Classical conditioning in a simple withdrawal reflex in Aplysia californica (original) (raw)
Related papers
The Journal of Neuroscience the Official Journal of the Society For Neuroscience, 1997
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 siphonwithdrawal reflex in this preparation. We next wished to identify the sensory neurons that participate in the reflex and examine their plasticity more directly. To investigate the contribution of the LE siphon mechanosensory cells, we recorded from them and gill or siphon motor neurons during the same siphon stimulation that has been used in behavioral experiments in this preparation. Our results indicate that the LE cells make a substantial contribution to the evoked response in the motor neurons under these conditions, but they suggest that other as yet unidentified siphon sensory neurons with lower thresholds and shorter latencies also contribute. In addition, we find that homosynaptic depression of monosynaptic postsynaptic potentials (PSPs) from LE sensory cells makes an important contribution to habituation of the response in the motor neurons. To investigate plasticity of PSPs from the unidentified sensory neurons, we recorded the PSP that was produced in a motor neuron by water-movement stimulation of the siphon, which does not cause firing of LE cells. Our results suggest that PSPs from the unidentified sensory neurons and the LE neurons undergo similar plasticity during habituation and dishabituation training. These results support the idea that plasticity at synapses of both LE and unidentified sensory neurons contributes to habituation and dishabituation of the reflex response in this preparation.
Proceedings of the National Academy of Sciences, 1989
A semi-intact preparation was used to study the effects ofclassical conditioning on the type ofsiphon response elicited by a conditioned stimulus to the mantle ofAplysia. Five pairings of the conditioned stimulus with an unconditioned stimulus to nerves from the tail transformed the constricting alpha response of the siphon into a conditioned flaring response resembling the unconditioned response to stimulation of the tail nerves. Although some pseudoconditioning occurred, an associative component was indicated by the significantly greater incidence of flaring responses after paired training than after unpaired presentations of the conditioned and unconditioned stimulus or the unconditioned stimulus alone. Previously described cellular plasticity in the underlying neural circuits suggests a testable model based on cell-wide rather than synapsespecific mechanisms, which can account for specific conditioned responses. In this model, effective stimulus-response associations are produced by a concatenation of stimulus-specific facilitation of sensory neurons (a mechanism for alpha conditioning) and response-specific facilitation of motor neurons (a mechanism for pseudoconditioning).
Brain Research Reviews, 2003
The gill withdrawal reflex of Aplysia is generally depicted as a simple behaviour mediated by a simple neural circuit in a simple organism. Such a view has permitted a clear focus upon synapses between relatively small numbers of identified neurones, which are known to participate in the reflex and its plasticity. Ensuing research has provided some of the first and still among the most powerful explanations of the cellular underpinnings of learning and memory. In reality, however, the reflexive withdrawal of the gill and other mantle organs is anything but simple. First, the behaviour itself is complex and varies depending upon the strength of the tactile stimulus and where it is applied. In addition, over 100 central neurones are activated by stimuli, which elicit the withdrawal reflex and likely change their activities during learning (although not all of these cells necessarily contribute to the actual withdrawal response). Moreover, multiple mechanisms are activated at both presynaptic and postsynaptic sites to orchestrate the numerous modifications that underlie observed changes in synaptic efficacy. The picture becomes even more complicated when hundreds of additional peripheral neurones, which are known to participate in various aspects of the response, are also considered. Recent work has shifted attention back to these peripheral cells by suggesting that they might be the previously unidentified light touch receptors that mediate both central and peripheral components of the reflex. While daunting, the complexity of the total circuitry mediating the gill withdrawal reflex may provide yet another important lesson: even in simple systems, memory may not be localized to specific loci, but rather may be an emergent property of physiological mechanisms distributed throughout the entire circuitry. D
Associative learning phenomena in the snail (Helix aspersa): Conditioned inhibition
Learning & Behavior, 2012
Two experiments using garden snails (Helix aspersa) showed conditioned inhibition using both retardation and summation tests. Conditioned inhibition is a procedure by which a stimulus becomes a predictor of the absence of a relevant event-the unconditioned stimulus (US). Typically, conditioned inhibition consists of pairings between an initially neutral conditioned stimulus, CS 2 , and an effective excitatory conditioned stimulus, CS 1 , in the absence of the US. Retardation and summation tests are required in order to confirm that CS 2 has acquired inhibitory properties. Conditioned inhibition has previously been found in invertebrates; however, these demonstrations did not use the retardation and summation tests required for an unambiguous demonstration of inhibition, allowing for alternative explanations. The implications of our results for the fields of comparative cognition and invertebrate physiological models of learning are discussed.
Biological Reviews, 1989
The gill withdrawal reflex (GWR), an important model system for neural mechanisms of learn- ing, varies in form and amplitude within as well as between preparations and is therefore a heterogeneous collection of action patterns, not a reflex. At least 4 action patterns occur in response to mechanical stimulation of the siphon. It is often impossible to categorize a particular movement unambiguously. All may occur spontaneously. Gill movements may be described as combinations of 10 actions; 4 involving vein movements are described here. All actions and action patterns can occur in preparations lacking the central nervous system. Some vein move- ments may generate considerable force without markedly altering gill area. It is suggested that this explains why some early studies failed to identify the important role of the peripheral nervous system in the GWR. Studies based on the assumption that the GWR involves a single type of movement controlled by cells of the parietovisceral ganglion require reevaluation.
2000
We compared the spike activity of individual neurons in the Aplysia abdominal ganglion with the movement of the gill during the gill-withdrawal reflex. We discriminated four populations that collectively encompass approximately half of the active neurons in the ganglion: (1) second-order sensory neurons that respond to the onset and offset of stimulation of the gill and are active before the movement starts; (2) neurons whose activity is correlated with the position of the gill and typically have a tonic output during gill withdrawal; (3) neurons whose activity is correlated with the velocity of the movement and typically fire in a phasic manner; and (4) neurons whose activity is correlated with both position and velocity. A reliable prediction of the position of the gill is achieved only with the combined output of 15-20 neurons, whereas a reliable prediction of the velocity depends on the combined output of 40 or more cells.