Self-Organized Criticality as a Neurodynamical Correlate of Consciousness: A neurophysiological approach to measure states of consciousness based on EEG-complexity features

Background and Objectives This thesis was based on the hypothesis that the physics-derived theoretical framework of self-organized criticality can be applied to the neuronal dynamics of the human brain. From a consciousness science perspective, this is especially appealing as critical brain dynamics imply a vicinity a phase transition, which is associated with optimized information processing functions as well as the largest repertoire of configurations that a system explores throughout its temporal evolution. Hence, self-organised criticality could serve as a neurodynamical correlate for consciousness, which provides the possibility of deriving empirically testable neurophysiological indices suitable to characterise and quantify states of consciousness. The purpose of this work was to experimentally examine the feasibility of the self-organized criticality theory as a correlate for states of consciousness. Therefore, it was aimed at answering the following research questions based on the analysis of three 64 channel EEG datasets: (i) Can signatures of self-organized criticality be found on the level of the EEG in terms of scale-free distribution of neuronal avalanches and the presence of long-range temporal correlations (LRTC) in neuronal oscillations? (ii) Are criticality features suitable to differentiate state of consciousness in the spectrum of wakefulness? (iii) Can the neuronal dynamics be shifted towards the critical point of a phase transition associated with optimized information processing function by mind-body interventions? (iv) Can an explicit relationship to other nonlinear complexity features and power spectral density parameter be identified? (v) Do EEG-based criticality features reflect individual temperament traits? Material and Methods (1): Re-analysis: Thirty participants highly proficient in meditation (mean age 47 years, 11 females/19 males, meditation experience of at least 5 years practice or more than 1000 h of total meditation time) were measured with 64-channel EEG during one session consisting of a task-free baseline resting, a reading condition and three meditation conditions, namely thoughtless emptiness, presence monitoring and focused attention. (2): 64-channel EEG was recorded from 34 participants (mean age 36.0 ±13.4 years, 24 females/ 10 males) before, during and after a professional singing bowl massage. Further, psychometric data was assessed including absorption capacity defined as the individual’s capacity for engaging attentional resources in sensory and imaginative experiences measured by the Tellegen-Absorption Scale (TAS-D), subjective changes in in body sensation, emotional state, and mental state (CSP-14) as well as the phenomenology of consciousness (PCI-K). (3): Electrophysiological data (64 channels of EEG, EOG, ECG, skin conductance, and respiration) was recorded from 116 participants (mean age 40.0 ±13.4 years, 83 females/ 33 males) – in collaboration with the Institute of Psychology, Bundeswehr University Munich - during a task-free baseline resting state. The individual level of sensory processing sensitivity was assessed using the High Sensitive Person Scale (HSPS-G). The datasets were analysed applying analytical tools from self-organized criticality theory (detrended fluctuation analysis, neuronal avalanche analysis), nonlinear complexity algorithms (multiscale entropy, Higuchi’s fractal dimension) and power spectral density. In study 1 and 2, task conditions were contrasted, and effect sizes were compared using a paired two-tailed t-test calculated across participants, and features. T-values were corrected for multiple testing using false discovery rate. To calculate correlations between the EEG features, Spearman’s rank correlation was applied after determining that the distribution was not appropriate for parametric testing by the Shapiro-Wilk test. In addition, in study 1, a discrimination analysis was carried out to determine the classification performance of the EEG features. Here, partial least squares regression and receiver operating characteristics analysis was applied. To determine whether the EEG features reflect individual temperament traits, the individual level of absorption capacity (study 2) and sensory processing sensitivity (study 3) was correlated with the EEG features using Spearman’s rank correlation. Results Signatures of self-organized criticality in the form of scale-free distribution of neuronal avalanches and long-range temporal correlations (LRTCs) in the amplitude of neural oscillations were observed in three distinct EEG-datasets. EEG criticality as well as complexity features were suitable to characterise distinct states of consciousness. In study 1, compared to the task-free resting condition, all three meditative states revealed significantly reduced long-range temporal correlation with moderate effect sizes (presence monitoring: d= -0.49, p<.001; thoughtless emptiness: d= -0.37, p<.001; and focused attention: d= -0.28, p=.003). The critical exponent was suitable to differentiate between focused attention and presence monitoring (d= -0.32, p=.02). Further, in study 2, the criticality features significantly changed during the course of the experiment, whereby values indicated a shift towards the critical regime during the sound condition. Both analyses of the first and second dataset revealed that the critical exponent was significantly negatively correlated with the sample entropy, the scaling exponent resulting from the DFA denoting the amount of long-range temporal correlations as well as Higuchi’s fractal dimension in each condition, respectively. In addition, the critical scaling exponent was found to be significantly negatively correlated with the trait absorption (Spearman's ρ= -0.39, p= .007), whereas an association between critical dynamics and the level of sensory processing sensitivity could not be verified (study 3). Conclusion The findings of this thesis suggest that neuronal dynamics are governed by the phenomena of self-organized criticality. EEG-based criticality features were shown to be sensitive to detect experimentally induced alterations in the state of consciousness. Further, an explicit relationship with nonlinear measures determining the degree of neuronal complexity was identified. Thus, self-organized criticality seems feasible as a neurodynamical correlate for consciousness with the potential to quantify and characterize states of consciousness. Its agreement with the current most influencing theories in the field of consciousness research is discussed

