One of the hottest areas of brain research today is that in the field of mirror neurons. Neuroscientist Marco Iacoboni has written a book on that subject entitled "Mirroring People". Your humble blogger has just finished this book. Mirror neurons are neurons that fire not only when a person is doing a motor action but also when the motor action is being viewed or a sound associated with the motor action is being heard. One of the most interesting things about mirror neurons (at least to your humble blogger) is that there is strong evidence that they are involved in the etiology of autism.
Mirror neurons were discovered by accident in a laboratory in Italy. Neuroscientists were doing research on neuron firing in the motor cortex and premotor cortex area of macaque monkeys, particularly in the area called F5 in the frontal lobe. When one of the researchers was eating something or picking something up to grasp it, the neuron fired. The neurons also fired on hearing the sound of an action. Intrigued, the researchers ruled out all of the possibilities other than the neuron was firing upon viewing the action or hearing the sound. Therefore, it seemed that these neurons had to do with imitation of an action or learning an action.
For obvious reasons, the experiments involving the implanting of electrodes in single neurons that had been done on the monkeys could not be done on human beings (at least not ethically). However, using functional magnetic resonance imaging, which measures the level of blood flow to certain areas of the brain, experiments can be done on human subjects to see if certain areas of the brain are activated when doing a given task or viewing a picture or face. It was shown that both during movements and viewing of pictures of the movement the areas of the human brain that were analogous to those of the monkeys in the experiments were active. This suggested that human beings have mirror neurons as well.
The area F5 on the macaque monkey motor cortex is equivalent to Broca's area in the human brain. Broca's area is the center that is responsible for expressive speech. The ability to imitate it would seem comes from mirror neurons. As most interested in autism know, one of the cardinal symptoms of autism is a speech delay before age three. There are studies going back to the 1950's showing that autistics have deficits in imitation. Research was also done showing that mirror neurons played a factor in the emotion of empathy as well as the ability to make friends. In experiments done in which children were asked to imitate facial expressions, the part of the brain near broca's area was measured by blood oxygen uptake using fMRI. It was found that there was a correlation between activity in these brain levels and the number of friends and playdates these children had (Pfeifer, et. al. 2008) .
For these reasons it was speculated that mirror neurons might play a role in the etiology of autism. At about this time Vilayanur Ramachandran and Lindsay Oberman at the University of California at San Diego were doing research on what is called mu wave suppression in autistic children. Mu waves are a form of brain waves, which are electrical impulses which eminate from the brain that are reflective of activity (or inactivity) in various parts of the brain. Mu waves are suppressed in typical people both when they move parts of their own body and observe movement of those same body parts in other people, analogous to the mirror neuron firing in the monkeys that I discussed previously. The research of Ramachandran and Oberman found that when autistics moved their own body parts, their mu waves were suppressed. However, upon observing the motions of other people or a hand on a video, the autistics had no mu wave suppression. One of the limitations of this work was that all 9 of the autistic subjects were high functioning males. They acknowleged the limitations in their paper, emphasizing they were not sure whether or not these findings could be generalized to lower functioning autistics and female autistics. However, this is a problem that often occurs in autism research. Compliance is needed by the subjects in order to study brain waves or brain activity measured by an fMRI. The lower functioning autistics would not be compliant and would move around and this would cause artifacts in the measurements, making the findings worthless. Though autistic males outnumber autistic females by about 4 to 1, the ratio may be as high as 10:1 in the higher functioning groups. Ergo, in many research studies we see a biased sample of research subjects as opposed to the entire population of autistics.
Mirella Dapretto (who happens to be Dr. Iacoboni's wife) has also done a study comparing activity of subjects with high functioning autism in an area of the brain called the pars opercularis (which is a part of broca's area) in which mirror neurons exist to normal controls matched for approximate age and sex (again all of the autistic subjects were high functioning males). She found significantly greater activity in this area for the autistics. Additionally she found negative correlations between the activity levels and the severity of the autism as measured by the ADOS diagnostic scale.
One of the findings on autopsies of autistic brains has been abnormalities of the limbic system which controls emotion in which exist the hippocampus and amygdala. I seem to remember autopsies have shown differences in the amygdalas of autistics as opposed to normal controls. An area of the brain called the insula connects the pars opercularis (and maybe the rest of Broca's area also) to the limbic system. A variety of researchers besides these have also done experiments showing of a mirror neuron dysfunction in autistics. So there is strong evidence suggesting that there is a dysfunction in the pathways between the pars opercularis and limbic system connected by the insula.
There is also a mirror neuron system in the parietal lobe of the brain as well as the frontal lobe. Riitta Hari has done research using a technology magnoelectroencephalogram which picks up tiny magnetic activity in various brain areas with Asperger's subjects. She asked them to imitate simple movements of the mouth and face while using this technology and measured the activity. Her research demonstrated abnormally slow communication between the mirror neurons in the frontal lobes and mirror neurons in the parietal lobes of these subjects. It was speculated that this faulty wiring might be responsible for the social deficits of people with Asperger's.
There are also gender differences in mu wave rhythms of the mirror neuron system I have to admit I have not actually read this study but I have linked to the abstract. If anyone is interested I guess they can pursue the matter further. I believe this may be relevant in light of the high male to female ratio found in autistics.
Anne Corwin, another of the infamous neurodiversity rogues and author of the existence is wonderful blog gives her take on mirror neurons. She trots out the traditional "different not broken" neurodiversity homily in her essay. The interested reader can read the link.
I am not sure what to make of this research. Prior to this research a lot of the emphasis in autistic neuroanatomy was on the cerebellum and the limbic system. The insula connecting the the pars opercularis and the limbic system could give an explaination for the limbic system involvement in autism. However, what of the cerebellar abnormalities that have been found in autistics in various studies, albeit with mixed results. What role do the mirror neurons located in the frontal and parietal lobes play? Also, why don't people with Broca's aphasia from CVAs exhibit the same behavioral characteristics as autistics since part of their mirror neuron system has been damaged also. As I have mentioned in previous blog posts, Eric Courchesne (and Matthew Belmonte also) have told me that developmental lesions are different than adult lesions. When I speculated to Courchesne that because of the speech motor output problems of autistics perhaps autism could be either a problem in Broca's area or the connections between Broca's and Wernicke's area (Wernicke's area in the temporal lobe is responsible for the reception of language as opposed to the expresison of language of Broca's), he replied that because of the differences in developmental and adult lesions this might not be a fruitful area of research. The recent findings of evidence of a dysfunction in the mirror neuron system of autistics would not seem to bear out Courchesne's contention.
If anyone with more expertise in neuroscience than I have happens to read this, I would certain welcome comments and speculations from them. I know that irrational hope makes me think that mirror neurons may be the holy grail of autism work rather than yet another seeming dead end street. I just wish that mirror neuron research could lead to more effective treatments or even possibly the cure that neurodiversitites such as Anne Corwin detest so much.