Biomedical Engineering Reference
In-Depth Information
skin, and we investigated whether or not a nonlinear phenomenon such as
the “phantom sensation” or some kind of interaction may occur between the
two sensations evoked by electrically stimulating two sensory nerve fibers
simultaneously [195].
The experimental arrangement was basically the same as that used in the
experiments described in Sect. 4.7.3.2. The difference was that two tungsten
microelectrodes were separately and simultaneously inserted percutaneously
into the median nerve at two points on the forearm (around 2 cm and 10 cm
proximal to the wrist joint, respectively) of each subject. After investigating
the type of mechanoreceptor unit and the physical properties of the evoked
sensation (quality, magnitude, and projected area) by giving electrical stimu-
lation (a series of electrical pulses) to each electrode individually, electrical
stimulation was then given to these two electrodes simultaneously, and the
resulting changes in the properties of the evoked sensation and its projec-
tedareawerethencomparedwiththesituationinwhicheachelectrodewas
stimulated individually.
In our experiments, combinations of types of mechanoreceptor units sti-
mulated simultaneously were slowly adapting I (SA I) and SA I in most cases.
In some cases, however, combinations of types of mechanoreceptor units bet-
ween Pacinian (PC) and SA I, and between PC and PC were also examined.
From the results obtained to date, it may be concluded that the combi-
ned evoked sensation when two nerve fibers are stimulated simultaneously
became a simple algebraical summation of two evoked sensations evoked by
the electrical stimulation of the individual mechanoreceptor unit. It may the-
refore not be necessary to pay attention to nonlinear interactions between
the properties of the evoked sensation of each sensory fiber when we give el-
ectrical stimulation to each sensory nerve fiber in accordance with the output
signal from the sensor system of an artificial arm system.
However, further research is needed in order to reach conclusive results,
because the number of the experiments is still too small, mainly due to the
diculty in fixing the positions of the microelectrodes for a long time, so that
a nerve signal from a single mechanoreceptor unit can be recorded by each
electrode.
The Development of a System of Interpreting Somatic Sensations
for Use with Artificial Hands and Limbs.
Based on the results of the
abovementioned studies, we developed a prototype of an artificial arm system
capable of sensing mechanical stimuli and then transferring these stimuli to
the subject, so that the subject may experience the stimuli as the correspon-
ding somatic sensations [196].
The system consists of: 1) an artificial arm system whose palm and fin-
gers were covered with pressure-conductive rubber [197] in order to detect
pressure applied to the artificial hand (Fig. 4.60); 2) an electrical stimulator
(pulse generator) which can provide microelectrical stimulation to the nerve
