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L Naccache

Publications and source records attributed to L Naccache.

17 recordsLinked to original sources
PubMed2004

The relationship of intracranial pressure Lundberg waves to electroencephalograph fluctuations in patients with severe head trauma.

Lundberg (or B) waves, defined as repetitive changes in intracranial pressure (ICP) occurring at frequencies of 0.5 to 2 waves/min, have been attributed to cerebral blood flow fluctuations induced by central nervous system pace-makers or cerebral pressure autoregulation. We prospectively recorded and digitalized at a frequency rate of 10 Hz (AcqKnowledge software) the following parameters in 6 brain injured patients: mean arterial pressure, heart rate, ICP, mean flow velocity of the middle cerebral artery (MFVMCA) (transcranial Doppler WAKI) and left and right spectral edge frequency (SEFl, SEFr) of continuous electroencephalogram (EEG) recordings (Philips technologies). All patients were sedated using a combination of sufentanil and midazolam and mechanically ventilated. Cerebral electrical activity (oscillations of SEF at a mean frequency of 26+/-9 mHz) and MFVMCA fluctuations were found strongly correlated with the intracranial Lundberg B waves (mean frequency 23+/-7 mHz). These result support the existence of a neuropacemaker at the origin of the Lundberg B waves. The change in cerebral electrical activity, resulting from cerebral pacemakers, could increase cerebral metabolic rate of oxygen (CMRO2) and thus lead to an increase in cerebral blood flow and secondarily of ICP through a change in cerebral blood volume.

Action Potentials↗
PubMed2004

[The cerebral substrate of visual consciousness: a neurological approach].

Since the last thirty Years, scientific study of the cerebral substrate of consciousness has been marked by significant achievements, resulting in part from a rich interaction between the exploration of cognition in both brain-damaged patients and healthy subjects. Several neuropsychological syndromes contain spectacular dissociations which permit to identify principles related to the neurophysiology of consciousness. The generality of those principles can then be evaluated in the healthy subject using the combination of experimental psychology paradigms, and functional brain-imaging tools. In this paper, we review some of the recent results relevant to visual phenomenal consciousness, which is the most scientifically investigated aspect of consciousness. We isolate several of those general principles through the exploration of neuropsychological syndromes such as "blindsight", visual agnosias and neglect, and expose how their generality has been demonstrated in the healthy subject using conditions such as visual illusions or subliminal perception. Finally, we describe the bases of a scientific model of consciousness, based on the concept of a "global workspace", which takes into account the data reviewed.

Attention↗
PubMed2004

Letter binding and invariant recognition of masked words: behavioral and neuroimaging evidence.

Fluent readers recognize visual words across changes in case and retinal location, while maintaining a high sensitivity to the arrangement of letters. To evaluate the automaticity and functional anatomy of invariant word recognition, we measured brain activity during subliminal masked priming. By preceding target words with an unrelated prime, a repeated prime, or an anagram made of the same letters, we separated letter-level and whole-word codes. By changing the case and the retinal location of primes and targets, we evaluated the invariance of those codes. Our results indicate that an invariant binding of letters into words is achieved unconsciously through a series of increasingly invariant stages in the left occipito-temporal pathway.

Adult↗
PubMed2002

Preferential survival of an MBP-specific T cell clone in an HLA-DR2 multiple sclerosis patient.

Anti-myelin basic protein (MBP) autoreactive T cells play a key role in the pathogenesis of multiple sclerosis. Thus, we applied the Immunoscope strategy to cerebrospinal fluid (CSF) and peripheral blood lymphocytes (PBLs) of an HLA-DR2 patient. Both compartments showed major expansion for the V(beta)13S5 chain, which was associated in peripheral blood with significant proliferation of PBLs in response to MBP and the 84-102 HLA-DR2-restricted peptide. Sequencing revealed a unique nucleotide sequence in the CSF that gives rise to the amino acid sequence V(beta)13S5-RPGQGDQETQ-J(beta)2.5 if translated. This CDR3 sequence had already been reported to be reactive against the 84-102 peptide. This specific sequence was not detected in PBLs on day 0, whereas it was readily detectable on day 6 culture samples. Thus, cell culture may lead to enrichment in a T cell clone identified as autoreactive.

Adult↗
PubMed2001

Towards a cognitive neuroscience of consciousness: basic evidence and a workspace framework.

