henhao
Sign in
Animal Behavior & CognitionbioRxiv
Preprint

Trained Planaria Retain Memories Through Head Regeneration: A Model System for Insights into Non-Neural Memory and Neurodegenerative Diseases

Nikhil Dev, Angelina Nguyen, Michael G. LeviniD

Abstract

Planaria exhibit remarkable regenerative ability, including the capacity to regrow complete heads and brains after decapitation. Here, we re-investigated whether regenerated planaria can preserve learned avoidance behavior, a phenomenon that has been reported previously but has been difficult to study due to unreliable experimental protocols. Using a light-to-food associative conditioning paradigm, planaria were trained to override their normal photophobic preference and then decapitated. Following a two-week regeneration period, behavioral responses to the conditioned stimulus were re-evaluated. Results indicated that the majority of regenerated planaria retained the learned response, supporting a model in which behavioral patterns can regenerate as well as anatomical patterns. By establishing a consistent, low-cost, and effective protocol for studying memory persistence through regeneration, such work may help inform future research on memory loss, resilience, and recovery in neurodegenerative diseases.

PDFDOI
Full-text digest ↓

02 /Specification & Classification

Click any tag to browse matching papers
Citations
1
OpenAlex Topics

In-depth summary

✦ Multi-agent verified full-text synthesis

Claude Opus 5.5 · xhigh effort · 8 Nov 2026 · from the full text of version 1 (11 Aug 2026) · CC BY 4.0

Planarians trained to associate light with food kept their light preference after decapitation and 14-day head regeneration (7.65 min after vs 6.87 min before, out of 10; 10 worms).

Earlier work, including an automated Dugesia japonica study, reported that planarians keep memories after regenerating a head, but unreliable protocols have made this hard to study. This work offers a manual, low-cost light-to-food conditioning protocol that relies on positive reinforcement over daily sessions rather than aversive stimuli or automated operant training.

Key results

  1. ShownTen daily sessions pairing light with food reversed the innate light avoidance of a 34-worm group. The reversal was still present 24 h after the last session, in a test with no food.

    Worms on the lit side at 2 min: 6/34 at baseline vs 30/34 after training. At 30 min: 3/34 vs 33/34 (chi-square p<0.01 for both). Both post-training counts differed from 50% chance (binomial p<0.01). At 10 min after training, 19 worms were on the light side and 15 on the dark side. · Baseline Preference Test; Training Protocol; Training Induced a Reversal of Innate Light…

  2. SuggestedTen individually tracked trained worms spent as much time in light after head regeneration as with their original brains, or slightly more, showing no detectable loss of the trained preference.

    Time on the lit side per 10-min trial was 7.65 ± 1.63 min after regeneration vs 6.87 ± 1.63 min before (mean ± SD; three trials per worm, reported as n=15 trials per condition; two-tailed paired t-test p > 0.05). The group mean rose by ∼47 s. · Post-Regeneration Memory Test; Data Analysis; Planaria Retain Learned Preference After Head…

  3. ClaimedUntrained controls, including worms that regenerated without training, are reported to have stayed light-avoidant. Their light-occupancy values and group sizes are not given.

    Control light occupancy was below chance (binomial p<0.01), and trained worms differed from controls after training (chi-square p<0.01). Regenerated untrained controls are described only in words, as generally settling in the dark area. · Post-Regeneration Memory Test; Training Induced a Reversal of Innate Light…; Behavioral Observations

  4. ClaimedRegenerated trained worms reportedly avoided bright light in a new environment, and some probed the old feeding spot in the training arena. The authors read this as a learned association tied to the arena, not a general change in light sensitivity.

    Qualitative observations only. No counts, durations or statistics are reported for the new-environment test or the probing behaviour. · Behavioral Observations

Methods, data and reproducibility

Laboratory planarians were trained in 10 daily 15-minute sessions with beef liver placed on the UV-lit half of a divided dish. They were then cut just behind the pharynx and kept unfed for 14 days while their heads regrew. Light-side occupancy was scored as group counts every 2 min over 30 min and, for 10 worms, as seconds in light during 10-min trials before and after regeneration.

  • Freshwater planarians from a laboratory colony (∼1-1.5 cm), used in group light/dark preference tests before and after training, then decapitated and regenerated · planarians (mixed Dugesia or Girardia species) · n = 34 worms; 30 survived the two-week regeneration
  • Subset tracked individually: seconds on the lit side in three 10-minute trials with the original brain and three with the regenerated brain (Table 2) · planarians (mixed Dugesia or Girardia species) · n = 10 worms
  • Untrained control worms decapitated and regenerated without prior training · planarians (mixed Dugesia or Girardia species)
Methods & tools
UV light source (365+395 nm, 5V 3W), 9 cm Petri dish light/dark arena, video tracking with manual stopwatch verification, two-tailed paired t-test, binomial test, chi-square test
Reproducibility gaps
No code or data repository is given; group counts and per-worm times are in supplementary tables (A1, A2, Table 2). The video-tracking software is not named, and the control group's size and measurements are not reported.
Limitations (5)
  • Only a simple environmental association was trained, not a complex episodic memory. Together with the differences between planarians and mammals, this calls for caution in extending the results to clinical settings. · stated by the authors
  • The study did not identify the mechanism that stores the memory. The authors propose tissue or single-cell transplants from trained to untrained worms, and drug-based loss-of-function experiments during regeneration, as future work. · stated by the authors
  • The authors frame the study as a replication with a simplified protocol, not an exact methodological replication of earlier experiments. · stated by the authors
  • The post-regeneration claim rests on 10 tracked worms of unstated selection and a within-subject test with p > 0.05. The regenerated untrained controls have no reported n or time-in-light data, so their light avoidance is asserted rather than measured. · noted in this summary
  • The text is internally inconsistent: 'n=15 trials pooled' does not match three trials for each of 10 worms, and tables A1 and A2 are cited inconsistently. It is also unclear when the pre-regeneration individual trials ran, since decapitation followed the group test immediately. · noted in this summary

Who should read:Read this if you want a low-cost, manual planarian conditioning protocol for testing memory retention through head regeneration, or are weighing behavioural evidence for memory storage outside the brain.

Reproducibility ledger

Nobody has reported trying to reproduce this paper yet. Did you replicate an experiment or run the code? Your report saves the next lab a week.

Sign in to file a reproducibility report.

Related papers

Similarity Map
SelectedSame fieldCross-field
THISShimojo '22Kelso '26Samuel '21Bray '24Jha '25Hanslik '19
75% semantic matchAnimal Behavior & Cognition
K. Shimojo, E. Shimojo, R. Katsuragi+2 more·bioRxiv·Oct 30, 2022