Neurophysiological Effects of a Singing Bowl Massage

Background and Objectives: In recent years, singing bowl sound interventions have been progressively implemented in the fields of well-being, therapy and education; however, the effectiveness has only scarcely been investigated. Therefore, this study was aimed at determining neurophysiological effects of a singing bowl massage. Materials and Methods: In this prospective cohort study 64-channel EEG, ECG and respiration was recorded from 34 participants (mean age 36.03 ± 13.43 years, 24 females/10 males) before, during and after a professional singing bowl massage. Further, subjective changes in well-being were assessed. EEG data were analyzed by determining the effect sizes of distinct frequency bands. Significant differences were calculated by a two-tailed t-test corrected for multiple comparisons. Heart rate variability metrics, heart rate and respiration rate were estimated and compared. Results: Overall EEG power decreased during the sound condition compared to a task-free resting state (d = −0.30, p = 0.002). After the intervention, global EEG power was further reduced (d = −0.46, p < 0.001), revealing a decrease in the beta 2 (d = −0.15, p = 0.002) and the gamma frequency band (d = −0.21, p = 0.004). The mean heart rate was significantly lower after the intervention (75.5 ± 19.8 vs. 71.5 ± 17.9, p < 0.001) and the respiration rate higher (13.5 ± 5.3 vs. 15.2 ± 6.3, p = 0.018). 91.2% of the participants felt more integrated, 97.1% more balanced and 76.5% more vitalized. Conclusions: The neurophysiological effects of a singing bowl sound massage may be interpreted as a shift towards a more mindful, meditative state of consciousness. The intervention was perceived as beneficial for the wellbeing

