Abstract
Frogs show escape behavior in response to a looming stimulus. It has been demonstrated that synchronized oscillations among retinal ganglion cells (Class-4 neurons) carry essential information for escape behavior (Ishikane et al., 2005). However, the information encoded by synchronized oscillations among Class-4 neurons is only one of the conditions necessary for eliciting escape behavior. Although synchronized oscillations can encode stimuli of any size and continuity, they cannot encode expansion. Activities of other types of retinal ganglion cells may play a functional role in escape behavior. To elucidate this issue, we recorded spikes from frog retinal ganglion cells with a planar multi-electrode array and conducted behavioral experiments. First, to identify neurons encoding the expansion at the retina, we presented two types of stimuli to all subtypes of ganglion cells: one was an expanding square and the other was a square that was gradually filled to the center from the outside. We found that compared with the other stimulus, Class-3 neurons respond preferentially to the expanding square. Following this, to investigate the relationship between activities of Class-3 neurons and escape behavior, we presented multiple squares. Each square was expanded or gradually filled to the center from the outside. These 25 squares eventually formed a single large square. Decreasing the number of expanded squares reduced both the responses of Class-3 neurons and escape rate. These stimuli caused strong synchronized oscillations among Class-4 neurons. Disrupting stimulus continuity did not reduce the responses of Class-3 neurons but inhibited synchronized oscillations among Class-4 neurons and the escape rate. These results suggest that Class-3 neurons could encode the expansion and contribute to the elicitation of escape behavior. The combination of activities of Class-3 neurons and synchronized oscillations among Class-4 neurons could trigger escape behavior.
Meeting abstract presented at VSS 2015