This introductory chapter attempts to clarify the philosophical, empirical, and theoretical bases on which a cognitive neuroscience approach to consciousness can be founded. We isolate three major empirical observations that any theory of consciousness should incorporate, namely (1) a considerable amount of processing is possible without consciousness, (2) attention is a prerequisite of consciousness, and (3) consciousness is required for some specific cognitive tasks, including those that require durable information maintenance, novel combinations of operations, or the spontaneous generation of intentional behavior. We then propose a theoretical framework that synthesizes those facts: the hypothesis of a global neuronal workspace. This framework postulates that, at any given time, many modular cerebral networks are active in parallel and process information in an unconscious manner. An information becomes conscious, however, if the neural population that represents it is mobilized by top-down attentional amplification into a brain-scale state of coherent activity that involves many neurons distributed throughout the brain. The long-distance connectivity of these 'workspace neurons' can, when they are active for a minimal duration, make the information available to a variety of processes including perceptual categorization, long-term memorization, evaluation, and intentional action. We postulate that this global availability of information through the workspace is what we subjectively experience as a conscious state. A complete theory of consciousness should explain why some cognitive and cerebral representations can be permanently or temporarily inaccessible to consciousness, what is the range of possible conscious contents, how they map onto specific cerebral circuits, and whether a generic neuronal mechanism underlies all of them. We confront the workspace model with those issues and identify novel experimental predictions. Neurophysiological, anatomical, and brain-imaging data strongly argue for a major role of prefrontal cortex, anterior cingulate, and the areas that connect to them, in creating the postulated brain-scale workspace.

Brain↗
PubMed2001

Unconscious semantic priming extends to novel unseen stimuli.

Many subliminal priming experiments are thought to demonstrate unconscious access to semantics. However, most of them can be reinterpreted in a non-semantic framework that supposes only that subjects learn to map non-semantic visual features of the subliminal stimuli onto motor responses. In order to clarify this issue, we engaged subjects in a number comparison task in which the target number was preceded by another invisible masked number. We show that unconscious semantic priming occurs even for prime stimuli that are never presented as target stimuli, and for which no stimulus-response learning could conceivably occur. We also report analyses of the impact of the numerical relation between prime and target, and of the impact of learning on priming, all of which confirm that unconscious utilization of semantic information is indeed possible.

Adolescent↗
PubMed2001

Cerebral mechanisms of word masking and unconscious repetition priming.

We used functional magnetic resonance imaging (fMRI) and event-related potentials (ERPs) to visualize the cerebral processing of unseen masked words. Within the areas associated with conscious reading, masked words activated left extrastriate, fusiform and precentral areas. Furthermore, masked words reduced the amount of activation evoked by a subsequent conscious presentation of the same word. In the left fusiform gyrus, this repetition suppression phenomenon was independent of whether the prime and target shared the same case, indicating that case-independent information about letter strings was extracted unconsciously. In comparison to an unmasked situation, however, the activation evoked by masked words was drastically reduced and was undetectable in prefrontal and parietal areas, correlating with participants' inability to report the masked words.

Adult↗
PubMed2001

The priming method: imaging unconscious repetition priming reveals an abstract representation of number in the parietal lobes.

Most of the current brain imaging methods are limited by the low spatial resolution of neuroimaging techniques and remain unable to measure activity at the scale of single neurons or small columns of neurons, which are the coding elements of the nervous system. In this work we have adapted the priming method, an emerging research strategy that can overcome some of these spatial limitations, to investigate the coding of numerical quantities in the human brain. This approach combines the logic of psychological priming experiments with the recently discovered neurophysiological phenomenon called repetition suppression (RS). In each trial, while subjects perform a constant task, a subliminal prime is presented prior to each target. By varying the relationship between prime and target, one can detect which brain areas present RS specifically for any given level of prime-target repetition. We first expose the general logic, potential and limitations of the priming method and then illustrate it by demonstrating that a region of parietal cortex is coding for numbers at the quantity level, independently of other stimulus attributes, and that this region processes both consciously and unconsciously perceived stimuli.

Adult↗
PubMed2001

Magnetic resonance imaging: a valuable method for the detection of synovial inflammation in rheumatoid arthritis.

