Assessing attention and cognitive function in completely locked in state with event related brain potentials and epidural electrocorticography.
OBJECTIVE Patients in the completely locked in state (CLIS) due to, for example, amyotrophic lateral sclerosis (ALS) no longer possess voluntary muscle control. Assessing attention and cognitive function in these patients during the course of the disease is a challenging but essential task for both nursing staff and physicians. APPROACH An electrophysiological cognition test battery, including auditory and semantic stimuli, was applied in a late stage ALS patient at four different time points during a six month epidural electrocorticography (ECoG) recording period. Event related cortical potentials (ERP) together with changes in the ECoG signal spectrum, were recorded via 128 channels that partially covered the left frontal, temporal and parietal cortex. MAIN RESULTS Auditory but not semantic stimuli induced significant and reproducible ERP projecting to specific temporal and parietal cortical areas. N1/P2 responses could be detected throughout the whole study period. The highest P3 ERP was measured immediately after the patient's last communication through voluntary muscle control, which was paralleled by low theta and high gamma spectral power. Three months after the patient's last communication, i.e. in the CLIS, P3 responses could no longer be detected. At the same time, increased activity in low frequency bands and a sharp drop of gamma spectral power were recorded. SIGNIFICANCE Cortical electrophysiological measures indicate at least partially intact attention and cognitive function during sparse volitional motor control for communication. Although the P3 ERP and frequency specific changes in the ECoG spectrum may serve as indicators for CLIS, a close meshed monitoring will be required to define the exact time point of the transition.
Journal of neural engineering