A sensory cortex implant restored touch sensation in people with spinal cord injuries for ten years

A sensory cortex implant restored touch sensation in people with spinal cord injuries for ten years

Five participants received microelectrode arrays, which are sets of thin electrodes, in the part of the sensory cortex associated with the hand. The study published in Science Translational Medicine on 15 July collected data over implantation periods ranging from two to ten years, covering more than 168 million electrical pulses and a combined 27 years of device operation.

To pick up a glass, a person cannot simply send the hand a command to close the fingers. The brain continuously receives feedback from the hand: whether the fingers have touched a surface, how much pressure they are applying, and whether the object is slipping. A severe spinal cord injury disrupts this feedback. A person may be able to control a robotic arm through a brain interface while still being unable to feel when it touches an object.

Intracortical microstimulation delivers brief electrical pulses directly to the sensory cortex, the part of the brain that contains a map of the body. Different points on this map correspond to different parts of the hand. When a microelectrode stimulates the relevant point, the person feels touch in the corresponding finger or area of the palm. A sensor on a robotic arm can be connected to this electrode, converting contact with an object into artificial touch.

Artificial touch has already improved performance in a task involving a robotic arm. In a 2021 study, a participant with tetraplegia completed the task in an average of 20,9 seconds using vision alone and in 10,2 seconds when artificial touch was added to visual feedback. A neuroprosthesis intended for everyday use requires the electrodes, brain tissue, and resulting sensations to remain functional for years.

In the new study, the group led by Charles Greenspon, Robert Gaunt, and Jennifer Collinger followed this sensory channel for up to ten years. Each of the five participants received two electrode arrays in the sensory cortex. During this period, the researchers delivered more than 168 million pulses. They found no serious complications associated with the stimulation and no evidence that the pulses themselves impaired electrode function.

The sensations continued to occur in the hand and remained localized. In one participant, 60% of the electrodes still worked reliably after ten years. The group average was 64%, with a 13% range among participants. Producing a sensation required a current that increased slowly over time, by approximately 3,5 microamperes per year. In rare cases, sensations persisted briefly after the pulse ended, but they did not require treatment.

Two days ago, bioengineer Takashi Kozai identified the preservation of living tissue around an electrode as a requirement for a brain interface that can function for decades. In this study, some electrodes gradually lost sensitivity. A sensor on the hand must continue transmitting a signal to the same point on the cortical hand map for years, while the system must preserve the sensation of contact as individual electrodes stop working.