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1.
Medicine (Baltimore) ; 99(30): e21303, 2020 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-32791716

RESUMO

The PLEM100 (Inbody Co., Ltd., Seoul, Korea) is a device for measuring phase lag entropy (PLE), a recently developed index for the quantification of consciousness during sedation and general anesthesia. In the present study, we assessed changes in PLE along with the level of consciousness during the induction of general anesthesia using propofol. PLE was compared with the bispectral index (BIS), which is currently the most commonly used index of consciousness.After obtaining Institutional Review Board approval and written informed consent, we enrolled 15 patients (8 men, 7 women; mean age: 37 ±â€Š9 years; mean height: 168 ±â€Š8 cm; mean weight; 68 ±â€Š11 kg) undergoing nasal bone reduction. PLE and BIS sensors were attached simultaneously, and general anesthesia was induced via target-controlled infusion (TCI) of propofol. PLE and BIS scores were recorded when the calculated effect site concentration shown on the TCI pump was equal to the target concentrations of 1.5, 2.0, 2.5, 2.8, 3.0, 3.2, 3.4, and 3.5 µg/mL (and at each 0.1 µg/mL increase, thereafter). Observer's Assessment of Alertness/Sedation (OAA/S) scores were also recorded until unconsciousness was achieved. Throughout the anesthesia period, all pairs of PLE and BIS data were collected using data acquisition software.The partial correlation coefficients between OAA/S scores and PLE, and between OAA/S scores and BIS were 0.778 (P < .001) and 0.846 (P < .001), respectively. Throughout the period of anesthesia, PLE and BIS exhibited a significant positive correlation. The partial correlation coefficient prior to the loss of consciousness was 0.838 (P < .001), and 0.669 (P < .001) following the loss of consciousness. Intra-class correlation between the 2 indices was 0.889 (P < .001) and 0.791 (P < .001) prior and following the loss of consciousness, respectively.PLE exhibited a strong and predictable correlation with both BIS and OAA/S scores. These results suggest that PLE is reliable for assessing the level of consciousness during sedation and general anesthesia.


Assuntos
Anestesia Geral/métodos , Anestésicos Intravenosos/administração & dosagem , Entropia , Propofol/administração & dosagem , Adulto , Estado de Consciência/efeitos dos fármacos , Estado de Consciência/fisiologia , Monitores de Consciência , Eletroencefalografia/instrumentação , Feminino , Humanos , Infusões Intravenosas/métodos , Masculino , Pessoa de Meia-Idade , Osso Nasal/cirurgia , Estudos Prospectivos
3.
PLoS One ; 15(8): e0236467, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32785238

RESUMO

Can people categorize complex visual scenes unconsciously? The possibility of unconscious perception remains controversial. Here, we addressed this question using psychophysical methods applied to unmasked visual stimuli presented for extremely short durations (in the µsec range) by means of a custom-built modern tachistoscope. Our experiment was composed of two phases. In the first phase, natural or urban scenes were either absent or present (for varying durations) on the tachistoscope screen, and participants were simply asked to evaluate their subjective perception using a 3-points scale (absence of stimulus, stimulus detection or stimulus identification). Participants' responses were tracked by means of two staircases. The first psychometric function aimed at defining participants' proportion of subjective detection responses (i.e., not having seen anything vs. having seen something without being able to identify it), while the second staircase tracked the proportion of subjective identification rates (i.e., being unaware of the stimulus' category vs. being aware of it). In the second phase, the same participants performed an objective categorization task in which they had to decide, on each trial, whether the image was a natural vs. an urban scene. A third staircase was used in this phase so as to build a psychometric curve reflecting the objective categorization performance of each participant. In this second phase, participants also rated their subjective perception of each stimulus on every trial, exactly as in the first phase of the experiment. Our main result is that objective categorization performance, here assumed to reflect the contribution of both conscious and unconscious trials, cannot be explained based exclusively on conscious trials. This clearly suggests that the categorization of complex visual scenes is possible even when participants report being unable to consciously perceive the contents of the stimulus.


