The study, published in the Journal Of Neuroscience Methods and Sensors And Actuators, used a camera 3mm long, 2.3mm wide and 2.4mm in depth, said Professor Jun Ohta at Nara Institute of Science and Technology in western Japan.

Working with researchers at Kinki University, Prof Ohta implanted the special semiconductor camera inside the hippocampus of the mouse's brain, designing the device so that a screen showed blue light whenever the camera captured memory being recorded by the brain.

The researchers also 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,' Prof Ohta said.

'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 triggers symptoms such as tremors.

Parkinson's disease is a disorder that affects nerve cells, or neurons, in a part of the brain that controls muscle movement.

REUTERS