visual process.
Poster
Design, Background and Pilot Data of Master Thesis. Please see the now available preprint: https://www.biorxiv.org/content/early/2018/05/17/323667
Article
Unlabelled: Studies have shown that synchrony or temporal coupling of gamma activity is involved in processing and integrating information in the brain. Comparing rapid eye movement (REM) sleep to waking and non-REM (NREM) sleep, interhemispheric temporal coupling is higher, but lower between the frontal and posterior association areas of the same hemisphere. However, the homeostatic response of REM sleep temporal coupling after selective REM sleep deprivation (REMD) has not been studied. This study proposed exploring the effect of one night of selective REMD on the temporal coupling of cortical gamma activity during recovery REM sleep. Two groups of healthy subjects were subjected to either REMD by awakening them at each REM sleep onset, or to NREM sleep interruptions. Subjects slept four consecutive nights in the laboratory: first for adaptation, second as baseline, third for sleep manipulation, and fourth for recovery. Interhemispheric and intrahemispheric EEG correlations were analyzed during tonic REM (no eye movements) for the first three REM sleep episodes during baseline sleep, and recovery sleep after one night of selective REMD. Temporal coupling between frontal lobes showed a significant homeostatic rebound that increased during recovery REM sleep relative to baseline and controls. Results showed a rebound in temporal coupling between the two frontal lobes after REM sleep deprivation, indicating that the enhanced gamma temporal coupling that occurs normally during REM sleep has functional consequences. Conclusion: results suggest that synchronized activity during REM sleep may play an important role in integrating and reprocessing information.
Article
Full-text available
Recently, we proposed a novel biophysical concept regarding on the appearance of brilliant lights during near death experiences (NDEs) (Bókkon and Salari, 2012). Specifically, perceiving brilliant light in NDEs has been proposed to arise due to the reperfusion that produces unregulated overproduction of free radicals and energetically excited molecules that can generate a transient enhancement of bioluminescent biophotons in different areas of the brain, including retinotopic visual areas. If this excess of bioluminescent photon emission exceeds a threshold in retinotopic visual areas, this can appear as (phosphene) lights because the brain interprets these intrinsic retinotopic bioluminescent photons as if they originated from the external physical world. Here, we review relevant literature that reported experimental studies (Imaizumi et al., 1984; Suzuki et al., 1985) that essentially support our previously published conception, i.e. that seeing lights in NDEs may be due to the transient enhancement of bioluminescent biophotons. Next, we briefly describe our biophysical visual representation model that may explain brilliant lights experienced during NDEs (by phosphenes as biophotons) and REM sleep associated dream-like intrinsic visual imageries through biophotons in NDEs. Finally, we link our biophysical visual representation notion to self-consciousness that may involve extremely low-energy quantum entanglements. This article is intended to introduce novel concepts for discussion and does not pretend to give the ultimate explanation for the currently unanswerable questions about matter, life and soul; their creation and their interrelationship.
Article
The most challenging objections to the Threat Simulation Theory (TST) of the function of dreaming include such issues as whether the competing Random Activation Theory can explain dreaming, whether TST can accommodate the apparently dysfunctional nature of post-traumatic nightmares, whether dreams are too bizarre and disorganized to constitute proper simulations, and whether dream recall is too biased to reveal the true nature of dreams. I show how these and many other objections can be accommodated by TST, and how several lines of new supporting evidence are provided by the commentators. Accordingly TST offers a promising new approach to the function of dreaming, covering a wide range of evidence and theoretically integrating psychological and biological levels of explanation.
Article
The pattern of rapid eye movement (REM) sleep was examined using a new scoring system for electroencephalogram (EEG) stages. An all-night polysomnogram (PSG) was recorded from 12 young healthy volunteers. First, all the data were scored according to the standard criteria of Rechtschaffen and Kales’A Manual of Standardized Terminology, Techniques and Scoring System for Sleep Stages of Human Subjects (1968), and epochs of typical REM sleep were collected. The extracted data were then re-scored for each 5 s using the criteria of seven EEG stages of REM sleep: (1) alpha wave, train; (2) alpha wave, intermittent A; (3) alpha wave, intermittent B; (4) EEG flattening; (5) theta wave; (6) sawtooth wave; and (7) movement time. The results showed that the EEG flattening (4) and theta wave stages (5) occupied 92.7% of the epochs of REM sleep. The most frequent transition pattern was also between these two stages (71.1%), and these stages rarely transitioned to other stages. The number of stage continuations within 2 epochs (10 s) was largest in EEG stage 4, and those in stage 5 followed it (64.5% and 54.2%, respectively). EEG stages 4 and 5 sometimes lasted for more than 13 epochs (over 1 min). The number of stages containing sawtooth waves was less than expected, and was more frequent at the beginning than at the end of REM sleep. The distinguishing feature of the REM sleep EEG pattern was the stability of the stages of EEG flattening and theta wave, compared with the sleep onset period EEG pattern.
