Multidimensional assessment of time perception along the continuum of Alzheimer's Disease and evidence of alterations in subjective cognitive decline.

Timing alterations occur in Alzheimer's disease (AD), even in early stages (mild cognitive impairment, MCI). Moreover, a stage named subjective cognitive decline (SCD), in which individuals perceive a change in cognitive performance not revealed by neuropsychological tests, has been identified as a preclinical phase of AD. However, no study to date has investigated different dimensions of time processing along the continuum from physiological to pathological aging, and whether timing alterations occur in SCD. Here a sample of participants with SCD, MCI, AD and healthy controls (HC) performed tasks assessing prospective duration estimation, production, reproduction, implicit temporal learning in conditions dependent from external cues (externally-cued learning, ECL) or independent from external cues (internally-based learning, IBL), retrospective duration estimation, the subjective experience of time and the temporal collocation of events. AD patients performed worse than HC and SCD in prospective timing, and in collocating events in time. The subjective experience of time did not differ between groups. Concerning temporal learning, AD performed worse in ECL than in IBL, whereas SCD performed worse in IBL than in ECL. SCD, MCI and AD patients all showed errors greater than HC in retrospective duration estimation. Results point to implicit temporal learning in externally-cued conditions and retrospective time estimation as possible early markers of cognitive decline.

Cortical complexity alterations in the medial temporal lobe are associated with Alzheimer's disease psychosis.

Psychosis is frequent in Alzheimer's disease (AD) and it is associated with a worse disease course. AD psychosis may represent a distinct AD phenotype, though its specific neurobiological underpinnings have yet to be identified. This study investigated neural underpinnings of AD psychosis using surface-based-morphometry.Data from 32 AD patients, 17 with psychosis (AD-P) and 15 without were analyzed. Average cortical complexity (fractal dimension, FD) was estimated for each theoretically motivated ROI and patient. First, we compared regional FD in AD-P and AD patients. Then we calculated the correlation coefficients between FD and the severity of misidentification and paranoid psychotic symptoms. AD-P showed decreased FD in ventral-visual-stream compared to AD, suggesting that perceptual processes might be pivotal in psychosis. A negative correlation was found between misidentification severity and FD in the entorhinal cortex suggesting that misidentification may be specifically associated with alterations in regions involved in high-level perceptual and contextualization processes.

Psychosis of Alzheimer's disease: Neuropsychological and neuroimaging longitudinal study.

OBJECTIVES: Psychosis of Alzheimer's disease (AD) may represent a distinct disease phenotype; however, neuropsychological profile and neural basis linked to this phenotype have not yet been clarified. In this study, we aimed at detecting whether impairment in specific cognitive domains predicts the onset of psychosis in AD patients and what grey matter alterations, their location, and the rate of atrophy are associated with psychosis of AD. METHODS: Longitudinal neuropsychological data from AD patients with and without psychosis were analysed to determine whether the neuropsychological profile can predict the onset of psychosis. A voxel-based morphometry (VBM) on longitudinal T1-weighted images was used to explore differences in grey matter volume and in the rate of atrophy between groups. RESULTS: Noncognitive domain predicted the psychosis onset. However, AD patients with psychosis exhibited greater atrophy in the right anterior-inferior temporal lobe, including the fusiform gyrus (cluster-p-family-wise error [pfwe] < 0.05; peak-p uncorrected [pUNC] < 0.001) as well as greater rate of atrophy in the right insula than nonpsychotic patients (cluster-pFWE = 0.075; peak-pUNC < 0.001). The anterior-inferior temporal lobe is part of the ventral visual stream, and the insula plays a key role in the salience network. CONCLUSIONS: This finding suggests that damage in these areas underpins an impairment in the visual processing of the objects and an impairment in the attribution of salience to the misperceived stimuli, which in turn leads to the onset of psychosis. These findings tie in well with the neuropsychological model of psychosis, according to which the simultaneous presence of two factors, namely misperception and misattribution, underlies psychosis in dementia.