Markers Of Consciousness Research Articles

Encapsulation and subjectivity from the standpoint of viewpoint theory.

The groundbreaking, viewpoint theory of Merker et al. explains several properties of the conscious field, including why the observer cannot directly apprehend itself. We propose that viewpoint theory might also provide a progressive, constitutive marker of consciousness and shed light on why most of the contents of consciousness are encapsulated.

Isoflurane effects on the N1 and other long-latency auditory evoked potentials in Wistar rats

Long-latency auditory evoked potentials (LLAEPs) may help further advances in understanding consciousness under general anesthesia and promote more objective means of assessing sedation depth than conventional clinical signs. Among the LLAEP components, the auditory N1 shows promise as a measure of sedation depth and a marker of consciousness, but findings are so far inconclusive. Research with animals can help elucidate the effects of various anesthetics on the N1 and other LLAEPs, but investigations of LLAEPs under anesthesia in animals is lacking. To address this deficit, we examined the P1, N1, P2, and N2, along with their corresponding peak-to-peak complexes, in 10 Wistar rats anesthetized with 1.5–2 % isoflurane in pure oxygen and again after recovery. While under anesthesia, subdermal needle electrodes were inserted and secured for electroencephalographic (EEG) recordings. LLAEPs were assessed during a 20-min, passive, two-tone (500 ms inter-tone interval) paradigm with randomized short (1 s) and long (5 s) inter-pair intervals (IPIs). Overall, while the LLAEP peaks under isoflurane were less defined, they were not eliminated. The peak-to-peak amplitudes, particularly the P1-N1, were significantly smaller under isoflurane than during post-recovery. Our preliminary findings indicate that isoflurane produces global suppression across LLAEP components, presumably reflecting impaired integration of top-down and bottom-up attention and sensory systems under profound sedation with isoflurane.

The neuroethics of agency: the problem of attributing mental states to people with disorders of consciousness

How can we be certain that another creature is a conscious being? One path is to rely on introspective reports we can grasp in communication or observation of their behavior. Another path is to infer mentality and consciousness by means of markers tied to their intentional behavior, that is, agency. In this paper we will argue that even if agency is a marker of consciousness in several normal instances (paradigmatically, for mature and healthy human beings), it is not a good marker in several pathological instances, such as the blindsight case, the vegetative state, the akinetic mutism and the locked-in syndrome. If we are right, this can be of great utility in neuroethics; for those kinds of disorders of consciousness are not, after all, instances of complete absence of consciousness.

Blinded by magic: Electrophysiological correlates of change blindness

Magicians can often hide their method for a trick in plain sight by effecting a phenomenon known as change blindness. The purpose of this study was to find the reason for why an individual is induced with change blindness. Alpha oscillations are known to impair detection of visual stimuli, but it is unclear if this is due to increased guess rate or decreased fidelity of the mental representation. Here we estimated fidelity and guess rate as a function of pre-stimulus alpha oscillations using a change blindness task. In this study, each trial began with an array of 6 Gabor patches with a fixated dot that subjects were instructed to keep their eyes on. As the array traveled to the center of the screen, it either changed direction vertically at 90 degrees or continued horizontally. When the array switched direction, one of the Gabor patches rotated 30 degrees simultaneously. Subjects were then asked to identify which patch rotated. EEG (electroencephalography) data was simultaneously recorded with eye-tracking as subjects performed the task. Twenty-eight participants performed this task, which included six blocks of forty-eight trials. There were two different types of trials: flexion, in which the array changed direction, and control, in which the array did not change direction. Reaction time tended to be slower in flexion trials, and we found that the change in direction affected the subject’s ability to see the Gabor patch rotation. Based on the event-related potential results, which are an average of EEG signals aligned to the start of a trial, we could see that the P300 differed between correct flexion, incorrect flexion, and control trials. The P300 can be interpreted as a marker of consciousness. This difference demonstrates that the subject’s attention is automatically drawn to a larger change in stimuli.

