Longitudinal analysis of visuomotor orientation after optic lobe lesions reveals brain plasticity in Drosophila

  1. Margarida Caio
  2. Dean Rance
  3. Christa Rhiner

  • Curated by eLife

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    eLife Assessment

    This valuable study uses longitudinal single-animal tracking in the Buridan arena to examine recovery of visually guided behavior after optic lobe injury in Drosophila and identifies a potential role for Myc-dependent neural progenitor activation in this process. The evidence is incomplete, as key controls and analyses are lacking to exclude alternative explanations for the behavioral recovery and to firmly establish the requirement for progenitor activation.

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Abstract

Acute brain injury disrupts neuro-glial networks leading to impaired brain function. Although injury induces diverse forms of plasticity, their contributions to brain injury outcome remain poorly understood. We previously showed that targeted stab lesions to the optic lobe (OL) of the adult fly brain induce proliferation of glial and neural progenitor cells. Here, we examined the effect of OL lesions on distinct features of fly behavior, which revealed a specific drop in visual stripe fixation performance acutely after injury, whereas locomotor behavior remained mostly unaffected. Using longitudinal studies of injured individuals, we found that flies significantly regain stripe fixation capacity and idiosyncratic traits one week post injury, suggesting a role for plasticity mechanisms. When the proliferation of adult neural progenitor cells is specifically blocked prior to injury, individuals showed no significant improvements of visual orientation during the identified plasticity window suggesting that progenitor activation may support recovery of stripe approach behavior. Hence the individual tracking of orientation behavior emerges as a suitable quantitative framework for studying functional recovery and inter-individual variability in the adult Drosophila brain following brain injury.

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  1. eLife

    eLife Assessment

    This valuable study uses longitudinal single-animal tracking in the Buridan arena to examine recovery of visually guided behavior after optic lobe injury in Drosophila and identifies a potential role for Myc-dependent neural progenitor activation in this process. The evidence is incomplete, as key controls and analyses are lacking to exclude alternative explanations for the behavioral recovery and to firmly establish the requirement for progenitor activation.

  2. eLife

    Reviewer #1 (Public review):

    Summary:

    Acute brain injury can disrupt neural circuits, thereby altering brain function. While such injuries can induce various forms of plasticity, the mechanisms by which they contribute to improved functional outcomes post-injury remain inadequately understood. This study investigates this plasticity by assessing the effects of an optic lobe lesion on specific fly behaviors. The findings indicate a significant impairment in the ability to fixate on visual stripes immediately following the injury, whereas locomotor behavior remains largely unaffected. Notably, longitudinal studies of the injured flies demonstrate substantial recovery in stripe fixation ability and unique behavioral traits one week post-injury, suggesting the involvement of plasticity mechanisms. Inhibition of adult neural progenitor cell proliferation prior to injury prevents significant improvements in visual orientation during the identified plasticity window, indicating that progenitor activation may facilitate the recovery of stripe-oriented behavior. Thus, individual tracking of orientation behavior in *Drosophila* provides an effective quantitative framework for examining functional recovery and inter-individual variability in the adult brain following injury.

    Strengths:

    This study demonstrates that flies with localized damage to the optic lobes exhibit significant recovery in stripe-fixation behavior, a function specifically impaired by lesions in these lobes. By employing quantitative tracking of individuals in the Buridan arena, the study elucidates individual recovery trajectories during a critical window of plasticity. These trajectories are partially influenced by injury-induced plasticity, particularly through the activation of progenitor cells. The findings underscore the potential of optic lobe lesions in Drosophila as a promising model for further exploring the relationship between altered cellular interactions and the recovery of brain function following acute injury.

    Weaknesses:

    The article possesses potential strengths; however, these are not explicitly demonstrated. Specifically, the analyses conducted are inadequate to fully support the manuscript's primary claims with the data provided. A comprehensive characterization of the lesions at one and three weeks post-injury is essential, employing markers for neuronal progenitors and glia, the neuropil, and cell proliferation or death. Moreover, the connection between the dorsal cluster neurons (DCN) and the potential enhancement in visual behavior post-injury remains ambiguous. Consequently, a morphological analysis of this cluster in both control and lesioned flies is necessary to substantiate the study's conclusions. Furthermore, inactivating this cluster, for example, through the use of UAS-Kir2.1, would ascertain its significance in the plasticity process described herein.

