To evaluate the performance with respect to selectivity of the effect of the wings bending in the cone coil relative to the double coil in transcranial magnetic stimulation. The focal area and the width vector of the central lobe of the induced electrical field distributed along an elliptic surface approximating the cortex were computed for four coil models. The models represented the real coils, the double B70 and the cone B80 Medtronic, and their corresponding simulated flat coils (B70flat and B80flat). A response function was evaluated in 10 subjects for distal and proximal muscles of the upper limb by stimulation of the motor cortex along a line approximating the central sulcus. The width of the response function, at the level of the center of gravity, provided a quantitative measure for coil focality. The focal area for B70, B70flat, B80, and B80flat calculated from the model was 31.4, 32.2, 94.4, and 50.6 cm2, respectively. The width of the central lobe along the stimulation line was: 36.2, 37, 46, and 48.6 mm, respectively. Mean values of focality measure obtained experimentally were in distal muscles, 5.06 RPU (relative position units) for B70 and 5.99 RPU for B80; in proximal muscles, 4.11 RPU for B70 and 5.13 RPU for B80, with a mean RPU value of 11.13 mm. The difference, a 19% focality measure increase in B80 relative to B70 in distal muscles, was statistically significant (P < 0.001). The focality was demonstrated to be highest for the double coil. The width of the central lobe of the induced electrical field distribution is well reflected in the width of the response function. The increase in B80 is mainly due to wing geometry and relative placement of wings and is not due to the wing bending. The width of the central lobe characterizes the spread of the induced current below the wing junction, and it is a better focality estimator than the focal area for cone coils.

For an individual with tetraplegia assistive robotic arms provide a potentially invaluable opportunity for rehabilitation. However, there is a lack of available control methods to allow these individuals to fully control the assistive arms. Here we show that it is possible for an individual with tetraplegia to use the tongue to fully control all 14 movements of an assistive robotic arm in a three dimensional space using a wireless intraoral control system, thus allowing for numerous activities of daily living. We developed a tongue-based robotic control method incorporating a multi-sensor inductive tongue interface. One abled-bodied individual and one individual with tetraplegia performed a proof of concept study by controlling the robot with their tongue using direct actuator control and endpoint control, respectively. After 30 min of training, the able-bodied experimental participant tongue controlled the assistive robot to pick up a roll of tape in 80% of the attempts. Further, the individual with tetraplegia succeeded in fully tongue controlling the assistive robot to reach for and touch a roll of tape in 100% of the attempts and to pick up the roll in 50% of the attempts. Furthermore, she controlled the robot to grasp a bottle of water and pour its contents into a cup; her first functional action in 19 years. To our knowledge, this is the first time that an individual with tetraplegia has been able to fully control an assistive robotic arm using a wireless intraoral tongue interface. The tongue interface used to control the robot is currently available for control of computers and of powered wheelchairs, and the robot employed in this study is also commercially available. Therefore, the presented results may translate into available solutions within reasonable time.

Alternative and effective methods for controlling powered wheelchairs are important to individuals with tetraplegia and similar impairments whom are unable to use the standard joystick. This paper describes a system where tongue movements are used to control a powered wheelchair thus providing users, with high level spinal cord injuries, full control of their wheelchair. The system is based on an inductive tongue control system developed at Center for Sensory-Motor Interaction (SMI), Aalborg University. The system emulates a standard analog joystick in order to interface the wheelchair, thus ensuring that the system works with almost any wheelchair. The total embedment of the tongue interface into the mouth makes the control practically invisible. A fuzzy system combining 8 sensors for directional control allows for multidirectional control of the wheelchair. Preliminary test results show navigation abilities, which are highly competitive when compared to other tongue control system.

The paper introduces a novel design of air-core inductive sensors in printed circuit board (PCB) technology for a tongue control system. The tongue control system provides a quadriplegic person with a keyboard and a joystick type of mouse for interaction with a computer or for control of an assistive device. Activation of inductive sensors was performed with a cylindrical, soft ferromagnetic material (activation unit). Comparative analysis of inductive sensors in PCB technology with existing hand-made inductive sensors was performed with respect to inductance, resistance, and sensitivity to activation when the activation unit was placed in the center of the sensor. Optimisation of the activation unit was performed in a finite element model. PCBs with air-core inductive sensors were manufactured in a 10 layers, 100 microm and 120 microm line width technology. These sensors provided quality signals that could drive the electronics of the hand-made sensors. Furthermore, changing the geometry of the sensors allowed generation of variable signals correlated with the 2D movement of the activation unit at the sensors' surface. PCB technology for inductive sensors allows flexibility in design, automation of production and ease of possible integration with supplying electronics. The basic switch function of the inductive sensor can be extended to two-dimensional movement detection for pointing devices.

The induced electric field transverse to peripheral nerve trunks has been shown to lead to stimulation, contrary to predictions of the cable equation. Two possible mechanisms of activation have been documented in literature: the change in the transmembrane voltage due to an electric field transverse to the membrane of a cylindrical fiber and the transverse field projection on the undulating fiber path within the fascicle. To distinguish between these alternatives, an analysis of the stimulation site was performed in vitro along 15 phrenic nerves from pigs, with a 5-cm-diameter round coil. Stimulation with induced electric field having longitudinal and attenuated transverse components resulted in stimulation sites in the vicinity of the negative peak of the spatial derivative of the longitudinal electric field and threshold variations with coil positions along the nerve trunk. Stimulation with a transverse field yielded patterns of one, two, or three stimulation sites, scattered or uniformly distributed around the location of the two field maxima. A nerve structure analysis outlined the fiber undulation within the fascicle and a network of wavy fascicles. The presence of this network and the variations of the stimulation site, and of the threshold suggest that the path of the fiber has a major undulation due to the undulation of the fascicles within the nerve trunk, which may be responsible for the stimulation with an electric field transverse to the nerve trunk.