Article
Event-related potentials (ERPs) are an electrophysiological index of various cognitive processes such as attention. However, this kind of analysis does not allow observation of differences in the spectral content taking place during a sensory, cognitive or motor task. The goal of the present work was to compute the temporal dynamics of EEG oscillations using a technique called temporal spectral evolution (TSE). The electroencephalogram (EEG) was recorded during the presentation of flashed stimuli that were randomly presented to the left or right visual field. Subjects were asked to pay attention, alternately in different blocks of trials, to the left or to the right to detect an infrequent target. The results showed a decrease in the α band in a time window of 375–500 ms and an increase in the β band at 500–875 ms after stimulus onset, for both attended and unattended stimuli. Statistical analysis showed that the decrease in α and the increase in β were more marked during the attentional condition. In conclusion, these results demonstrate that the decrease in α band and the increase in β band are electrophysiological markers of visual spatial attention.
Article
El estudio de los ritmos cerebrales puede ser abordado mediante el análisis de sus propiedades electrofisiológicas usando técnicas de EEG cuantitativo. En aquellos casos donde una misma actividad aparece espontáneamente en diferentes estados de activación cerebral, el estudio de estas propiedades ayudaría a establecer diferencias funcionales asociadas a cada uno de estos estados. El presente trabajo revisa aquellos estudios que han determinado las propiedades electrofisiológicas de las diferentes variantes normales de alfa que aparecen en el continuo vigilia-sueño, más concretamente en vigilia relajada, somnolencia y durante la fase REM del sueño. Los resultados indican que cada variante normal de alfa, aun mostrando una distribución topográfica similar en cada uno de los estados cerebrales, presenta características diferenciales atendiendo a su composición espectral, relaciones funcionales entre regiones corticales, y micro-estados cerebrales subyacentes. De acuerdo con estos hallazgos, cada variante de alfa desempeñaría diferentes funciones cerebrales. El ritmo alfa de vigilia parece ser el resultado de una máxima sincronización neuronal como consecuencia de la ausencia de procesamiento sensorial, mientras que la presencia de actividad alfa durante la somnolencia estaría más asociada al procesamiento de las imágenes hipnagógicas que ocurren al comienzo del sueño. Los brotes de alfa de REM, sin embargo, constituirían un punto de contacto entre el cerebro dormido y el ambiente externo. Esta caracterización electrofisiológica encuentra su campo de aplicación más directo en el diseño de algoritmos para clasificar el sueño de forma automática, así como en el diagnóstico y evaluación de determinadas patologías donde pudieran verse afectados los mecanismos cerebrales de generación de esta actividad a lo largo del continuo vigilia-sueño.
Article
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There is debate in dream research as to whether ponto-geniculo-occipital (PGO) waves or cortical arousal during sleep underlie the biological mechanisms of dreaming. This study comprised 2 experiments. As eye movements (EMs) are currently considered the best noninvasive indicator of PGO burst activity in humans, the aim of the first experiment was to investigate the effect of low-intensity repeated auditory stimulation on EMs (and inferred PGO burst activity) during REM sleep. It was predicted that such auditory stimuli during REM sleep would have a suppressive effect on EMs. The aim of the second experiment was to examine the effects of this auditory stimulation on subsequent dream reporting on awakening. Repeated measures design with counterbalanced order of experimental and control conditions across participants. Sleep laboratory based polysomnography (PSG) PARTICIPANTS: Experiment 1 : 5 males and 10 females aged 18-35 years (M = 20.8, SD = 5.4). Experiment 2 : 7 males and 13 females aged 18-35 years (M = 23.3, SD = 5.5). Below-waking threshold tone presentations during REM sleep compared to control REM sleep conditions without tone presentations. PSG records were manually scored for sleep stages, EEG arousals, and EMs. Auditory stimulation during REM sleep was related to: (a) an increase in EEG arousal, (b) a decrease in the amplitude and frequency of EMs, and (c) a decrease in the frequency of visual imagery reports on awakening. The results of this study provide phenomenological support for PGO-based theories of dream reporting on awakening from sleep in humans.
