[Assessing occipital nerve stimulation efficacy for chronic refractory headaches]. / Efficacité de la stimulation du nerf occipital pour les céphalées chroniques réfractaires - Une étude prospective lausannoise.

We prospectively followed a cohort of 26 subjects for an average period of 41 months who benefited from occipital nerve stimulation (ONS) in the context of chronic refractory headaches. In 17 patients treated, the frequency of headache decreased, and quality of life scores improved significantly. Among these patients, the "very good" response rate was 34 %. In this cohort, treatment-related adverse events are relatively common (42 %) but not severe. While it is difficult to anticipate the risk factors for non-response to treatment, we estimate that the risk of failure may not be related to the duration of the disease, but rather to the number of different preventives attempted prior to ONS.

Nous avons suivi prospectivement durant une période d'en moyenne 41 mois une cohorte de 26 patients romands qui ont bénéficié d'une stimulation du nerf occipital (ONS) dans le cadre de céphalées chroniques réfractaires. Chez 17 patients non explantés, la fréquence des céphalées a diminué et les scores de qualité de vie se sont améliorés de façon significative. Parmi ces patients, le taux de « très bonne ¼ réponse est de 34 %. On constate dans cette cohorte que les effets indésirables liés au traitement sont relativement courants (42 %) mais non sévères. Même s'il est difficile d'anticiper les facteurs de risque de non-réponse au traitement, nous estimons que la probabilité d'échec ne serait pas corrélée à la durée de la maladie mais plutôt au nombre de traitements préventifs tentés avant l'ONS.

Treatment in early psychosis with N-acetyl-cysteine for 6months improves low-level auditory processing: Pilot study.

Sensory impairments constitute core dysfunctions in schizophrenia. In the auditory modality, impaired mismatch negativity (MMN) has been observed in chronic schizophrenia and may reflect N-methyl-d-aspartate (NMDA) hypo-function, consistent with models of schizophrenia based on oxidative stress. Moreover, a recent study demonstrated deficits in the N100 component of the auditory evoked potential (AEP) in early psychosis patients. Previous work has shown that add-on administration of the glutathione precursor N-acetyl-cysteine (NAC) improves the MMN and clinical symptoms in chronic schizophrenia. To date, it remains unknown whether NAC also improves general low-level auditory processing and if its efficacy would extend to early-phase psychosis. We addressed these issues with a randomized, double-blind study of a small sample (N=15) of early psychosis (EP) patients and 18 healthy controls from whom AEPs were recorded during an active, auditory oddball task. Patients were recorded twice: once prior to NAC/placebo administration and once after six months of treatment. The N100 component was significantly smaller in patients before NAC administration versus controls. Critically, NAC administration improved this AEP deficit. Source estimations revealed increased activity in the left temporo-parietal lobe in patients after NAC administration. Overall, the data from this pilot study, which call for replication in a larger sample, indicate that NAC improves low-level auditory processing in early psychosis.

From bird to sparrow: Learning-induced modulations in fine-grained semantic discrimination.

Recognition of environmental sounds is believed to proceed through discrimination steps from broad to more narrow categories. Very little is known about the neural processes that underlie fine-grained discrimination within narrow categories or about their plasticity in relation to newly acquired expertise. We investigated how the cortical representation of birdsongs is modulated by brief training to recognize individual species. During a 60-minute session, participants learned to recognize a set of birdsongs; they improved significantly their performance for trained (T) but not control species (C), which were counterbalanced across participants. Auditory evoked potentials (AEPs) were recorded during pre- and post-training sessions. Pre vs. post changes in AEPs were significantly different between T and C i) at 206-232ms post stimulus onset within a cluster on the anterior part of the left superior temporal gyrus; ii) at 246-291ms in the left middle frontal gyrus; and iii) 512-545ms in the left middle temporal gyrus as well as bilaterally in the cingulate cortex. All effects were driven by weaker activity for T than C species. Thus, expertise in discriminating T species modulated early stages of semantic processing, during and immediately after the time window that sustains the discrimination between human vs. animal vocalizations. Moreover, the training-induced plasticity is reflected by the sharpening of a left lateralized semantic network, including the anterior part of the temporal convexity and the frontal cortex. Training to identify birdsongs influenced, however, also the processing of C species, but at a much later stage. Correct discrimination of untrained sounds seems to require an additional step which results from lower-level features analysis such as apperception. We therefore suggest that the access to objects within an auditory semantic category is different and depends on subject's level of expertise. More specifically, correct intra-categorical auditory discrimination for untrained items follows the temporal hierarchy and transpires in a late stage of semantic processing. On the other hand, correct categorization of individually trained stimuli occurs earlier, during a period contemporaneous with human vs. animal vocalization discrimination, and involves a parallel semantic pathway requiring expertise.

Representation of Sound Objects within Early-Stage Auditory Areas: A Repetition Effect Study Using 7T fMRI.

Environmental sounds are highly complex stimuli whose recognition depends on the interaction of top-down and bottom-up processes in the brain. Their semantic representations were shown to yield repetition suppression effects, i. e. a decrease in activity during exposure to a sound that is perceived as belonging to the same source as a preceding sound. Making use of the high spatial resolution of 7T fMRI we have investigated the representations of sound objects within early-stage auditory areas on the supratemporal plane. The primary auditory cortex was identified by means of tonotopic mapping and the non-primary areas by comparison with previous histological studies. Repeated presentations of different exemplars of the same sound source, as compared to the presentation of different sound sources, yielded significant repetition suppression effects within a subset of early-stage areas. This effect was found within the right hemisphere in primary areas A1 and R as well as two non-primary areas on the antero-medial part of the planum temporale, and within the left hemisphere in A1 and a non-primary area on the medial part of Heschl's gyrus. Thus, several, but not all early-stage auditory areas encode the meaning of environmental sounds.

Emotional pre-eminence of human vocalizations.

Human vocalizations (HV), as well as environmental sounds, convey a wide range of information, including emotional expressions. The latter have been relatively rarely investigated, and, in particular, it is unclear if duration-controlled non-linguistic HV sequences can reliably convey both positive and negative emotional information. The aims of the present psychophysical study were: (i) to generate a battery of duration-controlled and acoustically controlled extreme valence stimuli, and (ii) to compare the emotional impact of HV with that of other environmental sounds. A set of 144 HV and other environmental sounds was selected to cover emotionally positive, negative, and neutral values. Sequences of 2 s duration were rated on Likert scales by 16 listeners along three emotional dimensions (arousal, intensity, and valence) and two non-emotional dimensions (confidence in identifying the sound source and perceived loudness). The 2 s stimuli were reliably perceived as emotionally positive, negative or neutral. We observed a linear relationship between intensity and arousal ratings and a "boomerang-shaped" intensity-valence distribution, as previously reported for longer, duration-variable stimuli. In addition, the emotional intensity ratings for HV were higher than for other environmental sounds, suggesting that HV constitute a characteristic class of emotional auditory stimuli. In addition, emotionally positive HV were more readily identified than other sounds, and emotionally negative stimuli, irrespective of their source, were perceived as louder than their positive and neutral counterparts. In conclusion, HV are a distinct emotional category of environmental sounds and they retain this emotional pre-eminence even when presented for brief periods.