Original ContributionsMechanisms of Electrical Stimulation with Neural Prostheses
Section snippets
INTRODUCTION
Which neural elements are activated by electrical stimulation in different parts of the nervous system? What are the principles to control complex neural processes with neural prostheses? We analyze local responses and network influences to handle these questions.
The first response of long homogeneous nerve or muscle fibers to an electric field is proportional to the second derivative of the electric potential along the fiber (1., 2., 3., 4.). This theory of the activating function is based on
Computer Simulation
The direct influence of a neuro-prosthetic device on a target neuron can be modeled in a two-step procedure. First we have to compute the electric potential Ve along the neural structures. This can be done with finite element (28,36,38), finite difference (40), boundary element (41), or Galerkin methods (42); all these methods are described in Ref. 43. In basic investigations authors often follow (1., 2., 3.,32,34,37) an assumption of the pioneering McNeal model (44) where for a point source in
Cochlear Neuron
For a given electrode position spike initiation regions in a target neuron depend on polarity and stimulus strength. Small variations in the pulse amplitude may cause essentially different arrival times at the axon terminal. This is demonstrated with a bipolar neuron close to a stimulating electrode of a cochlear implant (Fig. 3). Extracellular resistivity Ve = 0.3 kOhm.cm and calculation of potential from a 1 mA point source results in 1 V at r = 0.24 mm (Eq. 1), which is assumed as electrode
DISCUSSION
Fortunately, it is not necessary to generate an exact copy of the natural firing pattern when a neuroprosthetic device is used. The surprising amount of plasticity of the brain was demonstrated by successfully applying quite different stimulating strategies in cochlear implants or by a four-electrode cuff around the optic nerve that—after training—allows a blind patient to recognize different shapes, line orientations, and even letters depending on duration, amplitude, and repetition rate of
ACKNOWLEDGMENT
This work was supported by the Austrian Ministry of Transport, Innovation and Technology, the Austrian Science Fund (FWF), research project No. P15469; and a grant from the Kent Waldrep National Paralysis Foundation in Addison, TX.
REFERENCES (83)
Ways to approximate current-distance relations for electrically stimulated fibers
J Theor Biol
(1987)- et al.
Retinal prosthesis for the blind
Surv Ophthalmol
(2002) - et al.
The effect of dorsal column stimulation on the nociceptive response of dorsal horn cells and its relevance for pain suppression
Pain
(1977) The basic mechanism for the electrical stimulation of the nervous system
Neuroscience
(1999)Basics of hearing theory and noise in cochlear implants
Chaos Solitons Fractals
(2000)- et al.
A model of the electrically excited human cochlear neuron. I. Contribution of neural substructures to the generation and propagation of spikes
Hear Res
(2001) - et al.
A model of the electrically excited human cochlear neuron. II. Influence of the 3-dimensional cochlear structure on neural excitability
Hear Res
(2001) - et al.
Modeling the repetitive firing of retinal ganglion cells
Brain Res
(1990) - et al.
Ionic current model of bipolar cells in the lower vertenrate retina
Vision Res
(1996) - et al.
A study of the application of the Hodgkin-Huxley and the Frankenhaeuser-Huxley model for electrostimulation of the acoustic nerve
Neuroscience
(1986)