1.
Kantonen, Oskari, et al.
(författare)
Decreased Thalamic Activity Is a Correlate for Disconnectedness during Anesthesia with Propofol, Dexmedetomidine and Sevoflurane But Not S-Ketamine
2023
Ingår i: Journal of Neuroscience. - : Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 43:26, s. 4884-4895
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.
2.
Filimonov, Dmitri, et al.
(författare)
Is auditory awareness graded or dichotomous : Electrophysiological correlates of consciousness at different depths of stimulus processing
2024
Ingår i: Consciousness and Cognition. - : Elsevier. - 1053-8100 .- 1090-2376. ; 123
Tidskriftsartikel (refereegranskat) abstract
The level-of-processing (LoP) hypothesis postulates that transition from unaware to aware visualstimuli is either graded or dichotomous depending on the depth of stimulus processing. Humanscan be progressively aware of the low-level features, such as colors or shapes, while the high-levelfeatures, such as semantic category, enter consciousness in an all-or none fashion. Unlike invision, sounds always unfold in time, which might require mechanisms dissimilar from visualprocessing. We tested the LoP hypothesis in hearing for the first time by presenting participantswith words of different categories, spoken in different pitches near the perceptual threshold. Wealso assessed whether different electrophysiological correlates of consciousness, the auditoryawareness negativity (AAN) and late positivity (LP), were associated with LoP. Our findingsindicate that LoP also applies to the auditory modality. AAN is an early correlate of awarenessindependent of LoP, while LP was modulated by awareness, performance accuracy and the levelof processing.
3.
Filimonov, Dmitri, et al.
(författare)
Modality-specific and modality-general electrophysiological correlates of visual and auditory awareness : Evidence from a bimodal ERP experiment
2022
Ingår i: Neuropsychologia. - : Elsevier. - 0028-3932 .- 1873-3514. ; 166
Tidskriftsartikel (refereegranskat) abstract
To date, most studies on the event-related potential (ERP) correlates of conscious perception have examined a single perceptual modality. We compared electrophysiological correlates of visual and auditory awareness in the same experiment to test whether there are modality-specific and modality-general correlates of conscious perception. We used near threshold stimulation and analyzed event-related potentials in response to aware and unaware trials in visual, auditory and bimodal conditions. The results showed modality-specific negative amplitude correlates of conscious perception between 200 and 300 ms after stimulus onset. A combination of these auditory and visual awareness negativities was observed in the bimodal condition. A later positive amplitude difference, whose early part was modality-specific, possibly reflecting access to global workspace, and later part shared modality-general features, possibly indicating higher level cognitive processing involving the decision making, was also observed.
4.
Filimonov, Dmitri, et al.
(författare)
The influence of feature-based attention and response requirements on ERP correlates of auditory awareness
2024
Ingår i: Neuroscience of Consciousness. - : Oxford University Press. - 2057-2107. ; 2024:1
Tidskriftsartikel (refereegranskat) abstract
In search for the neural correlates of consciousness (NCCs), it is important to isolate the true NCCs from their prerequisites, consequences, and co-occurring processes. To date, little is known about how attention affects the event-related potential (ERP) correlates of auditory awareness and there is contradictory evidence on whether one of them, the late positivity (LP), is affected by response requirements. By implementing a GO-NOGO design with target and nontarget stimuli, we controlled for feature-based attention and response requirements in the same experiment, while participants rated their awareness using a perceptual awareness scale. The results showed a prolonged auditory awareness negativity (AAN) for aware trials, which was influenced neither by attention nor by response requirement. The LP was affected by both attention and response requirements. Consistent with the levels of processing hypothesis, the LP was related to consciousness as a correlate of the processing of higher-level stimulus features, likely requiring access to a "global workspace." Our findings further suggest that AAN is a proper ERP correlate of auditory consciousness and thus a true NCC in the auditory modality.
5.
Förster, Jona, et al.
