Delta Waves and Face Transplants
Photo by Freepik
One of the most significant capabilities of the human body and brain is the ability to adapt. From any kind of learning task to playing sports to healing brain damage, neural plasticity plays a pivotal role in human life. Face transplants, a relatively new operation to fix severe facial trauma or deformities, are one of the best demonstrations of human adaptability; the brain must somehow accommodate completely foreign tissue and transform it into a functional face. During the initial stages of the transplant process, the patient’s face appears extremely disfigured, however, the brain has the ability to mend the face over time until it is remarkably difficult to differentiate from a natural human face. See some images here from the New England Journal of Medicine.
This physical adaptation is one of the most fascinating feats of neural plasticity, making it an appealing option for more deeply understanding the brain’s key function of adaptation. Right now, fewer than 50 facial transplants have been performed, however, the effectiveness of the healing process varied by participant from remarkably transformative to only a partial recovery. Therefore, it is imperative to understand the mechanisms behind these differing levels of recovery. Even outside the context of face transplants, the process of neural adaptation, in general, is extremely prevalent. In a recent study led by Esra Suzen at the University of Akdeniz, Turkey, researchers investigate the recovery process in face transplant patients with EEG (electroencephalograms), establishing a connection between delta waves and healing capacity.
EEG analysis involves the measurement of electrical signals emitted by neurons on the human scalp. The raw signals are quite noisy, however, breaking the data down with a mathematical technique called the Wavelet Packet Transform reduces it into nine separate frequencies of waves. Each of these frequencies of waves typically corresponds with a certain brain function, however, this research focuses on delta waves (1-3 Hz). Delta waves are related to rest, recovery, and sleep, and can be split further into upper and lower delta waves, corresponding to separate phases of sleep.
The experimental process involved three facial transplant patients and four severe facial lesion patients, who underwent a similar process of recovery. Additionally, there was a control group of ten with completely healthy faces. In the study, four different physical stimuli would be performed (one on each hand and cheek), and the EEG delta waves would be measured in the corresponding region of the somatosensory cortex. This was done because the neural area associated with the face is located directly next to the area associated with the hands, and it was hypothesized that the adaptation of a certain neural area would have effects on its surroundings.
Below are the results of the test, averaged over each experimental group (C=control, T=transplant, L=lesion):
There were numerous significant results for the facial lesion patients, especially for the upper delta waves. The WPE distribution (wavelet packet energy distribution) can be understood simply as the strength of the signal as a reaction to the stimulus. Although the transplant patients themselves did not return as many significant results as the lesion transplants, there are still many takeaways from this study. Furthermore, it is important to note that sampling size is still a major problem in these studies, which may partially explain the lack of results in the face transplant group.
The first clear takeaway from this is the fact that there is a very clear connection between delta waves and the recovery process. This is extremely helpful for modeling recovery plans for patients since the delta wave concentrations can be used to predict the effectiveness of certain techniques used for healing. Furthermore, this study demonstrated that the upper delta waves, in particular, likely have a stronger effect on healing since the calculated p-values (a measure of statistical significance) were lower than for the lower frequency delta waves. Although the process of healing and neural accommodation is not yet fully understood, these developments set a solid baseline for future studies to build upon, establishing the fact that upper delta waves are strongly associated with the recovery process.
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