Brains creating stories of selves: the neural basis of autobiographical reasoning.

in Social Cognitive and Affective Neuroscience (in press)

Personal identity critically depends on the creation of stories about the self and one's life. The present study investigates the neural substrates of autobiographical reasoning, a process central to the ... [more ▼]

Personal identity critically depends on the creation of stories about the self and one's life. The present study investigates the neural substrates of autobiographical reasoning, a process central to the construction of such narratives. During fMRI scanning, participants approached a set of personally significant memories in two different ways: on some trials, they remembered the concrete content of the events (autobiographical remembering), whereas on other trials they reflected on the broader meaning and implications of their memories (autobiographical reasoning). Relative to remembering, autobiographical reasoning recruited a left-lateralized network involved in conceptual processing (including the dorsal medial prefrontal cortex (MPFC), inferior frontal gyrus, middle temporal gyrus, and angular gyrus). The ventral MPFC-an area that may function to generate personal/affective meaning-was not consistently engaged during autobiographical reasoning across participants but, interestingly, the activity of this region was modulated by individual differences in interest and willingness to engage in self-reflection. These findings support the notion that autobiographical reasoning and the construction of personal narratives go beyond mere remembering in that they require deriving meaning and value from past experiences. [less ▲]

Relationships between brain metabolism decrease in normal aging and changes in structural and functional connectivity

in NeuroImage (in press)

Normal aging is characterized by brain glucose metabolism decline predominantly in the prefrontal cortex. The goal of the present study was to assess whether this change was associated with age-related ... [more ▼]

Normal aging is characterized by brain glucose metabolism decline predominantly in the prefrontal cortex. The goal of the present study was to assess whether this change was associated with age-related alteration of white matter (WM) structural integrity and/or functional connectivity. FDG-PET data from 40 young and 57 elderly healthy participants from two research centres (n=49/48 in Centre 1/2) were analyzed. WM volume from T1-weighted MRI (Centre 1), fractional anisotropy from diffusion-tensor imaging (Centre 2), and resting-state fMRI data (Centre 1) were also obtained. Group comparisons were performed within each imaging modality. Then, positive correlations were assessed, within the elderly, between metabolism in the most affected region and the other neuroimaging modalities. Metabolism decline in the elderly predominated in the left inferior frontal junction (LIFJ). LIFJ hypometabolism was significantly associated with macrostructural and microstructural WM disturbances in long association fronto-temporo-occipital fibers, while no relationship was found with functional connectivity. The findings offer new perspectives to understand normal aging processes and open avenues for future studies to explore causality between age-related metabolism and connectivity changes. [less ▲]

Item familiarity and controlled associative retrieval in Alzheimer's disease: An fMRI study

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

Brain metabolic dysfunction in Capgras syndrome during Alzheimer’s disease: a positron emission tomography study

Poster (2013, June)

The neural correlates of recollection and familiarity during aging

Poster (2013)

Metabolic and structural connectivity within the default mode network relates to working memory performance in young healthy adults

in NeuroImage (2013)

Studies of functional connectivity suggest that the default mode network (DMN) might be relevant for cognitive functions. Here, we examined metabolic and structural connectivity between major DMN nodes ... [more ▼]

Studies of functional connectivity suggest that the default mode network (DMN) might be relevant for cognitive functions. Here, we examined metabolic and structural connectivity between major DMN nodes, the posterior cingulate (PCC) and medial prefrontal cortex (MPFC), in relation to normal working memory (WM). DMN was captured using independent component analysis of [18F]fluorodeoxyglucose positron emission tomography (FDG-PET) data from 35 young healthy adults (27.1±5.1 years). Metabolic connectivity, a correlation between FDG uptake in PCC and MPFC, was examined in groups of subjects with (relative to median) low (n=18) and high (n=17) performance on digit span backward test as an index of verbal WM. In addition, fiber tractography based on PCC and MPFC nodes as way points was performed in a subset of subjects. FDG uptake in the DMN nodes did not differ between high and low performers. However, significantly (p=0.01) lower metabolic connectivity was found in the group of low performers. Furthermore, as compared to high performers, low performers showed lower density of the left superior cingulate bundle. Verbal WM performance is related to metabolic and structural connectivity within the DMN in young healthy adults. Metabolic connectivity as quantified with FDG-PET might be a sensitive marker of the normal variability in some cognitive functions. [less ▲]