Weak experiences sufficient for creating illusory figures that influence perception of actual lines.

The question of whether conscious experience is best viewed as graded or dichotomous has received much scientific attention in recent years as the answer is relevant not only to models of consciousness, but also to the examination of neural markers of consciousness in patients and infants. Although some studies have found evidence of graded perception, it is unclear whether such perception is simply composed of individual stimulus features perceived in an all-or-none manner. Here, we examined whether the Kanizsa triangle (an illusory figure that is supposedly only perceived when all its parts are visible) has an impact on line length discrimination across four degrees of subjective visibility. We found that the presence of the Kanizsa triangle biases line length judgments (a phenomenon called the Ponzo illusion) when participants reported any experience (even a weak glimpse) of the stimulus. The results support the view that consciousness is a graded phenomenon. The strength of this support depends on the assumption that all parts of the illusory figure must be perceived for the illusion to work but this assumption is not resolved in the present literature. Currently, evidence can be found both for and against this notion.

LP29: Considering transcallosal coherence as a marker of consciousness

Results: The statistics did not reveal notable differences between MCSand UWS-patients. The comparison of DOC-patients and healthy subjects revealed statistical trends (p<0.05, uncorrected) in about 53.66% of the computed tests. We found an interesting pattern of common differences between DOC-patients and healthy subjects in a frequency of 6Hz. Conclusions: Transcallosal coherence of MCS- and UWS-patients seems not to differ systematically. Due to the differences of DOC-patients and healthy subjects, one might conclude that the impairment of DOC-patients is based on a common mechanism to a certain extent. The earlier mentioned interesting pattern of common differences might reflect a damage to frontal midline theta coherence which in turn might reflect an impairment of the working memory [3].

State of consciousness and ERP (event-related potential) measures. Diagnostic and prognostic value of electrophysiology for disorders of consciousness

Disorders of consciousness were amply studied in the recent years. At this regards new methodologies and technologies were applied to explore the diagnostic and prognostic criteria that may be applied to the patients. Specifically electrophysiological measures were used to verify the degree of awareness and responsiveness in coma, vegetative states (VS), minimal consciousness state (MC), and locked-in syndrome (LI). Recently, ERPs (event-related potentials) were adopted to integrate the classical neuroimaging measures. Between the others, MMN (mismatch negativity) and P300 deflections were found to represent a consistent index of the present state of consciousness and to be predictive of successive modifications of this state. Also frequency-based EEG measures, such as brain oscillations, were revealed to be relevant marker of consciousness and awareness, able to predict the future evolution of pathology.

Deactivation of the Default Mode Network as a Marker of Impaired Consciousness: An fMRI Study

Diagnosis of patients with a disorder of consciousness is very challenging. Previous studies investigating resting state networks demonstrate that 2 main features of the so-called default mode network (DMN), metabolism and functional connectivity, are impaired in patients with a disorder of consciousness. However, task-induced deactivation – a third main feature of the DMN – has not been explored in a group of patients. Deactivation of the DMN is supposed to reflect interruptions of introspective processes. Seventeen patients with unresponsive wakefulness syndrome (UWS, former vegetative state), 8 patients in minimally conscious state (MCS), and 25 healthy controls were investigated with functional magnetic resonance imaging during a passive sentence listening task. Results show that deactivation in medial regions is reduced in MCS and absent in UWS patients compared to healthy controls. Moreover, behavioral scores assessing the level of consciousness correlate with deactivation in patients. On single-subject level, all control subjects but only 2 patients in MCS and 6 with UWS exposed deactivation. Interestingly, all patients who deactivated during speech processing (except for one) showed activation in left frontal regions which are associated with conscious processing. Our results indicate that deactivation of the DMN can be associated with the level of consciousness by selecting those who are able to interrupt ongoing introspective processes. In consequence, deactivation of the DMN may function as a marker of consciousness.

Practice Advisory for Intraoperative Awareness and Brain Function Monitoring

Practice Advisory for Intraoperative Awareness and Brain Function Monitoring