We’ve wondered if psychopathy was some kind of myelin problem.
Given the role that disconnected white matter plays in the lack of a moral center (we surmise, see many, many posts in this blog), we’ve wondered if defective or missing myelin had something to do with it. The textbooks tell us that myelin uniformly covers axons, so spotty myelin would be problematic, no? It does speed up the communication between neurons, no?
So it was with interest that we noted a recent study that the brain cells involved in higher order thought are not uniformly myelinated (as was the conventional thinking). According to a paper published in Science on April 18, the normal and usual state of things is that, along axons in the pyramidal cells in the neocortex, myelin is spotty, here and there, with long stretches of unmylelinated axon. (Harvard press release here).
Giulio Srubek Tomassy, Daniel R. Berger, Hsu-Hsin Chen, Narayanan Kasthuri, Kenneth J. Hayworth, Alessandro Vercelli, H. Sebastian Seung, Jeff W. Lichtman, Paola Arlotta, ” Distinct Profiles of Myelin Distribution Along Single Axons of Pyramidal Neurons in the Neocortex, ” Science 344: 319-324 (2014) DOI: 10.1126/science.1249766:
Brain cells that are evolutionarily recent (in the neocortex) have patterns of intermittent myelination. This means that long axons have long stretches of nakedness. Like certain parades in San Francisco. Evolutionarily older brain cells are more uniformly myelinated. Cloaked, zipped in the lipid layers of myelin. Like, um, well, we can’t continue the analogy because we can’t think of any area in California that is mostly clothed. Maybe Bakersfield.
Now, giving this 30 seconds thought (which about all we can muster any more), we wonder: What is the purpose of incomplete myelination, when total myelination seems such a good idea?
The researchers hypothesize that where there is less myelin, there are more connections forming. (Myelin prevents new synaptic connections, for one thing.) So, in the newer parts of the brain, where more synaptic connections = better (mostly), having naked axons is a good thing.
We’re ok with that hypothesis, sounds good to us. Neocortex brain cells are involved with the thought processes that make us human — planning, socializing, language, that kind of thing. So of course you’d need to be growing and pruning connections dynamically.
But, this seems to fly in the face of the psychopaths in our orbit, who (in their heyday) had trouble with change. They continued a single way of thinking even in the face of new material facts. (Of course, their default position: how do I come out ahead on this?) Laziness, parasite-ness, the whole thing. All geared toward never thinking in a new way, and doing same ol’ same ol’. (That is, scamming.) Sclerotic. Ossified.
So, maybe they have extra myelin? Myelin that inhibits new synaptic connections? Or messed-up myelin itself?
Abnormal myelination/abnormal myelin composition has been associated with antisocial personality (see here ) as well as other brain conditions (depression, Alzheimer’s, bipolar, schizophrenia, e.g., here). In a non-human primate model of cocaine abuse, myelin had specific alterations (here). In alcohol-dependent rodents, the number of myelin producing cells went down, as well as the expression of myelin-related proteins, although pyrimidal neurons (in the cortex) increased dendritic arborization and spine density (here).
So: normal people have spotty myelin in high-level brain cells, antisocial folks (and those with other pathologies) have abnormal myelination and abnormal myelin composition, addicted mammals have abnormal myelin, or reduced cells that make myelin.
We have no idea what all this means.
But, that never stopped us from guessing!
So we guess that in psychopaths, it’s the myelin lipid structure that’s messed up.
Our previous posts on myelin:
White matter month 2013: Is psychopathy related to myelin? (Discussing two papers related to antisocial myelin composition)