Large-Scale Networks for Auditory Sensory Gating in the Awake Mouse.

The amplitude of the brain response to a repeated auditory stimulus is diminished as compared to the response to the first tone (T1) for interstimulus intervals (ISI) lasting up to hundreds of milliseconds. This adaptation process, called auditory sensory gating (ASG), is altered in various psychiatric diseases including schizophrenia and is classically studied by focusing on early evoked cortical responses to the second tone (T2) using 500-ms ISI. However, mechanisms underlying ASG are still not well-understood. We investigated ASG in awake mice from the brainstem to cortex at variable ISIs (125-2000 ms) using high-density EEG and intracerebral recordings. While ASG decreases at longer ISIs, it is still present at durations (500-2000 ms) far beyond the time during which brain responses to T1 could still be detected. T1 induces a sequence of specific stable scalp EEG topographies that correspond to the successive activation of distinct neural networks lasting about 350 ms. These brain states remain unaltered if T2 is presented during this period, although T2 is processed by the brain, suggesting that ongoing networks of brain activity are active for longer than early evoked-potentials and are not overwritten by an upcoming new stimulus. Intracerebral recordings demonstrate that ASG is already present at the level of ventral cochlear nucleus (vCN) and inferior colliculus and is amplified across the hierarchy in bottom-up direction. This study uncovers the extended stability of sensory-evoked brain states and long duration of ASG, and sheds light on generators of ASG and possible interactions between bottom-up and top-down mechanisms.

Audio-Tactile and Peripersonal Space Processing Around the Trunk in Human Parietal and Temporal Cortex: An Intracranial EEG Study.

Interactions with the environment happen within one's peripersonal space (PPS)-the space surrounding the body. Studies in monkeys and humans have highlighted a multisensory distributed cortical network representing the PPS. However, knowledge about the temporal dynamics of PPS processing around the trunk is lacking. Here, we recorded intracranial electroencephalography (iEEG) in humans while administering tactile stimulation (T), approaching auditory stimuli (A), and the 2 combined (AT). To map PPS, tactile stimulation was delivered when the sound was far, intermediate, or close to the body. The 19% of the electrodes showed AT multisensory integration. Among those, 30% showed a PPS effect, a modulation of the response as a function of the distance between the sound and body. AT multisensory integration and PPS effects had similar spatiotemporal characteristics, with an early response (~50 ms) in the insular cortex, and later responses (~200 ms) in precentral and postcentral gyri. Superior temporal cortex showed a different response pattern with AT multisensory integration at ~100 ms without a PPS effect. These results, represent the first iEEG delineation of PPS processing in humans and show that PPS and multisensory integration happen at similar neural sites and time periods, suggesting that PPS representation is based on a spatial modulation of multisensory integration.

Surgically relevant localization of the central sulcus with high-density somatosensory-evoked potentials compared with functional magnetic resonance imaging.

BACKGROUND: Resection of abnormal brain tissue lying near the sensorimotor cortex entails precise localization of the central sulcus. Mapping of this area is achieved by applying invasive direct cortical electrical stimulation. However, noninvasive methods, particularly functional magnetic resonance imaging (fMRI), are also used. As a supplement to fMRI, localization of somatosensory-evoked potentials (SEPs) recorded with an electroencephalogram (EEG) has been proposed, but has not found its place in clinical practice. OBJECTIVE: To assess localization accuracy of the hand somatosensory cortex with SEP source imaging. METHODS: We applied electrical source imaging in 49 subjects, recorded with high-density EEG (256 channels). We compared it with fMRI in 18 participants and with direct cortical electrical stimulation in 6 epileptic patients. RESULTS: Comparison of SEP source imaging with fMRI indicated differences of 3 to 8 mm, with the exception of the mesial-distal orientation, where variances of up to 20 mm were found. This discrepancy is explained by the fact that the source maximum of the first SEP peak is localized deep in the central sulcus (area 3b), where information initially arrives. Conversely, fMRI showed maximal signal change on the lateral surface of the postcentral gyrus (area 1), where sensory information is integrated later in time. Electrical source imaging and fMRI showed mean Euclidean distances of 13 and 14 mm, respectively, from the contacts where electrocorticography elicited sensory phenomena of the contralateral upper limb. CONCLUSION: SEP source imaging, based on high-density EEG, reliably identifies the depth of the central sulcus. Moreover, it is a simple, flexible, and relatively inexpensive alternative to fMRI.

[Positional plagiocephaly in infancy: diagnosis and management]. / Lagebedingter Plagiocephalus im Säuglingsalter: Diagnose und Behandlung.

