title: A ciliate memorizes the geometry of a swimming arena.
abstract: Previous studies on adaptive behaviour in single-celled organisms have given hints to the origin of their memorizing capacity. Here we report evidence that a protozoan ciliate Tetrahymena has the capacity to learn the shape and size of its swimming space. Cells confined in a small water droplet for a short period were found to recapitulate circular swimming trajectories upon release. The diameter of the circular trajectories and their duration reflected the size of the droplet and the period of confinement. We suggest a possible mechanism for this adaptive behaviour based on a Ca(2+) channel. In our model, repeated collisions with the walls of a confining droplet result in a slow rise in intracellular calcium that leads to a long-term increase in the reversal frequency of the ciliary beat.
authors.affiliation: Research Institute for Electronic Science, Hokkaido University, N20W10, Kita-Ward Sapporo 001-0020, Japan.
authors.forename: Itsuki
authors.initials: I
authors.lastname: Kunita
authors.affiliation: Graduate School of Mathematics, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Yamaguchi
authors.affiliation: Graduate School of Mathematics, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan Institute of Mathematics for Industry, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Tero
authors.affiliation: Research Institute for Electronic Science, Hokkaido University, N20W10, Kita-Ward Sapporo 001-0020, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Akiyama
authors.affiliation: Research Institute for Electronic Science, Hokkaido University, N20W10, Kita-Ward Sapporo 001-0020, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Kuroda
authors.affiliation: Research Institute for Electronic Science, Hokkaido University, N20W10, Kita-Ward Sapporo 001-0020, Japan nakagaki@es.hokudai.ac.jp.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Nakagaki
mesh_terms: D000220:Adaptation, Biological / Q000502:physiology*; D008568:Memory / Q000502:physiology*; D013550:Swimming / Q000502:physiology*; D013768:Tetrahymena / Q000502:physiology*
keywords: Hodgikin Huxley equation; ion channel; mathematical modelling; memory; tetrahymena