In this week’s article, Li et al overcome the main technical challenges associated with long-term two-photon imaging in awake behaving monkeys. The combination of a novel design of cranial optical window and stable genetically encoded indicators enables the authors to successfully image neuronal activity in the visual cortex as a response to visual stimuli across months. To date, some technical challenges have made it difficult to achieve long term stable two photon imaging in awake macaque monkeys, equivalent of what can be achieved in rodents.
Li et al overcome these challenges with i). the development of a new cranial window design combining the use of glass coverslip optical window and an artificial dura membrane insulating the window chamber as well as reinforced head restraints to stabilize the animal skull. ii) cortical tissue movement during experiments was addressed by image registration using 2D cross-correlation algorithm. The authors averaged 1000 frames at the middle of the imaging protocol to then use as a reference for image registration and hence movement correction. Finally iii) the use of stable calcium indicators delivered by AAV injection. These enabled the authors to image the same neurons at 100 days interval in awake behaving animal.
In addition, Li et al performed simultaneous electrophysiology studies under 2 photon imaging done with a Bruker Ultima system, using microelectrodes penetrating through micropores drilled through the glass imaging window.
Macaque monkeys are similar to human beings in many aspects of behavior, brain structure and function, making them good animal models for human neurological diseases as well as for visual cognition and other high order cognitive functions. In this article Li et al overcome the limitation associated with stable long-term study of neuronal activity in awake monkeys that will enable fundamental advances in our understanding of higher cognitive function at the level of molecular and neuronal circuits.