SILICON MODELS OF ASSOCIATIVE LEARNING IN APLYSIA

Relatively simple invertebrate animals exhibit an impressive variety of learning and memory behaviour including such associative learning tasks as classical or Pavlovian conditioning. The cellular machinery responsible for this behaviour is beginning to be understood by neurophysiologists in certain well-studied species such as the marine mollusc Aplysia. We describe analog CMOS circuits which can be used to qualitatively mimic the mechanisms of associative learning in this creature. In particular we model the synaptic plasticity and activity-dependent facilitation in sensorimotor synapses responsible for classical conditioning of the gill withdrawal reflex. The same circuits implement the nonassociative learning mechanisms of habituation and sensitization. We also discuss considerations in abstracting from the biological mechanisms when developing artificial neural systems. The specific circuits for Aplysia described in this paper are suggestive of ways to implement VLSI area-efficient associative learning circuits in general, especially those which perform in situ temporal associations on multiple synaptic inputs. © 1990.