In order to do so, he and others have developed the ‘Animat,’ a computer-simulated artifical animal which is controlled by the distributed activity of neurons cultured on a multi-electrode array (MEA), and allows the study of the dynamics of a living neural network, and the simultaneous monitoring of the electrical activity of the network.
Several thousand neurons can be grown on the MEA, which is attached to a computer or a robot. Electrodes record the extracellular activity of the neurons and therefore do not damage the cells; a culture method devised by Potter and his colleagues enables them to keep cultured cells alive for much longer than conventional culture methods, so that the activity of hundreds of neurons can be monitored over a period of months.
A multi-electrode array (Georgia Institue of Technology).
The MEA, which is manufactured by Multichannel Systems, consists of 60 indium-tin oxide microelectrodes embedded on the surface of a glass culture dish. Each electrode can record the activity from several surrounding neurons, which is sent to a computer and used to control the movements of a virtual animal through a simulated environment. Sensory and kinesthetic information obtained as the artificial mouse moves through its environment is fed back to the cultured neurons, which they then use to “learn” how to better navigate the animal.
“You get an interactive system between a culture of cells placed on a culture dish and the external physical world,” says Daniel Wagenaar, who collaborated with Potter to develop the Animat. “This is a very simple model of what happens in an actual organism.”
In the MEA pictured below, the electrodes (dark circles) are 10 micrometres in diameter and 100 micrometres apart. Dissociated neurons from the rat cortex form connections with each other within hours of being cultured on the array, and spontaneously establish a living neural network within days.
Rat neurons cultured on a multi-electrode array
The connectivity of the cultured neurons is examined using 2-photon time-lapse microscopy. Electrical activity can be measured with a temporal resolution of less than a millisecond using voltage-sensitive dyes and a high-speed camera.
Because the neurons cultured on the MEA form a living network, this method is the closest thing to examining these characteristcs in vivo, for which there are currently no methods.
Potter and his team have so far used the Animat to move a virtual mouse and to control a robotic arm to create artwork. In early experiments, it was noticed that the neurons cultured on an MEA fired synchronously in waves that spanned the whole culture dish, and which resembled the activity seen in conditions such as Alzheimer’s and epilepsy.
Using the Animat, Potter et al hope to gain a better understanding of how information is processed and encoded by the nervous system, during development and in learning and memory formation. Potter hopes that the Animat can eventually be used to control more complex robotic devices, and to aid in the development of advanced neuroprosthetics. It may also be of use to artificial intelligence theorists.