Neural mechanisms of operant conditioning and learning-induced behavioral plasticity in Aplysia

Abstract

Associative learning in goal-directed behaviors, in contrast to reflexive behaviors, can alter processes of decision-making in the selection of appropriate action and its initiation, thereby enabling animals, including humans, to gain a predictive understanding of their external environment. In the mollusc Aplysia, recent studies on appetitive operant conditioning in which the animal learns about the positive consequences of its behavior have provided insights into this form of associative learning which, although ubiquitous, remains mechanistically poorly understood. The findings support increasing evidence that central circuit- and cell-wide sites other than chemical synaptic connections, including electrical coupling and membrane conductances controlling intrinsic neuronal excitability and underlying voltage-dependent plateauing or oscillatory mechanisms, may serve as the neural substrates for behavioral plasticity resulting from operant conditioning. Aplysia therefore continues to provide a model system for understanding learning and memory formation that enables establishing the neurobiological links between behavioral, network, and cellular levels of analysis.

Effects of aversive stimuli beyond defensive neural circuits: Reduced excitability in an identified neuron critical for feeding in Aplysia

“…Combined with previous work that examined the effects of appetitive associative learning on B51 Mozzachiodi and Byrne 2010;Nargeot and Simmers 2011), our results provide further evidence of the decision-making nature of this neuron within the feeding neural circuit. Contrary to LTS training, operant reward learning enhances feeding in testing conditions identical to those used in this study (i.e., seaweed extract application) and increases B51 excitability (Brembs et al 2002).…”

Rapid and persistent suppression of feeding behavior induced by sensitization training in Aplysia

“…3) provides the framework for the characterization of its underlying cellular mechanisms, as it would allow us to identify the cellular sites of plasticity within the feeding neural circuit, while the effects of LTS training persist. Modifications at the level of the decision-making neuron B51, which is critical to bias the feeding neural circuit to generate the neurophysiological activity associated with bites (Plummer and Kirk 1990;Nargeot et al 1999a,b;Mozzachiodi and Byrne 2010;Nargeot and Simmers 2011), may contribute, at least in part, to the suppression of feeding produced by LTS training. In addition, pattern-initiating neurons B31/32 and B63 (Susswein and Byrne 1988;Hurwitz et al 1997) are two other putative loci of plasticity that may play a role in the suppression of feeding observed following LTS training.…”

Spontaneous decisions and operant conditioning in fruit flies

“…Parallel developments to isolate the operant behavior have been made in the sea slug Aplysia (Nargeot et al, 1997(Nargeot et al, , 1999a(Nargeot et al, ,b,d, 2007(Nargeot et al, , 2009Brembs et al, 2002;Nargeot, 2002;Lorenzetti et al, 2006;Lorenzetti et al, 2008;Nargeot and Simmers, 2010). There, freely moving animals generate feeding movements in the absence of eliciting stimuli.…”