| 1. |
- Kantonen, Oskari, et al.
(författare)
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Decreased Thalamic Activity Is a Correlate for Disconnectedness during Anesthesia with Propofol, Dexmedetomidine and Sevoflurane But Not S-Ketamine
- 2023
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Ingår i: Journal of Neuroscience. - : Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 43:26, s. 4884-4895
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Tidskriftsartikel (refereegranskat)abstract
- Establishing the neural mechanisms responsible for the altered global states of consciousness during anesthesia and dissociating these from other drug-related effects remains a challenge in consciousness research. We investigated differences in brain activity between connectedness and disconnectedness by administering various anesthetics at concentrations designed to render 50% of the subjects unresponsive. One hundred and sixty healthy male subjects were randomized to receive either propofol (1.7 μg/ml; n = 40), dexmedetomidine (1.5 ng/ml; n = 40), sevoflurane (0.9% end-tidal; n = 40), S-ketamine (0.75 μg/ml; n = 20), or saline placebo (n = 20) for 60 min using target-controlled infusions or vaporizer with end-tidal monitoring. Disconnectedness was defined as unresponsiveness to verbal commands probed at 2.5-min intervals and unawareness of external events in a postanesthesia interview. High-resolution positron emission tomography (PET) was used to quantify regional cerebral metabolic rates of glucose (CMRglu) utilization. Contrasting scans where the subjects were classified as connected and responsive versus disconnected and unresponsive revealed that for all anesthetics, except S-ketamine, the level of thalamic activity differed between these states. A conjunction analysis across the propofol, dexmedetomidine and sevoflurane groups confirmed the thalamus as the primary structure where reduced metabolic activity was related to disconnectedness. Widespread cortical metabolic suppression was observed when these subjects, classified as either connected or disconnected, were compared with the placebo group, suggesting that these findings may represent necessary but alone insufficient mechanisms for the change in the state of consciousness.
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| 2. |
- Koivisto, Mika, et al.
(författare)
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Recurrent Processing in V1/V2 Contributes ot Categorization of Natural Scenes
- 2011
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Ingår i: Journal of Neuroscience. - : Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 31:7, s. 2488-2492
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Tidskriftsartikel (refereegranskat)abstract
- Humans are able to categorize complex natural scenes very rapidly and effortlessly, which has led to an assumption that such ultra-rapid categorization is driven by feedforward activation of ventral brain areas. However, recent accounts of visual perception stress the role of recurrent interactions that start rapidly after the activation of V1. To study whether or not recurrent processes play a causal role in categorization, we applied fMRI-guided transcranial magnetic stimulation on early visual cortex (V1/V2) and lateral occipital cortex (LO) while the participants categorized natural images as containing animals or not. The results showed that V1/V2 contributed to categorization speed and to subjective perception during a long activity period before and after the contribution of LO had started. This pattern of results suggests that recurrent interactions in visual cortex between areas along the ventral stream and striate cortex play a causal role in categorization and perception of natural scenes.
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| 3. |
- Långsjö, Jaakko W., et al.
(författare)
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Returning from Oblivion : Imaging the Neural Core of Consciousness
- 2012
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Ingår i: Journal of Neuroscience. - : Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 32:14, s. 4935-4943
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Tidskriftsartikel (refereegranskat)abstract
- One of the greatest challenges of modern neuroscience is to discover the neural mechanisms of consciousness and to explain how they produce the conscious state. We sought the underlying neural substrate of human consciousness by manipulating the level of consciousness in volunteers with anesthetic agents and visualizing the resultant changes in brain activity using regional cerebral blood flow imaging with positron emission tomography. Study design and methodology were chosen to dissociate the state-related changes in consciousness from the effects of the anesthetic drugs. We found the emergence of consciousness, as assessed with a motor response to a spoken command, to be associated with the activation of a core network involving subcortical and limbic regions that become functionally coupled with parts of frontal and inferior parietal cortices upon awakening from unconsciousness. The neural core of consciousness thus involves forebrain arousal acting to link motor intentions originating in posterior sensory integration regions with motor action control arising in more anterior brain regions. These findings reveal the clearest picture yet of the minimal neural correlates required for a conscious state to emerge.
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| 4. |
- Perini, Irene, et al.