Assuntos
Estado de Consciência/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Inconsciente Psicológico , Percepção Visual/fisiologia , Adulto , Conscientização , Feminino , Humanos , Masculino , Estimulação Luminosa , Psicometria/métodos , Adulto Jovem
4.
PLoS One ; 15(8): e0238249, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32845935

RESUMO

Spontaneous electroencephalogram (EEG) and auditory evoked potentials (AEP) have been suggested to monitor the level of consciousness during anesthesia. As both signals reflect different neuronal pathways, a combination of parameters from both signals may provide broader information about the brain status during anesthesia. Appropriate parameter selection and combination to a single index is crucial to take advantage of this potential. The field of machine learning offers algorithms for both parameter selection and combination. In this study, several established machine learning approaches including a method for the selection of suitable signal parameters and classification algorithms are applied to construct an index which predicts responsiveness in anesthetized patients. The present analysis considers several classification algorithms, among those support vector machines, artificial neural networks and Bayesian learning algorithms. On the basis of data from the transition between consciousness and unconsciousness, a combination of EEG and AEP signal parameters developed with automated methods provides a maximum prediction probability of 0.935, which is higher than 0.916 (for EEG parameters) and 0.880 (for AEP parameters) using a cross-validation approach. This suggests that machine learning techniques can successfully be applied to develop an improved combined EEG and AEP parameter to separate consciousness from unconsciousness.


Assuntos
Monitores de Consciência , Estado de Consciência/fisiologia , Eletroencefalografia/métodos , Aprendizado de Máquina , Monitorização Intraoperatória/métodos , Algoritmos , Anestesia Geral/métodos , Anestésicos Intravenosos/uso terapêutico , Estado de Consciência/efeitos dos fármacos , Potenciais Evocados Auditivos/fisiologia , Humanos , Monitorização Fisiológica/métodos , Redes Neurais de Computação , Máquina de Vetores de Suporte
6.
Nature ; 581(7809): 428-433, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32461641

RESUMO

After severe brain injury, it can be difficult to determine the state of consciousness of a patient, to determine whether the patient is unresponsive or perhaps minimally conscious1, and to predict whether they will recover. These diagnoses and prognoses are crucial, as they determine therapeutic strategies such as pain management, and can underlie end-of-life decisions2,3. Nevertheless, there is an error rate of up to 40% in determining the state of consciousness in patients with brain injuries4,5. Olfaction relies on brain structures that are involved in the basic mechanisms of arousal6, and we therefore hypothesized that it may serve as a biomarker for consciousness7. Here we use a non-verbal non-task-dependent measure known as the sniff response8-11 to determine consciousness in patients with brain injuries. By measuring odorant-dependent sniffing, we gain a sensitive measure of olfactory function10-15. We measured the sniff response repeatedly over time in patients with severe brain injuries and found that sniff responses significantly discriminated between unresponsive and minimally conscious states at the group level. Notably, at the single-patient level, if an unresponsive patient had a sniff response, this assured future regaining of consciousness. In addition, olfactory sniff responses were associated with long-term survival rates. These results highlight the importance of olfaction in human brain function, and provide an accessible tool that signals consciousness and recovery in patients with brain injuries.


Assuntos
Lesões Encefálicas/diagnóstico , Lesões Encefálicas/fisiopatologia , Estado de Consciência/fisiologia , Percepção Olfatória/fisiologia , Estado Vegetativo Persistente/diagnóstico , Estado Vegetativo Persistente/fisiopatologia , Olfato/fisiologia , Adulto , Nível de Alerta , Erros de Diagnóstico/prevenção & controle , Feminino , Humanos , Masculino , Odorantes/análise , Prognóstico , Recuperação de Função Fisiológica/fisiologia , Sensibilidade e Especificidade , Análise de Sobrevida
7.
J Neurosci ; 40(25): 4925-4935, 2020 06 17.
Artigo em Inglês | MEDLINE | ID: mdl-32409620

RESUMO

To identify the neural correlates of perceptual awareness, researchers often compare the differences in neural activation between conditions in which an observer is or is not aware of a stimulus. While intuitive, this approach often contains a critical limitation: to link brain activity with perceptual awareness, observers traditionally report the contents of their perceptual experience. However, relying on observers' reports is problematic because it is difficult to know whether the neural responses being measured are associated with conscious perception or with postperceptual processes involved in the reporting task (e.g., working memory, decision-making). To address this issue, we combined a standard visual masking paradigm with a recently developed "no-report" paradigm in male/female human participants. In the visual masking paradigm, observers saw images of animals and objects that were visible or invisible, depending on their proximity to masks. Meanwhile, on half of the trials, observers reported the contents of their perceptual experience (i.e., report condition), while on the other half of trials they refrained from reporting about their experiences (i.e., no-report condition). We used electroencephalography to examine how visibility interacts with reporting by measuring the P3b event-related potential, one of the proposed canonical "signatures" of conscious processing. Overall, we found a robust P3b in the report condition, but no P3b whatsoever in the no-report condition. This finding suggests that the P3b itself is not a neural signature of conscious processing and highlights the importance of carefully distinguishing the neural correlates of perceptual awareness from postperceptual processing.SIGNIFICANCE STATEMENT What are the neural signatures that differentiate conscious and unconscious processing in the brain? Perhaps the most well established candidate signature is the P3b event-related potential, a late slow wave that appears when observers are aware of a stimulus, but disappears when a stimulus fails to reach awareness. Here, however, we found that the P3b does not track what observers are perceiving, but instead tracks what observers are reporting. When observers are aware of simple visual stimuli, the P3b is nowhere to be found unless observers are reporting the contents of their experience. These results challenge the well established notion of the P3b as a neural marker of awareness and highlight the need for new approaches to the neuroscience of consciousness.


