Researchers from Inserm, CNRS and the Université Joseph Fourier in Grenoble, in collaboration with Cambridge university, Strasbourg university and clinical practitioners from the Strasbourg University Hospital Centre, have analysed data from 17 comatose patients using functional MRI data. Their research reveals that the brain networks of these patients have been restructured. The results, published in PNAS on 26 November 2012, could help clinical practitioners diagnose comatose patients.

The researchers are focusing on analysing brain networks of brain-damaged comatose (non-traumatised) patients, a state where the individual is considered to be unconscious.

The authors of the study used an original graph theory-based methodology, where images were constructed using functional MRI data at rest and using robust statistical signal-processing methods. Local and overall effectiveness indices of functional brain networks were obtained for 17 brain-damaged patients and 20 healthy volunteers. Correlations in  417 brain regions were extracted to produce brain connection graphs using the statistically significant correlations.

Inserm unit 836 “Grenoble Institut des neurosciences”, CNRS researchers from the “GIPSA lab” and from the Behavioural and Clinical Neuroscience Institute in Cambridge, in collaboration with clinical practitioners from the Strasbourg University Hospital Centre, have been able to highlight restructured brain networks in brain-damaged (non-traumatized) comatose patients.

Through comparisons with the healthy subjects, the results demonstrate that the overall cerebral connectivity is preserved in comatose patients. By analysing the connectivity at a local level, the authors of the study have observed that some brain regions (“hubs”), which are highly connected in healthy volunteers, are less well connected in comatose patients. Conversely, the less densely connected regions in the network in healthy subjects become “hubs” in comatose patients.

Brain imaging obtained from connectivity graphs

Photos: © Sophie Achard – Petra Vertes

The connectivity graph method is used to summarize in a single image data acquired through MRI scanning. It translates the effectiveness of connections in a single region compared to all the others. By grouping the most interconnected regions, modules are revealed (each represented by a different colour). Patients and healthy volunteers both have different models in their spatial location, representing radical alterations to the brain connections.

According to current hypotheses, consciousness disorders in persistently comatose patients could be linked to disconnection phenomena between specific cortical regions, particularly the precuneus. The results of this study also point in this direction. “From an overall perspective, the topology of brain connections resists well to traumatism by reorganising the most interconnected regions in the network. It therefore seems that comas may be linked to changes in the location of “hubs” among the brain networks” suggests Chantal Delon Martin, an Inserm researcher.

A novel device that makes it possible to draw and write using just eye movements has been developed by a CNRS researcher at the Centre de Recherche de l’Institut du Cerveau et de la Moelle Epinière (CNRS/UPMC/Inserm). Subjects can use it like a pen to write numbers, letters, figures, their signature and even use their eyes to draw using a very simple technique comprising an oculometer[1] and a computer screen. This remarkable feat is based on a visual illusion that enables the eyes to follow smooth and clear trajectories after only several hours of training. This system could improve the living conditions of patients suffering from paralysis of the limbs. This work is published on the 26 July 2012 in the journal Current Biology.

©J Lorenceau, CNRS

Current writing devices using eye movements only allow users to choose from words or letters that are displayed on a screen but do not give them the freedom to draw their own figures. Until now, this was thought to be impossible. In fact, although the eye can follow a moving object very efficiently, it is not capable of performing smooth, regular movements in front of a static background. Any attempt in this sense results in a succession of quite irregular jerks.

To obtain smooth trajectories of the eye, Jean Lorenceau, CNRS researcher at the Centre de Recherche de l’Institut du Cerveau et de la Moelle Epinière (CNRS/UPMC/Inserm) came up with the idea of using a visual illusion called reverse-phi, which has been known since the 1970s but which has not until now found any applications. The illusion occurs when several hundred disks whose luminance[2] varies over time at a frequency of around 10-15 Hertz (Hz) are displayed on a screen. When the user’s eyes move over this flickering background, the subject has the clear impression that the disks move with the displacement of the eyes. Since the human eye is capable of following with precision moving objects, the illusory movement of the disks induced by the movement of the eyes gives them a sort of moving support, allowing them to realize regular and non-jerky trajectories. An oculometer¹ records the movements of the user’s eye and very simple software enables these movements to be visualized on a screen. Two to four training sessions lasting around 30 minutes are all that are needed to be able to manage eye movements and draw letters. In tests carried out, subjects firstly learned to perceive the reverse-phi movement then to “cling” onto this movement somewhat like a surfer who “clings” onto a wave. Then, the subjects progressively learned to “surf” on this visual illusion of movement to guide their eye movements at will. Thanks to this system, well-trained individuals can write with their eyes at more or less the same speed as with their hand. Although the concentration required to draw figures can become tiring in the beginning, training enables automatisms to be created that facilitate writing.

©J Lorenceau/CNRS

This device could give persons suffering from limb paralysis the means to personalize their writing, write their own signature and, more generally, to express themselves and communicate in a more creative and free manner.

While we sleep, our self-awareness and our awareness of the outside world are reduced. Why? Habib Benali, Director of Research at the Inserm functional imaging laboratory (Unit 678 Inserm/UPMC) and his team have been investigating this phenomenon. The research scientists have shown that during nonrapid eye movement sleep, the brain’s activity is re-organized into networks that communicate less with each other than during wakefulness. The results of this study on brain activity have been published in the PNAS review.

Deep slow sleep is a sleep phase in which our self-awareness and our consciousness of the outside world are considerably reduced. Yet the neurons in our brain are still highly active during this phase. So consciousness is not just associated to brain activity, but rather to its ability to process information. This is the conclusion of the study carried out by the research scientists from the functional imaging laboratory (Inserm/Université Pierre et Marie Curie) of Pitié Salpêtrière, and the Cyclotron research center of Liège.

By measuring the quantity of information exchanged between different areas of the brain, the research scientists were able to show that the flow of information in the brain during sleep was different from that observed during wakefulness.

“During sleep, the activity of the brain seems to be organized into a multitude of smaller networks. Inside each network, data exchange is just as active, even more active than during wakefulness, but communication between these networks decreases“, explains Habib Benali, Director of Research at Inserm.

The figure shows that the brain (B) contains different networks (colored circles) that group together several brain areas (small peripheral black dots). The longer the black lines connecting these structures (colored circles and black dots), the more able they are to process information independently. During sleep (situation on the right), the distance between these structures increases, meaning that the information in these small clusters of brain areas is processed on a more local scale.

The research team believes that this is due to a hierarchical reorganization of the flow of information during NREM sleep, since this has been observed repeatedly at several levels in the brain. “We suggest that the modification of the information flows between areas of the brain reduces the brain’s ability to generate a unified representation of the person and the outside World” states Habib Benali.