Minimal Consciousness Research Articles

Metabolomic Profiling of the Blood of Patients with Chronic Consciousness Disorders

The main variants of chronic consciousness disorder (CCD) developing in adverse coma outcome are vegetative state/unresponsive wakefulness syndrome (VS/UWS) and minimal consciousness state (MCS). The aim of the study was to investigate the main differences in metabolomic abnormalities in patients with VS / UWS and MCS, as well as to identify changes in metabolomics depending on sleep or wakefulness phase. Materials and Methods. Untargeted metabolome analysis of blood plasma of 10 patients in VS / UWS (group 1) and 6 patients in MCS (group 2) was performed using reversed-phase and hydrophilic chromatography methods. The underlying conditions of brain injury were TBI (2 in group 1 and 5 in group 2) and hypoxia (8 in group 1 and 1 in group 2). The internal jugular vein was catheterized in all patients, and blood was collected while awake during the daytime for 2 days. Aliquots of pooled plasma samples were purified from protein components and analyzed by high-performance liquid chromatography in two modes: reversed-phase and hydrophilic ones. Mass-spectrometric detection was performed in full ion current scanning mode: registration of positively charged ions in the m/z range from 50 to 1300 a.u. Data were adjusted and normalized using MS-DIAL software ver. 4.70 software; differences were identified using analysis of variance, discriminant and cluster analysis. The data were analyzed and visualized using MetaboAnalyst 5.0 software (https://www.metaboanalyst.ca). Results. Four major metabolites (at VIP > 0.5), which content was most modulated depending on the study group, were identified including 4 (m/z 124.0867, Rt = 17.67, p < 0.01), 33 (m/z 782.5722, Rt = 17.69, p < 0.01), 6 (m/z 125.0904, Rt = 18.43, p < 0.01) and 1 (m/z 463.2304, Rt = 15.78, p < 0.01), with no significant differences between daytime and nighttime blood samples. Significant quantitative differences were shown for three metabolites in the groups, 14 (m/z 162.1126, Rt = 10.28, p < 0.01), 35 (m/z 780.5483, Rt = 7.65, p < 0.01), and 41 (m/z 806.5649, Rt = 7.58, p < 0.01), and four metabolites when comparing the daytime and nighttime samples: 14 (m/z 162.1126, Rt = 10.28, p = 0.0201), 35 (m/z 780.5483, Rt = 7.65, p < 0.01), 41 (m/z 806.5649, Rt = 7.58, p < 0.01), and 48 (m/z 848.5354, Rt = 7.65, p < 0.01). Conclusion. Untargeted metabolomic analysis confirmed the hypothesis of likely significant quantitative and qualitative differences in metabolite composition depending on the type of CCD and circadian rhythm. The study established a set of metabolites that are potential biomarkers for differential diagnosis of VS/UWS and MCS including 4, 33, 6, 1 (in the experiment on the reversed-phase column) and 14, 35, 41, 48 (in the experiment on the hydrophilic column), based on their significant contribution to intergroup and intragroup differences. Further studies will be aimed to characterize the identified metabolites.

The Futures of the Past The Evolution of Imaginative Animals

We discuss the evolution of imagination in vertebrate animals within the framework of an evolutionary-transition approach. We define imaginative consciousness and the cognitive architecture that constitutes it and argue that the evolution of full-fledged imaginative consciousness that enables planning can be regarded as a major transition in the evolution of cognition. We explore the distribution and scope of a core capacity of imaginative cognition in non-human vertebrates — episodic-like memory (ELM) — by examining its behavioural manifestations as well as the organization and connectivity of the hippocampus, a central hub of episodic memory processes in vertebrates. Although the data are limited, we conclude that ELM evolved in parallel several times through the enrichment of minimal consciousness capacities, that there is a general correspondence between enhanced behavioural capacities and the size and complexity of the hippocampus during vertebrate evolution, and that the evolution of prospective, planning-enabling imagination is a major transition in cognition and consciousness.

