We can understand the actions of others because of mirror neurons — cells that are located in the movement and memory sections of our brains and which help us interpret the actions of others, scientists have long suspected. Now they have evidence.
Mirroring is believed to be the way in which the brain automatically interprets the actions, intentions and emotions of other people. Mirror neurons, the cells in the brain that activate when we perform a particular action or watch someone else perform that same action, were up until recently only a theory. Scientists knew that they existed deep in our minds and were responsible for making us empathize with others, but had no hard proof to show for it – until now.
While such neurons have only been directly measured in monkeys, scientists have previously conducted experiments using encephalograph (EEG) machines that led them to believe mirror neurons exist in human adults and infants. The latest research, using fine electrical conductors called depth electrodes, has resulted in the first ever direct recording of mirror neurons in the human brain.
"The study suggests that the distribution of these unique cells linking the activity of the self with that of others is wider than previously believed," said Dr. Itzhak Fried, the study's senior author and director of the UCLA Epilepsy Surgery Program.
Previously unexplored regions
Researchers studied the brains of 21 patients who were currently undergoing treatment for intractable epilepsy at the Ronald Reagan UCLA Medical Center. Because the patients had already been implanted with depth electrodes to identify seizure points for potential surgical treatment, researchers were able to conduct their experiments using the existing electrodes.
In this way, Fried and his colleagues garnered and recorded the neuron activity results directly from the patients' brains. The researchers noted single cell and multiple-cell activity in the motor regions of the brain where mirror neurons were thought to exist, as well as in regions involved in vision and in memory.
Brain activity was measured as the patients both observed and performed grasping actions and facial expressions. The patients first observed various actions presented on a laptop computer. Then they were asked to perform an action based on a word they were shown. In the control task, the same words were presented, but the patients were instructed not to execute the action.
The experiments showed that of the combined 1,177 neurons studied in the 21 patients, the neurons were most active when the individuals performed or observed a task. The results also revealed that certain areas of mirror cells increased their activity during the execution of an action, but decreased their activity when an action was only being observed.
"We hypothesize that the decreased activity from the cells when observing an action may be to inhibit the observer from automatically performing that same action," said Roy Mukamel, the study's lead author. "Furthermore, this subset of mirror neurons may help us distinguish the actions of other people from our own actions."
The active mirror neurons that responded to the tasks were located in the medial frontal cortex and medial temporal cortex neural systems. Mirroring responses on a singular-cell level have never been previously recorded in these two areas of the brain.
The autism link
Fried's study results show that mirror neurons are located in more regions of the human brain than previously believed. That researchers found mirror neurons firing in the medial frontal cortex for movement selection and in the medial temporal cortex for memory implicates that the brain activity involved in making us process and mirror the actions of others is quite complex.
The findings could also help scientists understand developmental disorders, such as autism, since mirroring is likely responsible for helping the brain recognize and comprehend the actions, intentions and emotions of other people. Now that scientists know what areas of the brain are involved in the deciphering of this information, they will be better equipped in developing treatment plans and therapies.
"There is evidence that patients with autism have deficits in these regions of the brain," Mukamel told LiveScienc.com. "Once we know the exact functions of the neuron, we can work on developing a diagnosis."