Assuntos
Conscientização/fisiologia , Encéfalo/fisiologia , Potencial Evocado P300/fisiologia , Mascaramento Perceptivo/fisiologia , Percepção Visual/fisiologia , Adulto , Estado de Consciência/fisiologia , Eletroencefalografia , Feminino , Humanos , Masculino , Adulto Jovem
8.
Proc Natl Acad Sci U S A ; 117(19): 10575-10584, 2020 05 12.
Artigo em Inglês | MEDLINE | ID: mdl-32341167

RESUMO

Even though humans are mostly not aware of their heartbeats, several heartbeat-related effects have been reported to influence conscious perception. It is not clear whether these effects are distinct or related phenomena, or whether they are early sensory effects or late decisional processes. Combining electroencephalography and electrocardiography, along with signal detection theory analyses, we identify two distinct heartbeat-related influences on conscious perception differentially related to early vs. late somatosensory processing. First, an effect on early sensory processing was found for the heartbeat-evoked potential (HEP), a marker of cardiac interoception. The amplitude of the prestimulus HEP negatively correlated with localization and detection of somatosensory stimuli, reflecting a more conservative detection bias (criterion). Importantly, higher HEP amplitudes were followed by decreases in early (P50) as well as late (N140, P300) somatosensory-evoked potential (SEP) amplitudes. Second, stimulus timing along the cardiac cycle also affected perception. During systole, stimuli were detected and correctly localized less frequently, relating to a shift in perceptual sensitivity. This perceptual attenuation was accompanied by the suppression of only late SEP components (P300) and was stronger for individuals with a more stable heart rate. Both heart-related effects were independent of alpha oscillations' influence on somatosensory processing. We explain cardiac cycle timing effects in a predictive coding account and suggest that HEP-related effects might reflect spontaneous shifts between interoception and exteroception or modulations of general attentional resources. Thus, our results provide a general conceptual framework to explain how internal signals can be integrated into our conscious perception of the world.


Assuntos
Frequência Cardíaca/fisiologia , Interocepção/fisiologia , Percepção/fisiologia , Adulto , Atenção/fisiologia , Conscientização/fisiologia , Encéfalo/fisiologia , Mapeamento Encefálico/métodos , Estado de Consciência/fisiologia , Eletrocardiografia/métodos , Eletroencefalografia/métodos , Potenciais Evocados/fisiologia , Potenciais Somatossensoriais Evocados/fisiologia , Feminino , Coração/fisiologia , Humanos , Masculino , Córtex Somatossensorial/fisiologia
9.
Cell Mol Life Sci ; 77(20): 3945-3961, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32306061

RESUMO

Disorders of consciousness (DoC) are acquired conditions of severe altered consciousness. During the past decades, some prognostic models for DoC have been explored on the basis of a variety of predictors, including demographics, neurological examinations, clinical diagnosis, neurophysiology and brain images. In this article, a systematic review of pertinent literature was conducted. We identified and evaluated 21 prognostic models involving a total of 1201 DoC patients. In terms of the reported accuracies of predicting the prognosis of DoC, these 21 models vary widely, ranging from 60 to 90%. Using improvement of consciousness level as favorable outcome criteria, we performed a quantitative meta-analysis, and found that the pooled sensitivity and specificity of the hybrid model that combined more than one technique were both superior to those of any single technique, including EEG and fMRI at the tasks and resting state. These results support the view that any single technique has its own advantages and limitations; and the integrations of multiple techniques, including diverse brain images and different paradigms, have the potential to improve predictive accuracy for DoC. Then, we provide methodological points of view and some prospects about future research. Totally, in comparison to a great many diagnostic methods for the DoC, the research of prognostic models is sparse and preliminary, still largely in its infancy with many challenges and opportunities.


