1 Introduction

High-prevalence and severe neurologic diseases are a dilemma for both patients and medical professionals since the latter significantly affects motor functions, dignified communication abilities, and, consequently, the quality of life. Conventional rehabilitation methods sometimes cannot ensure full recovery of a patient, keeping them highly disabled. Lately, brain-computer interface technology has developed as a feasible alternative, creating a new path to neurorehabilitation. Brain-Computer Interface (BCI) technology allows for direct communication of the brain with a computer, enabling control over an external movement or communication device and exploiting it to promote neuroplasticity. All of them shall allow a strong advance on the applications of BCI technology in neurorehabilitation, embracing not only current effectiveness but also key studies and future directions necessary to overcome the limitations in recent applications. Detailed descriptions of high-frequency and severe neurological disorders delineate the potentiality of BCI use as a fast-advancing technology, which significantly ensures better patient outcomes and increased independence. This review is an overview of the role that BCI technology can play in neurorehabilitation, from application in high-incidence neurologic disorders like stroke, traumatic brain injury, and spinal cord injury, to its use in more complex neurological conditions like amyotrophic lateral sclerosis and multiple sclerosis. The review gives an overview of current applications, important studies, and basic clinical research that has been conducted on the effectiveness of BCI systems in regard to motor recovery, communication, and independence. This review aims to underline the strong potential of BCI technology in changing neurorehabilitation and to point out which areas require further research and development of this technology in order to help overcome some of the existing limitations.

2 BCI Technology in Neurorehabilitation for High-Incidence Neurological Disorders

2.1 General Overview

High-incidence neurological disorders, such as stroke, Traumatic Brain Injury (TBI), and Spinal Cord Injury (SCI), are events that very importantly affect motor functions and the quality of life in patients. Traditional rehabilitation approaches most often remain inadequate for complete recovery, and patients retain different disabilities. BCI technology stands to offer an interesting alternative that enables patients to control external devices by brain signals, hence facilitating motor recovery and improving neuroplasticity.

Most of the BCI systems in neurorehabilitation use electroencephalogram (EEG) and aim to record activity during motor imagination or other mental tasks. The signals are further translated to commands, used to drive a robotic arm, or a virtual reality environment, among others. All this has an effect not only on physical rehabilitation but on neural pathways being fired again and again, which in turn helps in recovery.

2.2 Current Applications

The key areas of BCI technology's application in the fields of neurorehabilitation include motor imagery-based training, neurofeedback, and robotic assistance. The potential benefits of these modalities have been shown to considerably enhance motor recovery in patients suffering from highly prevalent neurological disorders.

Motor imagery is a process in which patients only imagine movements but do not actually act. The related brain activity is detected by the EEG-based BCI systems in order to control external devices. A number of studies have shown that practice with motor imagery can enhance motor recovery by activating neural circuits responsible for movement.

Neurofeedback refers to the process where an individual is provided with continuous moment-to-moment information about his or her brain activity. It enables a patient to modify that activity through practice. Such approaches have been applied in enhancing motor and cognitive functions of patients with neurological disorders. BCI systems that include a neurofeedback function provide means through which patients can perceive and control their brain activity, thus reorganizing and recovering their brain functions.

Robotic devices controlled by the BCI systems can assist the patient in making movements which he/she cannot do on their own. This assisted therapy helps in retraining motor pathways and improves functional recovery. Combination of robotic assistance with BCI technology has been very encouraging in improving motor function and independence in patients with stroke and spinal cord injury.

2.3 Key Studies and Clinical Research

Focuses on significant studies that have demonstrated the effectiveness of BCI systems in neurorehabilitation. These studies are critical in establishing the technology's potential and setting the stage for further clinical research. Distinguishes between key studies and clinical research, emphasizing the practical application of BCI technology in clinical settings. This section should explore how clinical trials have validated the findings of key studies and contributed to the development of BCI-based interventions.

Several important studies have shown that BCI technology is competent in neurorehabilitation. Ang conducted a randomized controlled trial to evaluate the effectiveness of an EEG-based motor imagery BCI system in stroke rehabilitation [1]. The study involved stroke patients participating in motor imagery-based BCI training. Results showed significant improvements in motor function as evaluated by the Fugl-Meyer Assessment. The study concluded that an EEG-based motor imagery BCI system effectively enhances motor recovery in stroke patients.

Daly and Wolpaw reviewed the use of BCI technology for neurorehabilitation, focusing on chronic stroke patients. The review highlighted various BCI applications, including motor imagery and neurofeedback, which showed significant improvements in motor function [2]. The authors emphasized the potential of BCIs to enhance neuroplasticity and promote functional recovery in chronic stroke patients.

Soekadar investigated the use of BCI-controlled robotic exoskeletons for spinal cord injury rehabilitation [3]. The study reported significant improvements in motor function and independence among patients using the BCI-controlled exoskeletons. The authors concluded that BCI technology could effectively re-establish motor function in spinal cord injury patients.

2.4 Basic Research

Basic research in BCI technology aims to understand the underlying principles of brain signal acquisition, processing, and translation into actionable commands. This includes both in vivo and in vitro studies.

2.4.1 In Vivo Studies

In vivo studies involve testing BCI systems on living organisms to observe how the technology interacts with biological tissues. This category of study is most important in providing invaluable insight into the practical application and possible consequences of BCI systems. For example, in vitro research has been conducted on how BCI systems can evoke neural plasticity and contribute to the restoration of motor functions.

2.4.2 In Vitro Studies

In vitro studies are conducted outside the normal biological context on biological samples. Laboratory tests will allow testing and refinement of BCI component and algorithm prior to their testing on subjects in a clinical trial. In vitro research specializes in the optimization of signal detection and processing techniques to raise the accuracy and reliability of BCI systems.

