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International audience; Background: Whilst modern awake intraoperative mapping has been widely accepted and implemented in the last decades in neuro-oncology, sparse reports have been published on the safety and efficiency of this approach in epilepsy surgery.Method: This article reports four cases with different locations of epileptogenic zones as examples of possible safe and efficient resections.Result: The results of the resections on seizure control were Engel 1 (no disabling seizures) in all cases and no patient experienced significant neurological deficits.Discussion: The discussion focuses on aspects of the future of epilepsy surgery in a hodotopical paradigm.

International audience; Gaining new insights into the anatomy of the human hypothalamus is crucial for the development of new treatment strategies involving functional stereotactic neurosurgery. Here, using anatomical comparisons between histology and magnetic resonance images of the human hypothalamus in the coronal plane, we show that discrete gray and white hypothalamic structures are consistently identifiable by MRI. Macroscopic and microscopic images were used to precisely annotate the MRI sequences realized in the coronal plane in twenty healthy volunteers. MRI was performed on a 1.5 T scanner, using a protocol including T1-weighted 3D fast field echo, T1-weighted inversion-recovery, turbo spin echo and T2-weighted 2D fast field echo imaging. For each gray matter structure as well as for white matter bundles, the different MRI sequences were analyzed in comparison to each other. The anterior commissure and the fornix were often identifiable, while the mammillothalamic tract was more difficult to spot. Qualitative analyses showed that MRI could also highlight finer structures such as the paraventricular nucleus, the ventromedial nucleus of the hypothalamus and the infundibular (arcuate) nucleus, brain nuclei that play key roles in the regulation of food intake and energy homeostasis. The posterior hypothalamic area, a target for deep brain stimulation in the treatment of cluster headaches, was readily identified, as was the lateral hypothalamic area, which similar to the aforementioned hypothalamic nuclei, could be a putative target for deep brain stimulation in the treatment of obesity. Finally, each of the identified structures was mapped to Montreal Neurological Institute (MNI) space.

International audience; Rats discriminate objects by scanning their surface with the facial vibrissae, producing spatiotemporally complex sequences of tactile contacts. The way in which the somatosensory cortex responds to these complex multivibrissal stimuli has not been explored. It is unclear yet whether contextual information from across the entire whisker pad influences cortical responses. Here, we delivered tactile stimuli to the rat vibrissae using a new 24 whisker stimulator. We tested sequences of rostrocaudal whisker deflections that generate multivibrissal motion patterns in different directions across the mystacial pad, allowing to disambiguate local from global sensory integration. Unitary electrophysiological recordings from different layers of the barrel cortex showed that a majority of neurons has direction selectivity for the multivibrissal stimulus. The selectivity resulted from nonlinear integration of responses across the mystacial pad. Our results indicate that the system extracts collective properties of a tactile scene.

International audience; Recruitment of executive attention is normally associated to a subjective feeling of mental effort. Here we investigate the nature of this coupling in a patient with a left mesio-frontal cortex lesion including the anterior cingulate cortex (ACC), and in a group of comparison subjects using a Stroop paradigm. We show that in normal subjects, subjective increases in effort associated with executive control correlate with higher skin-conductance responses (SCRs). However, our patient experienced no conscious feeling of mental effort and showed no SCR, in spite of exhibiting normal executive control, and residual right anterior cingulate activity measured with event-related potentials (ERPs). Finally, this patient demonstrated a pattern of impaired behavior and SCRs in the Iowa gambling task-elaborated by Damasio, Bechara and colleagues-replicating the findings reported by these authors for other patients with mesio-frontal lesions. Taken together, these results call for a theoretical refinement by revealing a decoupling between conscious cognitive control and consciously reportable feelings. Moreover, they reveal a fundamental distinction, observed here within the same patient, between the cognitive operations which are depending on normal somatic marker processing, and those which are withstanding to impairments of this system.

International audience; How are comparative judgments performed in the human brain? We scanned subjects with fMRI while they compared stimuli for size, luminance, or number. Regions involved in comparative judgments were identified using three criteria: task-related activation, presence of a distance effect, and interference of one dimension onto the other. We observed considerable overlap in the neural substrates of the three comparison tasks. Interestingly, the amount of overlap predicted the amount of cross-dimensional interference: in both behavior and fMRI, number interfered with size, and size with luminance, but number did not interfere with luminance. The results suggest that during comparative judgments, the relevant continuous quantities are represented in distributed and overlapping neural populations, with number and size engaging a common parietal spatial code, while size and luminance engage shared occipito-temporal perceptual representations.

International audience; The present study sought to assess neural correlates of implicit identification of objects by means of fMRI, using tasks that require matching of the physical properties of objects. Behavioural data suggests that there is automatic access to object identity when observers attend to a physical property of the form of an object (e.g. the object's orientation) and no evidence for semantic processing when subjects attend to colour. We evaluated whether, in addition to neural areas associated with decisions to specific perceptual properties, areas associated with access to semantic information were activated when tasks demanded processing of the global configuration of pictures. We used two perceptual matching tasks based on the global orientation or on the colour of line drawings. Our results confirmed behavioural data. Activations in the inferior occipital cortex, fusiform and inferior temporal gyri in both tasks (orientation and colour) account for perceptual and structural processing involved in each task. In contrast, activations in the posterior and medial parts of the fusiform gyrus, shown to be involved in explicit semantic judgements, were more pronounced in the orientation-matching task, suggesting that semantic information from the pictures is processed in an implicit way even when not required by the task. Thus, this study suggests that cortical regions usually involved in explicit semantic processing are also activated when implicit processing of objects occurs.

