Cognitive auditory evoked potentials in coma: can you hear me?

Decoding Analyses Show Dynamic Waxing and Waning of Event-Related Potentials in Coma Patients

Background/Objectives: Coma prognosis is challenging, as patient presentation can be misleading or uninformative when using behavioral assessments only. Event-related potentials have been shown to provide valuable information about a patient's chance of survival and emergence from coma. Our prior work revealed that the mismatch negativity (MMN) in particular waxes and wanes across 24 h in some coma patients. This "cycling" aspect of the presence/absence of neurophysiological responses may require fine-grained tools to increase the chances of detecting levels of neural processing in coma. This study implements multivariate pattern analysis (MVPA) to automatically quantify patterns of neural discrimination between duration deviant and standard tones over time at the single-subject level in seventeen healthy controls and in three comatose patients. Methods: One EEG recording, containing up to five blocks of an auditory oddball paradigm, was performed in controls over a 12 h period. For patients, two EEG sessions were conducted 3 days apart for up to 24 h, denoted as day 0 and day 3, respectively. MVPA was performed using a support-vector machine classifier. Results: Healthy controls exhibited reliable discrimination or classification performance during the latency intervals associated with MMN and P3a components. Two patients showed some intervals with significant discrimination around the second half of day 0, and all had significant results on day 3. Conclusions: These findings suggest that decoding analyses can accurately classify neural responses at a single-subject level in healthy controls and provide evidence of small but significant changes in auditory discrimination over time in coma patients. Further research is needed to confirm whether this approach represents an improved technology for assessing cognitive processing in coma.

Complex auditory regularity processing across levels of consciousness in coma: Stage 1 Registered Report

A key question for the scientific study of consciousness is whether it is possible to identify specific features in brain activity that are uniquely linked to conscious experience. This question has important implications for the development of markers to detect covert consciousness in unresponsive patients. In this regard, many studies have focused on investigating the neural response to complex auditory regularities. One noteworthy example is the local global paradigm, which allows for the investigation of auditory regularity encoding at the 'global' level, based on the repetition of groups of sounds. The inference of global regularities is thought to depend on conscious access to such complex auditory stimuli as mostly shown in chronic stages of disorders of consciousness patients. However, whether global regularity encoding can identify covert consciousness along the consciousness spectrum including earlier stages of these disorders remains controversial. Here, we aim to fill this gap by investigating whether the inference of global auditory regularities can occur in acute coma, in the absence of consciousness, and how this may be modulated by the severity of the patients' clinical condition and consciousness level measured using the Full Outline of UnResponsiveness (FOUR) score. We will acquire 63-channel continuous electroencephalography to measure the neural response to global auditory regularity in comatose patients (N = 30) during the first day after cardiac arrest, when patients are unconscious, sedated and under normothermia, and during the second day (with reduced or absent sedation and body temperature control). We hypothesize that global regularity encoding will persist in the absence of consciousness independent of patient outcome, observed as above chance decoding of the neural response to global regularities using multivariate decoding analyses. We further hypothesize that decoding performance will positively correlate with the FOUR score, which indexes consciousness level, and typically improves between the first and second day after coma onset following cardiac arrest in patients with favourable outcome. In an exploratory analysis, we will also evaluate whether global regularity encoding may be influenced by the patients' clinical management, specifically sedation, also shown to affect global deviance detection. Our results will shed light on the neurophysiological correlates of complex auditory regularity processing in unconscious patients and on the link to residual levels of consciousness during the underexplored state of coma upon the first days after cardiac arrest.

A neurophysiological profiling of the heartbeat-evoked potential in severe acquired brain injuries: A focus on unconsciousness

