How deep is your recovery? Rethinking true motor recovery versus compensation in neurorehabilitation.

Attempts to make a sharp distinction between ‘true’ recovery and compensation create ambiguity about the nature of motor improvement in neurological rehabilitation. This paper proposes a new framework to resolve this dichotomy: a stratified model where recovery is not a binary concept but is instead defined by its depth across the motor system’s multiple layers, from neurons to task performance. Our model frames the motor system as a hierarchy of causally linked strata, ranging from inner physiological layers (e.g. synaptic plasticity) to outer behavioural ones (e.g. task accomplishment). This framework allows motor improvement to be defined as a phenomenon that can occur at different layers, manifesting as a compensation–recovery gradient that propagates from inner-to-outer strata. The model’s central thesis is that the key question is not whether recovery is ‘true’, but how deep it is. We posit that a deeper recovery – one in which improvements in behavioural performance are underpinned by positive changes in inner physiological strata – constitutes a more complete and desirable clinical outcome. When comparing treatments with equivalent behavioural outcomes, those that also result in recovery in deeper physiological strata are superior and should be preferred. Therefore, this model directs neurorehabilitation research and practice toward interventions that also maximise recovery depth rather than focussing solely on behavioural outcomes. Assessing and demonstrating recovery depth requires that clinical psychometrics are complemented by quantitative metrics from instrumented movement analysis and neurophysiology, which can directly probe the inner, physiological strata of the motor system.