Séverine Samson

Functional MR evaluation of temporal and frontal language dominance compared with the Wada test

Objective: To evaluate the reliability of temporal and frontal functional MRI (fMRI) activation for the assessment of language dominance, as compared with the Wada test. Patients and Methods: Ten patients with temporal lobe epilepsy were studied using blood oxygen level dependent fMRI and echoplanar imaging (1.5-T). Three tasks were used: semantic verbal fluency, covert sentence repetition, and story listening. Data were analyzed using pixel by pixel autocorrelation and cross-correlation. fMRI laterality indices were defined for several regions of interest as the ratio (L − R)/(L + R), L being the number of activated voxels in the left hemisphere and R in the right hemisphere. Wada laterality indices were defined as the difference in the percentages of errors in language tests between left and right carotid injections. Results: Semantic verbal fluency: The asymmetry of frontal activation was correlated with Wada laterality indices. The strongest correlation was observed in the precentral/middle frontal gyrus/inferior frontal sulcus area. Story listening: The asymmetry of frontal, but not temporal, activation was correlated with Wada laterality indices. Covert sentence repetition: No correlation was observed. Conclusions: There was a good congruence between hemispheric dominance for language as assessed with the Wada test and fMRI laterality indices in the frontal but not in the temporal lobes. The story listening and the covert sentence repetition tasks increased the sensitivity of detection of posterior language sites that may be useful for brain lesion surgery.

How emotional auditory stimuli modulate time perception

Emotional and neutral sounds rated for valence and arousal were used to investigate the influence of emotions on timing in reproduction and verbal estimation tasks with durations from 2 s to 6 s. Results revealed an effect of emotion on temporal judgment, with emotional stimuli judged to be longer than neutral ones for a similar arousal level. Within scalar expectancy theory (J. Gibbon, R. Church, & W. Meck, 1984), this suggests that emotion-induced activation generates an increase in pacemaker rate, leading to a longer perceived duration. A further exploration of self-assessed emotional dimensions showed an effect of valence and arousal. Negative sounds were judged to be longer than positive ones, indicating that negative stimuli generate a greater increase of activation. High-arousing stimuli were perceived to be shorter than low-arousing ones. Consistent with attentional models of timing, this seems to reflect a decrease of attention devoted to time, leading to a shorter perceived duration. These effects, robust across the 2 tasks, are limited to short intervals and overall suggest that both activation and attentional processes modulate the timing of emotional events.

Productive and perceptive language reorganization in temporal lobe epilepsy.

The aim of this work was to determine whether productive and perceptive language functions are differentially affected in homogeneous groups of epilepsy patients with right and left temporal lobe epilepsy (TLE). Eighteen patients with left TLE, 18 with right TLE, and 17 healthy volunteers were studied using fMRI during performance of three tasks assessing the productive and perceptive aspects of language (covert semantic verbal fluency, covert sentence repetition, and story listening). Hemispheric dominance for language was calculated in the frontal and temporal regions using laterality indices (LI). Atypical lateralization was defined as a right-sided LI (LI<-0.20) in the frontal lobes during the verbal fluency task or in the temporal lobes during the story listening task. Control subjects and right TLE patients demonstrated a strong left lateralization for language in the frontal lobes during the fluency task, whereas activation was less lateralized to the left hemisphere in left TLE patients, although the difference did not reach significance. In the story listening and the repetition tasks, activation was significantly more right sided in the temporal lobes of patients with left TLE. Atypical language representation was found in 19% of TLE patients (five left and two right TLE). The shift toward the right hemisphere was significantly larger in the temporal than the frontal lobes in patients with atypical language lateralization compared to TLE patients with a typical language lateralization. Neuropsychological performances of patients with atypical language patterns were better than those of patients with typical patterns, suggesting that this reorganization may represent a compensatory mechanism.

Memory for Music in Alzheimer’s Disease: Unforgettable?