Article
Evidence suggests that an important contribution of spectral power in the alpha range is characteristic of human REM sleep. This contribution is, in part, due to the appearance of well-defined bursts of alpha activity not associated with arousals during both tonic and phasic REM fragments. The present study aims at determining if the REM-alpha bursts constitute a different alpha variant from the REM background alpha activity. Since previous findings showed a selective suppression of background alpha activity over occipital regions during phasic REM fragments and, on the other hand, the density of alpha bursts seem to be independent of the presence or absence of rapid eye movements, one expects to find the same spectral power contribution of alpha bursts in tonic and phasic REM fragments. The results indicated that REM-alpha bursts showed a similar power contribution and topographic distribution (maximum energy over occipital regions) both in tonic and phasic REM fragments. This suggests that two variants of alpha activity with different functional roles are present during the human REM sleep: i) background alpha activity, modulated over occipital regions by the presence of rapid eye movements, which may be an electrophysiological correlate of the visual dream contents; and ii) REM-alpha bursts, independent of the presence of rapid eye movements, which could be facilitating the connection between the dreaming brain and the external world, working as a micro-arousal in this brain state.
Article
Cortical oscillations in the range of alpha activity (8-13 Hz) are one of the fundamental electrophysiological phenomena of the human electroencephalogram (EEG). Evidence from quantitative EEG data has shown that their electrophysiological features, cortical generation mechanisms, and therefore, their functional correlates vary along the sleep-wake continuum. Specifically, spectral microstructure and EEG coherence levels between anterior and posterior cortical regions permit to differentiate among alpha activity spontaneously appearing in relaxed wakefulness with eyes closed, drowsiness period, and REM sleep, by reflecting distinct properties of neural networks involved in its cortical generation as well as a different interplay between cortical generators, respectively. Besides, the dissimilar spatiotemporal features of brain electrical microstates within the alpha range reveals a different geometry of active neural structures underlying each alpha variant or, simply, changes in the stability level of neural networks during each brain state. Studies reviewed in this paper support the hypothesis that two different alpha variants occur during human REM sleep: 'background responsive alpha activity', blocked over occipital regions when rapid eye movements are present, and 'REM-alpha bursts', non modulated by the alteration of tonic and phasic periods. Altogether, evidence suggests that electrophysiological features of human cortical oscillations in the alpha frequency range vary across different behavioural states, as well as within state, reflecting different cerebral phenomena with probably dissimilar functional meaning.
Article
It is currently claimed that congenitally blind do not have visual imagery and are therefore unable to present visual contents in their dreams. The aim of our study was to quantitatively evaluate the existence of visual imagery in born-blind dreams and to correlate it with objective measures, such as sleep EEG frequency components, namely with alpha attenuation (regarded as an indicator of visual activity), and graphical analysis of dream pictorial representations. The investigation was carried out via simultaneous recordings of dream reports and polysomnography, during nocturnal sleep at volunteers' homes; scheduled regular awakenings during the night provided the data for dream and EEG analysis. In the morning, subjects were asked to make a drawing of their dream images. Congenitally blind (n=10) were comparable to normal sighted subjects (n=9): the two groups presented equivalent visual activity indices, and no differences in the analysis of graphical representation of dreaming imagery. However, blind subjects presented a lower rate of dream recall than sighted (27% versus 42%). Both groups had significant negative correlation between Visual Activity Index (VAI) and alpha power in the central and occipital O2 derivations (blind: C4: r=-0.615, P<0.005; O2: r=-0.608, P<0.006; sighted: C4: r=-0.633, P<0.01; O2: r=-0.506, P<0.05). This correlation was weaker for the blind in O1 (r=-0.573, P<0.05) and non-existent for the sighted. Blind individuals have significantly lower alpha activity in the central derivation. In conclusion, the congenitally blind have visual content in their dreams and are able to draw it and, as expected, their VAI is negatively correlated with EEG alpha power.