2.5 Clinical Research

Discusses fundamental research underlying BCI technology, including in vivo and in vitro studies. This section explains how basic research contributes to the development of more effective BCI systems and their translation into clinical practice [4].

Clinical research is highly relevant for establishing the validity of BCI technologies within realistic clinical settings. Indeed, several clinical trials tested BCIs for neurorehabilitation, and the results showed different degrees of success and bore elements of aspects that could be improved.

Clinical trials have reported that patients with high incidence neurological disorders experienced significant improvement in motor and cognitive functions by using BCI systems. For instance, Pichiorri have revealed the capacity of BCI-assisted neurorehabilitation to advance motor recovery in chronic stroke patients [3]. Specularly, the works of Ramos-Murguialday have reported that the mentioned positive impact of BCI technology on patient rehabilitation was typical for even such patients with a spinal cord injury [5].

3 BCI Technology in Neurorehabilitation for Complex Neurological Disorders

3.1 General Overview

Complex neurologica disorders, such as amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), and cerebral palsy (CP), all present specific challenges for neurorehabilitation. In general, these disorders result in severe motor and cognitive impairments that significantly impact the level of independence and quality of life of patients. BCI technology has potential use in enhancing functional capability and the general sense of well-being in patients with complex disorders.

3.2 Current Applications

BCI has been used to allow patients suffering from a range of complicated neurological disorders to realize different facets of their lives, such as communication, mobility, and environmental control. Most BCI systems, however, depend on the recorded activity that bypasses damaged neural pathways to provide the brain with alternative means of interaction with the external environment.

The suffering of patients with ALS is similar to those with other complicated motor disorders in that it drastically handicaps communication. The BCI systems provide a way of communication by the patient via the brain, in which they control messages from their intention. The P300-based BCI systems, in particular, are known to be effective in communication, for it detects specific brain responses associated with attention.

Robotic exoskeletons and wheelchairs controlled by BCI systems can significantly improve the mobility of patients with even quite complex neurologic disorders. The devices enable patients to perform movements that they could not do without them; thus, it increases independence and the quality of life.

It can also enable the individual to control the environment, dim the lights, turn up the heat, and run other domestic utilities. This could help greatly in providing more freedom and comfort for subjects with profound motor disabilities.

3.3 Landmark Studies and Clinical Research

Reviews pivotal studies that have shaped the understanding and application of BCI technology in complex neurological disorders. Examines how clinical trials have tested the effectiveness of BCI systems in these complex cases, highlighting successes and areas needing improvement.

Discusses how BCI technology is applied in the management of complex neurological disorders like ALS and MS. addresses the specific benefits and limitations of BCI systems in these cases.

A number of landmark studies have demonstrated the potential of BCI technology in the treatment of difficult-to-manage neurological disorders. Kübler explored the use of a P300-based BCI communication system for patients with ALS. The study demonstrated that participants could successfully communicate using the BCI system, significantly improving their quality of life. The authors concluded that P300-based BCI systems can significantly enhance communication abilities in ALS patients. [6, 7].

Wolpaw reviewed the efficacy of EEG-based BCI systems in enabling communication for ALS patients. The review found significant improvements in communication, highlighting the potential of EEG-based BCI systems to enhance communication in ALS patients [8].

Birbaumer investigated the use of slow cortical potential-based BCIs for communication in ALS patients. The study reported significant communication improvements, concluding that slow cortical potential-based BCIs can effectively enhance communication in ALS patients [9].

3.4 Basic Research

Basic research in the context of complex neurological disorders focuses on understanding the neural mechanisms underlying these conditions and developing BCI systems that can effectively interface with the affected neural pathways.

Animal models of in vivo studies for complex neurologic disorders can be harnessed to see how BCI systems can modulate neural activity and bring about functional recovery. These studies provide insights into the possible therapeutic applications of BCIs in human patients.

Impulse tests are those in which BCI parts and algorithms are tested in vitro, on neural tissues obtained from a patient suffering from complex neurologic disorders. The goal of these studies is the development of the technology, attuning its application specifically, and testing its safety and effectiveness next to a clinical trial.

3.5 Clinical Research

Focuses on the fundamental research supporting BCI applications in complex disorders, including studies that explore neural mechanisms and the development of tailored BCI systems.

Without conducting clinical research, the translation from basic research to patient treatment of people suffering from complex neurologic disorders is not possible. A series of clinical trials have been conducted in which the use of BCIs was under close scrutiny.

The results from these clinical trials indicate that BCI systems can significantly enhance communication, mobility, and environmental control in patients with such complex neurological disorders. For example, Sellers and Donchin, has shown the performance of P300-based BCIs in restoring communication for ALS patients, while Leeb, showed similar results but for MS patients [10,11].

4 Limitations and Future Directions

Despite the promising results, BCI technology in neurorehabilitation has many limitations at present. These include difficulties in signal acquisition, processing, interpretation, and individualized training. Improvements should be made regarding the accuracy and reliability of BCI systems, the development of interfaces that are user-friendly, and finding of new applications in neurorehabilitation. Further studies are required in large-scale clinical trials so that the long-term efficacy and safety of BCI technologies can be validated.

5 Conclusion

This review accentuated the state-of-the-art BCI technology and its application in neurorehabilitation. High-incidence and complex neurological disorders have shown promising results in motor recovery, communication, and independence using BCI systems. This was possible with noted efficacy in motor imagery-based training, neurofeedback, and robotic assistance leading toward improved functional outcomes. Furthermore, BCI technology has brought valuable solutions for communication, mobility, and environmental control in severely impaired patients.