Self-organized criticality as a framework for consciousness: A review study

Objective: No current model of consciousness is univocally accepted on either theoretical or empirical grounds, and the need for a solid unifying framework is evident. Special attention has been given to the premise that self-organized criticality (SOC) is a fundamental property of neural system. SOC provides a competitive model to describe the physical mechanisms underlying spontaneous brain activity, and thus, critical dynamics were proposed as general gauges of information processing representing a strong candidate for a surrogate measure of consciousness. As SOC could be a neurodynamical framework, which may be able to bring together existing theories and experimental evidence, the purpose of this work was to provide a comprehensive overview of progress of research on SOC in association with consciousness. Methods: A comprehensive search of publications on consciousness and SOC published between 1998 and 2021 was conducted. The Web of Science database was searched, and annual number of publications and citations, type of articles, and applied methods were determined. Results: A total of 71 publications were identified. The annual number of citations steadily increased over the years. Original articles comprised 50.7% and reviews/theoretical articles 43.6%. Sixteen studies reported on human data and in seven studies data were recorded in animals. Computational models were utilized in n = 12 studies. EcoG data were assessed in n = 4 articles, fMRI in n = 4 studies, and EEG/MEG in n = 10 studies. Notably, different analytical tools were applied in the EEG/MEG studies to assess a surrogate measure of criticality such as the detrended fluctuation analysis, the pair correlation function, parameters from the neuronal avalanche analysis and the spectral exponent. Conclusion: Recent studies pointed out agreements of critical dynamics with the current most influencing theories in the field of consciousness research, the global workspace theory and the integrated information theory. Thus, the framework of SOC as a neurodynamical parameter for consciousness seems promising. However, identified experimental work was small in numbers, and a heterogeneity of applied analytical tools as a surrogate measure of criticality was observable, which limits the generalizability of findings

Determining states of consciousness in the electroencephalogram based on spectral, complexity, and criticality features

This study was based on the contemporary proposal that distinct states of consciousness are quantifiable by neural complexity and critical dynamics. To test this hypothesis, it was aimed at comparing the electrophysiological correlates of three meditation conditions using nonlinear techniques from the complexity and criticality framework as well as power spectral density. Thirty participants highly proficient in meditation were measured with 64-channel electroencephalography (EEG) during one session consisting of a task-free baseline resting (eyes closed and eyes open), a reading condition, and three meditation conditions (thoughtless emptiness, presence monitoring, and focused attention). The data were analyzed applying analytical tools from criticality theory (detrended fluctuation analysis, neuronal avalanche analysis), complexity measures (multiscale entropy, Higuchi’s fractal dimension), and power spectral density. Task conditions were contrasted, and effect sizes were compared. Partial least square regression and receiver operating characteristics analysis were applied to determine the discrimination accuracy of each measure. Compared to resting with eyes closed, the meditation categories emptiness and focused attention showed higher values of entropy and fractal dimension. Long-range temporal correlations were declined in all meditation conditions. The critical exponent yielded the lowest values for focused attention and reading. The highest discrimination accuracy was found for the gamma band (0.83–0.98), the global power spectral density (0.78–0.96), and the sample entropy (0.86–0.90). Electrophysiological correlates of distinct meditation states were identified and the relationship between nonlinear complexity, critical brain dynamics, and spectral features was determined. The meditation states could be discriminated with nonlinear measures and quantified by the degree of neuronal complexity, long-range temporal correlations, and power law distributions in neuronal avalanches

Treatment of Fracture-Related Infections with Bone Abscess Formation after K-Wire Fixation of Pediatric Distal Radius Fractures in Adolescents—A Report of Two Clinical Cases

Abstract Closed reduction and K-wire fixation of displaced distal radius fractures in children and adolescents is an established and successful surgical procedure. Fracture-related infections after K-wire fixation are rare but can have significant consequences for the patient. There is a lack of literature on the treatment of K-wire-associated fracture-related infections in children and adolescents. Herein, we report two cases of fracture-related infection after initial closed reduction and Kirschner wire fixation in two adolescents. One 13-year-old boy and one 11-year-old girl were seen for fracture-related infections 4 and 8 weeks after closed reduction and percutaneous K-wire fixation of a distal radius, respectively. X-ray and magnetic resonance imaging (MRI) revealed a healed fracture with osteolytic changes in the metaphyseal radius with periosteal reaction and abscess formation of the surrounding soft tissue structures. A two-staged procedure was performed with adequate debridement of the bone and dead space management with an antibiotic-loaded polymethyl methacrylate (PMMA) spacer at stage 1. After infection control, the spacer was removed and the defect was filled with autologous bone in one case and with a calcium sulphate–hydroxyapatite biomaterial in the other case. In each of the two patients, the infection was controlled and a stable consolidation of the distal radius in good alignment was achieved. In one case, the epiphyseal plate was impaired by the infection and premature closure of the epiphyseal plate was noted resulting in a post-infection ulna plus variant. In conclusion, a fracture-related infection after Kirschner wire fixation of pediatric distal radius fractures is a rare complication but can occur. A two-stage procedure with infection control and subsequent bone defect reconstruction was successful in the presented two cases. Premature closure of the epiphyseal growth plate of the distal radius is a potential complication