International audience; We recently demonstrated that rats with dorsal anterior cingulate (ACd) cortical lesions were disrupted in the acquisition of a temporal Go/No-Go alternation task, suggesting either an involvement of this medial prefrontal subregion in sequencing temporally ordered behaviors or alternatively in more general response selection processes 'Gisquet-Verrier et al., Psychobiology 28 (2000) 248'. In the present study, the effects of ACd lesions were investigated in two different training situations. Both tasks involved response selection but only one of the two tasks required behavioral sequencing. In experiment 1, rats with ACd lesions were normally able to select Go and No-Go responses, when selection processes were based on a tone/light conditional rule that does not require temporal patterning. In experiment 2, ACd-lesioned rats were disrupted during the acquisition of a spatial alternation task that relies on temporal patterning. These results provide further evidence of ACd involvement in behavioral sequencing, regardless of the nature (spatial or non-spatial) of chained responses. A comparison of ACd lesions-induced effects with those obtained with lesions to the adjacent prelimbic-infralimbic area 'Delatour & Gisquet-Verrier, Behav. Neurosci. 110 (1996) 1282; Delatour & Gisquet-Verrier, Behav. Neurosci. 113 (1999) 941' reveals a double dissociation of these two regions that reflects a functional regionalization of the medial prefrontal cortex in the rat.

International audience; Autoradiographic studies of the distribution of the histamine H2 receptor and its messenger RNAs were performed on serial frontal and a few sagittal sections of guinea-pig brain using [(125)I]iodoaminopotentidine for radioligand binding and a 33P-labelled complementary RNA probe for in situ hybridization, respectively. Both probes were validated by assessing non-specific labelling using non-radioactive competing H2 receptor ligands and a sense probe for binding sites and gene transcripts, respectively. In some areas, e.g., cerebral cortex, hippocampal complex or cerebellum, such studies were completed by identification of neurons expressing the H2 receptor messenger RNAs on emulsion-dipped sections. Nissl-stained sections from comparable levels were used to localize brain structures. In many brain areas, the distribution of the H2 receptor and its messenger RNAs appeared to parallel that known for histaminergic axons. For instance. high levels of both H2 receptor markers were detected in striatal and limbic areas known to receive abundant histaminergic projections. In contrast, in septum, hypothalamic, pontine and several thalamic nuclei, a comparatively low density of both H2 receptor markers was detected, suggesting that histamine actions in these areas are mediated by H1 and/or H3 receptors. Generally, the distribution of H2 receptor messenger RNA correlates well with that of [(125)I]iodoaminopotentidine binding sites, although some differences were observed. In a few regions (e.g., substantia nigra, locus coeruleus) high or moderate densities of binding sites were accompanied by a much more restricted expression of H2 receptor transcripts. Conversely, the mammillary region and the pontine nucleus exhibited higher levels of hybridization than of binding sites. In hippocampus, cerebral and cerebellar cortex there was a selective localization of the H2 receptor messenger RNA in the granule cells of dentate gyrus, pyramidal cells of the Ammon's horn and cerebral cortex, and Purkinje cells of cerebellum, whereas [(125)I]iodoaminopotentidine binding sites were located in layers where the dendritic trees of these messenger RNA-expressing neurons extend. The same discrepancy between messenger RNAs and binding sites suggests that striatonigral endings are endowed with the H2 receptor. The histamine H1 and H2 receptors both appear to be present in several brain areas, in some cases in a way suggesting their potential co-expression by the same neuronal populations, e.g., in granule and pyramidal cells in the hippocampal formation. This co-expression accounts for synergic responses, e.g., on cAMP generation, previously observed upon co-stimulation of both receptor subtypes. The widespread distribution of the H2 receptor, namely in thalamic nuclei or in telencephalic areas such as most layers of the cerebral cortex, together with its excitatory role previously established in electrophysiological studies, support its alleged function in mediating the histamine-driven control of arousal mechanisms. In addition, the detection of H2 receptor expression in brainstem areas from which other monoaminergic pathways involved in the control of states of sleep and wakefulness emanate, e.g., several raphe nuclei, locus coeruleus or substantia innominata, suggests possible interrelationships between all of these systems with highly divergent projections to the thalamus and telencephalon. The present mapping of the H2 receptor and its gene transcripts should facilitate neurochemical, neurophysiological and behavioural studies aimed at clarifying the role of histaminergic systems in brain.

