Differential Influence of Levodopa on Reward-Based Learning in Parkinson's Disease

The mesocorticolimbic dopamine (DA) system linking the dopaminergic midbrain to the prefrontal cortex and subcortical striatum has been shown to be sensitive to reinforcement in animals and humans. Within this system, coexistent segregated striato-frontal circuits have been linked to different functions. In the present study, we tested patients with Parkinson's disease (PD), a neurodegenerative disorder characterized by dopaminergic cell loss, on two reward-based learning tasks assumed to differentially involve dorsal and ventral striato-frontal circuits. 15 non-depressed and non-demented PD patients on levodopa monotherapy were tested both on and off medication. Levodopa had beneficial effects on the performance on an instrumental learning task with constant stimulus-reward associations, hypothesized to rely on dorsal striato-frontal circuits. In contrast, performance on a reversal learning task with changing reward contingencies, relying on ventral striato-frontal structures, was better in the unmedicated state. These results are in line with the “overdose hypothesis” which assumes detrimental effects of dopaminergic medication on functions relying upon less affected regions in PD. This study demonstrates, in a within-subject design, a double dissociation of dopaminergic medication and performance on two reward-based learning tasks differing in regard to whether reward contingencies are constant or dynamic. There was no evidence for a dose effect of levodopa on reward-based behavior with the patients’ actual levodopa dose being uncorrelated to their performance on the reward-based learning tasks

Local Fatty Acid Channeling into Phospholipid Synthesis Drives Phagophore Expansion during Autophagy

Autophagy is a conserved catabolic homeostasis process central for cellular and organismal health. During autophagy, small single-membrane phagophores rapidly expand into large double-membrane autophagosomes to encapsulate diverse cargoes for degradation. It is thought that autophagic membranes are mainly derived from preformed organelle membranes. Instead, here we delineate a pathway that expands the phagophore membrane by localized phospholipid synthesis. Specifically, we find that the conserved acyl-CoA synthetase Faa1 accumulates on nucleated phagophores and locally activates fatty acids (FAs) required for phagophore elongation and autophagy. Strikingly, using isotopic FA tracing, we directly show that Faa1 channels activated FAs into the synthesis of phospholipids and promotes their assembly into autophagic membranes. Indeed, the first committed steps of de novo phospholipid synthesis at the ER, which forms stable contacts with nascent autophagosomes, are essential for autophagy. Together, our work illuminates how cells spatially tune synthesis and flux of phospholipids for autophagosome biogenesis during autophagy

Using the Rey Auditory Verbal Learning Test (RAVLT) to differentiate Alzheimer's dementia and behavioural variant fronto-temporal dementia

In patients with focal lesions, patterns of learning, retrieval, and recognition deficits vary according to site of damage. Because different brain regions are affected by the underlying pathology in Alzheimer's dementia (AD) and behavioral variant fronto-temporal dementia (bvFTD), one might predict that the two disorders would result in different sorts of memory deficits on the Rey Auditory Verbal Learning Test (RAVLT). The aim of this investigation was to find a way to differentiate AD, bvFTD, and normal controls (NC) reliably based on RAVLT scores from retrospective samples of 82 Italian and 43 Australian participants. Results indicated that the groups differed on measures of learning, retroactive interference, delayed recall, and delayed recognition. Although delayed recall distinguished participants in the three groups across both samples, no one set of cut-offs could be obtained with adequate sensitivity and specificity. However, when we created a combined score (the "RAVLT Memory Efficiency Index": {[(delayed recall A/15)/(RAVLT Trials 1-5/75)] + [(delayed recognition hits/15) - (false positive/total number of distractors)]}), we were able to find cut-offs that differentiated the groups with good sensitivity and specificity across variations in RAVLT methodology, participant samples, and languages. This index will increase the usefulness of the RAVLT in differential diagnoses of early dementia.16 page(s