The scale of neurodegeneration in moderate-to-severe traumatic brain injury: a systematic review protocol.

BACKGROUND: Our understanding of recovery after moderate-to-severe traumatic brain injury (TBI) has shifted. Until recently, it was presumed that following a period of acute neurological vulnerability, the brain remained stable in the chronic stages of injury. However, recent research has shown neurodegeneration in the chronic stages of moderate-to-severe TBI, challenging the assumption of neurological stability. While there is extensive evidence that neurodegeneration occurs, debate remains regarding the scale and timing. This systematic review will evaluate the scale and timelines of neurodegeneration in adult patients with moderate-to-severe TBI. METHODS: Literature searches will be conducted in six electronic databases (from inception onwards), including MEDLINE, EMBASE, PsycINFO, CINAHL, SportDiscus, and Cochrane Central Register of Controlled Trials. We will include observational studies that examine neurodegenerative changes within a single sample of TBI patients or studies that compare neuroimaging outcomes between TBI patients and healthy controls. Our primary outcome is structural neuroimaging, and our secondary outcome is diffusion tensor imaging for detection of post-injury white matter changes. All screening, data extraction, and study quality appraisal will be performed independently by the same two study members. It is expected that a narrative summary of the literature will be produced. If feasible, we will conduct a random-effects meta-analysis. However, given the expected heterogeneity between studies (with respect to, for example, timing of imaging, regions imaged) we do not expect to perform a meta-analysis; rather, a narrative synthesis of our findings is expected to be performed. DISCUSSION: Understanding the scale and timelines of neurodegeneration in moderate-to-severe TBI (as well as which brain areas are most vulnerable to chronic declines) can inform intervention research designed to offset such changes. This may help improve patient outcome following moderate-to-severe TBI and, in turn, reduce the burden of the injury. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42019117548.

Early cognitive decline in older adults better predicts object than scene recognition performance.

There is an ongoing debate regarding the nature of memory deficits that occur in the early stages of mild cognitive impairment (MCI). MCI has been associated with atrophy to regions that process objects, namely perirhinal and lateral entorhinal cortices. However, it is currently unclear whether older adults with early MCI will show memory deficits that are specific to objects, or whether they will also show memory deficits for other stimulus classes, such as scenes. We tested 75 older adults using an object and scene recognition task with stimulus-specific interference (i.e., exposure to irrelevant object or scene stimuli). We found an interaction (P = 0.05) whereby scores on the Montreal Cognitive Assessment, a neuropsychological test with high sensitivity to MCI, shared a stronger relationship with object recognition than with scene recognition performance. Interestingly, this relationship was not modulated by the stimulus category of interfering items. To further explore these findings, we also tested an amnesic patient (DA) with known medial temporal lobe damage. Like older adults with early signs of MCI, DA showed poorer object recognition than scene recognition performance. Additionally, his performance was not modulated by the stimulus category of interfering material. By demonstrating that object memory is more predictive of cognitive decline than scene memory, these findings support the notion of perirhinal and lateral entorhinal cortex dysfunction in the early stages of MCI. © 2016 Wiley Periodicals, Inc.