Long-Term Facilitation in A Swimming Sea Anemone

The peculiar behaviour of the anemone, Stomphia coccinea (O. F. Müller), in response to certain starfishes was noted by Yentsch & Pierce (1955). More detailed description of the swimming reaction and attempts to identify the stimulating factor involved were made by Sund (1958). The easily measured sequence of events which constitutes the response provides an opportunity to analyse quantitatively integrated behaviour in a coelenterate. This study is an attempt to identify and measure a process which might be considered a type of learning in an animal with simple neural organization. Guessing that the relationship between the starfish Dermasterias and Stomphia might be a predator-prey one (although no evidence favours this assumption) it seemed likely that encounters which resulted in no harm to the anemone might result in habituation. Experiments have therefore been done to test whether the swimming behaviour of this animal is modified by previous occurrences of the stimulus. It was a surprise to find that the reaction is enhanced by repetition. The results indicate long-lasting changes within the animal which have been called here long-term facilitation. This is a kind of modification of behaviour of the same apparent complexity as habituation but with opposite sign. Facilitation of monosynaptic reflexes lasting minutes or hours has been mentioned by Eccles (1958), but while such relatively simple neural mechanism for modifiability of response has been demonstrated, no comparable type of learning is currently included in several reviews of animal behaviour, though it is recognized that a facilitation process could be the basis of imprinting. In the attacking response of young cephalopods Wells (1958) has demonstrated facilitation without reward.