In a recent study described in the journal Neuron, the Emily Macé and collaborators of the Botond Roska team demonstrated how functional ultrasound imaging can produce high-resolution full-motion images of the brain for specific behaviors in mice. This non-invasive technique has broad application prospects in ophthalmology, neurological and psychiatric diseases.
“Functional ultrasound imaging produces higher resolution images, and is simpler, cheaper, and easier to use than functional magnetic resonance imaging (fMRI),” explains Botond Roska. “The most important thing is that this technology allows us to study the consequences of ophthalmic diseases, monitor the effects of treatment and the progress of whole brain rehabilitation in mice.”
During the mouse activity, a large number of brain regions are active. Whole brain activity maps can help us systematically understand the relationship between brain activity and specific behaviors. A team of international scientists from the Basel Institute of Molecular and Clinical Ophthalmology, FMI and Neuroelectronics Research Flanders developed high-resolution functional ultrasound imaging to record the activity throughout the brain during mice behavior.
The team is particularly interested in brain regions involved in visual reflexes. The optokinetic reflection stabilizes the image that drifts on the retina in the horizontal and vertical directions by moving the eye in the direction of image drift. For example, when we look out of the train window, our eyes move reflexively to follow the passing landscape. This reflection is innate and is very conservative in a variety of species, from mice to humans.
In their study, the researchers found that in all of the 181 brain regions identified in all animals, activity in 87 regions of the entire brain was regulated during visual reflexes.
To study the function of these brain regions, the team compared the brain activity of healthy mice with mice lacking visual reflexes—this is because hereditary diseases cause the retina to be unable to produce reflexes or because the eye movement is mechanically blocked. Most of the brain regions that are active in normal mouse eye movements become inactive in mice with the genetic disease, indicating that they are involved in producing reflexes. In these regions, some regions of the thalamus are particularly interesting: they still function in normal mice with impaired eye movement, but not in mice with the genetic disease, indicating that they are independent of the motor output of the reflex.
The first author, Emilie Macé, a postdoctoral researcher at the Botond Roska group, developed the concept of functional ultrasound imaging during his work in Paris, commenting: “We are surprised that we are able to accurately map the activity of the entire brain and how many brain regions are active during this period. Our brain-wide approach reveals new areas that can now be studied more accurately, trying to understand the logic of sensory motion transitions at the microcircuit level.” Botond Roska also highlights the value of future applications of this technology in different medical fields: “The simplicity of whole-brain ultrasound imaging, low cost, ease of use, and the ability to accurately identify brain regions, provides a system for accurate judgment of brain activity in other types of behavioral and animal models of neurological or psychiatric disorders.”
émilie Macé et al. Whole-Brain Functional Ultrasound Imaging Reveals Brain Modules for Visuomotor Integration. Neuron, 2018; 100 (5): 1241 DOI: 10.1016/j.neuron.2018.11.031