Markus Bongard

Development of a cortical visual neuroprosthesis for the blind: the relevance of neuroplasticity

Clinical applications such as artificial vision require extraordinary, diverse, lengthy and intimate collaborations among basic scientists, engineers and clinicians. In this review, we present the state of research on a visual neuroprosthesis designed to interface with the occipital visual cortex as a means through which a limited, but useful, visual sense could be restored in profoundly blind individuals. We review the most important physiological principles regarding this neuroprosthetic approach and emphasize the role of neural plasticity in order to achieve desired behavioral outcomes. While full restoration of fine detailed vision with current technology is unlikely in the immediate near future, the discrimination of shapes and the localization of objects should be possible allowing blind subjects to navigate in a unfamiliar environment and perhaps even to read enlarged text. Continued research and development in neuroprosthesis technology will likely result in a substantial improvement in the quality of life of blind and visually impaired individuals.

Conditioned spikes: a simple and fast method to represent rates and temporal patterns in multielectrode recordings

Increasing evidence suggests that the brain utilizes distributed codes that can only be analyzed by simultaneously recording the activity of multiple neurons. This paper introduces a new methodology for studying neural ensemble recordings. The method uses a novel representation to provide complementary information about the stimuli which are contained in the temporal pattern of the spike sequence. By using this procedure, a high correlation of synchronized events with stimuli times is apparent. To quantify the results and to compare the performance of this method against the most traditional raster plot, we have used Fano factor and cross-correlation analysis. Our results suggest that several consecutive spikes from different neurons within an extended time window may encode behaviorally relevant information. We propose that this new representation, in addition to the other approaches currently used (standard raster plots, multivariate statistical methods, neuronal networks, information theory, etc.), can be a useful procedure to describe population spike dynamics.

Decoding the Population Responses of Retinal Ganglions Cells Using Information Theory

In this paper information theory is used to analyze the coding capabilities of populations of retinal ganglions cells for transmitting information. The study of a single code versus a distributed code has been contrasted using this methodology. The redundancy inherent in the code has been quantified by computing the bits of information transmitted by increasing number of neurons. Although initially there is a linear growth, when certain numbers of neurons are included, information saturates. Our results support the view that redundancy is a crucial feature in visual information processing.

Neural Coding Analysis in Retinal Ganglion Cells Using Information Theory

Information Theory is used for analyzing the neural code of retinal ganglion cells. This approximation may quantify the amount of information transmitted by the whole population, versus single cells. The redundancy inherent in the code may be determined by obtaining the information bits of increasing cells datasets and by analyzing the relation between the joint information compared with the addition the information achieved by aisle cells. The results support the view that redundancy may play a crucial feature in visual information processing.

Temporally Faithful Representation of Salient Stimulus Movement Patterns in the Early Visual System

In human visual search, the time required to detect an object that starts to move is approximately independent of the number of distractors in the visual field (pop-out effect)1. Motion onset is therefore considered as being a “basic feature”. Several theoretical models of the visual system attempt to explain the interplay of such basic features, attentional selection, and higher-level processing2,3,4,5. Local contrast of basic features is thought to be calculated in parallel across the visual field in a first step. On the basis of this feature contrast computation, salient positions are determined. The most salient one is then selected by some form of winner-take-all mechanism, the output of which is used to direct attention to this potentially most interesting part of the visual scene.