COGNITIVE PROCESSING AND BRAIN COMMUNICATION IN AMYOTROPHIC LATERAL SCLEROSIS

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive paralysis of limbs and bulbar musculature. This severe physical impairment makes cognitive evaluation a big challenge, thus there is a great need for an assessment that does not require overt motor responses. Moreover, we need of augmentative communication strategies because the disease generally leads to complete paralysis and, therefore, patients are unable to communicate with the external world by any means. For this purpose, Brain Computer Interfaces (BCIs) seem a promising approach to facilitate communication with these patients. The aim of this thesis is twofold. First, assessing cognitive processing in ALS by means of a novel evaluation tool. Second, allowing brain communication in completely paralyzed ALS patients who had lost their vision in order to eliminate the unbearable loss of communication in paralysis (“unlocking the locked-in”). The first study introduces a novel approach for assessing cognitive functions in ALS. This approach uses neuropsychological tests that require minimal overt motor or verbal responses; together with vibro-tactile P300s. Results indicate mild cognitive impairment in oral language comprehension tasks and reduced vibro-tactile P300 amplitudes in patients compared to healthy controls. Importantly, correlations between the vibro-tactile P300 latency and psychometric test results suggest that the former measure could serve as a neurophysiological marker of cognitive decline in ALS patients. The second study introduces a distraction paradigm based in auditory event-related potentials (ERPs) to evaluate the ability of change detection, focusing, and re-orientation of attention in ALS. The results revealed a modification of the amplitude and the latency of the N200, the P300 and the re-orienting negativity (RON) components. This could suggest an alteration of the endogenous mechanism that controls the detection of change, thus resulting in a reduction of the allocation and the re-orientation of attentional resources. The third study aimed at testing the feasibility of a Near Infrared Spectroscopy (NIRS) -based BCI communication approach for patients in the Completely Locked-in Stage (CLIS) due to ALS. For this purpose two CLIS patients were trained to control their cerebral-cortex´s functional-activations in response to auditory processing of correct or incorrect statements assessed with NIRS. The results of the study are very promising, showing that both CLIS patients communicated with fronto-cortical oxygenation based BCI at an average correct response rate of 70% over a period of several weeks. We conclude that this novel approach of brain-communication is safe and, reliable, representing, so far, the best communication possible for patients in completely locked-in state. In conclusion we propose a) the novel combination of vibro-tactile or acoustic ERPs and motor-independent neuropsychological tests as an alternative and easily implementable way for assessing cognitive functions in ALS and b) we confirm the usefulness and effectiveness of above mentioned electrophysiological approaches in the late stage of ALS either to assess cognitive processing or to establish communication with a BCI system.