The Epidemiology of Osteomyelitis in Children

Pediatric osteomyelitis remains challenging to treat. Detailed epidemiological data are required to estimate future developments. Therefore, we aimed to analyze how the incidence has changed over the last decade depending on age, gender, osteomyelitis subtype, and anatomical localization. Cases were quantified for patients aged 20 years or younger, using yearly reported ICD-10 diagnosis codes from German medical institutions for the time period 2009 to 2019. Incidence rates of osteomyelitis increased by 11.7% from 8.2 cases per 100,000 children in 2009 to 9.2 cases per 100,000 children in 2019. The age-specific incidence rate revealed the highest occurrence of osteomyelitis in patients aged 10–15 years (15.3/100,000 children), which increased by 23% over the observation period, followed by the age group 5–10 years (9.7/100,000 children). In 2019, out of all diagnoses, 39.2% were classified as acute, 38.4% as chronic, and 22.4% were unspecified, whereby chronic cases increased by 38.7%. The lower extremity was mainly affected, with 58.9% of osteomyelitis diagnoses in 2019. In conclusion, pediatric osteomyelitis is a serious issue, even in a developed and industrialized country such as Germany. Considering the recent incidence increase, the permanent need for appropriate treatment should let pediatricians and orthopedic surgeons deal with diagnosis and treatment protocols

The patients‘ perspective - a qualitative analysis of experiencing a fracture-related infection

Introduction: Fracture-related infection is a devastating complication confronting the patient with several challenges. To improve the management and to enhance the patients’ wellbeing the focus of this study was to understand the emotional impact and patients’ experiences during the process to identify challenges, difficulties, and resources. For this, a qualitative content analysis of semi-structured interviews according to Graneheim and Lundman was performed. Methods: In total n = 20 patients of a German university orthopedic trauma centre specialized in bone and joint infections were recruited using a purposive sampling strategy. The patients were treated at the hospital between 2019 and 2021 and underwent at least one surgery. Individual in-person interviews were performed by one researcher based on a semi-structured guide, which was previously conceptualized. Content analysis according to Graneheim and Lundman was performed on the transcripts by two of the researchers independently. Results: The following major themes emerged: (i) the emotional and mental aspects highlighting the fact that FRI patients faced severe restrictions in their day-to-day life, which resulted in dependency on others and frustration, as well as future concerns showing that patients could not overcome a state of anxiety and fear even after successful treatment, (ii) socioeconomic consequences confronting patients with consequences on the job and in finances where they often feel helpless, and (iii) resources emphasizing the role of spirituality as a coping strategy and yoga exercises for keeping the positivity. Conclusion: This study emphasized the challenge of fracture-related infection management and associated consequences from the patients’ perspective. Not being well informed about possible negative outcomes or restrictions makes it harder for patients to accept the situation and patients expressed a need for better information and certainty. Also, patients developed constant anxiety and other psychological disturbances, highlighting the potential benefit of psychological support and patient-peer support to exchange experiences

What is the burden of osteomyelitis in Germany? An analysis of inpatient data from 2008 through 2018