  3. eLife

    Reviewer #2 (Public review):

    Summary:

    Caio and colleagues ask whether localized injury to the adult Drosophila optic lobe (OL) produces a measurable deficit in visually guided behavior, and whether flies recover that behavior over time. Building on the authors' earlier work showing that OL stab lesions reactivate quiescent, deadpan-positive neural progenitors, they use the Buridan arena to record locomotion and orientation towards two inaccessible vertical stripes. They report that bilateral OL lesions selectively increase the stripe deviation angle one day after injury while leaving most locomotor parameters intact; that flies tracked longitudinally improve their orientation by one week post-injury and then plateau or decline; that a majority of individuals re-express their pre-injury left/right approach bias; and that RNAi knockdown of myc in adult progenitors, which the authors have previously shown blocks injury-induced proliferation, abolishes the one-week improvement. From this, they propose that activation of adult progenitors supports behavioral recovery during an early plasticity window.

    Strengths:

    (1) The behavioral paradigm is well matched to the lesion: Rather than a global measure such as climbing or negative geotaxis, the authors use a readout - stripe fixation - that depends on the structure they damage and on an identified circuit element (dorsal cluster neurons, DCNs). The demonstration that stripe deviation changes (while activity time, number of walks, and most other CeTrAn software parameters do not) is the most persuasive part of the paper and is supported by two independent, reasonably large cohorts.

    (2) Longitudinal within-individual tracking is a real methodological contribution: Most invertebrate injury studies compare independent groups at successive timepoints. Recording each fly at baseline, 1 dpi, 1 wpi, and 2 wpi, and then plotting individual recovery trajectories, is the right design for a question about recovery, and it is what makes the question about idiosyncratic traits askable at all. The field would benefit from this becoming standard.

    (3) Baseline pre-screening is a thoughtful design choice: Selecting high-responder flies before injury (Figure 2B) sensibly removes the large fraction of animals whose baseline stripe fixation is too weak for a deficit to be detectable, and the inclusion of a thorax-puncture group addresses the generic-wounding alternative, at least in part.

    (4) The study links a cellular phenomenon the laboratory has characterized in detail to a functional outcome: Attempting to connect adult neurogenesis in the fly to behavior, rather than stopping at cell counts, is the right ambition and is unusual in this literature.

    (5) The individuality framing is novel and interesting: Asking whether an animal recovers not merely a species-typical behavior but its own idiosyncratic version of it is a genuinely original question, and one for which Drosophila is unusually well suited.

    Weaknesses:

    (1) The title implies more than the data show:

    No measure of plasticity, such as cellular, synaptic, or circuit, is made in this manuscript; what is measured is behavioral recovery, with one genetic perturbation (using one RNA line) implicating progenitors. A title and abstract framed around behavioral recovery and its progenitor dependence would match the evidence. In addition, the proposal that newly generated medulla neurons integrate within seven days to restore a developmentally specified, individual-specific approach bias is a strong claim that warrants explicit discussion against simpler alternatives (circuit-level compensation, synaptic adaptation, resolution of peripheral damage). Lastly, the manuscript lacks a paragraph that discusses the study's limitations.

    (2) Damage to the eye itself is not excluded as the cause of either the deficit or the recovery:

    The lesion is made by passing a 0.2 mm filament through the compound eye to the level of the medulla. Relative to the dimensions of the fly head, this is a substantial injury to the retina, and photoreceptor loss, corneal damage, hemolymph leakage, or melanization would all be expected to degrade stripe fixation without any optic lobe circuit involvement - and would all be expected to resolve or stabilize over roughly a week. The manuscript contains no histology of the lesion site, no documentation of lesion extent or reproducibility, and no independent assay of peripheral visual function (electroretinogram, optomotor response, phototaxis) at any timepoint. The thorax puncture controls for systemic wounding but not for eye damage, which is the relevant confound here.

    (3) Specificity to optic lobe damage is overstated relative to what Figure 2C shows:

    The text describes the thorax-injury group as showing "a very mild increase... except for 2 individuals", but the mean of this group in Figure 2C rises appreciably from baseline, and the within-group statistics for that comparison are not reported. If thoracic puncture alone degrades stripe fixation, then part of the OL effect is attributable to general injury, illness, or reduced arousal, and the conclusion that the deficit is "strongly dependent on OL injury" needs to be toned down.

