Features and neural foundation of the L∪M framework.

A. L∪M model: formalization of the dynamic links spanning language production and declarative memory as an interactive oblique model (i.e., as a composite function). Latent dimensions (RT-CM-TA) are individually associated with specific brain networks (SAL-FPN-DMN, respectively). In terms of behavior, internal encoding implied in verbal comprehension, for example, consists of encoding declarative inputs (engaging the TA System) via more or less attentive listening of verbal indications (involving the RT and CM dimensions). Here, language "feeds" memory (MoL). Externalization, in its most accomplished form, leads to the “production” of language involving a mapping of internal verbal representations and thoughts (TA System) with the corresponding ordered output forms (thus involving manipulation of Systems CM and RT up to verbal evocation). Here, memory "feeds" language (LoM). To ensure dynamics between language and memory, processes engage a synergy of RT-CM-TA latent operations, supported by continuous interactions between networks, performed in parallel and executed in a more or less controlled manner.

B. Global functional topography of the links between brain regions belonging to different networks and projected in a reduced space (n = 48 healthy controls, at rest). This global topology has been observed in other recent studies (Barnett et al., 2021) and corroborates the dimensions and interactions proposed in the L∪M framework (i.e., the connectivity between high-level SAL-FPN-DMN networks supporting RT-CM-TA linkages).

C. Example of functional local SAL-FPN-DMN continuums (connector hubs). These functional convergence zones correspond to structural convergence zones where the terminations of traditionally described language and/or memory bundles are intertwined (Arcuate fascicle: AF; and branches II and III of the superior longitudinal fascicle: SLF II-III). Together with peripheral hubs, these connector hubs could play an important role in language-memory behavior (see description in the body text).