Development of behavior and learning inAplysia

Summary A set of fundamental issues in neuroethology concerns the neural mechanisms underlying behavior and behavioral plasticity. We have recently analyzed these issues by combining a simple systems approach in the marine molluscAplysia with a developmental analysis aimed at examining the emergence and maturation of different forms of behavior and learning. We have focussed on two kinds of questions: 1) How are specific neural circuits developmentally assembled to mediate different types of behaviors? and 2) how is plasticity integrated with these circuits to give rise to different forms of learning? From our analysis of the development of learning and memory inAplysia, several themes have emerged: 1) Different forms of learning emerge according to different developmental timetables. 2) Cellular analogs of learning have the same developmental timetables as their respective forms of behavioral learing. 3) An analysis of non-decremented responses prior to the emergence of sensitization reveals a novel inhibitory process on both behavioral and cellular levels. 4) Sensitization emerges simultaneously in diverse response systems, suggesting an underlying general process. 5) A widespread proliferation of central neurons occurs in the same developmental stage as the emergence of sensitization, raising the possibility that some aspect of the trigger for neuronal proliferation may also contribute to the expression of sensitization.     

Mechanisms of circulatory homeostasis and response in Aplysia.

This review concerns the organization and function of arterial vasculature in Aplysia californica, especially the vasomotor reflexes that support circulatory homeostasis, and fixed patterns of response that may reroute blood flow during changes in behavioral state. The observations presented here raise three hypotheses for further study: 1) Arterial vasculature is functionally organized with precisely structured, independently regulated subdivisions; these are most evident for arterial systems serving digestive and reproductive processes; 2) arterial musculature is inherently responsive to local pressure changes, having both static and dynamic reflexes that promote efficient, evenly-distributed flow of blood; and 3) complex, long-lasting behaviors like egg laying have, as part of their makeup, equally prolonged and stereotypical changes in the pattern of circulation. Taken together, these observations support the view that maintenance and adjustment of blood flow in gastropod molluscs is an unexpectedly complex and highly integrated component of behavior.     

Insect behavior at the leaf surface and learning as aspects of host plant selection

Summary Direct observations on the feeding behavior of insect herbivores are uncommon, but important. The important aspects of host-plant selection by phytophagous insects that have been revealed by such observations are the role of chemicals in the leaf surface, and learning. There are few detailed reports of behavior at the leaf surface, but these indicate that many, if not all, insects exhibit behavior pattenrs that can be interpreted as an examination of the quality of the surface and acceptance or rejection may follow without further testing. A number of experiments show that chemicals from the leaf surface commonly contribute to the acceptability or otherwise of a plant and in most cases so far the active chemicals are of widespread occurrence, not having a specific association with the host plant. Some experiments show that the association between surface chemicals and plant palatability is learned, but in other cases there is evidence of an innate response. Habituation to deterrent chemicals has been demonstrated in the laboratory, but not in the field. Food aversion learning also occurs and may be important in dietary switching by polyphagous insects.     

Shock induces a long-lasting elevation of blood glucose in Aplysia.

Glucose, and not trehalose, was found to be the main blood sugar in Aplysia californica. Changes in blood glucose in response to stress produced by electric shock were measured in blood obtained both from animals dissected within ten minutes of shocking and from catheterized animals at various intervals, up to two and a half hours after the shock. Electric shock increased blood glucose levels. The rise in blood sugar continued as long as two and a half hours after shock.     

Peptidergic co-transmission in Aplysia: functional implications for rhythmic behaviors.

Despite their ubiquitous presence in the central and peripheral nervous systems, the behavioral functions of peptide co-transmitters remain to be elucidated. The marine mollusc Aplysia, whose simple nervous system facilitates the study of the neural basis of behavior, was used to investigate the role of peptidergic co-transmission in feeding behavior. Several novel modulatory neuropeptides were purified, and localized to identified cholinergic motorneurons. Physiological and biochemical studies demonstrated that these peptides are released when the motorneurons fire at frequencies that occur during normal behavior, and that the peptides modify the relationship between muscle contraction amplitude and relaxation rate so as to maintain optimal motor output when the intensity and frequency of feeding behavior change.     

Control of the cardiovascular system of Aplysia by identified neurons.

The neural network that controls the cardiovascular system of Aplysia adapts cardiovascular function to a variety of different physiological and behavioral situations. It (1) coordinates the cardiovascular system with the renal and respiratory systems; (2) modifies both systemic and regional blood flow during food-elicited arousal and feeding; and (3) changes the tension of longitudinal vascular muscle to adapt the arterial tree to changes in body shape. Indirect evidence suggests that the cardiovascular control circuit may also play a role in maintaining homeostasis during egg laying. Several putative neurotransmitters, including acetylcholine, serotonin, R15 alpha 1 and R15 alpha 2 peptides, have been localized to identified neurons in this circuit.     

A possible age-related decrement in the conduction velocity of Aplysia neuron R2.

In late winter and in spring, the conduction velocity of the R2 axon of Aplysia californica is 0.48 m/sec or more in all specimens. However, in the summer, fall and early winter, some sexually mature animals exhibit markedly diminished R2 conduction rates (as low as 0.24 m/sec). It is possible that this reduced velocity is a reflection of the age of the specimen from which the axon is taken.     

Aplysianin-A, an antibacterial and antineoplastic glycoprotein in the albumen gland of a sea hare, Aplysia kurodai

Aplysianin-A, an antibacterial and antineoplastic factor in the albumen gland of the sea hare Aplysia kurodai, was isolated. It had a molecular weight of approximately 320 kD and consisted of subunits with a molecular weight of 85 kD. It contained 9.8% neutral sugar. Aplysianin A showed 50% inhibition of Bacillus subtilis growth at a concentration of 4 microgram protein/ml and 50% lysis of murine MM46 tumor cells at 14 ng protein/ml. A partial identity of antigenic specificity of the purified specimen with an antineoplastic factor from Aplysia eggs was observed in immunodiffusion tests.     

Aplysianin-A,an antibacterial and antineoplastic glycoprotein in the albumen gland of a sea hare,Aplysia kurodai

Summary Aplysianin-A, an antibacterial and antineoplastic factor in the albumen gland of the sea hareAplysia kurodai, was isolated. It had a molecular weight of approximately 320 kD and consisted of subunits with a molecular weight of 85 kD. It contained 9.8% neutral sugar. Aplysianin A showed 50% inhibition ofBacillus subtilis growth at a concentration of 4 g protein/ml and 50% lysis of murine MM46 tumor cells at 14 ng protein/ml. A partial identity of antigenic specificity of the purified specimen with an antineoplastic factor fromAplysia eggs was observed in immunodiffusion tests.Acknowledgment. We are indebted to the staff of Fisheries Research Laboratory, Faculty of Agriculture, University of Tokyo, Maisaka, for the collection of sea hares.     

Temperature acclimation and learning in fish

Summary Control fish acclimated at 21°C learned to swim upright following the attachment of floats to their ventral surfaces, while fish acclimated at both 5°C and 33°C failed to learn the swimming skill. Fish previously acclimated at 5°C and then transferred to 21°C 48 h before the task, learnt the swimming skill better than the control fish, but fish acclimated at 33°C and transferred to 21°C failed to acquire the new skill. Acclimation temperature, therefore, significantly modifies the learning behaviour of fish.     

机器学习面临的挑战

该文讨论了机器学习目前面临的几个挑战,包括：高维特征空间和数据量问题,大数据量的计算困难,寻求最优解的困难和可解释性差等问题．然后针对当前很多人关心的几个重要问题,例如大数据问题,深度学习,概率图模型等做了分析,以引起深入思考．