Assuntos
Transtornos da Consciência/patologia , Estado de Consciência/fisiologia , Humanos , Imagem por Ressonância Magnética/métodos , Prognóstico , Recuperação de Função Fisiológica/fisiologia
10.
Neuron ; 105(5): 776-798, 2020 03 04.
Artigo em Inglês | MEDLINE | ID: mdl-32135090

RESUMO

We review the central tenets and neuroanatomical basis of the global neuronal workspace (GNW) hypothesis, which attempts to account for the main scientific observations regarding the elementary mechanisms of conscious processing in the human brain. The GNW hypothesis proposes that, in the conscious state, a non-linear network ignition associated with recurrent processing amplifies and sustains a neural representation, allowing the corresponding information to be globally accessed by local processors. We examine this hypothesis in light of recent data that contrast brain activity evoked by either conscious or non-conscious contents, as well as during conscious or non-conscious states, particularly general anesthesia. We also discuss the relationship between the intertwined concepts of conscious processing, attention, and working memory.


Assuntos
Atenção/fisiologia , Encéfalo/fisiologia , Cognição/fisiologia , Estado de Consciência/fisiologia , Memória de Curto Prazo/fisiologia , Anestesia Geral , Humanos , Neurônios/fisiologia , Teoria Psicológica
11.
Proc Natl Acad Sci U S A ; 117(13): 7437-7446, 2020 03 31.
Artigo em Inglês | MEDLINE | ID: mdl-32184331

RESUMO

An increasing number of studies highlight common brain regions and processes in mediating conscious sensory experience. While most studies have been performed in the visual modality, it is implicitly assumed that similar processes are involved in other sensory modalities. However, the existence of supramodal neural processes related to conscious perception has not been convincingly shown so far. Here, we aim to directly address this issue by investigating whether neural correlates of conscious perception in one modality can predict conscious perception in a different modality. In two separate experiments, we presented participants with successive blocks of near-threshold tasks involving subjective reports of tactile, visual, or auditory stimuli during the same magnetoencephalography (MEG) acquisition. Using decoding analysis in the poststimulus period between sensory modalities, our first experiment uncovered supramodal spatiotemporal neural activity patterns predicting conscious perception of the feeble stimulation. Strikingly, these supramodal patterns included activity in primary sensory regions not directly relevant to the task (e.g., neural activity in visual cortex predicting conscious perception of auditory near-threshold stimulation). We carefully replicate our results in a control experiment that furthermore show that the relevant patterns are independent of the type of report (i.e., whether conscious perception was reported by pressing or withholding a button press). Using standard paradigms for probing neural correlates of conscious perception, our findings reveal a common signature of conscious access across sensory modalities and illustrate the temporally late and widespread broadcasting of neural representations, even into task-unrelated primary sensory processing regions.


Assuntos
Estado de Consciência/fisiologia , Percepção/fisiologia , Estimulação Acústica/métodos , Adulto , Percepção Auditiva/fisiologia , Encéfalo/fisiologia , Mapeamento Encefálico/métodos , Feminino , Humanos , Magnetoencefalografia/métodos , Masculino , Análise Multivariada , Estimulação Luminosa/métodos , Estimulação Física/métodos , Tato/fisiologia , Percepção do Tato/fisiologia , Percepção Visual/fisiologia
12.
Arch Sex Behav ; 49(4): 1215-1229, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32140872

RESUMO

As we are often inundated with images of violence and pornography in modern times with the aid of mobile devices and unrestricted online access and content, the non-conscious effect of such exposure is an area of concern. To date, many clinicians and researchers in behavioral sciences rely on conscious responses from their clients to determine affective content. In doing so, they overlook the effect the non-conscious has on an individual's emotions. The present study aimed to examine variations in conscious and non-conscious responses to emotion-inducing images following varying amounts of exposure to violent and pornographic images. Eighteen participants who self-reported as being low pornography users were presented with emotion-inducing images after no exposure (Session 1), after one round of exposure to 50 pornographic and 50 violent images (Session 2) and after a further nine rounds of exposure to 50 pornographic and 50 violent images (Session 3). Sessions were temporally separated by at least 2 days while startle reflex modulation (SRM) and scalp-recorded event-related potentials (ERPs) were used to determine non-conscious emotion-related responses to pre-evaluated emotion pictures. Explicit valence and arousal ratings were assessed for each of those emotion pictures to determine conscious emotion effects potentially changing as a function of increasing controlled exposure to pornographic and violent visual material. Conscious explicit ratings and SRM amplitudes revealed no significant difference between the sessions. However, frontal ERP analysis revealed significant changes between processing of "violent" and "unpleasant" images at later ERP time windows, further supporting the growing body of research which shows that relying on self-report data does not result in a full understanding of emotional responses.


