Main Paper: Chamberlain S, Naomi F, Andrew B, Trevor R, Barbara S (2006) Motor Inhibition and Cognitive Flexibility in Obsessive-Compulsive Disorder and Trichotillomania, American Journal of Psychiatry, 163, 1282-1284.
Summary: Obsessive-compulsive disorder has a spectrum of related disorders, each accompanied with their own obsessions and compulsions. Most notable from these are trichotillomania, excoriation (skin-picking disorder), and body dysmorphia. OCD and trichotillomania share concerns with the person's inability to regulate their motor functions. With trichotillomania, this is seen mostly in automatic hair pulling, which is when the person is pulling their hair out without realizing they're doing it; the inability to stop pulling once it has started is also indicated by TTM's association with motor functioning issues. In the DSM-IV, OCD is described with recurring thoughts and actions that carry out those thoughts, usually kept to a strict routine. Theories have been formed about attempting to stop those behaviors with a change of attention--if the person can't focus on their thoughts because they're thinking about or doing other things, then they can't carry out those thoughts through actions, either. The Stop-Signal Task was used in this study: it is supposed to measure how long it takes to mentally block the desire to carry out motor actions. The Stop-Signal Task is a test on the computer in which patients view left/right arrows and hit the corresponding keyboard button, and are supposed to hit no button when an audio prompt is played.
It was found that participants with TTM took the longest time to respond to the "stop" audio prompt, as opposed to the OCD and control groups. The OCD group took the second longest time to respond, and the controls responded the fastest, by not pressing any button. These results imply that trichotillomania is a difficult motor function to attempt to suppress, and people with the disorder struggle to do so.
Main Author: Samuel Chamberlain
Where is the author in life?: His website is definitely old & could use some renovation, but as far as it shows, he's teaching and researching at the University of Southampton in England. He is the Professor of Psychiatry at that University. He researches compulsive/obsessive/behaviorally addictive disorders (TTM, ADHD, OCD, gambling disorder, skin-picking disorder, all in adults) and how they coexist with each other and with the general public.
What is the author's overall research goal?: He wants to ensure that current research practices are valid & work well; examine brain circuits & cognitive problems associated with his research topics. Also to check out existing treatments, as well as potentially develop new ones.
Second Paper: Chamberlain S, Lara M, Naomi F, Natalia C, John S, Kevin C, Ulrich M, Trevor R, Edward B, Barbara S (2018) Gray matter abnormalities in trichotillomania: morphometric magnetic resonance imaging study, The British Journal of Psychiatry, 193, 3, 216-221.
Relation to First Paper: Zooming into whole-brain analysis for trichotillomania, to establish broad differences in the brains of people with and without TTM.
Summary: TTM has some overlap with OCD & Tourette's. Most obsessive-compusive-spectrum disorders have had whole brain studies, leading to conclusions about brain areas associated with the issue; disorders falling on that spectrum are most commonly liked to larger sections of the brain, such as disruption within a circuit, rather than a specific brain piece. So, since trichotillomania doesn't have any whole brain studies, there is a huge lack of knowledge about the disorder. This study is to look into brain matter differences between white and gray matter in people with trichotillomania, compared to people without.
18 (originally 20 but two people's brain scans were extraordinarily abnormal so the participants were asked to leave) unmedicated people with TTM vs. 19 without--validated by the DSM-IV diagnosis for TTM.
MRI scan.
Gray matter density increases were found in three regions in participants with tricho-"a mean density increase of 18% in the striatum (left putamen) and limbic system (left amygdalo-hippocampal cortex), increase of 23% in bilateral frontal regions (cingulate, supplemental motor, and superior cortices), and a mean density increase of 21% in left occipital and left parietal areas". Nothing significant regarding white matter was found.
Discussion
Unmedicated patients with trichotillomania had abnormally higher density of gray matter in the brain than the control group. These were found in the left amygdalo-hippocampal complex, and other cortical areas. An increase in gray matter has also been found in obsessive-compulsive disorder and Tourette syndrome, but not very consistently. This common neurological ground, though not entirely reliable, gives a link between TTM and OCD that was previously not backed by any neuroanatomical research.
Other studies have shown a decrease in gray matter tissue throughout adolesence, which is also TTM's peak prevalence. This lead researchers to think that maybe the increase in gray matter density in the trichotillomania patients may reflect some sort of developmental impediment. Alternatively, the increase in gray matter may have been the result of utilizing areas of the brain involved with learning habits and grooming. Other research has shown that learning and training motor skills may increase gray matter concentration in the cerebrum.
Research has shown that the striatum plays a part in habit learning and chunking information. Previous research with damaging the striatum in rats altered their hygine habits, similar to hair pulling in humans. This striatal damage is another link between TTM and OCD.
The researchers did not anticipate gray matter abnormalities regarding the amygdalo-hippocampal region, but it makes sense that that area would be abnormal in people with TTM. Emotional regulation, the amygdala's forte, is a huge factor in hair pulling--sometimes people with TTM pull because they're nervous or anxious, and pulling their hair alleviates some of that stress.
Third Paper: Grant J, Darin D, Samuel C (2020) Prevalence, gender correlates, and co-morbidity of trichotillomania, Psychiatry Research, 288.
Relation to First Paper: Zooming out to more general prevalence of trichotillomania in different areas of the population.
Summary: Over 10,000 people were given surveys in this study. They found a 2.5% lifetime prevalence of TTM in males, and 2.4% lifetime prevalence in women--tricho has no gender or ethnic preference. Trichotillomania was more present and notable in people under 50 years old. Tricho was found to be comorbid with other disorders such as anxiety, depression, OCD, skin-picking disorder, PTSD, and more. People rated TTM as more annoying than their other disorders about 30% of the time, which is interesting since it's more common and life-disturbing than people think, for a disorder with no treatment. Almost 80% of the people in this study had more than one disorder, including trichotillomania.