Positional plagiocephaly in the newborn corresponds to a posterior flattening and asymetry of the head. Its incidence has significantly increased since the "back to sleep" campain in the nineteen nineties to prevent sudden infant death syndrome. The posterior deformation usually worsens during the first six months of life when the skull is susceptible to posterior constant pressure which induces the deformation. Spontaneous outcome can be favorable. Treatment is always conservative and consists in positionnal exercise, physiotherapy and osteopathy. In some cases treatment with a helmet is recommended for a period of three months usually. Posterior positionnal plagiocephaly has no consequences on the brain's developement an is considered as an esthetic issue. In most cases good results are obtained after management with a custom fitted helmet when needed.

La palagiocéphalie positionnelle du nourisson se traduit le plus souvent par une asymétrie postérieure de la forme de la tête. L'incidence de la plagiocéphalie positionnelle a augmenté de manière significative depuis les années nonantes avec les campagnes menées pour prévenir la mort subite du nourisson en préconisant une position stricte sur le dos dans le berceau jusqu'à l'âge de six mois. La déformation postérieure visible s'aggrave en général au cours des six premiers mois de la vie, car le crâne est sensible à cet âge aux phénomènes de pressions constantes. L'évolution spontannée peut être favorable. Le traitement toujours conservateur peut consister en des manoeuvres de positionnement régulières, de l'ostéopathie ou du port d'un casque selon la sévérité de la déformation. C'est un problème esthétique sans conséquence sur le développement cérébrale. En général le traitement par casque sur mesure conduit à de bons résultats.

Noninvasive language mapping in patients with epilepsy or brain tumors.

BACKGROUND: Functional magnetic resonance imaging (fMRI) has become part of routine brain mapping in patients with epilepsy or tumor undergoing resective surgery. However, robust localization of crucial functional areas is required. OBJECTIVE: To establish a simple, short fMRI task that reliably localizes crucial language areas in individual patients who undergo respective surgery. METHODS: fMRI was measured during an 8-minute auditory semantic decision task in 28 healthy controls and 35 consecutive patients who had focal epilepsy or a brain tumor. Nineteen underwent resective surgery. Group and individual analyses were performed. Results in patients were compared with postsurgical language outcome and electrocortical stimulation when available. RESULTS: fMRI activations concordant with the anterior and posterior language areas were found in 96% and 89% of the controls, respectively. The anterior and posterior language areas were both activated in 93% of the patients. These results were concordant with electrocortical stimulation results in 5 patients. Transient postsurgical language deficits were found in 2 patients in whom surgery was performed in the vicinity of the fMRI activations or who had postsurgical complications implicating areas of fMRI activations. CONCLUSION: The proposed fast fMRI language protocol reliably localized the most relevant language areas in individual subjects. It appears to be a valuable complementary tool for surgical planning of epileptogenic foci and of brain tumors.

Influence of dietary factors, age and nickel contact dermatitis on nickel excretion.

BACKGROUND: Nickel is a frequently detected cause of allergic contact dermatitis. Ingestion of nickel may lead to flares of nickel contact dermatitis. METHODS: We examined nickel excretion in the urine of 164 female patients with and without nickel contact dermatitis. The associations between age, atopic dermatitis, nickel contact dermatitis and nickel exposure through nutrition (e.g. dietary supplements) and by patch tests were investigated prospectively. Nickel was measured with atomic absorption spectrometry with two different standardized methods. RESULTS: A nickel detection limit of 0.2 µg/l was exceeded by all samples. The 95th percentiles of urine nickel concentration were 3.77 µg/l (age 18-30 years) and 3.98 µg/l (age 31-46 years). Bivariate analyses pointed to significantly increased nickel excretion with increasing age, ingestion of dietary supplements, drinking of stagnant tap water, and consumption of nickel-rich food. In the multivariate analysis, age and dietary supplements remained significant predictors of high nickel excretion. A non-significant increase in the median concentration of nickel was observed after the administration of conventional nickel patch tests. Patients with atopic eczema showed urine nickel concentrations similar to those in non-atopic controls. CONCLUSIONS: The 95th percentile of nickel excretion in our study population markedly exceeded the actual reference value of 3 µg/l. Age and consumption of dietary supplements are the most important predictors. The use of stagnant tap water and consumption of nickel-rich food contribute to the total load. These factors should be explicitly mentioned when allergic patients on a low-nickel diet are counselled. In contrast, existing nickel contact sensitization was not more frequent in subjects with higher nickel excretion. Nickel patch testing may cause transient minor systemic nickel exposure. The findings of this study extend our understanding and management of factors associated with nickel allergy.