Entropy Metrics Correlating with Higher Residual Functioning in Patients with Chronic Disorders of Consciousness.

To test the ability of different entropy measures to classify patients with different conditions of chronic disorder of consciousness, we applied the Lempel–Ziv complexity, the amplitude coalition entropy (ACE), and the synchrony coalition entropy (SCE) to the EEG signals recorded in 32 patients, clinically evaluated using the coma recovery scale revised (CRS-R). All the entropy measures indicated that differences found in the theta and alpha bands can distinguish patients in a minimal consciousness state (MCS) with respect to those in a vegetative state/unresponsive wakefulness state (VS/UWS). These differences were significant comparing the entropy measure performed on the anterior region of the left hemisphere and midline region. The values of theta-alpha entropy positively correlated with those of the CRS-R scores. Among the entropy measures, ACE most often highlighted significant differences. The higher values found in MCS were for the less impaired patients, according to their CRS-R, suggest that the preservation of signal entropy on the anterior region of the dominant hemisphere correlates with better preservation of consciousness, even in chronic conditions.

An implementation of different minimal consciousness's variants for a cyber-physical system

The article discusses the principles of operation of the minimal consciousness of a cognitive cyber-physical system and an example of the implementation of this system in the form of an autonomous trolley with three supports. The trolley is equipped with minimal consciousness and will navigate locally and follow a predetermined route. The minimal consciousness will control the actions of the trolley based on the analysis of data of its own position, speed, deviation from the given route, etc. It is proposed to implement two variants of minimal consciousness: 1) in the form of stream production system that may be presented as a composition of finite-state machines with feedback and finite-state automates; 2) in the form of a temporal-casual neural network. Experiments to compare the two implementation variants will be aimed at further improvement of robotic platforms and an expansion of their versatility. The design of cyber-physical systems equipped with machine consciousness is the key to obtaining reliable systems, as it potentially increases their behavioral flexibility in new or changing environments, their resilience to failures in the operation or interaction of their components.

Disrupted Control Architecture of Brain Network in Disorder of Consciousness.

The human brain controls various cognitive functions via the functional coordination of multiple brain regions in an efficient and robust way. However, the relationship between consciousness state and the control mode of brain networks is poorly explored. Using multi-channel EEG, the present study aimed to characterize the abnormal control architecture of functional brain networks in the patients with disorders of consciousness (DOC). Resting state EEG data were collected from 40 DOC patients with different consciousness levels and 24 healthy subjects. Functional brain networks were constructed in five different EEG frequency bands and the broadband in the source level. Subsequently, a control architecture framework based on the minimum dominating set was applied to investigate the of control mode of functional brain networks for the subjects with different conscious states. Results showed that regardless of the consciousness levels, the functional networks of human brain operate in a distributed and overlapping control architecture different from that of random networks. Compared to the healthy controls, the patients have a higher control cost manifested by more minimum dominating nodes and increased degree of distributed control, especially in the alpha band. The ability to withstand network attack for the control architecture is positive correlated with the consciousness levels. The distributed of control increased correlation levels with Coma Recovery Scale-Revised score and improved separation between unresponsive wakefulness syndrome and minimal consciousness state. These findings may benefit our understanding of consciousness and provide potential biomarkers for the assessment of consciousness levels.

Understanding Disorders of Consciousness: Opportunities for Critical Care Nurses.

