Reconsidering the evidence for learning in single cells

  1. Samuel J Gershman  Is a corresponding author
  2. Petra EM Balbi
  3. C Randy Gallistel
  4. Jeremy Gunawardena  Is a corresponding author
  1. Department of Psychology and Center for Brain Science, Harvard University, United States
  2. Center for Brains, Mind and Machines, MIT, United States
  3. Department of Systems Biology, Harvard Medical School, United States
  4. Rutgers Center for Cognitive Science, Rutgers University at New Brunswick, United States
2 figures and 1 table


News story about Beatrice Gelber from the Tucson Daily Citizen October 19, 1960.

© 1960, USA TODAY NETWORK. This image is not covered by the CC-BY 4.0 licence and may not be separated from the article.

Design of experiments reported in Gelber, 1952.

In Experiment 1 (top), one group of Paramecia was exposed to intermittent training trials in which a wire was coated with bacteria (every 3rd trial during the training phase). This group acquired a conditioned response to the clean wire, as measured by adherence to the wire in final test trials. In contrast, an untrained group did not show a conditioned response. Experiment 2 (bottom) demonstrated that the wire by itself did not drive conditioned responding.


Table 1
Molecules/pathways known to be involved in learning and memory, with homologues in ciliates.
Molecules/pathways known to be involved in learning/memory Ciliates with reported homologues References
N-methyl-D-aspartate receptor (NMDAR) P. primaurelia (only partial sequences) Ramoino et al., 2014
Glutamate receptor P. tetraureliaVan Houten et al., 2000
CalmodulinP. tetraureliaPlattner and Verkhratsky, 2018
cAMPP. tetraureliaPlattner and Verkhratsky, 2018
cAMP-dependent protein kinaseP. tetraureliaPlattner and Verkhratsky, 2018
Mitogen activated protein kinase (MAPK) P. caudatum Wada and Watanabe, 2007
Protein kinase C (PKC) T. thermophilia Hegyesi and Csaba, 1994
CalcineurinP. tetraureliaPlattner and Verkhratsky, 2018
DNA methyltransferases (DNMTs)T. thermophilia Gutiérrez et al., 2000
Histone acetyltransferases (HATs)T. thermophilia Vavra et al., 1982
Histone deacetylases (HADCs)T. thermophiliaWiley et al., 2005

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  1. Samuel J Gershman
  2. Petra EM Balbi
  3. C Randy Gallistel
  4. Jeremy Gunawardena
Reconsidering the evidence for learning in single cells
eLife 10:e61907.