What Is Brain Plasticity Really and How Does It Relate to Psychedelic Therapy?

In everyday speech we talk about “plasticity” when something can be shaped, like modelling clay. In neuroscience, however, the term refers to an induced change in brain function or structure, often linked to learning. This technical use can cause confusion: some markers of brain plasticity, rather than increasing flexibility, tend to fix behaviors, a phenomenon called phenotypic canalization, which is the opposite of true plasticity. The authors point out that using “plasticity” as a blanket term risks conflating two distinct ideas and drawing hasty conclusions about mental‑health benefits. To clear the ambiguity they propose a new construct called “mediational and recalibrative plasticity” (MR‑P). This concept directly ties observed brain changes to the real capacity for adaptation of mental states and traits, such as mood or stress resilience. In other words, MR‑P tries to link what we see in the lab—for example shifts in BDNF levels or synaptic connectivity—with concrete improvements in psychological well‑being, especially in the context of psychedelic therapy, where substances like psilocybin appear to foster a more authentic functional remodeling. By distinguishing true plasticity from mere evoked responses, the work paves the way for more precise studies on how the brain can genuinely change to improve mental health.

The distinction between intrinsic plasticity (PP) and brain‑induced plasticity is crucial to avoid misinterpretation of biomarkers. PP denotes the inherent ability of a system to change shape in response to external forces without permanent structural alteration—a material property like elastomer deformability. In neuroscience, neuroplasticity refers to synaptic, myelination, or neurogenesis changes that follow experience, a drug, or stimulation. Many lab assays measure shifts in neurotrophic factor levels (BDNF, NGF), dendritic spine density, or EEG oscillation power; these reflect an evoked process, often linked to long‑term potentiation (LTP) or long‑term depression (LTD). Intriguingly, activation of such pathways can increase neural circuit stability, reducing behavioral variability—this is phenotypic canalization, where the system becomes less plastic despite markers indicating “plasticity”. The authors propose that the MR‑P construct captures precisely the change component that promotes behavioral adaptation, integrating activation signals (e.g., BDNF rise) with contextual signals (e.g., relaxed state, therapeutic setting). In psychedelic therapy, compounds like lysergide and psilocybin act on 5‑HT2A receptors, producing a transient increase in synaptic plasticity and a dampening of default mode network (DMN) signaling. This heightened neural entropy appears to allow a “re‑calibration” of rigid thought patterns, translating into clinical improvements in depression, anxiety, and PTSD. Directly measuring MR‑P would require combining molecular markers (e.g., CREB phosphorylation), functional connectivity (resting‑state fMRI), and behavioral measures (cognitive flexibility, mindfulness). Only then can we distinguish a brain change that merely accompanies the psychedelic experience from one that truly underlies a lasting mental adaptation.