Disorders of consciousness are powerful predictors of outcomes including mortality among critically ill patients. Encephalopathy, delirium, and coma are disorders of consciousness frequently encountered by critical care nurses but often classified incorrectly. To provide a greater understanding of disorders of consciousness and to provide standardized assessments and nursing interventions for these disorders. A literature search was conducted by using the terms consciousness, mental status, awareness, arousal, wakefulness, assessment, disorders of consciousness, delirium, encephalopathy, coma, vegetative state, and minimal consciousness. Articles were published in the past 10 years in CINAHL and PubMed. Articles were excluded if they were not in English or directly related to caring for patients with a disorder of consciousness. The remaining 142 articles were evaluated for inclusion; 81 articles received full review. A disorder of consciousness signifies that the threshold for compensation has been surpassed with potentially irreversible damage. Altered thalamocortical interactions and reduced cortical activity impair communication networks across the various parts of the brain, causing a disturbance in consciousness. The cue-response theory is a model that describes the process and impact of nursing care on recovery from acute brain injury. Appropriate standardized assessments and interventions must be used to manage altered levels of consciousness in critically ill patients. Paying close attention to neurological changes and monitoring them with standardized assessments are critical to implementing early measures to prevent complications.

A Framework for Evolution and Consciousness: Panpsychism Without Tears?

Giving an account of the relation between evolution and consciousness is painted as posing a dilemma between panpsychism, with minimal consciousness in every grain of matter, and radical emergence, with consciousness appearing as from nowhere in living structures. Panpsychism has been seen as suffering from a combination problem and radical emergence as unjustified in physics. The underpinning of physics now lies in field theory, which may provide a way out on both sides. Only, and always, in a field theory account do influences at different points in space-time combine in the same indivisible event. Radical emergence is also inherent to field theory. Moreover, by providing rich patterns of influence involving both discrete identities and quantitative values, field theory might provide a basis for sensed propositional meaning with subjects and predicates. Ordered condensed matter within living tissue may support unusual emergent dynamic units uniquely suited to building representations of the world with sensed meaning. The evolution of consciousness may then be seen as a tractable biological problem centred on increasingly sophisticated ways for external world dynamics to be mirrored by internal representations with semantic content, based in field relations within condensed matter with genetically encoded complex order.

Consciousness in Jawless Fishes.

Jawless fishes were the first vertebrates to evolve. It is thus important to investigate them to determine whether consciousness was acquired in the common ancestor of all vertebrates. Most jawless fish lineages are extinct, and cyclostomes (lampreys and hagfish) are the sole survivors. Here, I review the empirical knowledge on the neurobiology of cyclostomes with special reference to recently proposed “markers” of primary, minimal consciousness. The adult lamprey appears to meet the neuroanatomical criteria but there is a practical limitation to behavioral examination of its learning ability. In addition, the consciousness-related neuroarchitecture of larvae and its reconstruction during metamorphosis remain largely uninvestigated. Even less is known of hagfish neurobiology. The hagfish forebrain forms the central prosencephalic complex, and the homology of its components to the brain regions of other vertebrates needs to be confirmed using modern techniques. Nevertheless, as behavioral responses to olfactory stimuli in aquariums have been reported, it is easier to investigate the learning ability of the hagfish than that of the lamprey. Based on these facts, I finally discuss the potential future directions of empirical studies for examining the existence of consciousness in jawless fishes.

Modulated Neuroprotection in Unresponsive Wakefulness Syndrome after Severe Traumatic Brain Injury.

Background: We aimed to assess the effects of modulated neuroprotection with intermittent administration in patients with unresponsive wakefulness syndrome (UWS) after severe traumatic brain injury (TBI). Methods: Retrospective analysis of 60 patients divided into two groups, with and without neuroprotective treatment with Actovegin, Cerebrolysin, pyritinol, L-phosphothreonine, L-glutamine, hydroxocobalamin, alpha-lipoic acid, carotene, DL-α-tocopherol, ascorbic acid, thiamine, pyridoxine, cyanocobalamin, Q 10 coenzyme, and L-carnitine alongside standard treatment. Main outcome measures: Glasgow Coma Scale (GCS) after TBI, Extended Glasgow Coma Scale (GOS E), Disability Rankin Scale (DRS), Functional Independence Measurement (FIM), and Montreal Cognitive Assessment (MOCA), all assessed at 1, 3, 6, 12, and 24 months after TBI. Results: Patients receiving neuroprotective treatment recovered more rapidly from UWS than controls (p = 0.007) passing through a state of minimal consciousness and gradually progressing until the final evaluation (p = 0.000), towards a high cognitive level MOCA = 22 ± 6 points, upper moderate disability GOS-E = 6 ± 1, DRS = 6 ± 4, and an assisted gait, FIM =101 ± 25. The improvement in cognitive and physical functioning was strongly correlated with lower UWS duration (−0.8532) and higher GCS score (0.9803). Conclusion: Modulated long-term neuroprotection may be the therapeutic key for patients to overcome UWS after severe TBI.

