Alexandre Comte

Patterns of cerebral activation during olfactory and trigeminal stimulations.

It is well known that most odorants stimulate both the olfactory system and the trigeminal system. However, the overlap between the brain processes involved in each of these sensorial perceptions is still poorly documented. This study aims to compare fMRI brain activations while smelling two odorants of a similar perceived intensity and pleasantness: phenyl ethyl alcohol (a pure olfactory stimulus) and iso‐amyl‐acetate (a bimodal olfactory‐trigeminal stimulus) in a homogeneous sample of 15 healthy, right‐handed female subjects. The analysis deals with the contrasts of brain activation patterns between these two odorant conditions. The results showed a significant recruitment of the right insular cortex, and bilaterally in the cingulate in response to the trigeminal component. These findings are discussed in relation to the characteristics of these odorants compared with those tested in previous studies. Hum Brain Mapp, 2009.

The role of the amygdala in the perception of positive emotions: an “intensity detector”

The specific role of the amygdala remains controversial even though the development of functional imaging techniques has established its implication in the emotional process. The aim of this study was to highlight the sensitivity of the amygdala to emotional intensity (arousal). We conducted an analysis of the modulation of amygdala activation according to variation in emotional intensity via an fMRI event-related protocol. Monitoring of electrodermal activity, a marker of psychophysiological emotional perception and a reflection of the activation of the autonomic nervous system, was carried out concurrently. Eighteen subjects (10 men; aged from 22 to 29 years) looked at emotionally positive photographs. We demonstrated that the left and right amygdalae were sensitive to changes in emotional intensity, activating more in response to stimuli with higher intensity. Furthermore, electrodermal responses were more frequent for the most intense stimuli, demonstrating the concomitant activation of the autonomic nervous system. These results highlight the sensitivity of the amygdala to the intensity of positively valenced visual stimuli, and in conjunction with results in the literature on negative emotions, reinforce the role of the amygdala in the perception of intensity.

Using a contrast-enhanced imaging sequence at 3-minute delay in 3-T magnetic resonance imaging for acute infarct evaluation.

Objectives:To investigate the performance of a delayed-enhancement (DE) sequence adapted for a 3-minute delay after bolus injection of a contrast media in cardiac magnetic resonance imaging (MRI) in acute reperfused myocardial infarction. Materials and Methods:Sixty-three patients with recent myocardial infarction underwent contrast-enhanced MRI. Sequences of first-pass (FP) perfusion imaging and DE imaging at 3 and 15 minutes were performed at the acute phase. Of these patients, 49 had a follow-up cardiac magnetic resonance examination. Infarct sizes were quantified by 2 experienced users with a 17-segment model at the acute phase (at FP and at 3- and 15-minute delay) and at the chronic phase (at 15 minutes because only fibrous areas hyperenhance late). Areas of hypoenhancement and hyperenhancement were also calculated. Results from the 3-minute imaging sequence at the acute phase were compared with the FP (taking into account dark signal areas), with the 15-minute DE imaging sequence results at the acute phase [taking into account dark signal and hyperenhanced (white plus dark signal) areas] and with the 15-minute DE imaging sequence from the chronic phase (taking into account hyperenhanced areas). Least squares regression and Bland-Altman plots were performed for the comparisons. Results:For the evaluation of hyperenhancement, the comparison between imaging sequence results at 3 minutes versus 15-minute DE at the acute phase (respectively, at the chronic phase) shows a good correlation (r2 = 0.941; respectively r2 = 0.862, at the chronic phase) and the Bland-Altman plot indicates a good concordance (m =−0.43; SD = 2.69; respectively m = 2.76; SD = 3.92); For the evaluation of hypoenhancement, the comparison between imaging sequence results at 3 minutes versus FP (respectively, 15 minutes at the acute phase) also shows a good correlation (r2 = 0.751; respectively r2 = 0.71) and the Bland-Altman plot indicates a good concordance (m = −1.06; SD = 3.34; respectively m = 2.90; SD = 3.11). Finally, the interobserver study provides a very good kappa coefficient (κ = 0.82), and good kappa coefficients from the intraobserver study (κ1 = 0.78 and κ2 = 0.86). Conclusions:The use of a delayed contrast-enhanced sequence adapted for a 3-minute delay after the bolus injection has the potential to obtain quickly reliable information comparable with the perfusion delay at FP and reliable information from the infarct size at 15 minutes and at the chronic phase.