Assuntos
Estado de Consciência/fisiologia , Emoções/fisiologia , Literatura Erótica/psicologia , Violência/psicologia , Adolescente , Adulto , Feminino , Humanos , Masculino , Adulto Jovem
13.
Psychopharmacology (Berl) ; 237(5): 1371-1382, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32144438

RESUMO

RATIONALE: Is it possible to have a psychedelic experience from a placebo alone? Most psychedelic studies find few effects in the placebo control group, yet these effects may have been obscured by the study design, setting, or analysis decisions. OBJECTIVE: We examined individual variation in placebo effects in a naturalistic environment resembling a typical psychedelic party. METHODS: Thirty-three students completed a single-arm study ostensibly examining how a psychedelic drug affects creativity. The 4-h study took place in a group setting with music, paintings, coloured lights, and visual projections. Participants consumed a placebo that we described as a drug resembling psilocybin, which is found in psychedelic mushrooms. To boost expectations, confederates subtly acted out the stated effects of the drug and participants were led to believe that there was no placebo control group. The participants later completed the 5-Dimensional Altered States of Consciousness Rating Scale, which measures changes in conscious experience. RESULTS: There was considerable individual variation in the placebo effects; many participants reported no changes while others showed effects with magnitudes typically associated with moderate or high doses of psilocybin. In addition, the majority (61%) of participants verbally reported some effect of the drug. Several stated that they saw the paintings on the walls "move" or "reshape" themselves, others felt "heavy… as if gravity [had] a stronger hold", and one had a "come down" before another "wave" hit her. CONCLUSION: Understanding how context and expectations promote psychedelic-like effects, even without the drug, will help researchers to isolate drug effects and clinicians to maximise their therapeutic potential.


Assuntos
Criatividade , Alucinógenos/administração & dosagem , Música/psicologia , Recreação/psicologia , Meio Social , Adolescente , Adulto , Estado de Consciência/efeitos dos fármacos , Estado de Consciência/fisiologia , Emoções/efeitos dos fármacos , Emoções/fisiologia , Feminino , Humanos , Masculino , Efeito Placebo , Adulto Jovem
14.
Brain Connect ; 10(2): 83-94, 2020 03.
Artigo em Inglês | MEDLINE | ID: mdl-32195610

RESUMO

Recent evidence on resting-state functional magnetic resonance imaging (rs-fMRI) suggests that healthy human brains have a temporal organization represented in a widely complex time-delay structure. This structure seems to underlie brain communication flow, integration/propagation of brain activity, as well as information processing. Therefore, it is probably linked to the emergence of highly coordinated complex brain phenomena, such as consciousness. Nevertheless, possible changes in this structure during an altered state of consciousness remain poorly investigated. In this work, we hypothesized that due to a disruption in high-order functions and alterations of the brain communication flow, patients with disorders of consciousness (DOC) might exhibit changes in their time-delay structure of spontaneous brain activity. We explored this hypothesis by comparing the time-delay projections from fMRI resting-state data acquired in resting state from 48 patients with DOC and 27 healthy controls (HC) subjects. Results suggest that time-delay structure modifies for patients with DOC conditions when compared with HC. Specifically, the average value and the directionality of latency inside the midcingulate cortex (mCC) shift with the level of consciousness. In particular, positive values of latency inside the mCC relate to preserved states of consciousness, whereas negative values change proportionally with the level of consciousness in patients with DOC. These results suggest that the mCC may play a critical role as an integrator of brain activity in HC subjects, but this role vanishes in an altered state of consciousness.


Assuntos
Encéfalo/diagnóstico por imagem , Transtornos da Consciência/diagnóstico por imagem , Estado de Consciência/fisiologia , Imagem por Ressonância Magnética/métodos , Oxigênio/sangue , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Encéfalo/fisiopatologia , Transtornos da Consciência/fisiopatologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Descanso , Índice de Gravidade de Doença , Fatores de Tempo , Adulto Jovem
15.
Behav Neurol ; 2020: 9370891, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32148565