Can Music Influence Patients With Disorders of Consciousness? An Event-Related Potential Study.

BackgroundLong-term disorders of consciousness (DOC) are a huge burden on both patients and their families. Previously, music intervention has been attempted as a potential therapy in DOC, with results indicating an enhancement of arousal and awareness; yet, to date, there are limited studies on music interventions in DOC with electroencephalogram monitoring. Meanwhile, prediction of awareness recovery is a challenge facing clinicians. The predictive value mismatch negativity (MMN), as a classical cognitive component in event-related potential, is still controversial. In this study, we use auditory event-related potential to probe the effect of music in DOC, and investigate whether music may improve the predictive value of MMN in awareness recovery.MethodsFourteen DOC patients were included in the prospective study. Auditory oddball electroencephalogram data were recorded twice with each patient, before and after 5 min of listening to a Chinese symphony that has joyful associations. The outcome was assessed 6 months later.ResultsSignificant differences of MMN amplitude were found between healthy controls and pre-music DOC patients (p < 0.001), but no significant differences were found between healthy controls and post-music DOC patients. The presence of MMN before music was not correlated with favorable outcome, and 50% of patients with MMN did not recover awareness. When MMN was absent, 50% of patients awoke. After listening to music, among the 11 patients who showed MMN, seven patients recovered awareness. When MMN was absent, no one recovered awareness.ConclusionsSome DOC patients, even those in a minimal consciousness state and those with unresponsive wakefulness syndrome (UWS), were affected by music. The MMN amplitude was elevated by the music to some extent. A single test of MMN did not have a good prognostic value of our study; however, retesting of MMN after stimulation with familiar music that has joyful associations might be valuable for observation and detection of possible recovery. The musical processing in DOC patients and the effect of musical therapeutic practices need further investigations.

Options for the recovery of mental activity in children after acute brain damage

IntroductionChildren with acute brain damage make up a large group of patients who require multi-stage rehabilitation. Rehabilitation requires the creation of special conditions for psychiatric care and psychological and pedagogical correction of the consequences of severe damage to the nervous system.ObjectivesTo identify the options for mental activity during the restoration of the level of consciousness in children after acute severe brain damage.Methods210 children under the age of 18 with severe brain damage (traumatic brain injury, hypoxia, hydrocephalus). Clinical-psychopathological, pedagogical methods were used; additionally diagnostic scales, questionnaires.Results4 groups were formed: 1st 37 (18%) patients had manifestations of mental activity with physical, cognitive and social capabilities in the minimal consciousness “+” (a- / hyperkinetic mutism with emotional reactions, understanding of addressed speech); 2nd 67 (32%) - manifestations of physical and cognitive abilities with minimal consciousness “-” (a- / hyperkinetic mutism without reactions); 3rd 95 (40%) - only the manifestation of physical capabilities at the exit from the vegetative status. 4th 11 (10%) - a low manifestation of mental activity in the form of physical capabilities with a vegetative status.Conclusions4 variants of mental activity in children after acute severe brain damage have been identified: from minimal involuntary reactions or their absence in vegetative status to voluntary actions according to the instructions of an adult in minimal consciousness “+”. Taking into account the variability of mental activity helps to differentiate the methods of psychiatric and psychological-pedagogical assistance in the recovery of children already in the early stages of rehabilitation.