The notion that memory for music can be preserved in patients with Alzheimer’s Disease (AD) has been raised by a number of case studies. In this paper, we review the current research examining musical memory in patients with AD. In keeping with models of memory described in the non-musical domain, we propose that various forms of musical memory exist, and may be differentially impaired in AD, reflecting the pattern of neuropathological changes associated with the condition. Our synthesis of this literature reveals a dissociation between explicit and implicit musical memory functions. Implicit, specifically procedural musical memory, or the ability to play a musical instrument, can be spared in musicians with AD. In contrast, explicit musical memory, or the recognition of familiar or unfamiliar melodies, is typically impaired. Thus, the notion that music is unforgettable in AD is not wholly supported. Rather, it appears that the ability to play a musical instrument may be unforgettable in some musicians with AD.

Structural connectivity differences in left and right temporal lobe epilepsy.

Our knowledge on temporal lobe epilepsy (TLE) with hippocampal sclerosis has evolved towards the view that this syndrome affects widespread brain networks. Diffusion weighted imaging studies have shown alterations of large white matter tracts, most notably in left temporal lobe epilepsy, but the degree of altered connections between cortical and subcortical structures remains to be clarified. We performed a whole brain connectome analysis in 39 patients with refractory temporal lobe epilepsy and unilateral hippocampal sclerosis (20 right and 19 left) and 28 healthy subjects. We performed whole-brain probabilistic fiber tracking using MRtrix and segmented 164 cortical and subcortical structures with Freesurfer. Individual structural connectivity graphs based on these 164 nodes were computed by mapping the mean fractional anisotropy (FA) onto each tract. Connectomes were then compared using two complementary methods: permutation tests for pair-wise connections and Network Based Statistics to probe for differences in large network components. Comparison of pair-wise connections revealed a marked reduction of connectivity between left TLE patients and controls, which was strongly lateralized to the ipsilateral temporal lobe. Specifically, infero-lateral cortex and temporal pole were strongly affected, and so was the perisylvian cortex. In contrast, for right TLE, focal connectivity loss was much less pronounced and restricted to bilateral limbic structures and right temporal cortex. Analysis of large network components revealed furthermore that both left and right hippocampal sclerosis affected diffuse global and interhemispheric connectivity. Thus, left temporal lobe epilepsy was associated with a much more pronounced pattern of reduced FA, that included major landmarks of perisylvian language circuitry. These distinct patterns of connectivity associated with unilateral hippocampal sclerosis show how a focal pathology influences global network architecture, and how left or right-sided lesions may have differential and specific impacts on cerebral connectivity.

Auditory discrimination of anisochrony: influence of the tempo and musical backgrounds of listeners.

This study explored the influence of several factors, physical and human, on anisochronys thresholds measured with an adaptive two alternative forced choice paradigm. The effect of the number and duration of sounds on anisochrony discrimination was tested in the first experiment as well as potential interactions between each of these factors and tempo. In the second experiment, the tempo or the inter onset interval (IOI) was varied systematically between 80 and 1000 ms. The results showed that just noticeable differences increase linearly and proportionally with IOI in accordance with Webers law except for quickest tempo (IOI of 80 ms). The third experiment investigated the role of musical training on anisochrony thresholds obtained for different IOI. It focused on differential effects of musical experiences by comparing non-musicians, instrumentalists, and percussionists thresholds. The results of the present study replicated the findings of previous experiments regarding the adequacy of Webers law for slow rhythm and provided evidence for its departure for fast tempos. Moreover, thresholds from percussionists seem distinguishable from the ones of other listeners by their highest sensitivity to temporal shifts suggesting therefore the necessity to control the nature of musical experiences. The results are discussed according to current models of time perception.

Functional MR Imaging or Wada Test: Which Is the Better Predictor of Individual Postoperative Memory Outcome?

