We have begun to analyze several elementary forms of learning in a simple preparation consisting of the isolated mantle organs and abdominal ganglion of Aplysia. Previous studies suggested that plasticity at siphon sensory neuron synapses contributes to habituation and dishabituation of the gill- and siphon-withdrawal reflex in this preparation. We next wished to identify the sensory neurons th...

Whether gravity challenges blood supply to the brain in standing man is a much-disputed topic in physiology. Burton (3) stated that “it is no harder in the circulation for the blood to flow uphill than downhill” and “differences in the level of different parts of the vascular bed do not in any way affect the driving forces for flow and so do not directly affect the circulation” (3). The prerequ...

Many studies of the neural mechanisms of learning have focused on habituation, a simple form of learning in which a response decrements with repeated stimulation. In the siphon-elicited siphon withdrawal reflex (S-SWR) of the marine mollusk Aplysia, the prevailing view is that homosynaptic depression of primary sensory afferents underlies short-term habituation. Here we examined whether this me...

A tactile stimulus to the siphon of Aplysia produces a defensive withdrawal reflex consisting of contraction of the siphon, the gill, and the mantle shelf. We studied long-term habituation of this reflex using two types of preparations, one focusing on the siphon component and the other on the gill component of the reflex. Siphon withdrawal, studied in unrestrained animals, showed marked habitu...

.025), while the responses of the sham-operated were not significantly changed. After the operation the scores of the deganglionated group were significantly lower than the scores of the sham-operated group (P = .013). These results suggest that the siphon withdrawal component of the defensive reflex is mediated primarily by the central nervous system. This does not mean that all siphon withdra...

We analysed video records of three mating events involving nine free-living whitetip reef sharks in Cocos Islands, Costa Rica to examine reproductive behaviour in this species. We describe several behaviours never before documented in this species, and four behaviours never before documented in any elasmobranch. Here, we also present the first hypothesis for the function of the male’s paired re...

An α-siphon of width w is the locus of points in the plane that are at the same distance w from a 1-corner polygonal chain C such that α is the interior angle of C. Given a set P of n points in the plane and a fixed angle α, we want to compute the widest empty α-siphon that splits P into two non-empty sets. We present an efficient O(n log n)-time algorithm for computing the widest oriented α-si...