Long Term Modulation and Control of Neuronal Firing in Excitable Tissue Using Optogenetics - Foundations on Natural and Artificial Computation - page 265

Long Term Modulation and Control of Neuronal
Firing in Excitable Tissue Using Optogenetics

L. Humphreys 1 , 3 , J.M. Ferrandez 1 , 2 ,andE.Fernandez 1 , 3

1 Instituto de Bioingenierıa, Universidad Miguel Hernandez, Alicante
2 Dpto. Electronica, Tecnologıa de Computadoras, Univ. Politecnica de Cartagena
3 CIBER-BBN
[e-mail]

Abstract. Since the initial demonstration of nerve excitation and the
subsequent action potential generation by Hodgkin and Huxley in 1952,
most efforts in modulating or restoring neural activity to cure diseases
or injury have concentrated on using neural interfaces for electrical stim-
ulation with electrodes. However, it was soon appreciated that repeated
chronic stimulations necessary for lasting rehabilitation could have its
drawbacks. Namely, the eventual degradation of tissue and electrodes,
issues of biocompatibility and immune responses to foreign objects. Nev-
ertheless, new innovative methods are emerging which can improve the
quality and duration of neural stimulations. Here we review and sug-
gest an alternative approach to modulate activity using optogenetics in
therapy.

1 Introduction

Neuroprosthetic devices have been implemented in therapies based on their abil-
ity to interface with the central and peripheral nervous system. These devices
normally consist of electrodes which are chronically implanted to perform stimu-
lation and recordings of excitable cells, effectively monitoring and re-introducing
the activity absent to the effected areas. Therapeutic applications are widespread
ranging from, limb prostheses, retinal and cortical prostheses, spinal cord inner-
vation, stroke, pain and depression alleviation to name a few [1] [2]. Some devices
have had profound implications on the quality of patient's lifes, in particular,
cochlear implants [3] and deep brain stimulation (DBS) for tremor treatment
in Parkinson's disease [4]. However, chronic stimulation of excitable tissue has
also been met with considerable complications which eventuate in the deteriora-
tion of stimulation and recording quality. Most efforts have focused on resolving
issues of biocompatibility which primarily depend on the mechanical properties
of the neural interface and interaction of the surrounding tissue. Other examples
include micromovements of the electrodes, trauma from the initial insertion of
which can lead to intrinsic foreign body responses and glial inflammation and
neuronal loss near the implant [5]. Normally, electrical stimulation induces a
functional response by depolarizing the membranes of excitable cells through
the application of biphasic current pulses. The importance of a charge balanced