Substitute or complement? Defining the relative place of EEG and fMRI in the detection of voluntary brain reactions.

To improve the assessment of awareness in patients with disorders of consciousness, recent protocols using functional Magnetic Resonance Imaging (fMRI) have been developed, and led some specialized coma centers to use this method on a routine basis. Recently, promising results have also been observed with electroencephalography (EEG), a less expensive and widely available technique. However, since the spatiotemporal nature of the recorded signal differs between both EEG and fMRI, the question of whether one method could substitute or should complement the other method is a matter of debate. In this study, we compared the neural processes of two well-known EEG and fMRI mental imagery protocols to define the relative place of each method in the assessment of awareness. A group of 20 healthy volunteers performed both EEG and fMRI command-following and communication tasks. Distinct command following was found with both EEG and fMRI for five subjects, only with fMRI for 12 subjects, and only with EEG for one subject. In the communication task, neither EEG nor fMRI alone gave satisfactory results and no reliable communication could be established in approximately 1/3rd of the participants. If fMRI showed the best performance to detect volitional reactions in mental imagery tasks, our results provide evidence that the use of EEG must not be underestimated since a better detection was found with this method for at least one subject. More than being used as a substitute, EEG should complement fMRI to improve the detection of sign of awareness, and to reduce the risks of misjudgments.

Time course of odorant- and trigeminal-induced activation in the human brain: an event-related functional magnetic resonance imaging study

It is well known that most odorants stimulate the trigeminal system but the time course of the brain regions activated by these chemical stimulations remains poorly documented, especially regarding the trigeminal system. This functional magnetic resonance imaging (fMRI) study compares brain activations resulting from the contrast between two odorant conditions (one bimodal odor and one relatively pure olfactory stimulant) according to the duration of the stimulation (i.e. one inhalation, or three or six successive inhalations). The results show striking differences in the main brain regions activated according to these durations. The caudate nucleus and the orbitofrontal cortex are only involved in short-duration stimulations, and the posterior insular cortex and post-central gyrus (SI) are only activated by long duration stimulations. Different regions of the frontal, temporal and occipital lobe are activated depending on the duration but mainly during medium-duration stimulations. These results expand on the findings of previous studies and contribute to the description of temporal networks in trigeminal perception.

Automatic fuzzy classification of the washout curves from magnetic resonance first-pass perfusion imaging after myocardial infarction.

Objectives:We sought to investigate the diagnostic ability of cardiac magnetic resonance imaging (MRI) perfusion in acute reperfused myocardial infarction. The study used fuzzy logic to automatically classify signal intensity-time curves from myocardial segments into 3 categories: normal, hypointense, and Hyperintense. Materials and Methods:Thirty-eight patients with myocardial infarction underwent short-axis cine-MRI and contrast-enhanced MRI to provide data on wall thickening and the transmural extent of infarction. Of these, 17 had a second cardiac MRI to ascertain the functional recovery in each segment. Results:The fuzzy logic based classification performs well (kappa= 0.87, P < 0.01) in comparison with a visual approach. Segments providing “hypo” curves do not recover (Δ = 0.11 SD = 0.96) whereas segments demonstrating the other curve types recover (Δ = 1 SD = 1.98 for “hyper” curves and Δ = 1.54 SD = 1.77 for “normal” curves). Conclusions:The proposed automatic signal intensity-time curve classification has a prognostic value when studying the functional recovery of pathologic segments and clearly identifies the no-reflow phenomenon known to induce poor recovery.