Unconsciousness in severe acquired brain injury (sABI) patients occurs with different cognitive and neural profiles. Perturbational approaches, which enable the estimation of proxies for brain reorganization, have added a new avenue for investigating the non-behavioural diagnosis of consciousness. In this prospective observational study, we conducted a comparative analysis of the topological patterns of heartbeat-evoked potentials (HEP) between patients experiencing a prolonged disorder of consciousness (pDoC) and patients emerging from a minimally consciousness state (eMCS). A total of 219 sABI patients were enrolled, each undergoing a synchronous EEG-ECG resting-state recording, together with a standardized consciousness diagnosis. A number of graph metrics were computed before/after the HEP (Before/After) using the R-peak on the ECG signal. The peak value of the global field power of the HEP was found to be significantly higher in eMCS patients with no difference in latency. Power spectrum was not able to discriminate consciousness neither Before nor After. Node assortativity and global efficiency were found to vary with different trends at unconsciousness. Lastly, the Perturbational Complexity Index of the HEP was found to be significantly higher in eMCS patients compared with pDoC. Given that cortical elaboration of peripheral inputs may serve as a non-behavioural determinant of consciousness, we have devised a low-cost and translatable technique capable of estimating causal proxies of brain functionality with an endogenous, non-invasive stimulus. Thus, we present an effective means to enhance consciousness assessment by incorporating the interaction between the autonomic nervous system (ANS) and central nervous system (CNS) into the loop.

Acoustic and Subjective Basis of Emotional Perception in Comatose Patients: A Comparative Study

Objective

: The acoustic stimulation in consciousness patients may improve the diagnosis assessment and the effectiveness of rehabilitation procedures. We aimed to investigate the event-related potential (ERP) response to emotional auditory stimuli in comatose patients.

Methods

: We measured the nonlinear and linear electroencephalogram (EEG) features, prepared the acoustic analysis of stimuli parameters, and assessed the subjective emotional rates of stimuli characteristics.

Results

: Patients with better outcomes had recognizable ERP responses and significant changes of the nonlinear EEG features to emotional sounds, unlike patients with worse outcomes. The response of comatose patients was attributed to acoustical features of emotional sounds, whereas the EEG response of healthy subjects was associated with their subjective feelings. The comatose patients demonstrated the variable EEG activity for neutral and emotional sounds.

Conclusion

: Thus, the EEG reactivity followed the better outcome of comatose patients to emotional stimuli. The study assumed the substantial differences of emotional stimuli perception in the healthy and unconscious brain.

Tracking auditory mismatch negativity responses during full conscious state and coma

The mismatch negativity (MMN) is considered the electrophysiological change-detection response of the brain, and therefore a valuable clinical tool for monitoring functional changes associated with return to consciousness after severe brain injury. Using an auditory multi-deviant oddball paradigm, we tracked auditory MMN responses in seventeen healthy controls over a 12-h period, and in three comatose patients assessed over 24 h at two time points. We investigated whether the MMN responses show fluctuations in detectability over time in full conscious awareness, or whether such fluctuations are rather a feature of coma. Three methods of analysis were utilized to determine whether the MMN and subsequent event-related potential (ERP) components could be identified: traditional visual analysis, permutation t-test, and Bayesian analysis. The results showed that the MMN responses elicited to the duration deviant-stimuli are elicited and reliably detected over the course of several hours in healthy controls, at both group and single-subject levels. Preliminary findings in three comatose patients provide further evidence that the MMN is often present in coma, varying within a single patient from easily detectable to undetectable at different times. This highlights the fact that regular and repeated assessments are extremely important when using MMN as a neurophysiological predictor of coma emergence.

Somatosensory and auditory deviance detection for outcome prediction during postanoxic coma

Objective

Prominent research in patients with disorders of consciousness investigated the electrophysiological correlates of auditory deviance detection as a marker of consciousness recovery. Here, we extend previous studies by investigating whether somatosensory deviance detection provides an added value for outcome prediction in postanoxic comatose patients.

Methods

Electroencephalography responses to frequent and rare stimuli were obtained from 66 patients on the first and second day after coma onset.

Results

Multivariate decoding analysis revealed an above chance‐level auditory discrimination in 25 patients on the first day and in 31 patients on the second day. Tactile discrimination was significant in 16 patients on the first day and in 23 patients on the second day. Single‐day sensory discrimination was unrelated to patients’ outcome in both modalities. However, improvement of auditory discrimination from first to the second day was predictive of good outcome with a positive predictive power (PPV) of 0.73 (CI = 0.52–0.88). Analyses considering the improvement of tactile, auditory and tactile, or either auditory or tactile discrimination showed no significant prediction of good outcome (PPVs = 0.58–0.68).

Interpretation

Our results show that in the acute phase of coma deviance detection is largely preserved for both auditory and tactile modalities. However, we found no evidence for an added value of somatosensory to auditory deviance detection function for coma‐outcome prediction.