RESUMO

Objective: Propofol is a classical anesthetic and induces consciousness loss, and gamma-aminobutyric-acid-type-A (GABA-A) receptor is its target. Righting reflex is associated with conscious response. The nucleus basalis (NB) acts as a major relay between the reticular activating system and the frontal cortex (FC). Propofol may mediate righting reflex by affecting GABA-A receptor in NB. Methods: Fifty male SD rats (250-350 g) were divided into parts I and II. In part I, 20 male SD rats were randomly divided into control group (CG) and NB-lesion group (NG, ibotenic acid-induced NB lesion). In part II, 30 male SD rats were treated with saline (0.9% NaCl, SG group), muscimol (a GABA-A receptor agonist, MG group), and gabazine (a GABA-A receptor antagonist, GG group) in NB, respectively. Two weeks later, the activity of the rats was measured between CG and NG groups. The rats were intravenously injected with propofol (50 mg/kg/h) to test the time of loss of righting reflex (LORR) in all rats. When LORR occurred, the rats received single administration of propofol (12 mg/kg) to measure the time of return of righting reflex (RORR). Electroencephalogram (EEG) activity of the frontal cortex (FC) was recorded. Results: The numbers of NB neurons were reduced by 44% in the NG group compared to the CG group (p < 0.05) whereas the activity of rats was reduced a little in the NG group when compared with the CG group, but the statistical difference was insignificant (p < 0.05) whereas the activity of rats was reduced a little in the NG group when compared with the CG group, but the statistical difference was insignificant (p < 0.05) whereas the activity of rats was reduced a little in the NG group when compared with the CG group, but the statistical difference was insignificant (p < 0.05) whereas the activity of rats was reduced a little in the NG group when compared with the CG group, but the statistical difference was insignificant (p < 0.05) whereas the activity of rats was reduced a little in the NG group when compared with the CG group, but the statistical difference was insignificant (p < 0.05) whereas the activity of rats was reduced a little in the NG group when compared with the CG group, but the statistical difference was insignificant (. Conclusions: The unilateral NB lesion increased the recovery time and FC delta power, and the NB region might be involved in the emergence after propofol administration. Propofol plays a crucial role for causing conscious loss by affecting GABA-A receptor in NB.


Assuntos
Núcleo Basal de Meynert/efeitos dos fármacos , Propofol/metabolismo , Receptores de GABA-A/efeitos dos fármacos , Animais , Núcleo Basal de Meynert/metabolismo , Estado de Consciência/efeitos dos fármacos , Estado de Consciência/fisiologia , Eletroencefalografia/métodos , Masculino , Muscimol/farmacologia , Propofol/farmacologia , Piridazinas/farmacologia , Ratos , Ratos Sprague-Dawley , Receptores de GABA-A/metabolismo
16.
Sci Adv ; 6(11): eaaz0087, 2020 03.
Artigo em Inglês | MEDLINE | ID: mdl-32195349

RESUMO

The ongoing stream of human consciousness relies on two distinct cortical systems, the default mode network and the dorsal attention network, which alternate their activity in an anticorrelated manner. We examined how the two systems are regulated in the conscious brain and how they are disrupted when consciousness is diminished. We provide evidence for a "temporal circuit" characterized by a set of trajectories along which dynamic brain activity occurs. We demonstrate that the transitions between default mode and dorsal attention networks are embedded in this temporal circuit, in which a balanced reciprocal accessibility of brain states is characteristic of consciousness. Conversely, isolation of the default mode and dorsal attention networks from the temporal circuit is associated with unresponsiveness of diverse etiologies. These findings advance the foundational understanding of the functional role of anticorrelated systems in consciousness.


Assuntos
Encéfalo , Estado de Consciência/fisiologia , Imagem por Ressonância Magnética , Rede Nervosa , Vias Neurais , Adulto , Idoso , Encéfalo/diagnóstico por imagem , Encéfalo/fisiologia , Mapeamento Encefálico , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Rede Nervosa/diagnóstico por imagem , Rede Nervosa/fisiologia , Vias Neurais/diagnóstico por imagem , Vias Neurais/fisiologia
17.
Brain ; 143(3): 833-843, 2020 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-32049333

RESUMO

How the brain recovers from general anaesthesia is poorly understood. Neurocognitive problems during anaesthesia recovery are associated with an increase in morbidity and mortality in patients. We studied intracortical neuronal dynamics during transitions from propofol-induced unconsciousness into consciousness by directly recording local field potentials and single neuron activity in a functionally and anatomically interconnecting somatosensory (S1, S2) and ventral premotor (PMv) network in primates. Macaque monkeys were trained for a behavioural task designed to determine trial-by-trial alertness and neuronal response to tactile and auditory stimulation. We found that neuronal dynamics were dissociated between S1 and higher-order PMv prior to return of consciousness. The return of consciousness was distinguishable by a distinctive return of interregionally coherent beta oscillations and disruption of the slow-delta oscillations. Clustering analysis demonstrated that these state transitions between wakefulness and unconsciousness were rapid and unstable. In contrast, return of pre-anaesthetic task performance was observed with a gradual increase in the coherent beta oscillations. We also found that recovery end points significantly varied intra-individually across sessions, as compared to a rather consistent loss of consciousness time. Recovery of single neuron multisensory responses appeared to be associated with the time of full performance recovery rather than the length of recovery time. Similar to loss of consciousness, return of consciousness was identified with an abrupt shift of dynamics and the regions were dissociated temporarily during the transition. However, the actual dynamics change during return of consciousness is not simply an inverse of loss of consciousness, suggesting a unique process.


