Combined action observation and motor imagery practice for upper limb recovery following stroke: a systematic review and meta-analysis

Abstract

Introduction: Optimal upper limb recovery requires high-dose physiotherapy; however, this essential component of rehabilitation is under-delivered. Mental practice represents an accessible and cost-effective adjunct to conventional therapy. We therefore evaluated the efficacy of an enhanced mental practice treatment (combined action observation and motor imagery, AO + MI) for promoting upper limb recovery post stroke.

Methods: Searching 10 databases, we identified 18 eligible studies (N = 336), comprising nine randomized controlled trials (RCTs) and nine non-randomized controlled trials (non-RCTs). RCTs were meta-analyzed using upper limb function outcomes (Fugl-Meyer Assessment for upper extremity, FMA-UE; Action Research Arm Test, ARAT). Non-RCTs (not eligible for meta-analysis) were narratively synthesized using upper limb and neuroimaging outcomes.

Results: Seven RCTs reported FMA-UE scores (n = 189), where the standardized mean difference (SMD) for AO + MI treatments was moderate (SMD = 0.58, 95%CI: 0.13-1.04, p = 0.02). Two additional RCTs reported ARAT scores. Meta-analyzing the combined FMA-UE and ARAT scores (n = 239) revealed SMD = 0.70 (95%CI: 0.32-1.09, p = 0.003). No significant correlations existed between the pooled effect size and several moderators (age, time since stroke, intervention duration, control condition, outcome measure and AO + MI arrangement), indicating consistent AO + MI practice effects. Overall, AO + MI significantly improved upper limb function across all nine RCTs, and all nine narratively synthesized studies, including neuroimaging outcomes. Limitations included inconsistent terminology, intervention design, clarity of reporting, and modality.

Discussion: AO + MI practice can promote upper limb recovery following stroke. AO + MI can therefore be used as a bridge between AO therapy (requiring little effort in early recovery), and the more cognitively demanding MI. Researchers must adopt standardized reporting protocols to further establish AO + MI practice efficacy.

Systematic review registration: The review was registered with PROSPERO under the registration number CRD42023418370. The registration is publicly accessible at the following URL: https://www.crd.york.ac.uk/PROSPERO/view/CRD42023418370.

Keywords: combined action observation and motor imagery; imitation learning; mental practice; mirror neurons; neuroplasticity; stroke rehabilitation; stroke survivors; upper limb recovery.

Figure 1

PRISMA flow diagram of study selection. The diagram illustrates the literature search and selection process, showing sources identified, records screened and excluded, and studies included in the final review.

Figure 2

ROB2 summary. Summary of Risk of Bias 2 (ROB2) assessments, showing methodological quality across domains: randomization, adherence to interventions, handling of missing data, outcome measurement, and selection of reported results.

Figure 3

ROBINS-I summary. Summary of the ROBINS-I (Risk of bias in non-randomized studies of interventions) assessment, showing risk of bias across key domains: confounding, participant selection, intervention classification, missing data, outcome measurement, and selective reporting.

Figure 4

Pooled mean treatment effects of AO + MI interventions on FMA-UE total score. Pooled mean treatment effects of AO + MI (Action Observation and Motor Imagery) interventions on the FMA-UE (Fugl-Meyer Assessment for Upper Extremity) total score, based on results from multiple studies. Standardized mean differences (Cohen’s d, SMD_d) between intervention and control groups are presented with confidence intervals indicating precision.

Figure 5

Pooled mean treatment effects of AO + MI interventions on combined FMA-UE and ARAT score. Pooled mean treatment effects of AO + MI (Action Observation and Motor Imagery) interventions on combined FMA-UE (Fugl-Meyer Assessment for Upper Extremity) and ARAT (Action Research Arm Test) total scores. Standardized mean differences (SMD, Cohen’s d) with confidence intervals summarize the impact of AO + MI interventions on upper limb motor function across multiple studies.

Figure 6

Estimated regression slopes and effect sizes in AO + MI interventions for upper limb function. Bubble size represents study weight, with larger bubbles representing studies with greater influence in the analysis. SMD_d = Cohen’s d. (A) 1 = early subacute (7 days to 3 months after stroke), 3 = late subacute (3–6 months after stroke), 6 = chronic (6 months or more after stroke). (B) Age is measured in years. (C) Intervention duration is measured in weeks. (D) 1 = synchronous AO + MI, 2 = asynchronous AO + MI. (E) 0 = non-BCI study, 1 = BCI study. (F) 0 = conventional therapy, 1 = AO, 2 = MI, 3 = asynchronous AO + MI. (G) 1 = FMA_UE, 2 = ARAT.

Figure 7

Funnel plot. This funnel plot visualizes the effect sizes of studies against their precision (standard error) in a meta-analysis. The x-axis represents the standardized mean differences (Cohen’s d, SMD_d = Cohen’s d), while the y-axis shows the precision of each study (inverse of standard error). A symmetric funnel indicates no publication bias, while asymmetry may suggest potential publication bias or heterogeneity among studies.