Olivier Joly

Evaluating Alzheimer's disease progression using rate of regional hippocampal atrophy.

Alzheimer’s disease (AD) is characterized by neurofibrillary tangle and neuropil thread deposition, which ultimately results in neuronal loss. A large number of magnetic resonance imaging studies have reported a smaller hippocampus in AD patients as compared to healthy elderlies. Even though this difference is often interpreted as atrophy, it is only an indirect measurement. A more direct way of measuring the atrophy is to use repeated MRIs within the same individual. Even though several groups have used this appropriate approach, the pattern of hippocampal atrophy still remains unclear and difficult to relate to underlying pathophysiology. Here, in this longitudinal study, we aimed to map hippocampal atrophy rates in patients with AD, mild cognitive impairment (MCI) and elderly controls. Data consisted of two MRI scans for each subject. The symmetric deformation field between the first and the second MRI was computed and mapped onto the three-dimensional hippocampal surface. The pattern of atrophy rate was similar in all three groups, but the rate was significantly higher in patients with AD than in control subjects. We also found higher atrophy rates in progressive MCI patients as compared to stable MCI, particularly in the antero-lateral portion of the right hippocampus. Importantly, the regions showing the highest atrophy rate correspond to those that were described to have the highest burden of tau deposition. Our results show that local hippocampal atrophy rate is a reliable biomarker of disease stage and progression and could also be considered as a method to objectively evaluate treatment effects.

Neuroimaging of amblyopia and binocular vision: a review

Amblyopia is a cerebral visual impairment considered to derive from abnormal visual experience (e.g., strabismus, anisometropia). Amblyopia, first considered as a monocular disorder, is now often seen as a primarily binocular disorder resulting in more and more studies examining the binocular deficits in the patients. The neural mechanisms of amblyopia are not completely understood even though they have been investigated with electrophysiological recordings in animal models and more recently with neuroimaging techniques in humans. In this review, we summarize the current knowledge about the brain regions that underlie the visual deficits associated with amblyopia with a focus on binocular vision using functional magnetic resonance imaging. The first studies focused on abnormal responses in the primary and secondary visual areas whereas recent evidence shows that there are also deficits at higher levels of the visual pathways within the parieto-occipital and temporal cortices. These higher level areas are part of the cortical network involved in 3D vision from binocular cues. Therefore, reduced responses in these areas could be related to the impaired binocular vision in amblyopic patients. Promising new binocular treatments might at least partially correct the activation in these areas. Future neuroimaging experiments could help to characterize the brain response changes associated with these treatments and help devise them.

The topography of frequency and time representation in primate auditory cortices.

Natural sounds can be characterised by their spectral content and temporal modulation, but how the brain is organized to analyse these two critical sound dimensions remains uncertain. Using functional magnetic resonance imaging, we demonstrate a topographical representation of amplitude modulation rate in the auditory cortex of awake macaques. The representation of this temporal dimension is organized in approximately concentric bands of equal rates across the superior temporal plane in both hemispheres, progressing from high rates in the posterior core to low rates in the anterior core and lateral belt cortex. In A1 the resulting gradient of modulation rate runs approximately perpendicular to the axis of the tonotopic gradient, suggesting an orthogonal organisation of spectral and temporal sound dimensions. In auditory belt areas this relationship is more complex. The data suggest a continuous representation of modulation rate across several physiological areas, in contradistinction to a separate representation of frequency within each area. DOI: http://dx.doi.org/10.7554/eLife.03256.001

A new approach to corpus callosum anomalies in idiopathic scoliosis using diffusion tensor magnetic resonance imaging.

