LAUSR

The past decade has seen the recognition of later-life emergent neuropsychiatric symptoms (NPS), referred to as mild behavioral impairment (MBI) (Ismail et al., 2016, Taragano et al., 2008), as a novel dementia-risk marker and a potential early clinical intervention target (Mortby et al., 2018a). Leveraging the well-known behavioral prodrome of frontotemporal dementia (FTD), MBI was first proposed by Taragano and colleagues (2008) as a predementia (primarily FTD) construct where a primarily behavioral presentation (late-life behavioral changes in the absence of major cognitive symptomatology) was associated with greater dementia risk, when contrasted to a primarily cognitive presentation (i.e. mild cognitive impairment). This definition was substantially revised by the MBI Working Group of the Alzheimer’s Association (AA) International Society to Advance Alzheimer’s Research andTreatment (ISTAART)Neuropsychiatric Syndromes Professional Interest Area, and published in 2016. The fundamental changes to the MBI construct, as described in the ISTAART–AA criteria, come from the harmonization of cognition and behavior, not as competing constructs but as parallel ones (a neurobehavioral axis and a neurocognitive axis), that can manifest concurrently or sequentially (as opposed to either/or). Further, these new criteria are explicit in that MBI can be a prodrome to dementia of any etiology, including Alzheimer’s disease, moving away from the prevailing belief that behavioral prodromes are uniquely associated with FTD. Additionally, specific behavioral domains were described, allowing the opportunity to distinguish between behavioral endophenotypes, potentially allowing for greater prognostic precision. The criteria exclude psychiatric illness a priori and require the onset of symptomatology in later-life and the presence of the behaviors for 6 or more months (Ismail et al., 2016). The AA–ISTAART MBI criteria provide the research field with a structured framework through which relevant NPS can be examined for their impact on cognition (Ismail et al., 2016). The five behavioral domains, which can be examined independently or collectively, include: (i) impaired drive and motivation (apathy); (ii) emotional dysregulation (mood and anxiety symptoms); (iii) impulse dyscontrol/agitation/abnormal reward salience (changes in response inhibition and self-regulation); (iv) social inappropriateness (impaired social cognition) and (v) abnormal thoughts/perceptions (psychosis e.g. hallucinations and delusions). The development of these construct-specific criteria has been crucial in the elucidation of the relationship between MBI and cognitive impairment. A concerted global research effort has since focused on the validation of the MBI construct as a neurobehavioral syndrome (e.g. Sherman et al., 2018, Ismail et al., 2018, Bateman et al., 2020, Desmarais et al., 2018, Fischer and Aguera-Ortiz, 2018, Mortby et al., 2018b, Sheikh et al., 2018, Creese et al., 2019). The ISTAART–AA MBI criteria, and the subsequent development of a construct-specific case ascertainment tool – the MBI Checklist (Ismail et al., 2017), have underpinned a paradigm shift, with greater recognition of MBI as a pre-clinical marker of dementia risk. These criteria have underpinned a rapidly growing international body of evidence linking MBI to accelerated cognitive decline/progression to dementia (e.g. Taragano et al., 2018, Creese et al., 2019, Matsuoka et al., 2019), validated Alzheimer’s disease genetic loci (Andrews et al., 2018, Creese et al., 2020) and neurobiological correlates (e.g. Naude et al., 2020, Lussier et al., 2020). Within this rapidly evolving research field, the work presented by Rouse and colleagues (2020) in their article “Mild Behavioral Impairment as a Predictor of Cognitive Functioning in Older Adults” provides a valuable addition to the current research paradigm and a starting point for longitudinal follow-up. Using data from the Florida Alzheimer’s Disease Research Center (FL-ADRC), the authors conducted a secondary data analysis of 497 cognitively healthy older adults and individuals with mild cognitive impairment and provide valuable insight into unique cognitive phonotypes associated with MBI. This was done by examining the impact of MBI on specific cognitive domains (executive function, attention, short-term memory and episodic memory) and further investigating the role of cognitive status (i.e. normal cognition vs. mild cognitive impairment) within this association. The authors International Psychogeriatrics (2021), 33:3, 209–212 © International Psychogeriatric Association 2021