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Searching for the neural code underlying consciousness and cognition is one of the most important activities in contemporary neuroscience. Research with neuronal oscillations at the level of single-neuron, local cell assemblies, and network system have provided invaluable insights into different mechanisms of synaptic interactions involved in the emergence of cognitive acts. A cognitive neuroscience of conscious experience is gradually emerging from behavioral and neuroimaging studies, which can be successfully complemented with the quantitative EEG findings discussed here. This review is an attempt to highlight the value of state-dependent changes in human neurophysiology for a better understanding of the neurobiological substrate underlying those aspects of cognition drastically affected by sleep states. Recent advances related to synchronization mechanisms potentially involved in brain integration processes are discussed, emphasizing the value of scalp and intracranial EEG recordings at determining local and large-scale dynamics in the human brain. Evidence supporting the critical role of state-dependent synchrony in brain integration comes mainly from studies on the theta and gamma oscillations across the wake-sleep continuum, as revealed by human intracranial recordings. This review blends results from different levels of analysis with the firm conviction that state-dependent brain dynamics at different levels of neural integration can provide a deeper understanding of neurobiological correlates of consciousness and sleep functions.
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We examined evoked and induced modulations in theta, alpha and gamma oscillations, and also the P2 and late positive component of event-related potentials, during a visual discrimination task with target and nontarget letters. Results for target letters showed a decrease in the amplitude of alpha-band (10-11 Hz) activity and an increase in theta (4-7 Hz) and gamma (40-44 Hz) activities around 350 ms after stimulation. P2 and late positive component presented a higher amplitude to target than to repeated nontarget letters. Alpha reduction was inversely related to theta and late positive component increase. Moreover, gamma oscillation amplitude was directly related to theta amplitude. The findings suggest the importance of occipitoparietal alpha reduction for the development of task-related neuronal activity.
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Magnetic measurements of average power of human alpha and beta activity over the occipital and parietal areas of the scalp reveal spatially selective suppression of the activity of the occipital cortex when abstract figures are briefly presented visually and subjects simply indicate that they saw the figure. However, the duration of the suppression increases markedly when subjects must indicate whether or not they had previously seen the figure. The reaction time is similarly prolonged during the search of visual memory, and is commensurate with the duration of selective suppression of brain activity. It is also demonstrated that alpha activity is not replaced by beta activity during this suppression, but that power in the beta band is also diminished during memory search. Low correlations between the scalp distributions of power in the beta and alpha bands indicate that partly different neuronal populations give rise to activity of these different frequency bands. Since magnetic fields are negligibly affected by intervening bone tissues, dramatic asymmetries in the distribution of alpha activity across the scalps of individuals and the differences in distribution between individuals cannot be ascribed to differences in skull thickness but are due instead to differences in underlying brain anatomy or function. Nevertheless, a common pattern of suppression of alpha activity is observed across subjects during well-controlled cognitive tasks. This implies that the visual system is involved in mental imagery.
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Positron emission tomography was used to measure cerebral activity and to evaluate regional interrelationships within visual cortices and their projections during rapid eye movement (REM) sleep in human subjects. REM sleep was associated with selective activation of extrastriate visual cortices, particularly within the ventral processing stream, and an unexpected attenuation of activity in the primary visual cortex; increases in regional cerebral blood flow in extrastriate areas were significantly correlated with decreases in the striate cortex. Extrastriate activity was also associated with concomitant activation of limbic and paralimbic regions, but with a marked reduction of activity in frontal association areas including lateral orbital and dorsolateral prefrontal cortices. This pattern suggests a model for brain mechanisms subserving REM sleep where visual association cortices and their paralimbic projections may operate as a closed system dissociated from the regions at either end of the visual hierarchy that mediate interactions with the external world.