OBJECTIVE: Clinical assessment of rheumatoid arthritis (RA) based on pain and swelling and physical examination is limited by observer error and interpretation. We compared magnetic resonance imaging (MRI) and clinical examination to detect synovitis in RA. METHODS: Twelve patients with active RA were assessed according to Ritchie index, swollen joint count and score, swollen joint count of hands and wrists [2 wrists, 10 metacarpophalangeal (MCP), 10 proximal interphalangeal (PIP)], morning stiffness, pain intensity, Disease Activity Score (DAS), erythrocyte sedimentation rate, and C-reactive protein. MR images of hands and wrists were obtained with an adapted device, on T1 weighted (T1W) spin echo (SE) coronal images before and after gadolinium DTPA, TIW SE axial images with gadolinium DTPA, T2* gradient echo recall coronal and axial sequences, and assessed by 2 radiologists (O = no synovitis, 1 = synovitis). RESULTS: The swollen joint count on hands and wrists was 59 on clinical examination (mean 5.08 +/- 3.15 per patient; 20/24 wrists, 7/120 MCP, 32/120 PIP) and 162 on MRI (mean 13.50+/- 5.65; 22/24 wrists, 70/120 MCP, 70/120 PIP). Statistically significant correlations were found between MRI synovitis count and swollen joint count (p = 0.015) and score (p = 0.019), Ritchie Index (p = 0.035), DAS (p = 0.02) and morning stiffness (p = 0.07). MRI revealed synovitis significantly more often than clinical examination (162 vs 59; p = 0.00002) [2-fold in PIP (70/32) and 10-fold in MCP (70/7)]. Clinical examination and MRI were concordant for 157/264 joints (59.5%). The association of normal MRI with synovitis on clinical examination was observed in 2 cases, the opposite in 105. CONCLUSION: MRI is more sensitive than clinical examination to detect synovitis of hands and wrists in RA, especially for MCP and PIP joints, and is valuable for assessment of inflammation in hands and wrists in RA.

Adult↗
PubMed2000

Further evidence for a central reorganisation of synaptic connectivity in patients with hypoglossal-facial anastomosis in man.

In normal subjects, electrical stimulation of trigeminal mucosal afferents (lingual nerve - V3) can elicit a short latency (12.5+/-0. 3 ms; mean+/-S.D.) reflex response in the ipsilateral genioglossus muscle (Maisonobe et al., Reflexes elicited from cutaneous and mucosal trigeminal afferents in normal human subjects. Brain Res. 1998;810:220-228). In the present study on patients with hypoglossal-facial (XII-VII) nerve anastomoses, we were able to record similar R1-type blink reflex responses in the orbicularis oculi muscles, following stimulation of either supraorbital nerve (V1) or lingual nerve (V3) afferents. However, these responses were not present in normal control subjects. Voluntary swallowing movements produced clear-cut facilitations of the R1 blink reflex response elicited by stimulation of V1 afferents. In a conditioning-test procedure with a variable inter-stimulus interval, the R1 blink reflex response elicited by supraorbital nerve stimulation was facilitated by an ipsilateral mucosal conditioning stimulus in the V3 region. This facilitatory effect was maximal when the two stimuli (conditioning and test) were applied simultaneously. This effect was not observed on the R1 component of the blink reflex in the normal control subjects. These data strongly suggest that in patients with XII-VII anastomoses, but not in normal subjects, both cutaneous (V1) and mucosal (V3) trigeminal afferents project onto the same interneurones in the trigeminal principal sensory nucleus. This clearly supports the idea that peripheral manipulation of the VIIth and the XIIth nerves induces a plastic change within this nucleus.

Adult↗
PubMed2000

Language and calculation within the parietal lobe: a combined cognitive, anatomical and fMRI study.

We report the case of a patient (ATH) who suffered from aphasia, deep dyslexia, and acalculia, following a lesion in her left perisylvian area. She showed a severe impairment in all tasks involving numbers in a verbal format, such as reading aloud, writing to dictation, or responding verbally to questions of numerical knowledge. In contrast, her ability to manipulate non-verbal representations of numbers, i.e., Arabic numerals and quantities, was comparatively well preserved, as evidenced for instance in number comparison or number bisection tasks. This dissociated impairment of verbal and non-verbal numerical abilities entailed a differential impairment of the four arithmetic operations. ATH performed much better with subtraction and addition, that can be solved on the basis of quantity manipulation, than with multiplication and division problems, that are commonly solved by retrieving stored verbal sequences. The brain lesion affected the classical language areas, but spared a subset of the left inferior parietal lobule that was active during calculation tasks, as demonstrated with functional MRI. Finally, the relative preservation of subtraction versus multiplication may be related to the fact that subtraction activated the intact right parietal lobe, while multiplication activated predominantly left-sided areas.

