## 4 Discussion
There are several possible causes contributing to the ERP variability, resulting in atypical average signals and the consequent low SNR and reduced discriminative power. These factors may include fluctuations in attention and vigilance levels, the cognitive workload demanded by the task, and the patient's limited working memory for sustaining attention on target symbols. These processes, which can be related to reduced executivefunctions, can lead to high variability in ERP latency and amplitude. Additionally, external factors such as repetitive stimulation, inducing SSVEPs, and distractors from adjacent stimuli may have also contributed to the variability and decrease in target discrimination. Nevertheless, the ERPs were more consistent than those obtained in our exploratory study [7] involving a CLIS patient. Previous research has shown that, while a unique common pattern in the EEG signal of CLIS patients could not be found, it was common for the EEG signal to show slowing and attenuation of alpha activity, along with significantly altered auditory-evoked potential responses compared to those of healthy individuals [29]. Additionally, an ECoG study involving a late-stage ALS patient [30] revealed that the P300 component of the signal, detectable when the patient was still able to communicate through voluntary muscle control, became undetectable three months after the last communication was made. Given the highly atypical nature of the observed patient's ERP waveforms, further methods and studies are required to understand what potential (confounding) factors affects target ERPs and to identify other neural correlates that can help predict BCI performance. To further elucidate potential signaling effects, future studies should incorporate BCI paradigms that systematically assess neural responses at different levels, including reflexive, perceptual, and cognitive processes and isolating the effects of different stimulus characteristics. This should occur early on at the LIS stage, when patients can provide more reliable feedback. Our study provides valuable insights into potential strategies to enhance the feasibility and efficacy of BCIs for CLIS patients. However, both neurophysiological and classification results cannot be generalizable to other CLIS patients, given the significant variability in individual characteristics and conditions within this population. EEG-based BCIs are still not a reliable communication system for at-home, day-to-day use for CLIS patients [17]. Moreover, there are only a handful of successful studies utilizing a functional BCI-based system for CLIS patients. Although we achieved three sessions with an online classification equal to or above 80%--surpassing the 56.9% achieved in [11] and comparable to accuracies in [6; 8], all achieved with non-invasive techniques--our results were not consistent and cannot be considered successful as there was no repetition of those results. However, this underscores the potential of the proposed approaches to be effective for these patients. The use of BCIs for communication in patients in CLIS would improve the quality of life of these patients by allowing them to regain a voice in the decision-making process of their caretaking needs, as well as allowing a level of social interaction with their surroundings, family members, and caretakers. In other words, this would represent a qualitative improvement within the goals of personalized medicine. Longitudinal studies are essential for achieving more effective BCIs and could provide us with additional insights into the neuronal changes during the transition from LIS to CLIS [31; 32]. For this to happen, BCI studies should start once a patient enters LIS, a state in which patients can still communicate with eye blinks, eye movements, or alternative communication tools, such as eye-tracking spellers.