A Quality Parameter for the detection of the intentionality of movement in patients with neurological tremor performing a finger-to-nose test

Abstract

The identification of the intentionality of movement is a key-aspect for the development of brain-computer interfaces (BCIs) applicable to daily life in neurological patients. We present a novel method of processing of electroencephalography (EEG) signals for the extraction of movement intention in neurological patients with upper limb tremor. This method is based on event-related EEG desynchronization, considering α (8-12 Hz), β (13-30 Hz), and γ (30-40 Hz) bands. We have analyzed the EEG signals from the sensorimotor areas of 4 neurological patients presenting an upper limb tremor (grade 1 to 3/4) and executing successive finger-to-nose movements. A Quality Parameter (QP) for the detection of intentionality of movement has been extracted, by considering: (a) the changes in the β²/α and β/α ratio (representing bursts of β-γ frequencies) during the pre-movement period; (b) an appropriate threshold predicting the movement; (c) the number of movements executed. This QP allows the prediction of the voluntary movement with a probability between 70% and 90%. This method could be implemented in a wearable BCI to detect the intentionality of movement and could be used, for instance, to trigger the electrical stimulation in selected muscles of upper limbs with the aim of blocking the emergence of tremor.

Quality parameters for a multimodal EEG/EMG/kinematic brain-computer interface (BCI) aiming to suppress neurological tremor in upper limbs

“…The mean QP was 82±12% (median = 83.5%) for the β/α ratio and 79.5±10.4% (median = 80%) for the β²/α ratio. We found no significant difference between the QP calculated from β/α ratio and β²/α ratio (p = 0.502) 8 . The highest QPs were found when the selected sub-band of frequency included the 30–35 Hz ( Figure 3).…”

“…However, the entire α band and its sub-bands never provided low values of QP. In terms of QP distribution on the scalp, the central areas of the brain showed the highest values of QPs 8 . The highest probability to predict efficiently the intention of the upper limb movement corresponded to the contralateral central area of the brain.…”

“…By considering: (i) the changes in the β²/α and β/α ratio (representing bursts of β-γ frequencies) during the pre-movement period; (ii) an appropriate threshold indicating which peaks of ratios are actually followed by a movement (and therefore may be considered as a predictor of movement); (iii) the number of movements executed, we extracted a QP for the detection of intentionality of movement 8 .…”

“…By applying (2) to the EEG power spectra from all the EEG channels and the successive runs, we obtained ratiograms which are spectrogram-like representations of EEG activities on the skull. The peaks (β/α and β²/α ratios) higher than a defined threshold were considered as indicators of a potential voluntary movement 8 , given that they represent the detection of the cortical motor preparation of the movement. To determine the occurrence of false positive results, the number of movements detected was added.…”

“…To determine the occurrence of false positive results, the number of movements detected was added. QP is the geometric mean of the probability of movement (true positive stimulations) and the percentage of movements predicted 8 .…”