Auditory and Somatosensory P3 Are Complementary for the Assessment of Patients with Disorders of Consciousness

Abstract

The evaluation of the level of consciousness in patients with disorders of consciousness (DOC) is primarily based on behavioural assessments. Patients with unresponsive wakefulness syndrome (UWS) do not show any sign of awareness of their environment, while minimally conscious state (MCS) patients show reproducible but fluctuating signs of awareness. Some patients, although with remaining cognitive abilities, are not able to exhibit overt voluntary responses at the bedside and may be misdiagnosed as UWS. Several studies investigated functional neuroimaging and neurophysiology as an additional tool to evaluate the level of consciousness and to detect covert command following in DOC. Most of these studies are based on auditory stimulation, neglecting patients suffering from decreased or absent hearing abilities. In the present study, we aim to assess the response to a P3-based paradigm in 40 patients with DOC and 12 healthy participants using auditory (AEP) and vibrotactile (VTP) stimulation. To this end, an EEG-based brain-computer interface was used at DOC patient’s bedside. We compared the significance of the P3 performance (i.e., the interpretation of significance of the evoked P3 response) as obtained by ‘direct processing’ (i.e., theoretical-based significance threshold) and ‘offline processing’ (i.e., permutation-based single subject level threshold). We evaluated whether the P3 performances were dependent on clinical variables such as diagnosis (UWS and MCS), aetiology and time since injury. Last we tested the dependency of AEP and VTP performances at the single subject level. Direct processing tends to overestimate P3 performance. We did not find any difference in the presence of a P3 performance according to the level of consciousness (UWS vs. MCS) or the aetiology (traumatic vs. non-traumatic brain injury). The performance achieved at the AEP paradigm was independent from what was achieved at the VTP paradigm, indicating that some patients performed better on the AEP task while others performed better on the VTP task. Our results support the importance of using multimodal approaches in the assessment of DOC patients in order to optimise the evaluation of patient’s abilities.

Narrative Review: Quantitative EEG in Disorders of Consciousness

“…They did not find differences in the P300 characteristics when comparing UWS to MCS patients or even when comparing traumatic vs. non-traumatic etiologies. The performances of the two different stimuli (auditory and vibrotactile) were independent of each other [120]. Investigating the P300 response in relation to the CRS-R score, it was shown that the amplitude of the novelty P300 is correlated with the CRS-R and even more with the auditory sub-score [105].…”

EEG-based vibrotactile evoked brain-computer interfaces system: A systematic review

“…Surprisingly, only around one-fifth of EVE-BCI studies were carried out for patients. These patients suffered from multiple levels of motor functioning loses caused by different diseases including the unresponsive wakefulness syndrome (UWS) [ 8 , 79 ], disorder of consciousness (DOC) [ 9 , 49 , 61 , 63 , 70 ], amyotrophic lateral sclerosis (ALS) [ 54 , 57 , 87 , 89 , 103 ], locked-in syndrome (LIS) [ 58 , 63 , 70 , 78 ], stroke [ 94 ], and minimally conscious state (MCS) [ 86 ]. On the other hand, most studies (83.54% of cases) alternatively focused on healthy subjects covering adults of all ages, including young people, the middle-aged, and elders.…”

“…Studies involving the above 20 participants contributed 7.59% of cases. The largest sample size among selected papers was 52, with forty DOC patients and twelve healthy people [ 49 ]. Only a tiny proportion represented the finding of a case study involving a single subject only, accounting for 5.06% of cases.…”

“…Similarly, Nam, Cichocki [ 32 ] only used a 0.5 to 40 Hz bandpass filter as the whole pre-processing step. On the contract, a relatively complex pipeline was performed in Annen, Mertel [ 49 ]’s study. The 0.01–30 Hz bandpass filter was firstly applied, followed by an artifact and outlier removal where trials were rejected if any data points exceeded the threshold of ±100μV.…”

Brain–Computer Interfaces for Awareness Detection, Auxiliary Diagnosis, Prognosis, and Rehabilitation in Patients with Disorders of Consciousness

“…Annen et al ( 2020) proposed a P300based paradigm with auditory and vibrotactile stimulation which was supposed to evoke auditory-evoked potentials (AEP) and vibrotactile-evoked somatosensory potentials (VTP). 34 Forty patients with DoC and 12 healthy participants were separated into four groups (healthy participants, patients in an EMCS, patients in an MCS, and patients in a VS/UWS). The relationships between groups and 'differentiated response' in none, either or both paradigms were investigated, and a logarithmic regression model was then used to analyze the recorded P300 response data.…”