Neurocomputing 70 (2007) 2817–2827 A neuroengineering suite of computational tools for visual prostheses Christian Morillas a,Ã , Samuel Romero a,b , Antonio Martı´nez a , Francisco Pelayo a , Leonardo Reyneri c , Markus Bongard d , Eduardo Ferna´ndez d a Department of Computer Architecture and Technology, University of Granada, Spain b Department of Computer Sciences, University of Jae´n, Spain c Department of Electronics, Politecnico of Torino, Italy d Department of Histology and Institute of Bioengineering, University Miguel Herna´ndez, Alicante, Spain Available online 26 May 2007 Abstract The cooperation between neuroscience and biomedical engineering gave rise to a recent, but growing research field, known as neuroengineering. We follow its principles to have a system providing basic descriptions of the visual world to the brain’s cortex. We describe a set of software and hardware tools to interface with neural tissue, in order to transmit visual information encoded into a bioinspired neural-like form. The set is composed of a retina-like encoder, and a platform to optimize electrical stimulation parameters for a multi-electrode implant. The main objective is to progress towards a functional visual neuroprosthesis for the blind. r 2007 Elsevier B.V. All rights reserved. Keywords: Neural processing and coding; Spiking neurons; Artificial retinas; Visual neuroprostheses; Electrical neurostimulation 1. Introduction The results and developments described in this paper are part of the outcomes of a research project named CORTIVIS (Cortical Visual Neuroprosthesis for the Blind, EC reference QLK6-CT-2001-00279) [9]. The project was conceived to design a device for translating images acquired by a mini-camera into electrical signals, to be delivered to the brain cortex. The electrical stimulation of the visual area of the cortex will create in the implanted individual a visual sensation in the form of bright spots, known as ‘‘phosphenes’’. The translation of digital images into phosphene patterns will provide the patient with a rudimentary, but functional, form of vision. Previous experiences, like those carried out by Brindley and Lewin [3], Dobelle et al. [5], or Schmidt et al. [21], have demonstrated the feasibility of eliciting controlled visual perceptions by injecting electrical currents into the neural tissue of the visual pathway. In this line, a number of research groups are working towards developing visual prostheses based on this principle. There are three main approaches for the implant, depending on the location of the visual pathway where the electrical interface is placed. Retinal implants, like the ones being developed by [8], apply electrical stimulation through a set of electrodes located below or onto the retina, aiming to replace the function of photoreceptors or performing a stimulation of ganglion cells, respectively. The major disadvantage of this approach is the fragility of the retina, making the implantation and stabilization of the interface quite difficult. A second alternative is to stimulate the optic nerve, as Veraart et al. [25] propose. This choice also presents difficult surgical access, and poor control of the position and size of the evoked phosphenes. The third option is to place the interface directly in the primary visual area of the brain. A classical example of this kind of implants is the one developed by Dobelle, which employs a set of planar electrodes located on the surface of the cortex [5]. In order to reach the appropriate layer of neurons, a large amount of current must be employed for stimulation (in the order of milliamperes). This high quantity of charge provokes eventually negative effects on the implanted ARTICLE IN PRESS www.elsevier.com/locate/neucom 0925-2312/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.neucom.2006.04.017 Ã Corresponding author. Tel.: +349 582 40459; fax: +349 582 48993. E-mail addresses: cmorillas@atc.ugr.es (C. Morillas), sromero@ ujaen.es, sromero@atc.ugr.es (S. Romero), amartinez@atc.ugr.es (A. Martı´nez), fpelayo@ugr.es (F. Pelayo), reyneri@polito.es (L. Reyneri), markus.bongard@umh.es (M. Bongard), e.fernandez@ umh.es (E. Ferna´ndez).