Simon P. Levine

Spatiotemporal patterns of beta desynchronization and gamma synchronization in corticographic data during self-paced movement

OBJECTIVE To study the spatiotemporal pattern of event-related desynchronization (ERD) and event-related synchronization (ERS) in electrocorticographic (ECoG) data with closely spaced electrodes. METHODS Four patients with epilepsy performed self-paced hand movements. The ERD/ERS was quantified and displayed in the form of time-frequency maps. RESULTS In all subjects, a significant beta ERD with embedded gamma ERS was found. CONCLUSIONS Self-paced movement is accompanied not only by a relatively widespread mu and beta ERD, but also by a more focused gamma ERS in the 60-90 Hz frequency band.

A direct brain interface based on event-related potentials

Cross-correlation between a trigger-averaged event-related potential (ERP) template and continuous electrocorticogram was used to detect movement-related ERPs. The accuracy of ERP detection for the five best subjects (of 17 studied), had hit percentages >90% and false positive percentages <10%. These cases were considered appropriate for operation of a direct brain interface.

Visualization of significant ERD/ERS patterns in multichannel EEG and ECoG data

OBJECTIVES Analysis of event-related desynchronization (ERD) and event-related synchronization (ERS) often requires the investigation of diverse frequency bands. Such analysis can be difficult, especially when using multichannel data. Therefore, an effective method for the visualization of event-related changes in oscillatory brain activity is required. METHODS A bootstrap-based method is presented which gives time-frequency maps showing only significant changes of ERD or ERS in predetermined frequency bands. RESULTS Examples from an electroencephalographic study and an electrocorticographic study are shown. The results demonstrate how easily reactive channels and their spatio-temporal and frequency-specific characteristics can be identified by means of this method. CONCLUSIONS The proposed method is a simple but effective way to visualize significant ERD/ERS patterns.

Toward a direct brain interface based on human subdural recordings and wavelet-packet analysis

Highly accurate asynchronous detection of movement related patterns in individual electrocorticogram channels has been shown using detection based on either event-related potentials (ERPs) or event-related desynchronization and synchronization (ERD/ERS). A method using wavelet-packet features selected with a genetic algorithm was proposed to simultaneously detect ERP and ERD/ERS and was tested on data from seven subjects and four motor tasks. The proposed wavelet method performed better than previous methods with perfect detection for four subject/task combinations and hit percentages greater than 90% with false positive percentages less than 15% for at least one task for all seven subjects.

Identification of electrocorticogram patterns as the basis for a direct brain interface.

This study reports on the first step in the development of a direct brain interface based on the identification of event-related potentials (ERPs) from an electrocorticogram obtained from the surface of the cortex. Ten epilepsy surgery patients, undergoing monitoring with subdural electrode strips and grid arrays, participated in this study. Electrocorticograms were continuously recorded while subjects performed multiple repetitions for each of several motor actions. ERP templates were identified from action-triggered electrocorticogram averages using an amplitude criterion. At least one ERP template was identified for all 10 subjects and in 56% of all electrode-recording sets resulting from a subject performing an action. These results were obtained with electrodes placed solely for clinical purposes and not for research needs. Eighty-two percent of the identified ERPs began before the trigger, indicating the presence of premovement ERP components. The regions yielding the highest probability of valid ERP identification were the sensorimotor cortex (precentral and postcentral gyri) and anterior frontal lobe, although a number were recorded from other areas as well. The recording locations for multiple ERPs arising from the performance of a specific action were usually found on close-by electrodes. ERPs associated with different actions were occasionally identified from the same recording site but often had noticeably different characteristics. The results of this study support the use of ERPs recorded from the cortical surface as a basis for a direct brain interface.

An assistive navigation system for wheelchairs based upon mobile robot obstacle avoidance

The NavChair assistive navigation system is being developed to meet the needs of multiply handicapped people who are unable to operate available wheelchair systems. The NavChair Project was conceived as an application of mobile robot obstacle avoidance to a power wheelchair. During the course of this project, the vector field histogram (VFH) method has been adapted for use in human-machine systems and the shortcomings of the wheelchair platform have been overcome. This paper briefly reviews the VFH method, describes interesting aspects of its application to a power wheelchair, and presents an experimental evaluation of system performance. Finally, unresolved problems of obstacle avoidance in human-operated vehicles are discussed.<<ETX>>

Adaptive shared control of a smart wheelchair operated by voice control

The NavChair Assistive Wheelchair Navigation System is being developed to reduce the cognitive and physical requirements of operating a power wheelchair. The NavChair is an adaptive shared control system, shared in that control is divided between the wheelchair and the wheelchair operator and adaptive in that how control is divided between the wheelchair and the wheelchair operator varies based on current task requirements. This paper describes the NavChairs method for automatically allocating control between the wheelchair and its operator and presents results evaluating the performance of the NavChairs automatic adaptation mechanism from an experiment in which able-bodied subjects used voice control to steer the NavChair through a navigation task requiring several transitions between operating modes.

Asymptomatic sensorimotor polyneuropathy in workers exposed to elemental mercury

Neurologic and electrodiagnostic evaluations and urine mercury level determinations were performed on 138 chlor-alkali plant workers, some of whom were chronically exposed to inorganic mercury vapor. Eighteen subjects had a mild polyneuropathy on clinical examination. These subjects had significantly (p < 0.05) elevated urine mercury indexes, reduced sensation on quantitative testing, prolonged distal latencies with reduced sensory evoked response amplitudes, and increased likelihood of abnormal needle electromyography compared with the remaining 120 subjects. Similar results were found for subgroups matched by sex and age. We conclude that elemental mercury exposure is associated with a sensorimotor polyneuropathy of the axonal type; the degree of neurologic impairment appears related to the magnitude of exposure.

Automatic adaptation in the NavChair Assistive Wheelchair Navigation System

The NavChair Assistive Wheelchair Navigation System [7] is an adaptive shared control system being developed to provide mobility to those individuals who would otherwise find it difficult or impossible to use a power wheelchair due to cognitive, perceptual, or motor impairments. The NavChair provides task-specific navigation assistance to the wheelchair operator in the form of several distinct operating modes, each of which distributes control differently between the wheelchair and the operator. This paper describes the NavChairs mechanism for automatically selecting the most appropriate operating mode based on a combination of the wheelchairs immediate situation and its global location. Results from two experimental evaluations of the adaptation method are presented.

Elemental mercury exposure: peripheral neurotoxicity.

Nerve conduction tests were performed on the right ulnar nerve of factory workers exposed to elemental mercury vapour. Time integrated urine mercury indices were used to measure the degree of exposure. Workers with prolonged distal latencies had significantly higher urine mercury concentrations when compared with those with normal latencies. Significant correlations between increasing urine mercury concentrations and prolonged motor and sensory distal latencies were established. Elemental mercury can affect both motor and sensory peripheral nerve conduction and the degree of involvement may be related to time-integrated urine mercury concentrations.