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Publications -- fMRI Research -- Electrophysiology

Keywords: Neurophysiology - Visual Cortex - Neuroprosthetics - Retina Implant

The Retina Implant Project

Macula degeneration and retinitis pigmentosa are the most frequently diagnosed ailments in blind people. The former is the leading cause of blindness in the western world. To restore some vision to blind patients suffering from these conditions, several research groups jointly aim at developing a micro-electronic prosthesis. The goal is to electrically stimulate neurons in the retina, evoking activity in corresponding cortical neurons and hence pseudo-visual sensations in blind patients. This concept is based on the finding that patterns of simple visual sensations can be elicited in response to epi-retinal pattern electrical stimulation [Humayun et al. (1999)]. Retinal stimulations are delivered by microelectrodes or prototype implants. In order to evaluate a visual prosthesis` use to blind people, we analyze the evoked cortical activation. We particularly aim at a retinotopic activation of sufficient spatio-temporal resolution to provide for a satisfactory perception of a visual scene. Based on conservative estimates, the best spatial resolution is in the range of 0.8 visual angle. This would give the blind patient a visus of 1/48. Temporal resolution of 40-60 impulses/s is achievable. We therefore expect a visual prosthesis based on electrical stimulation of the retina to fulfill the basic requirements of retinotopic activation of the visual cortex at a reasonable spatio-temporal resolution. Clinical experience with other neuro-prostheses (e.g. cochlear implant) indicates that the adjustment of the stimulation parameters in post implantation training can further improve the benefits to a blind patient.

Find out more about the project and our partners at this site.

Research Interests

  • Electrical recordings from the retina and the visual cortex
  • Properties of visual receptive fields of retinal and cortical neurons
  • Latency calculations for electrically evoked cortical spikes
  • Testing of prototype sub- and epi-retinal visual implants

multifocal visual stimulus

visual retina RFs

multifocal visual stimulus

Visual Stimulation

The monitor luminance at each stimulus position on a 28x28 grid is driven by a binary m-sequence. The stimulus sequence consists of 4095 samples and is presented at 101Hz.

cross-correlation maps

Visual Retina Receptive Fields

Cross-correlations between each stimulus sequence and the neuronal signals yield 2-dim correlation maps. Light colours indicate monitor stimulation pixels that were highly correlated with the occurrence of spikes of the respective type. Such receptive fields line up nicely along the approximate path of the ganglion axon fibre bundles.