Assuntos
Ondas Encefálicas/fisiologia , Estado de Consciência/fisiologia , Córtex Motor/fisiologia , Propofol/farmacologia , Córtex Somatossensorial/fisiologia , Inconsciência/fisiopatologia , Estimulação Acústica , Potenciais de Ação/fisiologia , Período de Recuperação da Anestesia , Animais , Nível de Alerta/fisiologia , Percepção Auditiva/fisiologia , Eletroencefalografia , Macaca , Masculino , Vias Neurais/fisiologia , Primatas , Percepção do Tato/fisiologia , Inconsciência/induzido quimicamente
18.
Anesthesiology ; 132(4): 750-762, 2020 04.
Artigo em Inglês | MEDLINE | ID: mdl-32053559

RESUMO

BACKGROUND: Ketamine is a noncompetitive N-methyl-D-aspartate antagonist and is known for unique electrophysiologic profiles in electroencephalography. However, the mechanisms of ketamine-induced unconsciousness are not clearly understood. The authors have investigated neuronal dynamics of ketamine-induced loss and return of consciousness and how multisensory processing is modified in the primate neocortex. METHODS: The authors performed intracortical recordings of local field potentials and single unit activity during ketamine-induced altered states of consciousness in a somatosensory and ventral premotor network. The animals were trained to perform a button holding task to indicate alertness. Air puff to face or sound was randomly delivered in each trial regardless of their behavioral response. Ketamine was infused for 60 min. RESULTS: Ketamine-induced loss of consciousness was identified during a gradual evolution of the high beta-gamma oscillations. The slow oscillations appeared to develop at a later stage of ketamine anesthesia. Return of consciousness and return of preanesthetic performance level (performance return) were observed during a gradual drift of the gamma oscillations toward the beta frequency. Ketamine-induced loss of consciousness, return of consciousness, and performance return are all identified during a gradual change of the dynamics, distinctive from the abrupt neural changes at propofol-induced loss of consciousness and return of consciousness. Multisensory responses indicate that puff evoked potentials and single-unit firing responses to puff were both preserved during ketamine anesthesia, but sound responses were selectively diminished. Units with suppressed responses and those with bimodal responses appeared to be inhibited under ketamine and delayed in recovery. CONCLUSIONS: Ketamine generates unique intracortical dynamics during its altered states of consciousness, suggesting fundamentally different neuronal processes from propofol. The gradually shifting dynamics suggest a continuously conscious or dreaming state while unresponsive under ketamine until its deeper stage with the slow-delta oscillations. Somatosensory processing is preserved during ketamine anesthesia, but multisensory processing appears to be diminished under ketamine and through recovery.


Assuntos
Anestésicos Dissociativos/administração & dosagem , Estado de Consciência/efeitos dos fármacos , Antagonistas de Aminoácidos Excitatórios/administração & dosagem , Ketamina/administração & dosagem , Neocórtex/efeitos dos fármacos , Inconsciência/induzido quimicamente , Animais , Estado de Consciência/fisiologia , Eletroencefalografia/efeitos dos fármacos , Eletroencefalografia/métodos , Infusões Intravenosas , Macaca mulatta , Masculino , Neocórtex/fisiologia , Inconsciência/fisiopatologia
19.
Anesthesiology ; 132(5): 1017-1033, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32032094

