Behavioral validation of novel high resolution attention decoding method from multi-units & local field potentials.

The ability to access brain information in real-time is crucial both for a better understanding of cognitive functions and for the development of therapeutic applications based on brain-machine interfaces. Great success has been achieved in the field of neural motor prosthesis. Progress is still needed in the real-time decoding of higher-order cognitive processes such as covert attention. Recently, we showed that we can track the location of the attentional spotlight using classification methods applied to prefrontal multi-unit activity (MUA) in the non-human primates. Importantly, we demonstrated that the decoded (x,y) attentional spotlight parametrically correlates with the behavior of the monkeys thus validating our decoding of attention. We also demonstrate that this spotlight is extremely dynamic. Here, in order to get closer to non-invasive decoding applications, we extend our previous work to local field potential signals (LFP). Specifically, we achieve, for the first time, high decoding accuracy of the (x,y) location of the attentional spotlight from prefrontal LFP signals, to a degree comparable to that achieved from MUA signals, and we show that this LFP content is predictive of behavior. This LFP attention-related information is maximal in the gamma band (30-250 Hz), peaking between 60 to 120 Hz. In addition, we introduce a novel two-step decoding procedure based on the labelling of maximally attention-informative trials during the decoding procedure. This procedure strongly improves the correlation between our real-time MUA and LFP based decoding and behavioral performance, thus further refining the functional relevance of this real-time decoding of the (x,y) locus of attention. This improvement is more marked for LFP signals than for MUA signals. Overall, this study demonstrates that the attentional spotlight can be accessed from LFP frequency content, in real-time, and can be used to drive high-information content cognitive brain-machine interfaces for the development of new therapeutic strategies.

Neurofeedback for cognitive enhancement and intervention and brain plasticity.

In recent years, neurofeedback has been used as a cognitive training tool to improve brain functions for clinical or recreational purposes. It is based on providing participants with feedback about their brain activity and training them to control it, initiating directional changes. The overarching hypothesis behind this method is that this control results in an enhancement of the cognitive abilities associated with this brain activity, and triggers specific structural and functional changes in the brain, promoted by learning and neuronal plasticity effects. Here, we review the general methodological principles behind neurofeedback and we describe its behavioural benefits in clinical and experimental contexts. We review the non-specific effects of neurofeedback on the reinforcement learning striato-frontal networks as well as the more specific changes in the cortical networks on which the neurofeedback control is exerted. Last, we analyse the current challenges faces by neurofeedback studies, including the quantification of the temporal dynamics of neurofeedback effects, the generalisation of its behavioural outcomes to everyday life situations, the design of appropriate controls to disambiguate placebo from true neurofeedback effects and the development of more advanced cortical signal processing to achieve a finer-grained real-time modelling of cognitive functions.

Eye position encoding in the macaque ventral intraparietal area (VIP).

Many neurons in area VIP encode the location of visual stimuli in a non-retinocentric frame of reference. In this context the question needed to be addressed whether the underlying coordinate transformation of the incoming visual signals could be generated within area VIP or whether this information would have to arrive from other areas. We tested 74 neurons in area VIP of two awake monkeys for an influence of eye position while animals performed a fixation task. More than half of the neurons (40/74) revealed an eye position effect. At the population level, however, this effect was balanced out. We suggest that local connections within area VIP could be used to generate an encoding of visual information in a non-retinocentric frame of reference.

[Brucella endocarditis on Starr aortic valve prosthesis]. / Endocardite brucellienne sur valve de Starr aortique.

The authors report the case of a 22 year old patient with brucella endocarditis on a Starr-Edwards aortic valve prosthesis implanted 5 years previously. Six blood cultures were positive for Brucella melitensis biovar I. Antibiotic therapy associating Rifampicin and Tetracycline and then Rifampicin and Ofloxacine did not prevent abscess formation and valve dehiscence. The poor haemodynamic status and persistent infection led to replacement of the valve prosthesis. Culture of the infected prosthesis grew a colony of brucella melitensis resistant to fluoro-quinolones. Valve replacement and antibiotic therapy led to clinical improvement and constant apyrexia with a 12 month follow-up. Brucella endocarditis on a valve prosthesis is a very rare occurrence. The combination of valve replacement and antibiotic therapy is usually required.

[Study of the sensitivity of non-typhoid salmonellae isolated at Sfax (Tunisia)]. / Etude de la sensibilité des salmonelles non typhiques isolées à Sfax (Tunisie).