PROFINTEG: A TOOL FOR REAL-LIFE ASSESSMENT OF ACTIVITIES OF DAILY LIVING IN PATIENTS WITH COGNITIVE IMPAIRMENT

in Psychologica Belgica (2013), 53(1), 3-22

Although there are many instruments for assessing activities of daily living (IADL) in brain injured patients, few instruments specifically target cognitive impairment and its impact on IADL. The present ... [more ▼]

Although there are many instruments for assessing activities of daily living (IADL) in brain injured patients, few instruments specifically target cognitive impairment and its impact on IADL. The present study presents the development of the Profinteg instrument, a tool for real-life assessment as well as rehabilitation of IADL in patients with cognitive impairment. This two-stage instrument covers over 90 activities. Psychometric properties of the different Profinteg measures were explored in twenty-five patients with mild to severe cognitive difficulties and twenty-five caregivers. The feasibility of the Profinteg rehabilitation procedure was explored in three patients. Excellent interrater reliability (r > 0.90, p < 0.01) was observed for all measures. Good sensitivity to changes in IADL disability over time was also observed (T = 2.37, p < 0.02). Significant improvement of IADL functioning was found after rehabilitation guided by Profinteg assessment. The Profinteg instrument detects with precision the difficulties patients encounter in their real-life setting via (1) assessment of a large number of activities and (2) detailed decomposition of activities into sub-activities. The Profinteg tool also provides promising results for guidance of IADL rehabilitation in the patient’s real-life environment. [less ▲]

Enhancing the salience of fluency improves recognition memory performance in mild Alzheimer’s disease

in Journal of Alzheimer's Disease [=JAD] (2013), 33

Recognition memory can rely on recollection (recall of the details from the encoding episode) and familiarity (feeling that some information is old without any recollection). In Alzheimer’s disease (AD ... [more ▼]

Recognition memory can rely on recollection (recall of the details from the encoding episode) and familiarity (feeling that some information is old without any recollection). In Alzheimer’s disease (AD), whereas there is a clear deficit of recollection, the evidence regarding familiarity is mixed, with some studies showing preserved familiarity and others reporting impairment. The current study examined whether recognition memory performance can be improved in AD when the use of familiarity is facilitated by the salience of processing fluency due to an earlier encounter with the information. Fifteen AD patients and 16 healthy controls performed a verbal recognition memory task where the salience of fluency was manipulated by means of letters overlap. Studied and unstudied words were constituted of either two separate sets of letters (no-overlap condition, high fluency salience) or the same set of letters (overlap condition, low fluency salience). The results showed that, although performance was globally poorer in AD patients than in the controls, both groups performed significantly better in the no-overlap condition than in the overlap condition. This suggests that AD patients benefited as much as the controls from the salience of fluency. [less ▲]

Performance Evaluation of the GE eXplore CT 120 Micro-CT for Various Scanning Protocols

Poster (2012, November 03)

The aim of this study was to evaluate the performance of the General Electric (GE) eXplore CT 120 micro-CT using the same methodology and image quality assurance vmCT phantom developed for the GE eXplore ... [more ▼]

