Application of neurosonography to experimental physiology

When Horsley and Clark invented the stereotaxic technique they revolutionized experimental neurobiology. For the first time it became possible to repeatably place experimental or surgical probes at precise locations within the skull. Unfortunately, variations in the position and size of neuroanatomical structures within the cranium have always limited the efficiency of this technology. Recent advances in diagnostic medical ultrasonography, however, allow for the real-time visualization of anatomical structures, in some cases with resolutions of up to 150 μm. We report here that commercially available ultrasonographs can be used in the laboratory to generate real-time in vivo images of brain structures in both anesthetized and awake-behaving animals. We found that ultrasonic imaging is compatible with many types of experimental probes including single neuron recording electrodes, microinjection pipettes, and electrodes for producing electrolytic lesions. Ultrasonic imaging can be used to place, monitor and visualize these probes in vivo. In our hands, commercially available ultrasonic probes designed for pediatric use allowed us to visualize anatomical structures with sub-millimeter resolution in primate brains. Finally, ultrasonic imaging allowed us to reduce the risk of accidentally damaging major blood vessels, greatly reducing the incidence of stroke as an unintended complication of an experimental neurosurgical procedure. Diagnostic ultrasound holds the promise of reducing the uncertainty associated with stereotaxic surgery, an improvement which would significantly improve the efficiency of many neurobiological investigations, reducing the number of animal subjects employed in this research. While this demonstration focuses on sonographic imaging in non-human primates, similar advances should also be possible for studies in other species, including rodents.