A nascent topic in cognitive neuroscience is the relatively seamless manner by which humans transition between externally evoked and internally driven expressions of memory. Barzykowski and Moulin (B&M) present a new framework under which seemingly divergent manifestations of spontaneous cognition might be accommodated within the same conceptual space. Two putative expressions of spontaneous memory – involuntary autobiographical memory and déjà vu – are conceptualised as interlinked processes that vary in terms of their content and associated phenomenology. By situating these processes along a representational continuum, the framework provides an interesting testbed for future empirical studies to capture variable manifestations of spontaneous cognition in health and disease.

Despite its broad appeal, several theoretical aspects warrant further development, particularly in relation to disorders of memory. First, the model proposes that the threshold for familiarity is intimately linked to the retrieval of contextual specifics. Accordingly, deterioration of episodic or semantic fluency signals should impede re-instantiation of the corresponding neural activation of the original experience, resulting in a subjective feeling of familiarity (reviewed by Renoult, Irish, Moscovitch, & Rugg, Reference Renoult, Irish, Moscovitch and Rugg2019). Degradation of the contextual memory trace and accompanying recollective experience is a transdiagnostic feature of dementia (Irish, Reference Irish2023; Irish, Piguet, & Hodges, Reference Irish, Piguet and Hodges2012). On formal tests of autobiographical memory, participants with Alzheimer's disease display a content-specific vulnerability, biasing the subjective experience towards a feeling of familiarity in the absence of detailed recollection (reviewed by Irish, Reference Irish2023). Thus, for deliberate forms of autobiographical retrieval, at least, the model's predictions of a coupling between content and phenomenology appear well supported.

Importantly, however, the B&M model focuses on involuntary expressions of memory that arise relatively unbidden or without deliberate intention. For involuntary autobiographical memories (IAM), the central premise is that a content-addressable memory springs to mind fully formed, reflecting an automatic bottom-up retrieval process in response to environmental cues. Few studies have explored the frequency, content or phenomenology of IAMs in dementia; however, studies of self-referential forms of spontaneous cognition provide initial insights (O'Callaghan & Irish, Reference O'Callaghan, Irish, Christoff and Fox2018). Participants with Alzheimer's disease have been shown to generate significantly fewer incidences of mind wandering relative to healthy older adults during ongoing performance of a sustained attention task (Gyurkovics, Balota, & Jackson, Reference Gyurkovics, Balota and Jackson2018). In contrast, work from our lab indicates that under conditions of low cognitive demand, some types of of self-referential mind wandering can be achieved in Alzheimer's disease (O'Callaghan, Shine, Hodges, Andrews-Hanna, & Irish, Reference O'Callaghan, Shine, Hodges, Andrews-Hanna and Irish2019). These conflicting findings suggest that the way in which we probe spontaneous cognition significantly influences the resultant content and subjective experience.

How, then, might incidental cues in the external environment give rise to somewhat aberrant expressions of memory, such as déjà vu? Here, Barzykowski and Moulin's (B&M) model diverges from previous literature by intimating that a loss of contextual detail could potentiate a feeling of déjà vu. Contexts that are repeatedly encountered might trigger a schema-driven sense of familiarity, which lacks the spatiotemporal specificity required for fully fledged episodic recollection (Irish & Vatansever, Reference Irish and Vatansever2020). In contexts where an appropriate detail threshold is not met and feelings of familiarity are not corroborated with sufficient detail, the ensuing representation might shift from a content-addressable memory to the subjective experience of déjà vu. Based on the B&M model, one might be tempted to predict elevated levels of déjà vu in dementia populations, reflecting a mismatch between preserved familiarity for an incidental cue or context in the absence of the comparator content from episodic memory. Empirical research on déjà vu in dementia, however, is extremely scant, given the inherent difficulties in operationalising and measuring a rare occurrence that requires high levels of metacognitive insight for its detection.

Finally, we must consider the endogenous processes by which spontaneous cognition emerges in response to incidental external triggers. Recent theoretical frameworks place incidental external triggers at the cornerstone of involuntary quirks of memory and their natural occurrence in everyday life. The spontaneous retrieval deficit hypothesis argues that spontaneous manifestations of autobiographical memory are disproportionately compromised in dementia due to an inability to endogenously generate appropriate content in response to stimuli encountered in the environment (Kvavilashvili, Niedzwienska, Gilbert, & Markostamou, Reference Kvavilashvili, Niedzwienska, Gilbert and Markostamou2020). This hypothesis emphasises the importance of automatic bottom-up retrieval of cue-driven representations as an early marker of Alzheimer's disease, but one which seems minimally affected in healthy aging (see also Irish, Goldberg, Alaeddin, O'Callaghan, & Andrews-Hanna, Reference Irish, Goldberg, Alaeddin, O'Callaghan and Andrews-Hanna2019). A marked attenuation of spontaneous phenomena, including IAMs and déjà vu, would therefore be predicted in any population where the endogenous generation of mental content is impaired (O'Callaghan & Irish, Reference O'Callaghan, Irish, Christoff and Fox2018).

While B&M's model offers an interesting glimpse into potential mechanisms driving spontaneous quirks of memory, its application in neurocognitive disorders raises several challenges and opportunities for future research. Further iterations of the model might explore the nature of external cues in determining the frequency and readout of spontaneous memory. Efforts to delineate how different levels of cue specificity influence the perceptual and conceptual fluency signals that drive familiarity processes in dementia will also be essential. Ultimately, by incorporating synergies and discontinuities from clinical populations, the model can progress towards a more integrative account.