Referred Sensation Areas in a Bilateral Toes Amputee

Various mechanisms in generating phantom limb pain (PLP) have been hypothesized in the literature. However, there still is no clear understanding of how PLP develops and why it presents. Amputation leads to permanent anatomical and physiological changes of the neural path previously supplying the brain with sensory input, as well as to formation of referred sensation areas (RSAs) on the stump or its vicinity. Sensations may be evoked in the lost body part upon stimulation of RSAs that may be exploited as artificial sensory input. In this work, we present the analysis of RSA maps from a 45-year-old female with bilateral toes amputation. Maps of the RSAs were identified in eight sessions over 107 days, characterized by dynamics in both location and type of associated evoked sensation. The evoked sensations were reported to be felt like current through and brushing of the phantom toes at low intensities close to the sensation threshold. Sensations evoked by electrical stimuli delivered through electrodes covering one or more RSAs approximated the sensation of summation of sensations evoked by mechanical stimuli (light brushing). No painful evoked sensations were observed

The Fascicle Undulation Effect on the Activating Function in Magnetic Stimulation of Peripheral Nerves with Transverse and Longitudinal Fields

Analysis of activating function for a long, myelinated nerve fiber with undulating path in transverse and longitudinal induced electric fields was performed. The induced electric field was computed using a finite element model composed by a round coil beneath a bath with saline solution. Longitudinal and transverse components of the induced electric field were computed along two axes, one tangential and the other axial to the coil. The influence of a transverse field on the modified activating function was analyzed when the fiber path was determined by the fascicle undulation, and by the fascicle undulation plus the fiber undulation inside the fascicle. For the first path type, undulation wavelength of 40 to 90 mm and 0.8 mm amplitude determined a classic activating function with: (a) multiple virtual cathodes that could generate two or three stimulation sites for axially oriented coil, and (b) virtual cathode with distorted shape in amplitude up to 35% and location up to 67% for tangentially oriented coil. For axially oriented coil, the transverse field term of the modified activating function was comparable in amplitude with the classic activating function, however significant attenuation could occur due to perineurium. For the second path type with wavelength of tenths of millimeters and amplitudes of a quarter of the wavelength, the classic activating function had such a dramatic increase in the spatial frequency that could not predict the stimulation site with the usual interpretation of the virtual cathode. Similarity between the results obtained with the first path type and the ones obtained in a previous in-vitro experiment suggests that the undulating fascicles within the nerve trunk can be responsible for stimulation with transverse fields

The Impact of Function Location on Typing and Pointing Tasks With an Intraoral Tongue-Computer Interface

Intraoral target (typing) and on-screen target (pointing/tracking) selection tasks were performed by 10 participants during 3 consecutive day sessions. Tasks were performed using 2 different intraoral sensor layouts. Reduction of undesired sensor activations while speaking as well as the influence of intraoral temperature variation on the signals of the intraoral interface was investigated. Results showed that intraoral target selection tasks were performed better when the respective sensor was located in the anterior area of the palate, reaching 78 and 16 activations per minute for repetitive and "unordered" sequences, respectively. Virtual target pointing and tracking tasks, of circles of 50, 70, and 100 pixels diameter, showed no significant difference in performance, reaching average pointing throughputs of 0.62 to 0.72 bits per second and relative time on target of 34% to 60%. Speaking tasks caused an average of 10 to 31 involuntary activations per minute in the anterior part of the palate. Intraoral temperature variation between 11.87 degrees C and 51.37 degrees C affected the sensor signal baseline in a range from -25.34% to 48.31%. Results from this study provide key design considerations to further increase the efficiency of tongue-computer interfaces for individuals with upper-limb mobility impairments

Effects of sensory feedback in intra-oral target selection tasks with the tongue

Purpose: To investigate the effects of visual and tactile intra-oral sensor-position feedback for target selection tasks with the tip of the tongue. Method: Target selection tasks were performed using an inductive tongue-computer interface (ITCI). Visual feedback was established by highlighting the area on a visual display corresponding to the activated intra-oral target. Tactile feedback was established using a sensor-border matrix over the sensor plates of the ITCI, which provided sensor-position tactile queues via the user’s tongue. Target selection tasks using an on-screen keyboard by controlling the mouse pointer with the ITCI’s was also evaluated. Results: Mean target selection rates of 23, 5 and 15 activations per minute were obtained using visual, tactile and “none” feedback techniques in the 3rd training session. On-screen keyboard target selection tasks averaged 10 activations per minute in the 3rd training session. Involuntary activations while speaking or drinking were significantly reduced either through a sensor-matrix or dwell time for sensor activation. Conclusions: These results provide key design considerations to further increase the typing efficiency of tongue-computer interfaces for individuals with upper-limb mobility impairments