Hidden differences in the brains of Asperger’s individuals revealed?

Important Note: Please take a look at the update at the bottom of my “About” page. In short, I’ve decided to narrow my focus a bit to what I know best – nutrition and neuroscience. BUT I plan to have monthly treats that will cover a topic outside of these areas. Let me know what you think! On to your regularly scheduled programming…

Albert Einstein is believed to have had Asperger’s syndrome.
Image source: Wikipedia 

Asperger’s syndrome is one disorder falling under the umbrella of the autism spectrum, in which the affected individual may show obsessive attention to detail, social awkwardness, and difficulty relating to others. Repetitive behaviors and highly focused, restricted interests (ex. obsession with trains, horses, etc) are also present. Unlike other autism spectrum disorders, cognitive development is not usually affected nor are early basic language skills. Higher order language abilities (ie. understanding inferences, nuance, and ambiguity), however, may be affected as the individual ages, and these deficits may be associated with the more classic deficits seen, such as social awkwardness.

Asperger’s individuals show anatomical abnormalities in a small region in the frontal lobe of the brain called Broca’s area. This region was named for Pierre Paul Broca, who discovered that impairments in language production – now called Broca’s aphasia – was associated with this region. Broca’s area is responsible for basic “lower-order” language skills, ie. speech production, which, again is not affected in Asperger’s individuals, yet anatomical abnormalities persist. Confused yet? Keep reading…

Researchers at Beth Israel Deaconess Medical Center in Boston, MA set out to uncover hidden functional deficits that may be associated with Broca’s area in Asperger’s individuals. They examined naming ability (a basic language skill which consists of verbally identifying a picture on a card), in which Asperger’s individuals (referred to as ASP from here on) and neurotypical individuals (meaning people in which neurological development, especially in terms of processing language and social cues, is considered “normal”; herein referred to as N) perform equally well, and then kind of ‘messed with’ Broca’s area using magnetic stimulation to see if naming ability was then different between the two groups.

Ok, I should clarify the “messed with” part. Subjects underwent a number of “repetitive transcranial magnetic stimulations” (or rTMS). RTMS involves producing weak electric currents in the brain by use of a magnetic field, causing activity (or suppressing activity in this case) in a targeted brain area, thereby allowing the function and connections within and around that region to be studied. “Repetitive transcranial magnetic stimulations”?…you are probably envisioning something akin to the “shock shop” in One Flew Over the Cuckoos Nest. But not to worry. Basically, a “stimulator unit” is simply placed on the subject’s head (see image below), the position of which is guided by a fancy imaging technique (MRI – magnetic resonance imaging), to ensure the correct part of the brain is being stimulated.

Image source: http://thertmscenter.com

The electrical stimulation itself does not cause any damage or pain. Some side effects reported by subjects in this study were sleepiness, dizziness, trouble concentrating, stiff neck, and increased emotionality (that’s a real word, I checked); however, several of these were also reported in individuals undergoing sham stimulation, where the magnet is blocked, suggesting these effects may not be real. Broca’s area, as shown below, is divided into 2 regions called the pars triangularis (which occupies the anterior portion of Broca’s area) and the pars opercularis (which occupies the posterior portion of Broca’s area), and both of these were stimulated, on both left and right sides of the brain.

(Side note: Wernicke’s area is also shown in this figure. It, along with Broca’s area, make up the two main language centers of the cerebral cortex. Damage to Wernicke’s area causes Wernicke’s aphasia in which the speech produced is normal (unlike Broca’s aphasia) in terms of grammar, syntax, rate, intonation and stress, but the words themselves are incorrect and may even consist of “made-up” words.)

Image source: Wikipedia

After these treatments, patients were again tested on the naming task, and HERE is where the interesting part happens. The time it took for the ASP subjects to come up with the answer was affected, while N subjects showed no change. When the left pars triangularis was stimulated, ASP patients performed better, ie. were faster at the naming task, whereas performance decreased when the left pars opercularis was stimulated. While this study did not determine what this difference is due to, the authors speculate that perhaps in the normal ASP brain (ie. no stimulation), the pars triangularis has kind of a choke-hold on the pars opercularis, inhibiting its activity (this is not seen in individuals without ASP syndrome). BUT, the electrical stimulation actually causes a suppression of activity in the brain region it is targeting (I know, its called “stimulation” but actually decreases activity…that’s science for ya). So when the pars triangularis is stimulated, it actually causes a suppression of activity in this region, causing it to release its choke-hold, allowing the pars opercularis to become active. This would also explain why naming ability is decreased when the opercularis is stimulated (since the stimulation is actually causing a suppression of activity). Further testing is needed to confirm this proposed mechanism.

Ok, all well and good, but of course there are weaknesses to the study (all acknowledged by the authors I should mention). 1) Limitations of both the stimulation and the imaging devices cast some doubt on whether the intended target areas were indeed specifically stimulated. Hmm, this seems like a big weakness, but I guess the researchers are limited here by the capabilities of their equipment. More sensitive imaging techniques would help to get around this issue. 2) Potential changes in brain activity caused by the rTMS were not measured, therefore the suppressive effect of rTMS may not have been identical between N and ASP individuals. 3) The two groups had significantly different average IQs (N=111.2, while ASP =122.4). While I’m not sure how this would specifically interfere with the findings (my own ignorance), it is possible different results would be found in IQ matched groups. 4) As with many human studies, the sample size was small (10 in each group, although groups were gender and age-matched) and therefore generalizing these findings to the general population is not warranted.

These limitations are definitely important to keep in mind, as results could actually be due to differences in stimulation target accuracy, rTMS-induced brain activity, and/or IQ differences between the two groups. Even so, the results are potentially interesting and further work needs to be done to a) determine whether these findings are actually true, and b) what these findings mean and the mechanisms behind them.

So let’s say for a moment that these findings are indeed, real. The ability to name objects develops early in life and is considered an indicator of future reading ability. Since stimulation to the left pars triangularis seemed to improve naming ability in ASP subjects, one could suggest that this could lead to improved communication skills and possibly social interactions, which are impaired in ASP individuals. This type of stimulation protocol has been used in stroke patients suffering from Broca’s aphasia. Stimulation lead to sustained enhanced language skills that actually improved even further over time, suggesting a permanent benefit. This study is also important in that it highlights the use of the stimulation technique (rTMS) itself for uncovering functional differences in neurotypical brains as well as those affected by disorders.

(Reference: Fecteau S et al. European Journal of Neuroscience, vol 34, p158-164, 2011)

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