(författare)
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Where Pain Meets Action in the Human Brain
- 2013
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Ingår i: Journal of Neuroscience. - : Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 33:40, s. 15930-15939
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Tidskriftsartikel (refereegranskat)abstract
- Pain's complex influence on behavior implies that it involves an action component, although little is known about how the human brain adaptively translates painful sensations into actions. The consistent activation of premotor and motor-related regions during pain, including the midcingulate cortex (MCC), raises the question of whether these areas contribute to an action component. In this fMRI experiment, we controlled for voluntary action-related processing during pain by introducing a motor task during painful or nonpainful stimulation. The MCC (particularly the caudal cingulate motor zone [CCZ]), motor cortex, thalamus, and cerebellum responded during action regardless of pain. Crucially, however, these regions did not respond to pain unless an action was performed. Reaction times were fastest during painful stimulation and correlated with CCZ activation. These findings are consistent with the results of an activation likelihood estimate meta-analysis in which activation across experiments involving pain, action execution, or action preparation (with a total of 4929 subjects) converged in a similar network. These findings suggest that specific motor-related areas, including the CCZ, play a vital role in the control and execution of context-sensitive behavioral responses to pain. In contrast, bilateral insular cortex responded to pain stimulation regardless of action.
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| 5. |
- Scheinin, Annalotta, et al.
(författare)
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Foundations of human consciousness : Imaging the twilight zone
- 2021
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Ingår i: Journal of Neuroscience. - : The Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 41:8, s. 1769-1778
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Tidskriftsartikel (refereegranskat)abstract
- What happens in the brain when conscious awareness of the surrounding world fades? We manipulated consciousness in two experiments in a group of healthy males and measured brain activity with positron emission tomography. Measurements were made during wakefulness, escalating and constant levels of two anesthetic agents (Experiment 1, n=39) and during sleep-deprived wakefulness and Non-Rapid Eye Movement sleep (Experiment 2, n=37). In Experiment 1, the subjects were randomized to receive either propofol or dexmedetomidine until unresponsiveness. In both experiments, forced awakenings were applied to achieve rapid recovery from an unresponsive to a responsive state, followed by immediate and detailed interviews of subjective experiences during the preceding unresponsive condition. Unresponsiveness rarely denoted unconsciousness, as the majority of the subjects had internally generated experiences. Unresponsive anesthetic states and verified sleep stages, where a subsequent report of mental content included no signs of awareness of the surrounding world, indicated a disconnected state. Functional brain imaging comparing responsive and connected vs. unresponsive and disconnected states of consciousness during constant anesthetic exposure revealed that activity of the thalamus, cingulate cortices and angular gyri are fundamental for human consciousness. These brain structures were affected independent from the pharmacologic agent, drug concentration and direction of change in the state of consciousness. Analogous findings were obtained when consciousness was regulated by physiological sleep. State-specific findings were distinct and separable from the overall effects of the interventions, which included widespread depression of brain activity across cortical areas. These findings identify a central core brain network critical for human consciousness. SIGNIFICANCE STATEMENT Trying to understand the biological basis of human consciousness is currently one of the greatest challenges of neuroscience. While the loss and return of consciousness regulated by anesthetic drugs and physiological sleep are employed as model systems in experimental studies on consciousness, previous research results have been confounded by drug effects, by confusing behavioral "unresponsiveness" and internally generated consciousness, and by comparing brain activity levels across states that differ in several other respects than only consciousness. Here, we present carefully designed studies that overcome many previous confounders and for the first time reveal the neural mechanisms underlying human consciousness and its disconnection from behavioral responsiveness, both during anesthesia and during normal sleep, and in the same study subjects.
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| 6. |
- Sikka, Pilleriin, et al.
(författare)
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EEG Frontal Alpha Asymmetry and Dream Affect : Alpha Oscillations Over the Right Frontal Cortex During REM Sleep and Pre-Sleep Wakefulness Predict Anger in REM Sleep Dreams
- 2019
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Ingår i: Journal of Neuroscience. - : Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 39:24, s. 4775-4784
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Tidskriftsartikel (refereegranskat)abstract
- Affective experiences are central not only to our waking life but also to rapid eye movement(REM) sleep dreams. Despite our increasing understanding of the neural correlates of dreaming, we know little about the neural correlates of dream affect. Frontal alpha asymmetry (FAA) is considered a marker of affective states and traits as well as affect regulation in the waking state. Here, we explored whether FAA during REM sleep and during evening resting wakefulness is related to affective experiences in REM sleep dreams. EEG recordings were obtained from 17humanparticipants (7men)whospent 2 nights in the sleep laboratory. Participants were awakened 5minafter the onset of everyREMstage after which they provided a dream report and rated their dream affect. Two-minute preawakening EEG segments were analyzed. Additionally, 8 min of evening presleep and morning postsleep EEG were recorded during resting wakefulness. Mean spectral power in the alpha band (8 –13 Hz and correspondingFAAwere calculated over the frontal (F4-F3) sites. Results showed that FAA during REM sleep, and during evening resting wakefulness, predicted ratings of dream anger. This suggests that individuals with greater alpha power in the right frontal hemisphere may be less able to regulate (i.e., inhibit) strong affective states, such as anger, in dreams. Additionally, FAA was positively correlated across wakefulness and REM sleep. Together, these findings imply that FAA may serve as a neural correlate of affect regulation not only in the waking but also in the dreaming state.
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