Evidence for sequential decision making in the medicinal leech

Teresa Esch, Karen A. Mesce, William B. Kristan

Research output: Contribution to journalArticlepeer-review

76 Scopus citations


Decision making can be a complex task involving a sequence of subdecisions. For example, we decide to pursue a goal (e.g., get something to eat), then decide how to accomplish that goal (e.g., go to a restaurant), and then make a sequence of more specific plans (e.g., which restaurant to go to, how to get there, what to order, etc.). In characterizing the effects of stimulating individual brain neurons in the isolated nervous system of the leech Hirudo medicinalis, we have found evidence that leeches also make decisions sequentially. In this study, we describe a pair of interneurons that elicited locomotory motor programs, either swimming or crawling, in isolated nerve cords. In semi-intact animals, stimulating the same neurons also produced either swimming or crawling, and which behavior was produced could be controlled experimentally by manipulating the depth of saline around the intact part of the leech. These same neurons were excited and fired strongly when swimming or crawling occurred spontaneously or in response to mechanosensory stimulation. We conclude that these brain interneurons help to decide on locomotion (i.e., they are "locomotory command-like neurons") and that the ultimate behavior is determined downstream, in a part of the decision-making hierarchy that monitors stimuli related to the depth of fluid surrounding the leech.

Original languageEnglish (US)
Pages (from-to)11045-11054
Number of pages10
JournalJournal of Neuroscience
Issue number24
StatePublished - Dec 15 2002


  • Choice behavior
  • Leeches
  • Locomotion
  • Motor patterns
  • Multifunctional neurons
  • Neural circuits

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