The study, published in the "Journal of Neuroscience Methods" and "Sensors and Actuators," used a camera 3 mm (0.1 inch) long, 2.3 mm wide and 2.4 mm in depth, said Jun Ohta, professor at Nara Institute of Science and Technology in western Japan.
Working with researchers at Kinki University, Ohta implanted the special semiconductor camera inside the hippocampus of the mouse's brain, designing the devise so that a screen showed blue light whenever the camera captured memory being recorded by the brain.
The researchers injected the mouse with a substance that lights up whenever there is brain activity. The camera then captures that light and the visuals come up on a screen.
The team now plans to use the camera while the mouse is walking.
"We are thinking about how to apply this to humans, though we must be very careful, as it involves implanting something into the brain," Ohta told Reuters. "It would take 10 years at the earliest."
The researchers hope the study will lead to new ways to treat Parkinson's disease, as they aim to have the camera track brain activity that trigger symptoms such as tremors.
(Reporting by Chisa Fujioka; Editing by David Fogarty)