Distinct vestibular effects on early and late somatosensory cortical processing in humans

In non-human primates several brain areas contain neurons that respond to both vestibular and somatosensory stimulation. In humans, vestibular stimulation activates several somatosensory brain regions and improves tactile perception. However, less is known about the spatio-temporal dynamics of such vestibular-somatosensory interactions in the human brain. To address this issue, we recorded high-density electroencephalography during left median nerve electrical stimulation to obtain Somatosensory Evoked Potentials (SEPs). We analyzed SEPs during vestibular activation following sudden decelerations from constant-velocity (90 degrees/s and 60 degrees/s) earth-vertical axis yaw rotations and SEPs during a non-vestibular control period. SEP analysis revealed two distinct temporal effects of vestibular activation: An early effect (28-32 ms post-stimulus) characterized by vestibular suppression of SEP response strength that depended on rotation velocity and a later effect (97-112 ms post-stimulus) characterized by vestibular modulation of SEP topographical pattern that was rotation velocity-independent. Source estimation localized these vestibular effects, during both time periods, to activation differences in a distributed cortical network including the right postcentral gyrus, right insula, left precuneus, and bilateral secondary somatosensory cortex. These results suggest that vestibular-somatosensory interactions in humans depend on processing in specific time periods in somatosensory and vestibular cortical regions. (C) 2015 Elsevier Inc. All rights reserved.

Morphology-driven automatic segmentation of MR images of the neonatal brain

Laura Ioana Gui, Michel Kocher, François Lazeyras, Radoslaw Lisowski

The segmentation of MR images of the neonatal brain is an essential step in the study and evaluation of infant brain development. State-of-the-art methods for adult brain MRI segmentation are not applicable to the neonatal brain, due to large differences in structure and tissue properties between newborn and adult brains. Existing newborn brain MRI segmentation methods either rely on manual interaction or require the use of atlases or templates, which unavoidably introduces a bias of the results towards the population that was used to derive the atlases. We propose a different approach for the segmentation of neonatal brain MRI, based on the infusion of high-level brain morphology knowledge, regarding relative tissue location, connectivity and structure. Our method does not require manual interaction, or the use of an atlas, and the generality of its priors makes it applicable to different neonatal populations, while avoiding atlas-related bias. The proposed algorithm segments the brain both globally (intracranial cavity, cerebellum, brainstem and the two hemispheres) and at tissue level (cortical and subcortical gray matter, myelinated and unmyelinated white matter, and cerebrospinal fluid). We validate our algorithm through visual inspection by medical experts, as well as by quantitative comparisons that demonstrate good agreement with expert manual segmentations. The algorithm's robustness is verified by testing on variable quality images acquired on different machines, and on subjects with variable anatomy (enlarged ventricles, preterm- vs. term-born). (C) 2012 Elsevier B.V. All rights reserved.

Elsevier Science Bv2012

Inferior frontal oscillations reveal visuo-motor matching for actions and speech: evidence from human intracranial recordings

Olaf Blanke, Pär Halje, Silvio Ionta

The neural correspondence between the systems responsible for the execution and recognition of actions has been suggested both in humans and non-human primates. Apart from being a key region of this visuo-motor observation-execution matching (OEM) system, the human inferior frontal gyrus (IFG) is also important for speech production. The functional overlap of visuo-motor OEM and speech, together with the phylogenetic history of the IFG as a motor area, has led to the idea that speech function has evolved from pre-existing motor systems and to the hypothesis that an OEM system may exist also for speech. However, visuo-motor OEM and speech OEM have never been compared directly. We used electrocorticography to analyze oscillations recorded from intracranial electrodes in human fronto-parie-to-temporal cortex during visuo-motor (executing or visually observing an action) and speech OEM tasks (verbally describing an action using the first or third person pronoun). The results show that neural activity related to visuo-motor OEM is widespread in the frontal, parietal, and temporal regions. Speech OEM also elicited widespread responses partly overlapping with visuo-motor OEM sites (bilaterally), including frontal, parietal, and temporal regions. Interestingly a more focal region, the inferior frontal gyrus (bilaterally), showed both visuo-motor OEM and speech OEM properties independent of orolingual speech-unrelated movements. Building on the methodological advantages in human invasive electrocorticography, the present findings provide highly precise spatial and temporal information to support the existence of a modality-independent action representation system in the human brain that is shared between systems for performing, interpreting and describing actions. (C) 2015 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2015

