News | Radiology Imaging | July 22, 2015

Intrinsic Optical Signals Allow Greater Assessment of Brain Function

Study finds the detection of aqueous influxes in neurons allows a better deciphering of cerebral functioning

fMRI, IOS, intrinsic optical signals, cerebral function, UNIGE, Cell Reports

July 22, 2015 - To observe the brain in action, scientists and physicians use imaging techniques such as functional magnetic resonance imaging (fMRI) to observe physiological modifications to the cerebral region of activated neurons. Until now, it was believed that these differences were only due to modifications of the blood influx towards the cells. By using intrinsic optical signals (IOS) imaging, researchers from the University of Geneva (UNIGE), Switzerland, demonstrated that, contrary to what was thought, another physiological variation is involved: the activated neurons swell due to the massive entry of water. This discovery provides evidence that a much finer analysis of the functioning of the brain - and of its dysfunctions - is possible. These results are published in the journal Cell Reports.

Mainly two types of brain imaging techniques are used to determine which cerebral areas are stimulated during a given activity. One of them is fMRI, which reflects the change of oxygen level and variations of the blood flow in the excited regions. The localization of these areas is based on a phenomenon termed "BOLD" (Blood Oxygen Level Dependant), related to the magnetic properties of hemoglobin, which vary according to its state of oxygenation.

The other technique, IOS imaging, detects modifications of light refraction on cerebral cells in action, by recording a lesser luminous intensity in the activated zones. This method is used as an alternative to fMRI, in particular when a magnetic field may disrupt the examination. Until now, scientists thought that this modification of light behavior was also due to hemodynamic changes.

Alan Carleton, professor at the Department of Fundamental Neurosciences of the Faculty of Medicine of UNIGE, uses IOS imaging to observe the functioning of the olfactory bulb. "We obtain highly contrasted images in answer to an odor, because thousands of nose sensory cells expressing the same olfactory receptor converge on a very small volume in the brain. We were however surprised to observe that, if the signals are visible immediately after emission of the sensory stimulus, the flow of blood is altered only more than one second later," explained the scientist. The temporal gap is important enough to confirm that, contrary to a well-established consensus, the detected signal has no hemodynamic origin.

What is the cellular origin of the signals? In collaboration with the team of Ivan Rodriguez, professor at the Department of Genetics and Evolution of the Faculty of Science of UNIGE, the electric activity of the various cells involved in response to odors was studied. This was done with mice genetically modified so that each type of cell of the olfactory bulb becomes fluorescent when stimulated. "We did not find any signal related to a change in hemoglobin oxygenation. However, we observed a signal emitted by the sensory neurons themselves, in response to their own electric activity," said the researcher.

What does this signal reflect? The researchers discovered that it is in fact caused by the entry of water into the activated neuron, at the level of its axon, the "cable" through which the electric impulse propagates towards another cell. Besides, they demonstrated that the imaging signal - the flow of water into the axons - is directly coupled with the electric activity. "We observe a mechanical and immediate effect of neuron activation, rather than a modification of the blood flow afterwards," noted Carleton. "Thus, we avoid the uncertainties of interpretation of the signals related to the blood flows, which, being delayed and acting more globally on the cerebral region studied, do not exactly reflect the activated area. "

Water movements observed thanks to IOS imaging can be also detected by fMRI. The Genevese scientists provide henceforth the proof of the cellular mechanism at work, thus demonstrating the potential of this method. "Both types of imaging technique converge: observing the movements of water, rather than examining the oxygenation of blood, improves the localization of active neurons and allows to detect potential pathologies. The problem does not lie in the fact of observing a signal, but of determining its origin, to be able to interpret what we see," concluded Rodriguez.

For more information: www.unige.ch

Related Content

Researchers Awarded 2018 Canon Medical Systems USA/RSNA Research Grants
News | Radiology Imaging | November 13, 2018
The Radiological Society of North America (RSNA) Research & Education (R&E) Foundation recently announced the...
Subtle Medical Showcases Artificial Intelligence for PET, MRI Scans at RSNA 2018
News | Artificial Intelligence | November 13, 2018
At the 2018 Radiological Society of North America annual meeting (RSNA 2018), Nov. 25-30 in Chicago, Subtle Medical...
News | Advanced Visualization | November 13, 2018
Canon Medical Systems USA and Applied Radiology will host a pair of expert-led forums in high-resolution imaging and...
Charles Ananian, M.D.

Charles Ananian, M.D.

Sponsored Content | Case Study | Digital Radiography (DR) | November 07, 2018
Whether it’s a premature baby or a critically ill child, treating little patients is a huge responsibility.
This is the Siemens Magnetom Sola RT edition 1.5T MRI system optimized for radiation therapy displayed for the first time since gaining FDA clearance in 2018. It was displayed at the American Society for Radiotherapy and Oncology (ASTRO) 2018 annual meeting. Read more about this system at ASTRO 2018. #ASTRO18 #ASTRO2018
360 Photos | 360 View Photos | November 07, 2018
This is the Siemens Magnetom Sola RT edition 1.5T MRI system optimized for...
Proton Therapy for Pediatric Brain Tumors Has Favorable Cognitive Outcomes
News | Proton Therapy | November 06, 2018
Proton therapy treatment for pediatric brain tumor patients is associated with better neurocognitive outcomes compared...
Results of the vertebrae-based analysis (383 vertebrae in 34 patients) for detection of BME.

Results of the vertebrae-based analysis (383 vertebrae in 34 patients) for detection of BME.

Sponsored Content | Case Study | Computed Tomography (CT) | November 06, 2018
The following is a summary of a study published in the
Deaconess Health System Chooses Sectra as Enterprise Imaging Vendor
News | Enterprise Imaging | November 02, 2018
International medical imaging information technology (IT) and cybersecurity company Sectra will install its enterprise...