Signs of Consciousness?

In this commentary I expand on the first of Noble’s illusions, the selection metaphor. Building on my work with Simona Ginsburg on the evolution of minimal consciousness, I argue that the existence of some complex sensory and motor patterns in the living world can be accounted for only through the evolution of conscious choice.

Quality of models of scales of consciousness level, functional state, and General somatic severity in patients with consequences of brain damage in intensive care and rehabilitation department.

Aims: development and substantiation of a typical scheme for the clinical use of scales of the level of consciousness, general somatic and functional status of patients with of brain damage. Methods: Included 118 patients on 20-50 days after traumatic brain injury, anoxic damage; consequences of acute cerebral circulatory disorders, and neurosurgical operations. In groups of patients who are in a coma, vegetative status, a state of minimal consciousness and a state of clear consciousness, the analysis of the statistical quality of clinical scales was carried out: scales of consciousness: the Glasgow coma Scale (GCS); FOUR (Full Outline of UnResponsiveness); CRS-R-Coma Recovery Scale-Revised; the Glasgow outcome Scale (COS); the extended scale of the Glasgow coma (COSE - Glasgow outcome scale extended); Rancho Los Amigos scale-scale of consciousness and interaction with the environment (the Rancho Los Amigos scale - RLAS); Functional status scales: DRS (the Disability Rating Scale); modified Rankin Scale mRS; Barthel Activities of Daily Living (ADL) Index; functional independence measure-FIM; Karnovsky Index; Rivermead Mobility Index self-assessment of everyday life opportunities in Merton and Sutton (checklist self-maintenance. Merton and Sutton community NHS trust); Scales of General somatic severity: assessment of multi-organ dysfunction on the APACHE II scale (Acute Physiology and Chronic Health Evaluation); APACHE IV scale; SAPS II scale (Simplified Acute Physiology Score); SOFA scale (Sequential Organ Failure Assessment). The functional state of the ANS was recorded using HRV parameters by recording 5-minute RR intervals of the electrocardiogram. Results: There are 4 groups of patients who are in a state of coma, vegetative status, a state of minimal consciousness and a state of clear consciousness. In 67 patients out of 118 examined (56.8%) the parameters of ANS functional activity are in the zone of pathological (sympathetic/parasympathetic hyperactivity) values. Conclusions: Various scales of the level of consciousness, functional and general somatic severity of patients objectively differ in clinical significance in the gradation of coma - vegetative status - minimal consciousness - clear consciousness.

Decannulation and improvement of responsiveness in patients with disorders of consciousness

ABSTRACT Decannulation is a rehabilitation milestone in patients with Disorders of Consciousness (DoC). investigate the relationship between decannulation and improvement of responsiveness (IR) in DoC. 236 tracheostomized patients with severe Acquired Brain Injury and DoC admitted in the Intensive Rehabilitation Unit were retrospectively included. They received personalized interdisciplinary rehabilitation. At discharge, IR was evaluated. The association between IR and demographic/clinical data was investigated using a logistic regression analysis, both in the Unresponsive Wakefulness Syndrome (UWS) and Minimal Consciousness State (MCS) group, divided according to their Coma Recovery Scale-Revised score at admission. In the UWS group (N = 107), only decannulation was associated with IR at discharge (OR: 5.94, CI: 2.08–16.91, p = .001). In the MCS group (N = 129) time post-injury (OR: 0.983, CI: 0.97–0.99, p = .012) and decannulation were associated with IR at discharge (OR: 17.9, CI: 6.39–50.13, p < .001). Decannulation and IR were found to be strongly related, independently from the initial clinical state. While the retrospective nature of the study could not exclude that decannulation may be a consequence of a spontaneous recovery, the obtained results may disclose its potential influence on the clinical history of patients with DoC.