On the difficulty to communicate with fMRI-based protocols used to identify covert awareness

Assessment of awareness in patients with disorders of consciousness such as patients in a vegetative state (unresponsive wakefulness syndrome, UWS) and patients in a minimally conscious state (MCS) remains difficult, with a high rate of misdiagnosis (around 40%). While patients with UWS have no awareness, patients with MCS have partial preservation of conscious awareness. To improve the assessment of awareness in these patients, recent functional neuroimaging protocols have been developed. However, does the complexity of realizing and interpreting these functional magnetic resonance imaging (fMRI) investigation protocols, which are currently carried out by only a few specialist teams, permit generalizable use in clinical routine? In this study, 32 healthy volunteers, by definition perfectly conscious and able to efficiently communicate, performed the protocol proposed by Monti et al. in 2010. Four methods (comprising the method proposed by Monti et al., a mean squared error-based method, a correlation-based method, and a support vector machine-based method) were tested for correctly and accurately interpreting the communication task. Firstly, the different instructions for the localizer and the communication tasks had no effect on activations. Secondly, 25% of participants (8/32) did not provide the expected patterns of activations during fMRI tasks (four for each imagery task). However, this did not necessarily prevent the classification methods from correctly guessing the answers during the communication task. Conversely, these classification methods may fail to detect the correct answers even though participants activated the expected brain areas. None of the four methods produced 100% correct detection during the communication phases. The correlation-based method obtained the best results with an error rate of 4.2%. The results of this study demonstrate that fMRI-based communication paradigms may not be robust enough to reliably detect awareness in all aware patients. There is still a need to develop new statistical and analytical methods before considering their generalization in clinical routine.

Effects of an ambient odor on brain activations during episodic retrieval of objects

This study investigated the brain areas involved in episodic memory retrieval of pictures depending on the characteristics of the contextual environment during encoding (i.e. presence or absence of an odor). In the first stage, subjects were presented with a series of 32 pictures. Half of the pictures were presented while the subjects smelled an odor (vanillin). No particular odor was associated with the presentation of the other half of the pictures. Two weeks later, a retrieval task was performed in which the same pictures were presented during an fMRI session but without any odor association involved. The results show that both conditions activate a common episodic memory network including the hippocampal formation. Compared with the “encoding without odor” condition, the “encoding with odor” condition shows greater activations in temporal, parietal and frontal cortices, notably within the area of the orbitofrontal cortex which constitutes a main site of the secondary olfactory cortex. No activated areas were observed in the inverse contrast. These results highlight the complexity of the networks involved in episodic memory according to the context during encoding.

Hemifacial spasm revealing contralateral peripheral facial palsy.

N.-C. Roche M. Bregigeon E. Sagui M. Oliver C. Brosset a Fédération des laboratoires, hôpital d’instruction des armées Laveran, 4, boulevard Laveran, 13384 Marseille, France b Service de neurologie, hôpital d’instruction des armées Laveran, 4, boulevard Laveran, 13384 Marseille, France was detected. Electrophysiological examination was not performed because it was too soon in the evolution of the PFP. The patient was treated with prednisolone and valacyclovir for five days. He completely recovered in 9 weeks. A right idiopathic facial paralysis beginning with contralateral hemifacial spasm was diagnosed. Literature described only few facial movement disorders contralateral to a PFP (Valls-Solé and Montero, 2003). They are mostly the enhancement of spontaneous blinking rate, happening within the first 24 h after the onset of the PFP and a few cases of blepharospasm. To our knowledge, our case is the first contralateral hemifacial r e v u e n e u r o l o g i q u e 1 6 9 ( 2 0 1 3 ) 1 0 1 0 – 1 0 1 7 1015

Automatic realignment of myocardial first-pass MR perfusion images

Magnetic resonance first-pass imaging of a bolus of contrast agent is well adapted to distinguish normal and hypoperfused areas of the myocardium. In most cases, the signal intensity-time curves in user defined regions of interest (ROI) are studied. As image acquisition is ECG-gated, the images are acquired at the same moment in the cardiac cycle, and the basic shape of the heart is similar from one view to the next. However, superficial respiratory motion can displace the heart in the short-axis plane. The aim of this study is to correct for the respiratory motion of the heart by performing an automatic realignment of the myocardial ROI based on a method tracking the movement of the lung-myocardium interface. Visual and quantitative analyses performed on 120 curves show a very good concordance between the automatic methods and the manual one.