Abstract
Damage to the fornix leads to significant memory impairment and executive dysfunction and is associated with dementia risk. We sought to identify if fornix integrity and fiber length are disrupted in mild cognitive impairment (MCI) and how they associate with cognition. Data from 14 healthy older adult controls (HCs) and 17 subjects with non-amnestic MCI (n-aMCI) were analyzed. Diffusion tensor imaging (DTI) at 1.5 Tesla MRI was performed to enable manual tracing of the fornix and calculation of DTI parameters. Higher fractional anisotropy of body and column of the fornix was associated with better executive functioning and memory, more strongly in the HC than in the n-aMCI group. Fornix fiber tract length (FTL) was associated with better executive function, more strongly in the n-aMCI than in the HC group, and with better memory, more strongly in the HC than in the n-aMCI group. These results highlight a decline in the contributions of the fornix to cognition in n-aMCI and suggest that maintenance of fornix FTL is essential for sustaining executive functioning in people with n-aMCI.
Highlights
60% of the world’s population lives in the Asia-Pacific region, where the prevalence of dementia is expected to rise from 23 million in 2015 to 71 million in 2050 (Venketasubramanian et al, 2010; Alzheimer’s Disease International, 2014, 2018, 2019), among which vascular dementia (VaD) is more prevalent than in western populations
Our results suggest that function and integrity in the BC (FABC) does not support executive function as efficiently in non-amnestic MCI (n-aMCI) compared to healthy older adult controls (HCs), as fractional anisotropy (FA) is less strongly associated with EF in the former group (Table 4)
Anterograde amnesia, the inability to create new memories, is one of the earliest symptoms in patients with fornix infarction or after traumatic brain injury (TBI) that damages limbic-related structures including the fornix (Baweja et al, 2015; Gupta et al, 2015; Turine et al, 2016; Kauppila et al, 2018; Takano et al, 2018; Wang et al, 2018; Zhu et al, 2018). These results suggest that one contributor to episodic memory deficits in n-aMCI is the subtle degradation of fornix integrity
Summary
60% of the world’s population lives in the Asia-Pacific region, where the prevalence of dementia is expected to rise from 23 million in 2015 to 71 million in 2050 (Venketasubramanian et al, 2010; Alzheimer’s Disease International, 2014, 2018, 2019), among which vascular dementia (VaD) is more prevalent than in western populations. The criteria for MCI (termed minor cognitive disorder by the American Psychiatric Association) include concerns about changes in cognition, impairment in one or more cognitive domains, preservation of independence in functional abilities, and no dementia (American Psychiatric Association, 2013). VaD is usually caused by decreased blood flow to the brain, with the risk of incident dementia within 5 years being 6.5 times higher after a stroke and 1.5 times higher after a transient ischemic attack (TIA) (Pendlebury et al, 2019). A decrease in cerebral blood flow (CBF) and hypoxia in the prefrontal cortex (PFC), basal ganglia, and hippocampus is typically associated with cognitive decline and behavioral changes in VaD (Iadecola, 2013; Venkat et al, 2015). Patients with smalland large-vessel VaD showed dysfunction in memory, executive function, and attention domains (Sengupta et al, 2019)
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