Abstract
Purpose::
The encoding of single aspects of the outside world by the retina and brain is still largely unsolved - often this encoding of the visual environment is described as "the concerted signaling of the retinal neurons". Due to the highly parallel processing of the visual information transmitted from the retina to the visual centers of the brain, and the distinct large variability of single neuron responses, we investigate the encoding of the visual information in ganglion cell ensembles and populations of the mammalian retina.
Methods::
The experiments employed superfused, flattened preparations of intact rabbit (Oryctolagus cuniculus) retinas. Responses of retinal ganglion cell populations with up to 400 neurons to different visual stimuli were recorded using a multi-electrode array (UCMEA). The population activity was analyzed by identifying population members as well as the emergence of coinciding events, robust multi-unit firing patterns and ensemble and population activity vectors.
Results::
Emerging coincidence on very small time scales (< 0.2 µs) and populations vectors can serve as spike train intrinsic time reference on which all further analysis of the data in the time domain was based. The analysis of the identified discrete and robust firing patterns based on this time reference reveals how the visual information is further encoded: the distributed coding within the firing patterns is based on a limited number neurons. These neurons can be identified and assigned to neuronal sub-ensembles of the population based on the temporal response behaviour. The "concerted" signaling between different ensembles of neurons within the recorded population, which are contributing to the "short" and robust spike sequences, reveals further important aspects of the visual code.
Conclusions::
Utilizing the metaphor of "concerted signaling" describing the encoding of the visual information we here present a way to identify the different "sections" of the retinal neuronal "orchestra" as well as how they contribute to the encoding. Further reminiscence to a musical score allows us to define the visual code itself in part based on "sets" which can be identified using the emerging coincidence within the neuronal firing or ensemble or population activity vectors. These firing pattern sets are composed of "bars" which are represented by the discrete and robust spike sequences which signaled by members of different neuronal ensembles or populations.
Keywords: neuro-ophthalmology: cortical function/rehabilitation