Discriminant BOLD Activation Patterns during Mental Imagery in Parkinson’s Disease

in Proceedings of MLINI 2012 (in press)

Using machine learning based models in clinical applications has become current practice and can prove useful to provide information at the subject’s level, such as predicting an (early) diagnosis or ... [more ▼]

Using machine learning based models in clinical applications has become current practice and can prove useful to provide information at the subject’s level, such as predicting an (early) diagnosis or monitoring the evolution of a disease. However, the performance of these models depends on the choice of a biomarker to detect the presence or absence of a disease. Choosing a biomarker is not straightforward, especially in the case of Parkinson’s disease when compared to healthy subjects. In the present work, we investigated the mental imagery of gait as a biomarker of Parkinson’s disease and showed that the signal in the mesencephalic locomotor region during the mental imagery of gait at a comfortable pace can discriminate significantly between idiopathic Parkinson’s disease patients and healthy subjects. Although there is room for improvement, the results of this preliminary study are promising. [less ▲]

Differential effects of aging on the neural correlates of recollection and familiarity

in Cortex : A Journal Devoted to the Study of the Nervous System & Behavior (in press)

The present experiment aimed to investigate age differences in the neural correlates of familiarity and recollection, while keeping performance similar across age groups by varying task difficulty. Twenty ... [more ▼]

The present experiment aimed to investigate age differences in the neural correlates of familiarity and recollection, while keeping performance similar across age groups by varying task difficulty. Twenty young and twenty older adults performed an episodic memory task in an event-related fMRI design. At encoding, participants were presented with pictures, either once or twice. Then, they performed a recognition task, with a Remember/Know paradigm. A similar performance was observed for the two groups in the Easy condition for recollection and in the Hard condition for familiarity. Imaging data revealed the classic recollection-related and familiarity-related networks, common to young and older groups. In addition, we observed that some activity related to recollection (left frontal, left temporal, left parietal cortices and left parahippocampus) and familiarity (bilateral anterior cingulate, right frontal gyrus and left superior temporal gyrus) was reduced in older compared to young adults. However, for recollection processes only, older adults additionally recruited the right precuneus, possibly to successfully compensate for their difficulties, as suggested by a positive correlation between recollection and precuneus activity. [less ▲]

PRoNTo: Pattern Recognition for Neuroimaging Toolbox

in Neuroinformatics (2013)

In the past years, mass univariate statistical analyses of neuroimaging data have been complemented by the use of multivariate pattern analyses, especially based on machine learning models. While these ... [more ▼]

In the past years, mass univariate statistical analyses of neuroimaging data have been complemented by the use of multivariate pattern analyses, especially based on machine learning models. While these allow an increased sensitivity for the detection of spatially distributed effects compared to univariate techniques, they lack an established and accessible software framework. The goal of this work was to build a toolbox comprising all the necessary functionalities formultivariate analyses of neuroimaging data, based on machine learning models. The “Pattern Recognition for Neuroimaging Toolbox” (PRoNTo) is open-source, cross-platform, MATLAB-based and SPM compatible, therefore being suitable for both cognitive and clinical neuroscience research. In addition, it is designed to facilitate novel contributions from developers, aiming to improve the interaction between the neuroimaging and machine learning communities. Here, we introduce PRoNTo by presenting examples of possible research questions that can be addressed with the machine learning framework implemented in PRoNTo, and cannot be easily investigated with mass univariate statistical analysis. [less ▲]

The impact of visual perceptual learning on sleep and local slow wave initiation

in Journal of Neuroscience (2013)

Dosimetry for 6-[18F]Fluoro-L-DOPA in humans based on in vivo microPET scans and ex vivo tissue distribution in mice

Poster (2012, September)

Radiation dosimetry of new radiopharmaceuticals generally starts with studies in small animals such as mice and rats. The traditional technique has long been ex vivo measurement of the biodistribution ... [more ▼]