    (4) The progenitor-dependence conclusion is underpowered:

    The key group (injured myc RNAi flies) contains 11 animals, against 29-30 for the injured control. The conclusion is drawn from the fact that improvement reaches significance in the control group and not in the myc RNAi group; this is a comparison of "presence vs. absence of significance", not a test of whether the two recovery trajectories differ, and with the difference in animal numbers, the asymmetry is expected on power grounds alone. The group/time interaction is not reported. In addition, there is no independent myc RNAi line, no rescue, no orthogonal means of blocking progenitor division, no driver-only or UAS-only controls at 29 {degree sign}C, and no verification in these particular cohorts that proliferation was in fact blocked. Myc is pleiotropic, and dpn-T2A-Gal4 expression is not restricted with certainty to the progenitors of interest, so an effect on behavior through a route other than blocked progenitor division cannot presently be excluded.

    (5) The assay's range is never established:

    No condition in the paper (blind flies, or the arena without stripes) defines the stripe deviation expected from an animal with no usable vision, so the reader cannot judge what fraction of the available dynamic range the deficit occupies.

    (6) Selection on a noisy post-injury measurement, without a selection-matched control, can generate apparent recovery in the absence of any biology:

    For the longitudinal experiments (Figures 3 and 4), the authors retain only flies whose stripe deviation exceeded 30{degree sign} at 1 dpi (e.g., 29 of 89 injured animals in Figure 3). Selecting individuals on the extreme value of a variable measured with error guarantees that, by regression to the mean alone, their next measurement will, on average, be closer to the population mean. The non-injured comparison group (n = 65) is the full, unselected cohort and was not subjected to an equivalent selection step, so the two trajectories are not comparable.

    (7) The idiosyncrasy result is not supported by a statistical test:

    Recovery of an individual's pre-injury left/right bias is scored as a binary outcome, and 62% is reported as recovery. For a binary trait, 50% is the chance expectation; no null model, no test, no confidence interval, and no sample size for the pie chart are given, and the test-retest stability of the bias in uninjured flies over the same interval, the necessary benchmark, is not shown.

    (8) "Plasticity window" is inferred from three time points:

    With measurements at 1 dpi, 1 wpi, and 2 wpi only, the time course between one day and one week is unsampled, so the onset, duration, and closure of the proposed window are not resolved. The 2 wpi decline is attributed to aging, which the non-injured controls support, but this also means aging and recovery act in opposite directions across the very interval used to define the window.

    Impact and utility:

    If the recovery phenomenon survives the controls outlined above, the approach would be genuinely useful to the field: a quantitative, individually resolved, repeatable behavioral assay for functional outcome after CNS injury in an organism with the genetic tools to dissect the underlying cellular events. That combination does not currently exist in Drosophila injury work, where functional outcome is typically scored coarsely. The idiosyncrasy angle also connects two literatures - injury/regeneration and behavioral individuality - that have developed largely independently, and the question of whether recovery restores the individual or merely the species-typical phenotype is worth asking well beyond the fly.

  4. eLife

    Reviewer #3 (Public review):

    Summary:

    This study characterizes the effect of optic lobe injury on optically guided behavior in adult flies and examines the extent to which this behavior recovers over time. The authors further investigate whether Myc function in dpn-positive cells is required for this recovery. The work provides a useful behavioral injury model and suggests a potential cellular and molecular contribution to recovery after optic lobe damage.

    Strengths:

    A strength of the study is that it uses a reliable model for optically guided responses and for the study of idiosyncratic behaviors. Temporal control of the RNAi using tubGal80[ts] is also a strength, restricting the start of the manipulation to 3 days before the assay, which is a reasonable compromise to allow time for the RNAi to act. The lack of temporal restriction could have led to neurodevelopmental artifacts and hence less-reliable results. That being said, it would be useful to demonstrate that Myc protein levels are indeed reduced in dpn-positive cells with that particular RNAi manipulation. Can the authors do this using an anti-Myc antibody, or cite work that demonstrates this following 3 days in neurons?

    Weaknesses:

    In its current state, the study has apparent weaknesses in writing, in the description of the methods, and in the statistical analyses of the data.

  5. Version published to 10.7554/elife.113192.1 on eLife
  6. Version published to 10.7554/elife.113192 on eLife
  7. Mentioned by @rridrobot.bsky.social on Bluesky

    Authors used Canton-S from #BloomingtonDrosophil in their study. Including #RRIDs will make this less ambiguous. SciScore made a table with this resource, see “Automated Services” module (download as csv, xml or #jats) #methodsmatter #OpenScience

  8. Mentioned by @biorxivpreprint.bsky.social on Bluesky

    Longitudinal analysis of visuomotor orientation after optic lobe lesions reveals brain plasticity in Drosophila https://www.biorxiv.org/content/10.64898/2026.08.20.745927v1

  9. Version published to 10.64898/2026.08.20.745927v1 on bioRxiv