The aim of this study was to evaluate the performance of the General Electric (GE) eXplore CT 120 micro-CT using the same methodology and image quality assurance vmCT phantom developed for the GE eXplore Ultra. In addition, Quality assurance in Radiology and Medicine (QRM) low contrast and bar pattern phantoms were used. The phantoms were imaged using the six protocols regularly used in our laboratory (Fast scan 220 (P1) or 360 (P2): 70 kV, 32 mA, 220 or 360 views; Soft tissue fast scan (P3): 70 kV, 50 mA, 220 views, Soft tissue step & shoot (P4): 80 kV, 32 mA, 220 views; Low Noise (P5): 100 kV, 50 mA, 720 views and In Vivo Bone scan (P6): 100 kV, 50 mA, 360 views). Data were reconstructed with an isotropic voxel size of 100 µm (50 µm when protocol detector-binning was reduced to 2x2). The MTF obtained with the slanted edge and coil methods agreed very well. A 10% modulation transfer function (MTF) was observed in the range 3.6-4.8 mm-1 (P1&2 = 4.2; P3&4 = 4.8; P5 = 3.6 and P6 = 3.8), corresponding to 95-138 µm resolutions. The smallest bars visually observed on the QRM pattern phantom image were 100 µm. The geometric accuracy was better than 0.1%. A highly linear (R2 > 0.999) relationship between measured and expected CT numbers for both the CT number accuracy and linearity sections of the phantom was observed with a voltage dependent slope. A cupping effect was observed on the uniform slices. This effect was clearly highlighted by the uniformity-to-noise ratio (P1 = 0.58, P2&3&4 = 0.75, P5 = 1.35 and P6 = 2.74) especially for the low-noise protocols P5 and P6. The best low contrast discrimination was observed for P2 and P5 protocols. In conclusion the eXplore CT 120 achieved a resolution in the range 95-138 µm. It was found to be linear and geometrically accurate. The major difference between the protocols was the noise level which limits the detectability of low contrasts. [less ▲]

Performance Measurements of the microPET FOCUS 120 for Iodine-124 Imaging

in IEEE Transactions on Nuclear Science (2012), PP

This study aimed to evaluate the performance of the microPET FOCUS 120 for 124I in terms of counting rate capability and image quality using the NEMA NU 4-2008 methodology. Scanner sensitivity was ... [more ▼]

This study aimed to evaluate the performance of the microPET FOCUS 120 for 124I in terms of counting rate capability and image quality using the NEMA NU 4-2008 methodology. Scanner sensitivity was measured for 124I for comparison and reached 75 cps/kBq, respectively, with the usual 350-650 keV energy window (EW) and 6 ns time window (TW). The noise equivalent count rate (NECR) index was defined as: NECR = RT2/(RP+RGP) (T = true, P = prompt, GP = γ-prompt). A rat phantom maximum NECR of 48 kcps was obtained for the 250-590 keV EW with 6 ns TW. An almost identical maximum NECR of 43 kcps was recorded for 350-590 and 350-650 keV EW and 6 ns TW. The 2 ns TW reduced the sensitivity and NECR by 40-50% for all EW. The mouse phantom NECR study was limited because of the maximum available activity concentration of 124I. The 250-590 keV EW showed the largest scatter and γ-prompt plus scatter fractions with 25.7% and 43%, respectively, for the rat phantom and 12.2% and 27% for the mouse phantom. With the 350-590 keV EW, these fractions decreased to 20% and 33.5% for the rat phantom and to 10% and 21% for the mouse phantom. The image quality was investigated with the NEMA NU 4-2008 dedicated phantom for four (two analytic and two iterative) 2D or 3D reconstruction methods. The lowest spillover ratios (SOR) for the phantom non-emitting regions were obtained for the 350-590 and 350-650 keV EWs. Recovery coefficients (RC) of the hot rods were the highest for the 350-590 keV EW except for the 1 mm rod. Scatter correction led to a large decrease in RC. The combination of the 350-590 keV EW with 6 ns TW appeared to be a good compromise between counting rate capability and image quality for the FOCUS 120, especially when maximum a posteriori reconstruction was used without scatter correction. Moreover this combination enabled the best quantification with an error as low as 0.36%. [less ▲]