Background The epidemiology of osteomyelitis in Germany is unknown, which makes it difficult to estimate future demands. Therefore, we aimed to analyse how the numbers of cases have developed over the last decade as a function of osteomyelitis subtype, age group, gender, and anatomical localization. Methods Osteomyelitis rates were quantified based on annual ICD-10 diagnosis codes from German medical institutions between 2008 through 2018, provided by the Federal Statistical Office of Germany (Destatis). Results Overall osteomyelitis prevalence increased by 10.44% from 15.5 to 16.7 cases per 100,000 inhabitants between 2008 through 2018. Out of 11,340 cases in 2018, 47.6% were diagnosed as chronic, 33.2% as acute and 19.2% as unspecified osteomyelitis. Men were often affected than women with 63.4% of all cases compared to 36.6%. The largest proportion of patients comprised the age group 60–69 years (22.1%), followed by 70–79 years (21.7%). A trend towards more osteomyelitis diagnoses in older patients was observed. Lower extremities were most frequently infected with 73.8% of all cases in 2018 (+ 10.8% change). Conclusions Osteomyelitis remains a serious problem for orthopedic and trauma surgery. Prevention methods and interdisciplinary approaches are strongly required

The epidemiology of fracture-related infections in Germany

The epidemiology of fracture-related infection (FRI) is unknown, which makes it difficult to estimate future demands and evaluate progress in infection prevention. Therefore, we aimed to determine the nationwide burden’s development over the last decade as a function of age group and gender. FRI prevalence as a function of age group and gender was quantified based on annual ICD-10 diagnosis codes from German medical institutions between 2008 through 2018, provided by the Federal Statistical Office of Germany (Destatis). The prevalence of FRI increased by 0.28 from 8.4 cases per 100,000 inhabitants to 10.7 cases per 100,000 inhabitants between 2008 and 2018. The proportion of fractures resulting in FRI increased from 1.05 to 1.23%. Gender distribution was equal. Patients aged 60–69 years and 70–79 years comprised the largest internal proportion with 20.2% and 20.7%, respectively, whereby prevalence increased with age group. A trend towards more diagnoses in older patients was observed with a growth rate of 0.63 for patients older than 90 years. Increasing rates of fracture-related infection especially in older patients indicate an upcoming challenge for stakeholders in health care systems. Newly emerging treatment strategies, prevention methods and interdisciplinary approaches are strongly required

Comment on Lunz et al. Impact and Modification of the New PJI-TNM Classification for Periprosthetic Joint Infections. J. Clin. Med. 2023, 12, 1262

We read with great interest the article by Lunz et al. [1], in which the authors dealt with the new Periprosthetic Joint Infection (PJI)-TNM classification that was recently published by our group (Table 1) [2–4]. PJI represents one of the most feared complications in the orthopedic field, resulting in impaired quality of life, repeated and prolonged hospital stays, and significant morbidity and mortality in affected patients. Still, there is no commonly used classification system that could facilitate the comparison of treatment strategies and patient outcomes [5,6]. Therefore, we are delighted with the authors’ conclusions that “clinicians and researchers should be familiar with the new PJI-TNM classification and start implementing it into their routine practice” [1]. The work of Lunz et al. [1] retrospectively assessed 80 consecutive PJI patients treated with a two-stage exchange and was the first to correlate the PJI-TNM classification to surgical parameters and some clinical outcome parameters, such as need for revision surgery after stage one surgery, the duration of the interim period, and mortality. In addition, Lunz et al. [1] believed that the initial PJI-TNM publication from our group could be improved through certain modifications to the TNM backbone, resulting in a “pTNM” version. An additional “p-status” (type of prosthesis) was proposed to distinguish between standard implants (p0), revision implants (p1), and megaprostheses (p2). Further suggestions were to add an “x” in front of the “p-status” to indicate a loosened implant and to limit the criteria parameters for p, T, N, and M to only 0 = least serious, 1 = moderate, and 2 = most serious by eliminating the letters for the subclassifications of the 0, 1, and 2 categories of our initially proposed classification. They also proposed the replacement of the CCI for the assessment of patients’ comorbidities with the American Society of Anesthesiologists (ASA) Physical Status Classification System [7]