The integrative memory model proposed by Bastin et al. is theoretically and clinically relevant as it provides a framework for the chronological pattern of recollection and familiarity processes in Alzheimer’s disease (AD), depending on the brain regions most affected at each stage of the disease. That being said, the framework can be extended to include the subjective experience of both recollection and familiarity and their abnormalities in patients with AD. Recollection and familiarity have been associated with distinct subjective experiences: Recollection is typically associated with a subjective experience of “mental time travel,” in which we experience the conscious sensation of traveling back in time to relive the original event and to see it in our mind's eye, whereas familiarity is typically associated with a feeling of knowing characterized by a vague and unspecific experience of remembering (Tulving Reference Tulving2002). Regarding Alzheimer's disease, patients typically demonstrate a shift from the ability to mentally relive past events (i.e., a shift from recollection) to a general sense of familiarity that may be expressed by the patients as a sense of “having experienced this before” (El Haj et al. Reference El Haj, Antoine, Nandrino and Kapogiannis2015).

The decline of recollection in Alzheimer’s disease can be attributed to decline in specific processes of the recollective experience. This decline has been pointed out by research demonstrating decline in the recollective experience during retrieval of past personal events in patients with AD, including decline in subjective processes, such as reliving, travel in time, remembering, realness, rehearsal, and visual imagery (El Haj et al. Reference El Haj, Kapogiannis and Antoine2016). Among these subjective processes, decline of visual imagery seems to play a key role in the decline of recollective experience in patients with AD. The decline of visual imagery in AD seems to deprive patients from the ability to retrieve and manipulate mental images during retrieval, and also deprive them from visual cues that mediate and/or accelerate their search through memory stores (El Haj et al. Reference El Haj, Gallouj and Antoine2019a; Reference El Haj, Moustafa, Gallouj and Robin2019b).

The relationship between decline of visual imagery and decline of the recollective experience in AD can be understood by highlighting research using the Field/Observer paradigm, which has been widely used to assess the subjective experience of recollection and familiarity in general populations (Nigro & Neisser Reference Nigro and Neisser1983; Rice & Rubin Reference Rice and Rubin2011). In one study in AD, patients were invited to retrieve past personal events and, subsequently, provide a “Field” response, if they could visualize the event through their own eyes, or an “Observer” response if they could visualize themselves in the scene as a spectator would (El Haj et al. Reference El Haj, Moustafa, Gallouj and Robin2019b). Results demonstrated increased “Field” and decreased “Observer” responses in patients, suggesting a diminished ability of patients with AD to construct vivid images when recollecting the past.

In summary, the decline of the recollective experience during retrieval can be associated with declines in several components of the subjective experience, such as reliving, travel in time, remembering, realness, and rehearsal. Critically, decline of visual imagery seems to deprive patients from the ability to construct mental images when recollecting the past. We propose that these processes should be considered by the integrative memory model, as proposed by Bastin et al., to better account for recollection deficits in patients with AD. We believe that a decline in the subjective experience during retrieval in patients with AD leads to a decline of recollection and, consequently, to the emergence of a general sense of familiarity that is typically associated with a sense of “having experienced this before.” As pointed out by Bastin et al., the integrative memory model is not comprehensive and should evolve to incorporate other mechanisms. Therefore, we propose that the integrative memory model is sufficiently flexible to include these subjective processes and may be enriched by this inclusion.