A fundamental question in neuroscience is how populations of neurons encode information relevant to the behavior of the organism by generating short electrical spikes called action potentials. These spikes, 1-3 ms in duration, are responsible for carrying information throughout the nervous system. An important test bed to study questions regarding the neural code is the retina. This is a very accessible sensory organ due to the extensive knowledge about single cell properties, anatomy and the fact that the function of the system is clear. We study the information encoding in the brain by asking how the retina tells the brain about the outside visual environment.
While the retina is the first stage of processing the visual scene, in order to put the study of the population code used by neuron in a global context, one needs to think about the path of information processing between the visual input at the retina and the motor output of an animal. Studying this path of decision-making by an animal requires appropriate selection of the animal model. In our lab we use the archer fish (Toxotes jaculatrix), which can shoot down insects hanging on foliage above water using a squirt of water from their mouth. The jet of water hits the insect and the insect falls into the water where the fish can feed on it. This remarkable ability relies, among other things, on the information streaming from the retina to the brain. In addition, it is possible to train an archer fish to shoot at an artificial target printed on a paper instead of an insect, making it possible to study the encoding of different features of the external visual environment by the retina. We study information encoding in the archer fish retina using a multi-electrode array technology. In this method, the isolated archer fish retina is placed on a multi-electrode array and then presented with a stimulus that matches the one used in the behavioral task. The multi-electrode array contains 100 to 256 microelectrodes that enable the simultaneous recording from many of ganglion cells. By studying the relation between the stimulus and the retinal response, we can understand the principles of the neural code of the archer fish retina.