From 1982 to 1986, 122 strains of non-typhoid Salmonellae were isolated at the University Hospital of Sfax (Tunisia). Both tests: serotype classification and sensitivity have demonstrated that the most frequent serotypes: S. wien and S. typhimurium have the highest degree of multiresistance. Ampicillin, cotrimoxazole and chloramphenicol are the most affected while cefotaxime, amikacin and colistin are still saved. Facing these facts, the authors insist on the seriousness of the excessive use of antibiotherapy which leads to the selection of such strains.

[Respiratory manifestations of carbamazepine. Apropos of a case]. / Les manifestations respiratoires de la carbamazépine. A propos d'un cas.

A 14-year-old girl developed skin rash, fever and dyspnea. The chest roentgenogram showed diffuse reticulonodular infiltration. Pulmonary function tests revealed mild restrictive defect and blood oxygen pressure at 71 mm Hg. BAL showed increased cell counts with lymphocytosis at 15% and neutrophilia at 3%. Outcome was good after carbamazepine withdrawal and without corticosteroid therapy. Relapse was observed after patient-induced rechallenge.

Decoding M1 neurons during multiple finger movements.

We tested several techniques for decoding the activity of primary motor cortex (M1) neurons during movements of single fingers or pairs of fingers. We report that single finger movements can be decoded with >99% accuracy using as few as 30 neurons randomly selected from populations of task-related neurons recorded from the M1 hand representation. This number was reduced to 20 neurons or less when the neurons were not picked randomly but selected on the basis of their information content. We extended techniques for decoding single finger movements to the problem of decoding the simultaneous movement of two fingers. Movements of pairs of fingers were decoded with 90.9% accuracy from 100 neurons. The techniques we used to obtain these results can be applied, not only to movements of single fingers and pairs of fingers as reported here, but also to movements of arbitrary combinations of fingers. The remarkably small number of neurons needed to decode a relatively large repertoire of movements involving either one or two effectors is encouraging for the development of neural prosthetics that will control hand movements.

Ocular fixation and visual activity in the monkey lateral intraparietal area.

The macaque lateral intraparietal area (LIP) has been implicated in visuospatial attention and saccade planning. Since area LIP also contains a representation of the central visual field, we investigated its possible role in fixation and foveal attention in a visual fixation task with gap (momentary disappearance of fixation point). In addition to the expected visual neurons ( n=119), two main categories were identified: (1) cells responding tonically both during the presence and momentary absence of the fixation stimulus( n=47); a subset of these neurons studied in a saccade task showed perisaccadic inhibition in half of the cases (14/27). The timing of this inhibition, however, is only loosely related to saccade timing; (2) cells responding mainly to the absence of the fixation stimulus, with either abrupt or gradual onset of activity during the gap ( n=62). During saccades, these neurons showed presaccadic buildup and/or postsaccadic activity, which was spatially tuned in about half of the tested cells (28/53). Ninety-one percent of the cells in the first category and 59% of the cells in the second category were located in the dorsal portion of area LIP (LIPd). These results are consistent with the hypothesis of an oculomotor-attentional network contributing to fixation engagement and disengagement in a subregion of LIP.

MSTd neuronal basis functions for the population encoding of heading direction.

Basis functions have been extensively used in models of neural computation because they can be combined linearly to approximate any nonlinear functions of the encoded variables. We investigated whether dorsal medial superior temporal (MSTd) area neurons use basis functions to simultaneously encode heading direction, eye position, and the velocity of ocular pursuit. Using optimal linear estimators, we first show that the head-centered and eye-centered position of a focus of expansion (FOE) in optic flow, pursuit direction, and eye position can all be estimated from the single-trial responses of 144 MSTd neurons with an average accuracy of 2-3 degrees, a value consistent with the discrimination thresholds measured in humans and monkeys. We then examined the format of the neural code for the head-centered position of the FOE, eye position, and pursuit direction. The basis function hypothesis predicts that a large majority of cells in MSTd should encode two or more signals simultaneously and combine these signals nonlinearly. Our analysis shows that 95% of the neurons encode two or more signals, whereas 76% code all three signals. Of the 95% of cells encoding two or more signals, 90% show nonlinear interactions between the encoded variables. These findings support the notion that MSTd may use basis functions to represent the FOE in optic flow, eye position, and pursuit.

Visual receptive field modulation in the lateral intraparietal area during attentive fixation and free gaze.