Integrated information as a possible basis for plant consciousness

It is commonly assumed that plants do not possess consciousness. Since the criterion for this assumption is usually human consciousness this assumption represents a top down attitude. It is obvious that plants are not animals and using animal criteria of consciousness will lead to its rejection in plants. However using a bottom up evolutionary approach and a leading theory of consciousness, Integrated Information Theory, we report that we find evidence that indicates that plant meristems act in a conscious fashion although probably at the level of minimal consciousness. Since many plants contain multiple meristems these observations highlight a very different evolutionary approach to consciousness in biological organisms.

Prognostication of Recovery of Consciousness in Patients in a Vegetative State Using Proton Magnetic Resonance Spectroscopy

Objectives. To study the predictive significance of proton magnetic resonance spectroscopy (MRS) in patients in a vegetative state. Materials and methods. Multivoxel MRS was carried out in 34 patients in a vegetative state with voxels in the thalamus, globus pallidus, putamen, internal capsule, fornix, brainstem, and the temporal and frontal areas of the cortex. Patients were divided into groups depending on the etiology of vegetative state: 22 patients had the sequelae of traumatic brain injury (TBI) and 12 patients had the sequelae of hypoxic brain damage. The groups were comparable in terms of age and the duration of the vegetative state (mean 2.3 months). Neurological status was assessed both during the hospitalization period and at 6–12 months using the Coma Recovery Scale (CRS-R). MRS results obtained at 6–12 months were compared with baseline data. The outcome of patients with the sequelae of TBI were as follows: persistent vegetative state in six patients, minimally conscious state plus in nine patients, recovery from the state of minimal consciousness in seven. Outcomes of patients with the sequelae of hypoxia were: persistent vegetative state in 10 patients and minimally conscious state plus in two. Results. Decreases in the N-acetylaspartate/creatinine ratio in the thalamus, internal capsule, and temporal cortex correlated with poor outcomes in both groups, while higher values correlated with further recovery of consciousness. Decreases in the N-acetylaspartate/creatinine ratio and the N-acetylaspartate/N-acetylaspartate + choline + creatine ratio in the midbrain correlated with poor outcomes only in patients with the sequelae of hypoxia. Conclusions. The results obtained here suggest that MRS provides a more accurate determination of the outcome in patients with hypoxic brain damage and patients with TBI, who showed recovery of consciousness to the level of coming out of the vegetative state.

The Dilemma of Hydrocephalus in Prolonged Disorders of Consciousness.

Prolonged disorders of consciousness (DOC) are considered to be among the most severe outcomes after acquired brain injury. Medical care for these patients is mainly focused on minimizing complications, given that treatment options for patients with unresponsive wakefulness or minimal consciousness remain scarce. The complication rate in patients with DOC is high, both in the acute hospital setting, as in the rehabilitation or long-term care phase. Hydrocephalus is one of these well-known complications and usually develops quickly after acute changes in cerebrospinal fluid (CSF) circulation after different types of brain damage. However, hydrocephalus may also develop with a significant delay, weeks, or even months after the initial injury, reducing the potential for natural recovery of consciousness. In this phase, hydrocephalus is likely to be missed in DOC patients, given that their limited behavioral responsiveness camouflages the classic signs of increased intracranial pressure or secondary normal-pressure hydrocephalus. Moreover, the development of late-onset hydrocephalus may exceed the period of regular outpatient follow-up. Several controversies remain about the diagnosis of clinical hydrocephalus in patients with ventricular enlargement after severe brain injury. In this article, we discuss both the difficulties in diagnosis and dilemmas in the treatment of CSF disorders in patients with prolonged DOC and review evidence from the literature to advance an active surveillance protocol for the detection of this late, but treatable, complication. Moreover, we advocate a low threshold for CSF diversion when hydrocephalus is suspected, even months or years after brain injury.

