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  • Time is of the essence.

    2 February 2018

    Timing is essential to human behaviour, but the neural mechanisms underlying time perception are still unclear. New findings from a brain-imaging study by Coull et al. show that activity in a network of motor-related areas varies parametrically with attention to time. Given that a system in which timing is important (but not the primary function) is recruited when temporal judgements are required, we should perhaps reassess the notion of a dedicated timing system in the brain.

  • Electrophysiological evidence implicates automatic low-level feature detectors in perceptual asymmetry.

    15 February 2018

    Perceptual asymmetry has been demonstrated behaviorally using frequency modulated (FM) stimuli: a modulated tone is easier to detect among unmodulated distracters than the converse. We demonstrate perceptual asymmetry for FM tones in the mismatch negativity (MMN) component of the event-related potential, regardless of whether the participant attends to the tones. These results suggest that perceptual asymmetry reflects the automatic activation of low-level feature detectors in the auditory system.

  • Acquisition of the temporal and ordinal structure of movement sequences in incidental learning.

    5 February 2018

    We investigated the acquisition and integration of temporal and ordinal sequence information in an incidental learning model of motor skill acquisition (the serial reaction time task). Human participants were exposed to a stimulus-response sequence that had temporal structure, ordinal structure, or both. By changing the temporal or ordinal structure, or both, we were able to ask two questions: first, does a regular temporal structure facilitate learning of an ordinal sequence and second, is a temporal sequence, presented in the context of a random ordinal sequence of finger movements, "picked up" through incidental learning? We found that a predictable temporal structure greatly facilitated the learning of an ordinal sequence but was not learned when presented in isolation. The results suggest that when motor skills are acquired under incidental learning conditions, timing is represented at a level specific to the ordinal sequence of movements rather than as an independent temporal template.

  • The cerebellum predicts the timing of perceptual events.

    5 February 2018

    Prospective (forward) temporal-spatial models are essential for both action and perception, but the literature on perceptual prediction has primarily been limited to the spatial domain. In this study we asked how the neural systems of perceptual prediction change, when change-over-time must be modeled. We used a naturalistic paradigm in which observers had to extrapolate the trajectory of an occluded moving object to make perceptual judgments based on the spatial (direction) or temporal-spatial (velocity) characteristics of object motion. Using functional magnetic resonance imaging we found that a region in posterior cerebellum (lobule VII crus 1) was engaged specifically when a temporal-spatial model was required (velocity judgment task), suggesting that circuitry involved in motor forward-modeling may also be engaged in perceptual prediction when a model of change-over-time is required. This cerebellar region appears to supply a temporal signal to cortical networks involved in spatial orienting: a frontal-parietal network associated with attentional orienting was engaged in both (spatial and temporal-spatial) tasks, but functional connectivity between these regions and the posterior cerebellum was enhanced in the temporal-spatial prediction task. In addition to the oculomotor spatial orienting network, regions involved in hand movements (aIP and PMv) were recruited in the temporal-spatial task, suggesting that the nature of perceptual prediction may bias the recruitment of sensory-motor networks in orienting. Finally, in temporal-spatial prediction, functional connectivity was enhanced between the cerebellum and the putamen, a structure which has been proposed to supply the brain's metric of time, in the temporal-spatial prediction task.

  • The WU-Minn Human Connectome Project: an overview.

    15 February 2018

    The Human Connectome Project consortium led by Washington University, University of Minnesota, and Oxford University is undertaking a systematic effort to map macroscopic human brain circuits and their relationship to behavior in a large population of healthy adults. This overview article focuses on progress made during the first half of the 5-year project in refining the methods for data acquisition and analysis. Preliminary analyses based on a finalized set of acquisition and preprocessing protocols demonstrate the exceptionally high quality of the data from each modality. The first quarterly release of imaging and behavioral data via the ConnectomeDB database demonstrates the commitment to making HCP datasets freely accessible. Altogether, the progress to date provides grounds for optimism that the HCP datasets and associated methods and software will become increasingly valuable resources for characterizing human brain connectivity and function, their relationship to behavior, and their heritability and genetic underpinnings.

  • Spectral characteristics of resting state networks.

