Prosthetic Neuronal Memory Silicon Chips

Prosthetic Neuronal Memory Silicon Chip is a device that imitates the brain’s process of creating long-term memories. This device was designed by Theodore Berger, a Biomedical Engineer and Neurologist at University of Southern California. Berger started to work on this chip in the early 1990s. He and his colleagues have been able to implant electrodes into rats and monkeys that restore their memories after previously being impaired. While researchers are well into developing an actual memory prosthesis in animals, they still need to show that their chips can form long-term memories in many different behavioral situations. Berger hopes to eventually use these chips as electronic implants for humans whose brains that suffer from diseases such as Alzheimer's that disrupt neuronal networks.

Theodore Berger's education, impact as a researcher, and inspiration for the chip

While Berger's aspirations of memory implant sounded unrealistic to his colleagues for a long time, Berger has continued to maintain a high level of determination, and has referred to many other successes in neuroprosthetics that once seemed unattainable. One of these is the use of cochlear implants, which currently help more than 200,000 deaf people hear by converting sound into electrical signals that are then sent to the auditory nerve for processing. In addition, past experiments have indicated that implanted electrodes can allow paralyzed people to control robotic arms using their thoughts. Researches have also had some success with artificial retinas for blind people.

Berger has spent 35 years of his life trying to develop a keen understanding of how neurons behave in the hippocampus.The hippocampus is a major component of the brain that belongs in the limbic system and consolidates information from short-term memory to long-term memory and spatial navigation. Through his research, he has been able to develop mathematical theorems that show how electrical signals move through the neurons of the hippocampus to form a long-term memory. Berger has been contemplating the possibilities of copying some of the brains' functions, modeling the brain and putting it into a device, and getting devices to work in any brain.

Technology and medical application

To begin making a brain prosthesis, Berger and his collaborator Valsilis Marmarelis, a biomedical engineer at USC, worked with the hippocampus slices of rats. Since they knew that neuronal signals travel from one side of the hippocampus to the other, the researchers sent random pulses into the hippocampus, recorded the signals at specific locales to see how they were changed, and then derived equations representing the changes. They then programmed those equations into the computer chips.

Next, they had to determine whether a chip could be used as a prosthesis, or implant, for a damaged region in the hippocampus. To do this, they had to figure out whether they could avoid a central component of the pathway in the brain slices. They put electrodes in the region, which carried electrical pulses to an external chip. The chip then executed the transformations that are normally carried out in the hippocampus, and other electrodes sent the signals back to the slice of brain.

Trials of the chip on rats and monkeys

While Berger and his research partners are yet to conduct tests on humans, their experiments indicate that a silicon chip that is connected to rat and monkey brains via electrodes can analyze information just like actual neurons. This means that it would allow living things with damaged neurons to generate memories. In one demonstration, Berger impaired the rats’ ability to form long-term memories by using pharmacological agents. These disrupted the neural circuitry that transfers messages between two subregions of the hippocampus. These subregions, CA1 and CA3, interact to create long-term memories. The rats were unable to remember which lever they needed to pull to obtain the reward. The researchers then developed an artificial hippocampus that could duplicate the pattern of interaction between CA3-CA1 interactions by analyzing the neural spikes in the cells with an electrode array, and then playing back the same pattern on the same array. After implanting the artificial hippocampi into the rats, their ability to identify the correct lever to pull improved dramatically. This artificial hippocampus played a significant role in the developmental stage of the chip, as it went on to show that if a prosthetic device and its associated electrodes were implanted in the animals with a normally functioning hippocampus, the device could potentially enhance the memory capability of normal rats.[1]

Last year, scientists conducted an experiment on monkeys where they placed electrodes in the monkeys’ brains to obtain the code formed in the prefrontal cortex that they believe allowed animals to remember an image that had been shown to them earlier. They then drugged the monkeys with cocaine, which impairs that part of the brain. The researchers were able to improve the monkey’s performance by using the implanted electrodes to send the correct code to the monkeys’ prefrontal cortex.

Goals for the future

Berger and his colleagues are working to possibly make this chip applicable to humans in the future. For people whose brains suffer damage from Alzheimer's, stroke, or injury, the disruption of neural networks often stops long-term memories from forming. This chip that Berger has designed allows the signal processing to take place that would occur naturally in undamaged neurons. Ultimately, Berger hopes to restore the ability to create long-term memories by implanting chips such as these into the brain.[2]

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