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In an intensive single-subject design, electroencephalographic (EEG) alpha power and receptive and expressive language in dreaming were studied in 12 dreams during rapid eye movement (REM) sleep on 12 separate nights. Bilateral EEG was recorded continuously from 21 sites and digitized. We used the Fast Fourier transformation (FFT) for power spectral analysis to measure EEG power in the alpha frequency range (8–12 Hz) at each of the EEG sites. The subject was awakened after about 14 minutes into the second REM period, and dream reports were collected. We scored the dream reports for expressive and receptive language. The lower the alpha power on the left sides of those homologous pairs that roughly correspond to Broca's (C3) or Wernicke's area (P3), the more expressive or receptive language in dream reports. The largest difference between the correlation of the left and that of the right homologous pair of regions was found in the central (C3, C4) area for expressive language and in the parietal (P3, P4) area for receptive language. Our finding suggests lateralized and localized cortical activation in relation to language in dreaming. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
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Kosslyn (psychology, Harvard U.) presents a 20-year research program on the nature of high-level vision and mental imagery--offering his research as a definitive resolution of the long-standing "imagery debate," which centers on the nature of the internal representation of visual mental imagery. He combines insights and empirical results from computer vision, neurobiology, and cognitive science to develop a general theory of visual mental imagery, its relation to visual perception, and its implementation in the human brain.
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The amount of observed eye movement was related to the degree of participation of Ss in the events of the dreams. The last eye movement before awakening corresponded in direction to the last reported fixation of the dreamer. Certain external and internal stimuli did not influence the dream content. The course of time in the dream was comparable to the time elapsing for that activity while awake. The implications of these findings are discussed. 15 references. (PsycINFO Database Record (c) 2006 APA, all rights reserved).
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Independent confirmation is offered that the amount of rapid eye movement during dreaming is associated with the dream content.
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The present study was designed to assess the patterning of occipital and sensorimotor EEG activation during self-generated visual and kinesthetic imagery. Twenty subjects were requested to imagine, in separate trials, a flashing light, a tapping sensation on the right forearm, and both the light and the tapping together. Prior to the imagery trials, subjects were exposed to the stimuli which they were asked to subsequently imagine. EEG was recorded from the left occipital and left sensorimotor regions, filtered for alpha and quantified on-line. The results indicated that self-generated visual imagery elicited greater relative occipital activation than comparable kinesthetic imagery. The imagine-both condition fell predictably in between the two unimodal imagery conditions. The difference between visual and kinesthetic imagery was primarily a function of greater occipital activation during the former versus the latter task. No difference in overall alpha abundance among the three imagery tasks was found. These findings suggest that the self-generation of imagery in different modalities elicits specific changes in the sensory regions of the brain responsible for processing information in the relevant modalities.
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Recent PET imaging and brain lesion studies in humans are integrated with new basic research findings at the cellular level in animals to explain how the formal cognitive features of dreaming may be the combined product of a shift in neuromodulatory balance of the brain and a related redistribution of regional blood flow. The human PET data indicate a preferential activation in REM of the pontine brain stem and of limbic and paralimbic cortical structures involved in mediating emotion and a corresponding deactivation of dorsolateral prefrontal cortical structures involved in the executive and mnemonic aspects of cognition. The pontine brainstem mechanisms controlling the neuromodulatory balance of the brain in rats and cats include noradrenergic and serotonergic influences which enhance waking and impede REM via anticholinergic mechanisms and cholinergic mechanisms which are essential to REM sleep and only come into full play when the serotonergic and noradrenergic systems are inhibited. In REM, the brain thus becomes activated but processes its internally generated data in a manner quite different from that of waking.
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Dream content elicited following the selective deprivation of rapid-eye-movement sleep was intensified compared to that elicited under nondeprivation conditions. This effect was observed both for repressers and for sensitizers, but was significant only for repressers. On nondeprivation nights, the dream periods of sensitizers were shorter and their dreams more intense than those of repressers.
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Based on the findings of our previously published positron emission tomography study, we proposed that recorded eye movements during REM sleep are visually targeted saccades. In the present study, we examined the correlation between the number of eye movements in REM sleep (EM) and visual imagery in dreaming (V) and provided further support for our proposal. All the observations (N = 11) were made with one individual to eliminate interindividual variation and were made during the second REM sleep period to control for a time-of-night effect. V, with or without dream report length partialled out, was strongly associated with EM only in the 1-min interval immediately preceding awakening. The time course of the association suggests that the strong EM-V association reflects a phasic, localized activation of the eye-movement-control system in association with REM sleep eye movements.
Article
Independent confirmation is offered that the amount of rapid eye movement during dreaming is associated with the dream content.
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