PurposeIdiopathic scoliosis (IS) is a frequent 3D structural deformity of the spine with a multi-factorial aetiology which remains largely unclear. In the last decade, human magnetic resonance imaging (MRI) morphometry studies (e.g. cortical thickness, 2D shape of the corpus callosum) have aimed to investigate the potential contribution of the central nervous system in the etiopathogenesis of IS. Recent developments in diffusion tensor imaging (DTI) allow us to extend the previous work to the study of white matter microstructure. Here, we hypothesized that part of the corpus callosum could show a difference in white matter microstructure in IS patients as compared to healthy controls.MethodsWe acquired DTI in 10 girls with IS and in 49 gender-matched controls to quantify the fractional anisotropy (FA) along the corpus callosum.ResultsDespite a very similar pattern of FA along the corpus callosum (maxima in the splenium and the genu and minimum in the isthmus), we found a significantly lower FA in the body in patients with IS as compared to control subjects. This region is known to connect the motor and premotor cortices of the two hemispheres.ConclusionThis first diffusion magnetic resonance imaging brain study in IS patients, suggests that differences in white matter development, such as synchronization of axonal myelination and pruning could be involved in the etiopathogenesis of IS.

Auditory motion-specific mechanisms in the primate brain

This work examined the mechanisms underlying auditory motion processing in the auditory cortex of awake monkeys using functional magnetic resonance imaging (fMRI). We tested to what extent auditory motion analysis can be explained by the linear combination of static spatial mechanisms, spectrotemporal processes, and their interaction. We found that the posterior auditory cortex, including A1 and the surrounding caudal belt and parabelt, is involved in auditory motion analysis. Static spatial and spectrotemporal processes were able to fully explain motion-induced activation in most parts of the auditory cortex, including A1, but not in circumscribed regions of the posterior belt and parabelt cortex. We show that in these regions motion-specific processes contribute to the activation, providing the first demonstration that auditory motion is not simply deduced from changes in static spatial location. These results demonstrate that parallel mechanisms for motion and static spatial analysis coexist within the auditory dorsal stream.

Merging functional and structural properties of the monkey auditory cortex.

Recent neuroimaging studies in primates aim to define the functional properties of auditory cortical areas, especially areas beyond A1, in order to further our understanding of the auditory cortical organization. Precise mapping of functional magnetic resonance imaging (fMRI) results and interpretation of their localizations among all the small auditory subfields remains challenging. To facilitate this mapping, we combined here information from cortical folding, micro-anatomy, surface-based atlas and tonotopic mapping. We used for the first time, phase-encoded fMRI design for mapping the monkey tonotopic organization. From posterior to anterior, we found a high-low-high progression of frequency preference on the superior temporal plane. We show a faithful representation of the fMRI results on a locally flattened surface of the superior temporal plane. In a tentative scheme to delineate core versus belt regions which share similar tonotopic organizations we used the ratio of T1-weighted and T2-weighted MR images as a measure of cortical myelination. Our results, presented along a co-registered surface-based atlas, can be interpreted in terms of a current model of the monkey auditory cortex.

A perceptual pitch boundary in a non-human primate.

Pitch is an auditory percept critical to the perception of music and speech, and for these harmonic sounds, pitch is closely related to the repetition rate of the acoustic wave. This paper reports a test of the assumption that non-human primates and especially rhesus monkeys perceive the pitch of these harmonic sounds much as humans do. A new procedure was developed to train macaques to discriminate the pitch of harmonic sounds and thereby demonstrate that the lower limit for pitch perception in macaques is close to 30 Hz, as it is in humans. Moreover, when the phases of successive harmonics are alternated to cause a pseudo-doubling of the repetition rate, the lower pitch boundary in macaques decreases substantially, as it does in humans. The results suggest that both species use neural firing times to discriminate pitch, at least for sounds with relatively low repetition rates.

Reply to the letter to the editor of J. Domenech et al. concerning "A new approach to corpus callosum anomalies in idiopathic scoliosis using diffusion tensor magnetic resonance imaging" by O. Joly et al. (2014) Eur Spine J; 23:2643-9.

We appreciate the well-advised comments on our paper on a new approach to corpus callosum anomalies in idiopathic scoliosis (IS) using diffusion tensor imaging (DTI). These comments emphasise three important methodological issues that are legitimate, all of them discussed during the reviewing process. Unfortunately, it seems they do not appear clearly in the final version of our manuscript. The first issue refers to the differences in scanning protocols (including field strength) applied to the IS patients and controls (database), the second refers to the age and sample size of our patient population and the third concerns the diagnosis of our (youngest) IS patients. We would like to use this opportunity to clarify and address these issues.