RESUMO

BACKGROUND: Investigations of the electrophysiology of gaseous anesthetics xenon and nitrous oxide are limited revealing inconsistent frequency-dependent alterations in spectral power and functional connectivity. Here, the authors describe the effects of sedative, equivalent, stepwise levels of xenon and nitrous oxide administration on oscillatory source power using a crossover design to investigate shared and disparate mechanisms of gaseous xenon and nitrous oxide anesthesia. METHODS: Twenty-one healthy males underwent simultaneous magnetoencephalography and electroencephalography recordings. In separate sessions, sedative, equivalent subanesthetic doses of gaseous anesthetic agents nitrous oxide and xenon (0.25, 0.50, and 0.75 equivalent minimum alveolar concentration-awake [MACawake]) and 1.30 MACawake xenon (for loss of responsiveness) were administered. Source power in various frequency bands were computed and statistically assessed relative to a conscious/pre-gas baseline. RESULTS: Observed changes in spectral-band power (P < 0.005) were found to depend not only on the gas delivered, but also on the recording modality. While xenon was found to increase low-frequency band power only at loss of responsiveness in both source-reconstructed magnetoencephalographic (delta, 208.3%, 95% CI [135.7, 281.0%]; theta, 107.4%, 95% CI [63.5, 151.4%]) and electroencephalographic recordings (delta, 260.3%, 95% CI [225.7, 294.9%]; theta, 116.3%, 95% CI [72.6, 160.0%]), nitrous oxide only produced significant magnetoencephalographic high-frequency band increases (low gamma, 46.3%, 95% CI [34.6, 57.9%]; high gamma, 45.7%, 95% CI [34.5, 56.8%]). Nitrous oxide-not xenon-produced consistent topologic (frontal) magnetoencephalographic reductions in alpha power at 0.75 MACawake doses (44.4%; 95% CI [-50.1, -38.6%]), whereas electroencephalographically nitrous oxide produced maximal reductions in alpha power at submaximal levels (0.50 MACawake, -44.0%; 95% CI [-48.1,-40.0%]). CONCLUSIONS: Electromagnetic source-level imaging revealed widespread power changes in xenon and nitrous oxide anesthesia, but failed to reveal clear universal features of action for these two gaseous anesthetics. Magnetoencephalographic and electroencephalographic power changes showed notable differences which will need to be taken into account to ensure the accurate monitoring of brain state during anaesthesia.


Assuntos
Anestésicos Inalatórios/administração & dosagem , Córtex Cerebral/efeitos dos fármacos , Córtex Cerebral/diagnóstico por imagem , Estado de Consciência/efeitos dos fármacos , Óxido Nitroso/administração & dosagem , Xenônio/administração & dosagem , Adulto , Córtex Cerebral/fisiologia , Estado de Consciência/fisiologia , Estudos Cross-Over , Eletroencefalografia/efeitos dos fármacos , Eletroencefalografia/métodos , Voluntários Saudáveis , Humanos , Imagem por Ressonância Magnética/métodos , Magnetoencefalografia/efeitos dos fármacos , Magnetoencefalografia/métodos , Masculino , Método Simples-Cego , Adulto Jovem
20.
PLoS One ; 15(2): e0223812, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32053587

RESUMO

Recent evidence suggests that the quantity and quality of conscious experience may be a function of the complexity of activity in the brain and that consciousness emerges in a critical zone between low and high-entropy states. We propose fractal shapes as a measure of proximity to this critical point, as fractal dimension encodes information about complexity beyond simple entropy or randomness, and fractal structures are known to emerge in systems nearing a critical point. To validate this, we tested several measures of fractal dimension on the brain activity from healthy volunteers and patients with disorders of consciousness of varying severity. We used a Compact Box Burning algorithm to compute the fractal dimension of cortical functional connectivity networks as well as computing the fractal dimension of the associated adjacency matrices using a 2D box-counting algorithm. To test whether brain activity is fractal in time as well as space, we used the Higuchi temporal fractal dimension on BOLD time-series. We found significant decreases in the fractal dimension between healthy volunteers (n = 15), patients in a minimally conscious state (n = 10), and patients in a vegetative state (n = 8), regardless of the mechanism of injury. We also found significant decreases in adjacency matrix fractal dimension and Higuchi temporal fractal dimension, which correlated with decreasing level of consciousness. These results suggest that cortical functional connectivity networks display fractal character and that this is associated with level of consciousness in a clinically relevant population, with higher fractal dimensions (i.e. more complex) networks being associated with higher levels of consciousness. This supports the hypothesis that level of consciousness and system complexity are positively associated, and is consistent with previous EEG, MEG, and fMRI studies.


Assuntos
Lesões Encefálicas/fisiopatologia , Encéfalo/fisiopatologia , Modelos Neurológicos , Rede Nervosa/fisiopatologia , Estado Vegetativo Persistente/fisiopatologia , Adulto , Algoritmos , Encéfalo/diagnóstico por imagem , Lesões Encefálicas/diagnóstico , Estado de Consciência/fisiologia , Feminino , Fractais , Voluntários Saudáveis , Humanos , Imagem por Ressonância Magnética , Estado Vegetativo Persistente/diagnóstico , Índice de Gravidade de Doença
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