    15 February 2018

    Resting state networks (RSNs), as imaged by functional MRI, are distributed maps of areas believed to be involved in the function of the "resting" brain, which appear in both resting and task data. The current dominant view is that such networks are associated with slow (∼0.015Hz), spontaneous fluctuations in the BOLD signal. To date, limited work has investigated the frequency characteristics of RSNs; here we investigate a range of issues relating to their spectral and phase characteristics. Our results indicate that RSNs, although dominated by low frequencies in the raw BOLD signal, are in fact broadband processes that show temporal coherences across a wide frequency spectrum. In addition, we show that RSNs exhibit different levels of phase synchrony at different frequencies. These findings challenge the notion that FMRI resting signals are simple "low frequency" spontaneous signal fluctuations.

  • Advances and pitfalls in the analysis and interpretation of resting-state FMRI data.

    15 February 2018

    The last 15 years have witnessed a steady increase in the number of resting-state functional neuroimaging studies. The connectivity patterns of multiple functional, distributed, large-scale networks of brain dynamics have been recognised for their potential as useful tools in the domain of systems and other neurosciences. The application of functional connectivity methods to areas such as cognitive psychology, clinical diagnosis and treatment progression has yielded promising preliminary results, but is yet to be fully realised. This is due, in part, to an array of methodological and interpretative issues that remain to be resolved. We here present a review of the methods most commonly applied in this rapidly advancing field, such as seed-based correlation analysis and independent component analysis, along with examples of their use at the individual subject and group analysis levels and a discussion of practical and theoretical issues arising from this data 'explosion'. We describe the similarities and differences across these varied statistical approaches to processing resting-state functional magnetic resonance imaging signals, and conclude that further technical optimisation and experimental refinement is required in order to fully delineate and characterise the gross complexity of the human neural functional architecture.

  • Homocysteine-lowering by B vitamins slows the rate of accelerated brain atrophy in mild cognitive impairment: a randomized controlled trial.

    16 February 2018

    BACKGROUND: An increased rate of brain atrophy is often observed in older subjects, in particular those who suffer from cognitive decline. Homocysteine is a risk factor for brain atrophy, cognitive impairment and dementia. Plasma concentrations of homocysteine can be lowered by dietary administration of B vitamins. OBJECTIVE: To determine whether supplementation with B vitamins that lower levels of plasma total homocysteine can slow the rate of brain atrophy in subjects with mild cognitive impairment in a randomised controlled trial (VITACOG, ISRCTN 94410159). METHODS AND FINDINGS: Single-center, randomized, double-blind controlled trial of high-dose folic acid, vitamins B(6) and B(12) in 271 individuals (of 646 screened) over 70 y old with mild cognitive impairment. A subset (187) volunteered to have cranial MRI scans at the start and finish of the study. Participants were randomly assigned to two groups of equal size, one treated with folic acid (0.8 mg/d), vitamin B(12) (0.5 mg/d) and vitamin B(6) (20 mg/d), the other with placebo; treatment was for 24 months. The main outcome measure was the change in the rate of atrophy of the whole brain assessed by serial volumetric MRI scans. RESULTS: A total of 168 participants (85 in active treatment group; 83 receiving placebo) completed the MRI section of the trial. The mean rate of brain atrophy per year was 0.76% [95% CI, 0.63-0.90] in the active treatment group and 1.08% [0.94-1.22] in the placebo group (P =  0.001). The treatment response was related to baseline homocysteine levels: the rate of atrophy in participants with homocysteine >13 µmol/L was 53% lower in the active treatment group (P =  0.001). A greater rate of atrophy was associated with a lower final cognitive test scores. There was no difference in serious adverse events according to treatment category. CONCLUSIONS AND SIGNIFICANCE: The accelerated rate of brain atrophy in elderly with mild cognitive impairment can be slowed by treatment with homocysteine-lowering B vitamins. Sixteen percent of those over 70 y old have mild cognitive impairment and half of these develop Alzheimer's disease. Since accelerated brain atrophy is a characteristic of subjects with mild cognitive impairment who convert to Alzheimer's disease, trials are needed to see if the same treatment will delay the development of Alzheimer's disease. TRIAL REGISTRATION: ISRCTN94410159.