We know that many traumatic brain injuries (TBIs) can be devastating. An important research topic is predicting what the effect a TBI of a particular type and severity will have on neuropathology and behavior.
Neuropathology is relatively easier to measure, but it is still hard to tell causality because a lot of the “markers” of TBI seen on neuropathologic exam are also sometimes seen in individuals who never had a TBI. Although their degree or distribution might be different.
Behavioral effects of TBI are especially hard to measure because you need standardized measures across time in both TBI-affected and TBI-unaffected individuals, controlling for all of the other factors that are known to affect behavior. A tough nut to crack.
Shively et al. recently described their clever study to address the causality of neuropathologic changes in TBI.
They compared the postmortem brains from donors with schizophrenia treated with prefrontal leucotomy (n = 5; more than 40 years prior to death) to age-matched donors with schizophrenia who hadn’t undergone leuctomy (n = 5).
Leucotomy, an obsolete treatment for schizophrenia, involved traumatic interruptions of white matter axons in the prefrontal cortex via burr holes. Here is what the lesions look like on MRI:
These authors looked at cortical tissue slices cut in the coronal plane at the leucotomy site, as well as slices rostral and caudal to the site.
Here were some of their findings:
- They found phosphorylated tau in neurons and astrocytes in cortex adjacent to the leucotomy site in 5/5 of the donors treated with leucotomy, but not in the rostral/caudal sites or in the donors who did not have leucotomy.
- The p-tau tended to be at sulcal depths or surrounding small blood vessels. This is similar to what is seen in CTE.
- They also found amyloid beta depositions in the cortex near the leucotomy sites, but only in the 3/5 donors who had at least one APOE ε4 allele.
Overall, this is really nice study that allows us to see the effect of TBI-associated axon injury in humans in a precisely controlled manner. What we see is that it causes phosphorylated tau accumulations in a similar distribution to that of CTE.