Radiation dosimetry of new radiopharmaceuticals generally starts with studies in small animals such as mice and rats. The traditional technique has long been ex vivo measurement of the biodistribution over time using harvested organs at different times post administration of the radiopharmaceutical. Since this approach requires a significant amount of animals, dynamic microPET studies, where the biodistribution of the tracer over time can be determined in vivo in a single scan, are an invaluable alternative. Due to known imaging artifacts and limitations, such as partial volume effect, a hybrid technique combining harvesting organs (post-scan) and dynamic imaging was introduced to achieve a cross-calibration to account for these limitations. Since 6-[18F]Fluoro-L-DOPA is a widely used PET tracer to study the dopaminergic system in neurology and oncology and there is no sound published dosimetry data, absorbed doses for major organs in humans were estimated using the traditional ex vivo technique and by dynamic microPET imaging in mice, allowing direct comparison of the results from the two techniques. The tissue distribution over time of 6-[18F]Fluoro-L-DOPA was determined by radioassay of harvested organs at 2, 5, 10, 30, 60, 120 minutes post administration (n=5 at each time point) in isoflurane-anaesthetized mice. Dynamic PET images were acquired with a FOCUS 120 microPET for 120 minutes after injection of 6-[18F]Fluoro-L-DOPA followed by radioassay of harvested organs (n=4). A bladder voiding scenario was used to simulate excretion every 2 h. The organ time-activity-curves (TACs) from both methods were extrapolated from a simulated 35 g standard mouse to a 70 kg standard male human using a technique based on organ to bodyweight ratios. The absorbed doses in major human organs were calculated with the commercially available human dosimetry software OLINDA/EXM (Version 1.1) using the extrapolated TACs. The extrapolated organ TACs obtained using the two methods showed a high correlation (average r = 0.94 ± 0.05, p < 0.001). However, TACs from PET alone under- or overestimated the activity in individual organs in contrast to TACs obtained using the cross-calibration of the PET data with the activity in post-scan dissected organs. Those organs in the excretion pathways, comprising bladder wall, kidneys and liver, received the highest organ doses. The total body absorbed dose was 0.0118 mGy/MBq for both the imaging based and harvesting based methods. The effective dose was 0.0193 mSv/MBq for the hybrid imaging-harvesting technique and 0.0189 mSv/MBq for the pure harvesting technique. Scaling errors in the PET TACs are likely caused by quantification errors such as partial volume effects and image artifacts. The use of a hybrid imaging technique to cross-calibrate the TACs improved the accuracy of the imaging-based dosimetry estimates. Therefore the hybrid technique combining dynamic imaging and harvesting organs (post-scan) is a suitable alternative to the gold standard ex vivo radioassay method. It yields comparable results yet reduces significantly the amount of animals needed in the study and can accelerate data acquisition. [less ▲]

Item familiarity and controlled associative retrieval in Alzheimer’s disease: an fMRI study.

in Proceedings of the Amsterdam Memory Slam 2012 (2012, August 30)

Alzheimer’s disease (AD) is characterised by altered recollection function, with impaired controlled retrieval of associations. In contrast, familiarity-based memory for individual items may sometimes be ... [more ▼]

Alzheimer’s disease (AD) is characterised by altered recollection function, with impaired controlled retrieval of associations. In contrast, familiarity-based memory for individual items may sometimes be preserved in early stages of the disease. This is the first study that directly examines whole brain regional activity engaged during one core aspect of the recollection function: associative controlled episodic retrieval (CER), contrasted to item familiarity in AD patients. Cerebral activity related to associative CER and item familiarity in AD patients and healthy controls (HC) was measured with functional magnetic resonance imaging during a word-pair recognition task to which the process dissociation procedure was applied. Some patients had null CER estimates (AD-), whereas others did show some CER abilities (AD+) although significantly less than HC. In contrast, familiarity estimates were equivalent in the three groups. In AD+ like in controls, associative CER activated the inferior precuneus/posterior cingulate cortex (PCC). However, during associative CER, functional connection between this region and the hippocampus, the inferior parietal and the dorsolateral prefrontal cortex was significantly higher in HC than in AD+. In the three groups, item familiarity was related to activation along the intraparietal sulcus (IPS). In conclusion, whereas the preserved automatic detection of an old item (without retrieval of accurate word association) is related to a parietal activation centred on the IPS, the inferior precuneus/PCC supports associative CER ability in AD patients as in HC. However, AD patients have deficient functional connectivity during associative CER suggesting that residual recollection function in these patients might be impoverished by lack of some recollection-related aspects such as autonoetic quality, episodic details and verification. [less ▲]

PRoNTo: Pattern Recognition for Neuroimaging Toolbox

Poster (2012, June 12)

Anisotropy preserving interpolation of diffusion tensors

Poster (2012, June)

Neural Correlates of Performance Variabilty during Motor Sequence Acquisition

in NeuroImage (2012), 60(1), 324-331

Influence of acute sleep loss on the neural correlates of alerting, orientating and executive attention components

in Journal of Sleep Research (2012), 21(6), 648-58