International audience; The aim of this study was to examine the afferents to the rat locus coeruleus by means of retrograde and anterograde tracing experiments using cholera-toxin B subunit and phaseolus leucoagglutinin. To obtain reliable injections of cholera-toxin B in the locus coeruleus, electrophysiological recordings were made through glass micropipettes containing the tracer and the noradrenergic neurons of the locus coeruleus were identified by their characteristic discharge properties. After iontophoretic injections of cholera-toxin B into the nuclear core of the locus coeruleus, we observed a substantial number of retrogradely labeled cells in the lateral paragigantocellular nucleus and the dorsomedial rostral medulla (ventromedial prepositus hypoglossi and dorsal paragigantocellular nuclei) as previously described. We also saw a substantial number of retrogradely labeled neurons in (1) the preoptic area dorsal to the supraoptic nucleus, (2) areas of the posterior hypothalamus, (3) the Kölliker-Fuse nucleus, (4) mesencephalic reticular formation. Fewer labeled cells were also observed in other regions including the hypothalamic paraventricular nucleus, dorsal raphe nucleus, median raphe nucleus, dorsal part of the periaqueductal gray, the area of the noradrenergic A5 group, the lateral parabrachial nucleus and the caudoventrolateral reticular nucleus. No or only occasional cells were found in the cortex, the central nucleus of the amygdala, the lateral part of the bed nucleus of the stria terminalis, the vestibular nuclei, the nucleus of the solitary tract or the spinal cord, structures which were previously reported as inputs to the locus coeruleus. Control injections of cholera-toxin B were made in areas surrounding the locus coeruleus, including (1) Barrington's nucleus, (2) the mesencephalic trigeminal nucleus, (3) a previously undefined area immediately rostral to the locus coeruleus and medial to the mesencephalic trigeminal nucleus that we named the peri-mesencephalic trigeminal nucleus, and (4) the medial vestibular nucleus lateral to the caudal tip of the locus coeruleus. These injections yielded patterns of retrograde labeling that differed from one another and also from that obtained with cholera-toxin B injection sites in the locus coeruleus. These results indicate that the area surrounding the locus coeruleus is divided into individual nuclei with distinct afferents. These results were confirmed and extended with anterograde transport of cholera-toxin B or phaseolus leucoagglutinin. Injections of these tracers in the lateral paragigantocellular nucleus, preoptic area dorsal to the supraoptic nucleus, the ventrolateral part of the periaqueductal gray, the Kölliker-Fuse nucleus yielded a substantial to large number of labeled fibers in the nuclear core of the locus coeruleus.(ABSTRACT TRUNCATED AT 400 WORDS)

International audience; The effects of unilateral basal forebrain stimulation on the tone-evoked responses recorded in the auditory cortex ipsilateral and contralateral to the stimulation site, were investigated in fully awake rats. After 10 tone alone presentations, 20 pairing trials were given during which the basal forebrain stimulation was followed by the tone 30 ms later. Ten test-tones were presented immediately, 15 min and 1 h after pairing. Immediately after pairing, the short-latency "on" and "off" tone-evoked responses were enhanced in the ipsilateral but not in the contralateral cortex. This enhancement did not persist 15 min later. Systemic atropine injection prevented the ipsilateral facilitation. The responses to the tone were not modified when tested after 20 basal forebrain stimulations delivered in the absence of the tone. These results are the first demonstration in awake animals that an activation of the auditory cortex by cholinergic neurons of the basal forebrain is able to facilitate cortical responsiveness. A temporal contiguity between the cholinergic activation and the neuronal discharges elicited by the sensory stimulus is required for the facilitation to take place. The results are compared to previous ones obtained in anesthetized animals, and the functional role of cholinergic activation from the basal forebrain in cortical processing is discussed.

International audience; [125I]Iodobolpyramine, a potent and selective histamine H1-receptor antagonist derived from mepyramine, was used to generate light microscopic autoradiograms on sections of guinea-pig brain and spinal cord. Histamine H1-receptors were labelled with high sensitivity over a low background as determined using mianserin or other H1-receptor antagonists as competing agents. An atlas of H1-receptors was established using five sagittal sections and 39 frontal sections, the latter serially prepared at 50 micron intervals. Labelled areas were identified by comparison with corresponding, classically stained sections and their density was rated according to an arbitrary scale. Autoradiographic grains were detected in a large variety of gray matter areas whereas they were generally absent from white matter areas. In the cerebral cortex, H1-receptors are present in all areas and layers with a higher density in lamina IV. In the hippocampal formation, H1-receptors display a laminated pattern of distribution and are the most abundant in the dentate gyrus (hilus and molecular layer) and in several areas of the subiculum and commissural complex. In the amygdaloid complex, the highest densities are found in the medial group of nuclei. In the basal forebrain, the striatum is moderately labelled whereas the nucleus accumbens, islands of Calleja and most septal nuclei are highly labelled. In the thalamus, H1-receptors are present in high density, particularly in the anterior, median and lateral groups of nuclei. In the hypothalamus the labelling is highly heterogeneous with high densities in, for example, medial preoptic area, dorsomedial, ventromedial and most posterior nuclei, including the tuberomammillary complex in which histaminergic perikarya and short axons are present.(ABSTRACT TRUNCATED AT 250 WORDS)