Getting Habituated with Investigating Learning and Memory

How do we learn and remember? How does our nervous system change to allow learning and memory? These are questions that neuroscientists are still tackling to this very day. Today we will go back to 1973 and look at one of the first papers by Thomas Carew and Eric Kandel addressing these questions.

To begin studying the neurobiology of learning and memory in the 1970s, scientists used more simple forms of learning and memory such as classical conditioning and habituation. The latter is the form used in the paper. Habituation is defined as a decrease in a behavioral response that results from repeated stimulation and does not include sensory or motor fatigue1. Another way of seeing habituation is as a way that an organism learns to ignore continually present sensory stimuli so that it may focus on new and more relevant sensory input.


In today’s paper, Carew and Kandel use the gill-withdrawal reflex of Aplysia to investigate neuronal changes that underlie habituation. This reflex occurs when the siphon of the Aplysia is touched gently causing the gill to withdraw into the mantle. This Aplysia reflexive behavior was used as a model system for two main reasons: 1) A limited set of neurons were known to underlie the gill-withdrawal reflex and; 2) These neurons were well characterized and easily identifiable organism to organism thus allowing electrophysiological recording of these neurons in a behaving organism.

One of the interesting findings of this paper was that even simple forms of learning and memory like habituation seem to have distinct short and long term stages and that relatively short habituation training could have such "prolonged plastic changes in neuronal function". Through this paper and a few others from the same group, a system was established that would go on to promote the identification and understanding of the molecular mechanisms that underlie both short term and long term learning and memory. Perhaps more importantly, these early studies also began to demonstrate that connections between neurons are not fixed, instead they can be plastic.

“Any man could, if he were so inclined, be the sculptor of his own brain.” ― Santiago Ramón y CajalAdvice for a Young Investigator


  1. Rankin et al (2009) Habituation Revisited: An Updated and Revised Description of the Behavioral Characteristics of Habituation. Neurobiology Learn Mem 92(2): 135-138
  3. Carew, T. and Kandel, E. (1973) Acquisition and retention of long-term habituation in Aplysia: Correlation of behavioral and cellular processes. Science Vol. 182