In the movie Avatar, humans operate the bodies of a human-hybrid species, called Na'vi, with their minds. Now, researchers from Harvard Medical School in Boston, MA, have carried out a similar technique in monkeys - using neural devices that allowed an alert monkey to control the mind of one that was temporarily paralyzed.
The research team, including Ziv Williams of the Department of Neurosurgery at Harvard Medical School, says the findings provide proof of concept that such strategies could be used in the rehabilitation of patients who are paralyzed.
The research was recently published in the journal Nature Communications.
According to the investigators, previous research has demonstrated that neurons in many parts of the brain are able to control external devices, such as a cursor on a computer screen. This direct communication is known as brain-machine interface (BMI).
The researchers say recent studies have even shown that using BMIs could potentially control robotic limbs.
In 2012, Medical News Today reported on a study detailing how a paralyzed woman was able to control a robotic prosthetic hand with her thoughts.
But the research team notes that although findings such as these are an important step forward in motor control, another important goal has been to determine how a paralyzed individual may be able to control the movement of their own limbs.
However, the study authors say there have been problems reaching this goal.
"Unlike the control of external devices, a distinct problem in attaining limb movement control is that the output of the motor system - for example, the corticospinal tract and its associated afferents - is generally not explicitly known," they explain.
"The exact combination of successive agonistic and antagonistic muscle contractions naturally used to produce limb movement to different targets in space is difﬁcult to explicitly ascertain or reproduce."
But the researchers say they aimed to address these problems by focusing on the specific movement targets themselves, rather than intervening in movement trajectory.
Avatar monkey controlled through pre-recorded neural activity
For the study, the research team used two Rhesus macaque monkeys aged between 6 and 8 years old.
One monkey was sedated and used as the "avatar," while the other was used as the "master" monkey. Both monkeys took turns being either the avatar or the master throughout various sessions.
The new study details how a "master" monkey was able to control the limb movements of a sedated "avatar" monkey using pre-recorded neural activity.
The researchers implanted a chip into the brain of the master monkey that monitored the activity of up to 100 neurons.
The avatar monkey had up to 36 electrodes implanted into its spinal cord. Tests were conducted to determine how various electrode combinations impacted the monkey's movement.
The physical movements of the master monkey were paired with the patterns of electrical activity that took place in the neurons.
Both monkeys were then connected to each other, with the master monkey sending movement signals to the spinal cord and muscles of the avatar monkey.
"The monkey functioning as the master was responsible for controlling movement based on cortically recorded neural activities, and the other sedated monkey functioned as the avatar and was responsible for generating movement based on distal spinal cord and/or muscle stimulations," the researchers explain.
The avatar monkey held a joystick, while the master monkey thought about directing a cursor presented on a screen.
"If the [master] monkey was thinking of moving their arm upwards, the spinal cord [of the avatar] would be stimulated to elicit limb movement to that same upward location," Williams explained to Medical News Today.
After conducting a series of experiments, the researchers found that the master monkey was able to accurately control the arm movement of the avatar monkey in 80-90% of tests.
Commenting on the findings, the research say:
"We demonstrate that both the decoded activities of premotor populations and their adaptive responses can be used, after brief training, to effectively direct an avatar's limb to distinct targets variably displayed on a screen."
Potential treatment for paralysis
According to the Christopher and Dana Reeve Foundation, there are approximately 6 million people in the US living with paralysis - the equivalent to 1 in 50 people.
The investigators conclude that they hope their findings will lead to approaches that enable faster recovery and restoration of limb movement in patients with paralysis.
Williams told Medical News Today:
"In the future, it may be possible to implant a microchip in one's brain and another microchip in the spinal cord below the site of injury, and then connect them using a mini-computer in order to create a functional brain-to-spine bypass that can reanimate one's own paralyzed limb."
He told us that the research team plans to create a similar neural process to what was used in this study, but one that will be able to "make movements at much finer resolution and in 3D space."
"Ultimately, our hope is to begin translating some of this work into clinical use," he added.
Medical News Today recently reported on a study detailing the first sensory-enhanced artificial hand that has enabled an amputee to "feel."