(författare)
ERP and MEG correlates of visual consciousness : The second decade
2020
Ingår i: Consciousness and Cognition. - : Elsevier. - 1053-8100 .- 1090-2376. ; 80
Tidskriftsartikel (refereegranskat) abstract
The first decade of event-related potential (ERP) research had established that the most consistent correlates of the onset of visual consciousness are the early visual awareness negativity (VAN), a posterior negative component in the N2 time range, and the late positivity (LP), an anterior positive component in the P3 time range. Two earlier extensive reviews ten years ago had concluded that VAN is the earliest and most reliable correlate of visual phenomenal consciousness, whereas LP probably reflects later processes associated with reflective/access consciousness. This article provides an update to those earlier reviews. ERP and MEG studies that have appeared since 2010 and directly compared ERPs between aware and unaware conditions are reviewed, and important new developments in the field are discussed. The result corroborates VAN as the earliest and most consistent signature of visual phenomenal consciousness, and casts further doubt on LP as an ERP correlate of phenomenal consciousness.
6.
Grassini, Simone, et al.
(författare)
Pattern matters : Snakes exhibiting triangular and diamond-shaped skin patterns modulate electrophysiological activity in human visual cortex
2019
Ingår i: Neuropsychologia. - : Elsevier. - 0028-3932 .- 1873-3514. ; 131, s. 62-72
Tidskriftsartikel (refereegranskat) abstract
The neural and perceptual mechanisms that support the efficient visual detection of snakes in humans are still not fully understood. According to the Snake Detection Theory, selection pressures posed by snakes on early primates have shaped the development of the visual system. Previous studies in humans have investigated early visual electrophysiological activity in response to snake images vs. various alternative dangerous or non-dangerous stimuli. These studies have shown that the Early Posterior Negativity (EPN) component is selectively elicited by snake or snake-like images. Recent findings yielded the complementary/alternative hypothesis that early humans (and possibly other primates) evolved an aversion especially for potentially harmful triangular shapes, such as teeth, claws or spikes. In the present study we investigated the effect of triangular and diamond-shaped patterns in snake skins on the ERP correlates of visual processing in humans. In the first experiment, we employed pictures of snakes displaying either triangular/diamond-shaped patterns or no particular pattern on their skins, and pictures of frogs as control. Participants observed a random visual presentation of these pictures. Consistent with previous studies, snakes elicited an enhanced negativity between 225 and 300 ms (EPN) compared to frogs. However, snakes featuring triangular/diamond-shaped patterns on their skin produced an enhanced EPN compared to the snakes that did not display such patterns. In a second experiment we used pictures displaying only skin patterns of snakes and frogs. Results from the second experiment confirmed the results of the first experiment, suggesting that triangular snake-skin patterns modulate the activity in human visual cortex. Taken together, our results constitute an important contribution to the snake detection theory.
7.
Grassini, Simone, et al.
(författare)
Processing of natural scenery is associated with lower attentional and cognitive load compared with urban ones
2019
Ingår i: Journal of Environmental Psychology. - : Academic Press. - 0272-4944 .- 1522-9610. ; 62, s. 1-11
Tidskriftsartikel (refereegranskat) abstract
Environmental psychology has provided evidence for psychologically favorable effects of exposure to natural settings, by means of controlled laboratory experiments as well as outdoor field studies. Most of these studies have employed subjective rating scales to assess processes and outcomes of exposure to nature, while only few of them have used physiological measures to assess the neural correlates of these benefits. The present study used electroencephalography (EEG) to explore how the brain engages in processing of images of natural vs. urban scenery. During EEG recording, the participants (n = 32) were presented with a series of photos depicting urban or natural scenery. Participants rated the sceneries for their subjective relaxing value. Images of natural scenery were rated as more relaxing compared to the images of urban scenery. Event related potentials suggested a lower attentional demand for images of natural scenery compared to urban ones. Signal spectral analyses revealed differences in brain activity level and cognitive demand between natural and urban scenery. Our data suggest that the visual perception of natural environments calls for less attentional and cognitive processing, compared with urban ones. © 2019 Elsevier Ltd
8.
Grassini, Simone, et al.