From the early steps of whisker formation to its evolutionary disappearance: the (curious) case of Prdm1 and its regulation

Pierluigi Giuseppe Manti

Whiskers (also known as vibrissae) are sensory organs that are thought to have first appeared in Therapsida, a group of synapsids that includes mammals and evolutionary ancestors like the Thrinaxodon(1). They are highly conserved among mammals to the notable exception of the higher primates and are important for behavior, especially for nocturnal animals and the ones living in burrows(2). Furthermore, the mechanoreceptors of the vibrissae signal to the primary somatosensory cortex, where a discrete and well-defined structure in layer 4 represents each whisker(3). This structure, known as barrel cortex, occupies a large portion of the rodent brain. Strikingly, Prdm1 conditional KO (cKO) mice are one of the rare transgenic strains that do not develop whiskers while forming a pelage; on the other hand, the other head structures expressing Prdm1 (including pelage hair follicles and teeth) grow normally(4). In the developing whisker pad, Prdm1 expression is confined to the mesenchyme underlying the embryonic epidermis that will later form the whisker epidermal placode; it lasts until dermal papilla formation, when a âswitchâ occurs to the precursors of the inner root sheath. The Prdm1 ablation study we conducted revealed the absence of the patterned up-regulation of Bmp2 (marker of placode formation), Shh (a protein secreted by the epidermal placode responsible for the first epidermal signal) and Bmp4 (expressed in the pre-follicle mesenchyme). On the other hand, Lef1 is expressed uniformly in the mesenchyme of the whisker pad, thus pointing out the integrity of the Î²Catenin-mediated first mesenchymal signal. Those results suggest the role of Prdm1 as a master gene in whisker development. Prdm1 expressing cells are mainly non-proliferative; however, a small subpopulation at the periphery is cycling. Being Sox2 coexpressed with Prdm1 in the whisker mesenchyme, we performed lineage tracing with Sox2CreERT2 and ROSAYFP transgenic strains. Those experiments revealed that Sox2/Prdm1 expressing cells contribute to the formation of the dermal papilla, dermal sheath and putative pericytes of the whisker follicle and thus constitute a population of embryonic progenitors crucial for whisker formation. We subsequently investigated the development of the barrel cortex in our cKO mice. Intriguingly, a disorganized pattern was observed in cKO mice, suggesting that the loss of expression of a single gene, and consequently the disappearance of vibrissae, drastically impacts the development of the whole somatosensory system. Finally, we hypothesized that the loss of Prdm1 expression might explain the disappearance of whisker follicles in the human during evolution. Prdm1 being no longer expressed in the human lineage during hair follicle development(5), we reasoned that the loss of regulatory elements of its upstream genes might contribute to this phenomenon; we demonstrated that Lef1 acts upstream of Prdm1 during whisker development and are currently testing the role of its potential enhancers (Leaf) during this process. Bibliography: 1: (http://en.wikipedia.org/wiki/therapsid) 2: Petersen, C. C. H. The Functional Organization of the Barrel Cortex. Neuron 56, 339â355 (2007) 3: Woolsey, T. A. & Van der Loos, H. The structural organization of layer IV in the somatosensory region (SI) of mouse cerebral cortex. The description of a cortical field composed of discrete cytoarchitectonic units. Brain Res. 17, 205â242 (1970) 4: Robertson, E. J. et al. Blimp1 regulates development of the posterior forelimb, caudal pharyngeal arches, heart and sensory vibrissae in mice. Development 134, 4335â4345 (2007). 5: Sellheyer, K. & Krahl, D. Blimp-1: a marker of terminal differentiation but not of sebocytic progenitor cells. J. Cutan. Pathol. 37, 362â370 (2010).