The receptive field (RF) of neurons recorded from the lateral intraparietal area (LIP) was quantified using a rapid, computer-driven mapping procedure. For each neuron, the RF was mapped: (1) during attentive fixation and (2) during free visual exploration. RF location, size and internal structure were modulated by the mapping context in over two-thirds of the recorded neurons. The major trend was a proportionally larger amount of neuronal visual resources allocated to central space during fixation, and an attenuated center-to-periphery gradient in the visual field representation during free gaze. A population approach shows that these spatial modulations are accompanied by changes in the signal-to-noise ratio of the information carried in the RF substructure. We related these neurophysiological observations to behavior, by comparing the characteristics of saccades elicited during fixation and free gaze. Together, the results suggest that the dynamics of LIP visual RFs may characterize both the state of engagement of attention and the power of resolution of visual analysis: during fixation, the neural population is locked in a filter state concentrating the processing resources at the fovea, while during free gaze, the population shifts to a detector state spreading the resources more evenly across the visual field.

[Jaundice and pregnancy. Apropos of 62 cases]. / Ictères et grossesses. A propos de 62 cas.

In this study, the authors have attempted to collect files of jaundice in pregnant women. 65 cases were included in this study, over a period of 4 years. Several etiologies of jaundice have been reported but viral hepatitis especially the non A, non B viral hepatitis remain the most frequent. The epidemiology, and the clinical and evolutive criteria of each disease are briefly summarized.

Representation of the visual field in the lateral intraparietal area of macaque monkeys: a quantitative receptive field analysis.

The representation of the visual field in the primate lateral intraparietal area (LIP) was examined, using a rapid, computer-driven receptive field (RF) mapping procedure. RF characteristics of single LIP neurons could thus be measured repeatedly under different behavioral conditions. Here we report data obtained using a standard ocular fixation task during which the animals were required to monitor small changes in color of the fixated target. In a first step, statistical analyses were conducted in order to establish the experimental limits of the mapping procedure on 171 LIP neurons recorded from three hemispheres of two macaque monkeys. The characteristics of the receptive fields of LIP neurons were analyzed at the single cell and at the population level. Although for many neurons the assumption of a simple two-dimensional gaussian profile with a central area of maximal excitability at the center and progressively decreasing response strength at the periphery can represent relatively accurately the spatial structure of the RF, about 19% of the cells had a markedly asymmetrical shape. At the population level, we observed, in agreement with prior studies, a systematic relation between RF size and eccentricity. However, we also found a more accentuated overrepresentation of the central visual field than had been previously reported and no marked differences between the upper and lower visual representation of space. This observation correlates with an extension of the definition of LIP from the posterior third of the lateral intraparietal sulcus to most of the middle and posterior thirds. Detailed histological analyses of the recorded hemispheres suggest that there exists, in this newly defined unitary functional cortical area, a coarse but systematic topographical organization in area LIP that supports the distinction between its dorsal and ventral regions, LIPd and LIPv, respectively. Paralleling the physiological data, the central visual field is mostly represented in the middle dorsal region and the visual periphery more ventral and posterior. An anteroposterior gradient from the lower to the upper visual field representations can also be identified. In conclusion, this study provides the basis for a reliable mapping method in awake monkeys and a reference for the organization of the properties of the visual space representation in an area LIP extended with respect to the previously described LIP and showing a relative emphasis of central visual field.

Spatial invariance of visual receptive fields in parietal cortex neurons.

Spatial information is conveyed to the primary visual cortex in retinal coordinates. Movement trajectory programming, however, requires a transformation from this sensory frame of reference into a frame appropriate for the selected part of the body, such as the eye, head or arms. To achieve this transformation, visual information must be combined with information from other sources: for instance, the location of an object of interest can be defined with respect to the observer's head if the position of the eyes in the orbit is known and is added to the object's retinal coordinates. Here we show that in a subdivision of the monkey parietal lobe, the ventral intraparietal area (VIP), the activity of visual neurons is modulated by eye-position signals, as in many other areas of the cortical visual system. We find that individual receptive fields of a population of VIP neurons are organized along a continuum, from eye to head coordinates. In the latter case, neurons encode the azimuth and/or elevation of a visual stimulus, independently of the direction in which the eyes are looking, thus representing spatial locations explicitly in at least a head-centred frame of reference.

[Candida glabrata perinephric abscess. A case report]. / Abcès périrénal à Candida glabrata.

We report a case of Candida glabrata perinephric abscess in a patient with diabetes mellitus who recently underwent ureteropelvic surgery for lithiasic urinary tract obstruction. Surgical drainage and amphotericin B treatment led to resolution of the infection. C. glabrata urinary infection has become more prevalent over the last decade in immunocompromised patients. Drainage is indicated for development of a fungal abscess in the perinephric area. Most authors recommend administration of an antifungal adjuvant treatment.