(författare)
Subjective ratings of fear are associated with frontal late positive potential asymmetry, but not with early brain activity over the occipital and centro-parietal cortices
2020
Ingår i: Psychophysiology. - : John Wiley & Sons. - 0048-5772 .- 1469-8986. ; 57:12
Tidskriftsartikel (refereegranskat) abstract
The human frontal cortex is asymmetrically involved in motivational and affective processing. Several studies have shown that the left-frontal hemisphere is related to positive and approach-related affect, whereas the right-frontal hemisphere is related to negative and withdrawal-related affect. The present study aimed to investigate whether evolutionarily threatening stimuli modulate asymmetrical frontal activity. We examined hemispheric differences in frontal late positive potentials (f-LPP asymmetry) and frontal alpha power activation (frontal alpha asymmetry, FAA) in response to images depicting snakes, spiders, butterflies, and birds. Results showed that the late component of f-LPP asymmetry, but not FAA, was modulated by the category of stimuli. Specifically, threatening stimuli (snakes and spiders) evoked a relatively large late f-LPP over the right-frontal hemisphere than non-threatening stimuli (birds and butterflies). Moreover, this relatively great right-frontal activity was positively associated with the subjective ratings of fear. Importantly, the subjective ratings of fear were not associated with early brain activity over the occipital or centro-parietal cortices. These results suggest that late f-LPP asymmetry may reflect higher order affective processes, specifically the subjective appraisal of threatening stimuli and the subjective experience of fear, that are independent of the fast and automatic processing of evolutionarily significant and affectively arousing stimuli.
9.
Hurme, Mikko, et al.
(författare)
Early processing in primary visual cortex is necessary for conscious and unconscious vision while late processing is necessary only for conscious vision in neurologically healthy humans
2017
Ingår i: NeuroImage. - : Elsevier. - 1053-8119 .- 1095-9572. ; 150, s. 230-238
Tidskriftsartikel (refereegranskat) abstract
The neural mechanisms underlying conscious and unconscious visual processes remain controversial. Blindsight patients may process visual stimuli unconsciously despite their VI lesion, promoting anatomical models, which suggest that pathways bypassing the VI support unconscious vision. On the other hand, physiological models argue that the major geniculostriate pathway via VI is involved in both unconscious and conscious vision, but in different time windows and in different types of neural activity. According to physiological models, feedforward activity via VI to higher areas mediates unconscious processes whereas feedback loops of recurrent activity from higher areas back to VI support conscious vision. With transcranial magnetic stimulation (TMS) it is possible to study the causal role of a brain region during specific time points in neurologically healthy participants. In the present study, we measured unconscious processing with redundant target effect, a phenomenon where participants respond faster to two stimuli than one even when one of the stimuli is not consciously perceived. We tested the physiological feedforward-feedback model of vision by suppressing conscious vision by interfering selectively either with early or later VI activity with TMS. Our results show that early VI activity (60 ms) is necessary for both unconscious and conscious vision. During later processing stages (90 ms), VI contributes selectively to conscious vision. These findings support the feedforward-feedback-model of consciousness.
10.
Hurme, Mikko, et al.
(författare)
V1 activity during feedforward and early feedback processing is necessary for both conscious and unconscious motion perception
2019
Ingår i: NeuroImage. - : Elsevier. - 1053-8119 .- 1095-9572. ; 185, s. 313-321
Tidskriftsartikel (refereegranskat) abstract
The study of blindsight has revealed a seminal dissociation between conscious vision and visually guided behavior: some patients who are blind due to V1 lesions seem to be able to employ unconscious visual information in their behavior. The standard assumption is that these findings generalize to the neurologically healthy. We tested whether unconscious processing of motion is possible without the contribution of V1 in neurologically healthy participants by disturbing activity in V1 using transcranial magnetic stimulation (TMS). Unconscious processing was measured with redundant target effect (RTE), a phenomenon where participants respond faster to two stimuli than to one stimulus, when the task is just to respond as fast as possible when one stimulus or two simultaneous stimuli are presented. We measured the RTE caused by a motion stimulus. V1 activity was interfered with different stimulus onset asynchronies (SOA) to test whether TMS delivered in a specific time window suppresses conscious perception (participant reports seeing only one of the two stimuli) but does not affect unconscious processing (RTE). We observed that at each SOA, when TMS suppressed conscious perception of the stimulus, the RTE was also eliminated. However, when visibility of the redundant target was suppressed with a visual mask, we found unconscious processing of motion. This suggests that unconscious processing of motion depends on V1 in neurologically healthy humans. We conclude that the neural mechanisms that enable motion processing in blindsight are modulated by neuroplastic changes in connectivity between subcortical areas and the visual cortex after the V1 lesion. Neurologically healthy observers cannot process motion unconsciously without functioning of V1.