Aphasia↗
PubMed2000

The visual word form area: spatial and temporal characterization of an initial stage of reading in normal subjects and posterior split-brain patients.

A standard model of word reading postulates that visual information is initially processed by occipitotemporal areas contralateral to the stimulated hemifield, from whence it is subsequently transferred to the visual word form (VWF) system, a left inferior temporal region specifically devoted to the processing of letter strings. For stimuli displayed in the left visual field, this transfer proceeds from the right to the left hemisphere through the posterior portion of the corpus callosum. In order to characterize the spatial and temporal organization of these processes, reading tasks with split-field presentation were performed by five control subjects and by two patients suffering from left hemialexia following posterior callosal lesions. The subjects' responses were studied using behavioural measures and functional brain imaging techniques, providing both high spatial resolution (functional MRI, fMRI) and high temporal resolution (high-density event-related potentials, ERPs). Early visual processing was revealed as activations contralateral to stimulation, located by fMRI in the inferior occipitotemporal region and presumably coincident with area V4. A negative wave occurring 150-160 ms post-stimulus, also strictly contralateral to stimulation, was recorded over posterior electrodes. In contrast with these hemifield-dependent effects, the VWF system was revealed as a strictly left-hemispheric activation which, in control subjects, was identical for stimuli presented in the left or in the right hemifield and was located in the middle portion of the left fusiform gyrus. The electrical signature of the VWF system consisted of a unilateral sharp negativity, recorded 180-200 ms post-stimulus over left inferior temporal electrodes. In callosal patients, due to the inability of visual information to pass across the posterior part of the corpus callosum, the VWF system was activated only by stimuli presented in the right visual field. Similarly, a significant influence of the word/non-word status on ERPs recorded over the left hemisphere was discernible for either hemifield in controls, while it affected only right-hemifield stimuli in callosal patients. These findings provide direct support for the main components of the classical model of reading and help specify their timing and cerebral substrates.

Adult↗
PubMed1999

["Boxer's dementia" without motor signs].

BACKGROUND: The neurological complications related to boxing include dementia. Boxer's dementia is generally associated with severe motor impairment. CASE REPORT: A former professional boxer presented dementia with no motor signs. The diagnostic discussion was based on clinical observations, and neuropsychological and supplementary explorations, and eliminated all other etiological hypotheses. DISCUSSION: This case draws attention to the possibility of cognitive disorders without motor impairment in the neurological complications of boxing.

Boxing↗
PubMed1999

Event-related fMRI analysis of the cerebral circuit for number comparison.

Cerebral activity during number comparison was studied with functional magnetic resonance imaging using an event-related design. We identified an extended network of task-related areas that showed a phasic activation following each trial, including anterior cingulate, bilateral sensorimotor areas, inferior occipito-temporal cortices, posterior parietal cortices, inferior and dorsolateral prefrontal cortices, and thalami. We then tested which of these areas were affected by number notation, numerical distance and response side, three variables that specifically target processes of visual identification, quantity manipulation and motor response in a serial-stage model of the number comparison task. Our results confirm the role of the right fusiform gyrus in digit identification processes, and of the inferior parietal lobule in the internal manipulation of numerical quantities.

Adult↗
PubMed1998

Imaging unconscious semantic priming.

Visual words that are masked and presented so briefly that they cannot be seen may nevertheless facilitate the subsequent processing of related words, a phenomenon called masked priming. It has been debated whether masked primes can activate cognitive processes without gaining access to consciousness. Here we use a combination of behavioural and brain-imaging techniques to estimate the depth of processing of masked numerical primes. Our results indicate that masked stimuli have a measurable influence on electrical and haemodynamic measures of brain activity. When subjects engage in an overt semantic comparison task with a clearly visible target numeral, measures of covert motor activity indicate that they also unconsciously apply the task instructions to an unseen masked numeral. A stream of perceptual, semantic and motor processes can therefore occur without awareness.

Adult↗