Clinical application of Chinese Nanjing persistent vegetative state scale

BackgroundIt is a challenge to characterize the consciousness level of patients with severe disturbance of consciousness and predict their prognosis effectively for Chinese doctors. We aimed to investigate the psychometric property and the diagnostic practicality of severe disturbance of consciousness by Chinese Nanjing persistent vegetative state scale (CNPVSS) which was first set up in 1996 and modified in 2001 and 2011.MethodsThe concurrent validity, inter-rater consistency and diagnostic accuracy of CNPVSS and Chinese version of coma recovery scale-revised (CRS-R) were investigated by assessment of 380 patients with severe disorders of consciousness.ResultsTotal scores of the CNPVSS were correlated significantly with that of the CRS-R, indicating acceptable concurrent validity. Sub-scale analysis showed moderate to high inter-rater reliability and test-retest reliability. CNPVSS was superior to CRS-R on the diagnosis sensitivity. The CNPVSS was able to distinguish 65 patients in emergence from minimal consciousness state who were misclassified as in minimal consciousness state (MCS) by the CRS-R, and it could also distinguish two patients in MCS who were misclassified as in vegetative state by the CRS-R.ConclusionThe CNPVSS is an appropriate measurement and is sensitive to distinguish the MCS patients from the VS patients.

Effects of comprehensive rehabilitation on complications and long-term prognoses of patients in vegetative and minimal consciousness states.

To understand the clinical characteristics, prognoses, and prognostic factors of vegetative state (VS) and minimal consciousness state (MCS) patients hospitalized for comprehensive rehabilitation. The data of VS and MCS patients admitted in the past six years were retrospectively analyzed. Age of onset, etiology, course of disease, complications, and retention of tracheal intubation, gastric tube, and urethral catheter were recorded. All patients were followed for one year after onset, and their Glasgow Outcome Scale (GOS) scores were assessed. Long-term prognostic factors were analyzed using logistic regression. The proportion of patients with traumatic brain injuries in the MCS group was higher than in the VS group (p<0.05), while hypoxic-ischemic encephalopathy accounted for a higher proportion in the VS group; the differences were statistically significant between the two groups. The occurrence of infection was the highest in both groups, followed by spasticity and epilepsy. The occurrence of other complications was slightly different between the two groups but did not reach statistical significance (p>0.05). Age, etiology, and consciousness at admission had a significant impact on the long-term prognoses of VS or MCS patients (p<0.05), and the age of onset was the most important factor (the highest OR). Infection, spasticity, and epilepsy are common complications in both VS and MCS patients. Recovery of consciousness after one year was shown to be affected by age, etiology, and consciousness at admission.

Auditory steady-state response to chirp-modulated tones: A pilot study in patients with disorders of consciousness.

Due to the problems with behavioral diagnosis of patients with prolonged DOC (disorders of consciousness), complementary approaches based on objective measurement of neural function are necessary. In this pilot study, we assessed the sensitivity of auditory chirp-evoked responses to the state of patients with severe brain injury as measured with CRS-R (Coma Recovery Scale - Revised). A convenience sample of fifteen DOC patients was included in the study. Auditory stimuli, chirp-modulated at 1-120 Hz were used to evoke auditory steady-state response (ASSR). Phase-locking index (PLI) estimates within low gamma and high gamma windows were evaluated. The PLI estimates within a narrow low gamma 38-42 Hz window positively correlated with the CRS-R total score and with the scores of the Auditory and Visual Function subscales. In the same low gamma window, significant difference in the PLIs was found between minimally conscious (MCS) and vegetative state (VS) patients. We did not observe any between-group differences nor any significant correlations with CRS-R scores in the high gamma window (80-110 Hz). Our results support the notion that the activity around 40 Hz may serve as a possible marker of the integrity of thalamocortical networks in prolonged DOC patients. Auditory steady-state responses at gamma-band frequencies highlight the role of upper parts of auditory system in evaluation of the level of consciousness in DOC patients.