PURPOSE To retrospectively determine whether blood oxygen level-dependent functional magnetic resonance (MR) imaging can aid prediction of postoperative memory changes in epileptic patients after temporal lobe surgery. MATERIALS AND METHODS This study was approved by the local ethics committee, and informed consent was obtained from all patients. Data were analyzed from 25 patients (12 women, 13 men; age range, 19-52 years) with refractory epilepsy in whom temporal lobe surgery was performed after they underwent preoperative functional MR imaging, the Wada test, and neuropsychological testing. The functional MR imaging protocol included three different memory tasks (24-hour delayed recognition, encoding, and immediate recognition). Individual activations were measured in medial temporal lobe (MTL) regions of both hemispheres. The prognostic accuracy of functional MR imaging for prediction of postoperative memory changes was compared with the accuracy of the Wada test and preoperative neuropsychological testing by using a backward multiple regression analysis. RESULTS An equation that was based on left functional MR imaging MTL activation during delayed recognition, side of the epileptic focus, and preoperative global verbal memory score was used to correctly predict worsening of verbal memory in 90% of patients. The right functional MR imaging MTL activation did not substantially correlate with the nonverbal memory outcome, which was only predicted by using the preoperative nonverbal global score. Wada test data were not good predictors of changes in either verbal or nonverbal memory. CONCLUSION Findings suggest that functional MR imaging activation during a delayed-recognition task is a better predictor of individual postoperative verbal memory outcome than is the Wada test.

Spatial memory deficits in patients with lesions affecting the medial temporal neocortex.

Lesion studies in monkeys suggest that neocortical subregions of the medial temporal lobe (MTL) carry memory functions independent of the hippocampal formation. The present study investigates possible differential contributions of MTL subregions to spatial memory in humans. Eye movements toward remembered spatial cues (memory‐guided saccades) with unpredictably varied memorization delays of up to 30 seconds were recorded in patients with postsurgical lesions of the right MTL, either restricted to the hippocampal formation (n = 3) or including the adjacent neocortex (n = 5) and in 10 controls. Although saccadic targeting errors of patients with selective hippocampal lesions did not differ from controls, saccadic targeting errors of patients with additional neocortical involvement showed a significant and contralaterally pronounced increase at memorization delays above 20 seconds. We conclude that the human medial temporal neocortex carries spatial memory functions independent of the hippocampal formation and distinct from spatial short‐term memory. Ann Neurol 1999;45:312–319

The Relationship of Lyrics and Tunes in the Processing of Unfamiliar Songs: A Functional Magnetic Resonance Adaptation Study

The cognitive relationship between lyrics and tunes in song is currently under debate, with some researchers arguing that lyrics and tunes are represented as separate components, while others suggest that they are processed in integration. The present study addressed this issue by means of a functional magnetic resonance adaptation paradigm during passive listening to unfamiliar songs. The repetition and variation of lyrics and/or tunes in blocks of six songs was crossed in a 2 × 2 factorial design to induce selective adaptation for each component. Reductions of the hemodynamic response were observed along the superior temporal sulcus and gyrus (STS/STG) bilaterally. Within these regions, the left mid-STS showed an interaction of the adaptation effects for lyrics and tunes, suggesting an integrated processing of the two components at prelexical, phonemic processing levels. The degree of integration decayed toward more anterior regions of the left STS, where the lack of such an interaction and the stronger adaptation for lyrics than for tunes was suggestive of an independent processing of lyrics, perhaps resulting from the processing of meaning. Finally, evidence for an integrated representation of lyrics and tunes was found in the left dorsal precentral gyrus (PrCG), possibly relating to the build-up of a vocal code for singing in which musical and linguistic features of song are fused. Overall, these results demonstrate that lyrics and tunes are processed at varying degrees of integration (and separation) through the consecutive processing levels allocated along the posterior–anterior axis of the left STS and the left PrCG.

Emotional power of music in patients with memory disorders: clinical implications of cognitive neuroscience.

By adapting methods of cognitive psychology to neuropsychology, we examined memory and familiarity abilities in music in relation to emotion. First we present data illustrating how the emotional content of stimuli influences memory for music. Second, we discuss recent findings obtained in patients with two different brain disorders (medically intractable epilepsy and Alzheimers disease) that show relatively spared memory performance for music, despite severe verbal memory disorders. Studies on musical memory and its relation to emotion open up paths for new strategies in cognitive rehabilitation and reinstate the importance of examining interactions between cognitive and clinical neurosciences.