A new, behaving, head restrained, eye movement-controlled feline model for chronic visual electrophysiological recordings

BACKGROUND: Anesthetized, paralyzed domestic cats are often used as model organisms in visual neurophysiology. However, in the last few decades, behaving animal models have gathered ground in neurophysiology, due to their advantages over anesthetized, paralyzed models. NEW METHOD: In the present study a new, behaving, awake feline model is described, which is suitable for chronic visual electrophysiological recordings. Two trained, head- fixed cats were suspended in a canvas harness in a specially designed stand. The animals had been trained to fixate the center of a monitor during static and dynamic visual stimulation. Eye movements were monitored with implanted scleral coil in a magnetic field. Cell-level activity was recorded with eight electrodes implanted in the caudate nucleus. RESULTS: Our two trained cats could maintain accurate fixation, even during optic flow stimulation, in an acceptance window of +/-2.5 degrees and +/-1.5 degrees , respectively. The model has yielded accurate recordings for over two years. COMPARISON WITH EXISTING METHOD(S): To our knowledge, this is the first awake, behaving feline model with rigorous eye movement control for chronic, cell-level visual electrophysiological recordings, which has actually proven to work during a longer period. CONCLUSIONS: The new model is optimal for chronic visual electrophysiological recordings in the awake, behaving domestic cat

Neuronal code of spatial visual information in the caudate nucleus

Earlier reports described huge overlapping visual receptive fields and the absence of retinotopic organization in the dorsolateral, caudal part of the caudate nucleus. In the present study we suggest a possible alternative mechanism for the coding of spatial visual information. Extracellular microelectrode recordings were carried out in halothane-anesthetized, immobilized, artificially ventilated cats. In order to investigate the responsiveness of the single neurons to visual information arriving from different sites of the receptive field, we divided the visual fields to 20 parts of equal size and stimulated the individual parts one-by-one. We found that each single visual caudate nucleus (CN) neuron can carry information about stimulus locations throughout the whole physically approachable visual field of the investigated eye. A large majority (85%) of these neurons exhibited significantly different responses to stimuli appearing in different regions of their huge receptive field. Thus these neurons appear to have the ability to provide information on the site of the stimulus via their discharge rate. The huge receptive fields in combination with the spatial selectivity suggest that these caudate nucleus neurons may serve as panoramic localizers. On the population level, the sites of maximal responsiveness of the visual neurons are distributed over the whole extent of the receptive fields. We argue that groups of these panoramic localizer neurons with different locations of maximal stimulus preference should have the ability to accurately code the locations of visual stimuli. We propose this distributed population code of visual information as an alternative information processing mechanism