Whole-brain optical access in small adult vertebrates with two- and three-photon microscopy

Although optical microscopy has allowed us to study the entire brain in early developmental stages, access to the brains of live, adult vertebrates has been limited. Danionella, a genus of miniature, transparent fish closely related to zebrafish has been introduced as a neuroscience model to study the entire adult vertebrate brain. However, the extent of optically accessible depth in these animals has not been quantitatively characterized. Here, we show that two- and three-photon microscopy can be used to access the entire depth of the adult wild type Danionella dracula brain without any modifications to the animal other than mechanical stabilization. Three-photon microscopy provides high signal to background ratio and optical sectioning through the deepest part of the brain. While vasculature can be observed with two-photon microscopy, the deeper regions have low contrast. We show that multiphoton microscopy is ideal for readily penetrating the entire adult brain within the geometry of these animals' head structures and without the need for pigment removal. With multiphoton microscopy enabling optical access to the entire adult brain and a repertoire of methods that allow observation of the larval brain, Danionella provides a model system for readily studying the entire brain over the lifetime of a vertebrate.

Inconsistency between the circulatory and the brain criteria of death in the Uniform Determination of Death Act

The Uniform Determination of Death Act (UDDA) provides that “an individual who has sustained either (1) irreversible cessation of circulatory and respiratory functions or (2) irreversible cessation of all functions of the entire brain, including the brain stem, is dead.” We show that the UDDA contains two conflicting interpretations of the phrase “cessation of functions”. By one interpretation, what matters for the determination of death is the cessation of spontaneous functions only, regardless of their generation by artificial means. By the other, what matters is the cessation of both spontaneous and artificially supported functions. Because each UDDA criterion uses a different interpretation, the law is conceptually inconsistent. A single consistent interpretation would lead to the conclusion that conscious individuals whose respiratory and circulatory functions are artificially supported are actually dead, or that individuals whose brain is entirely and irreversibly destroyed may be alive. We explore solutions to mitigate the inconsistency.

About the looped layer. Research by the method of rebirth

The most important conductor of sensitivity in the brain is, as is known, a system of fibers passing in the longitudinal direction through the entire brain stem and bearing the name of the loop layer. In view of the important physiological significance of this system, many anatomists have already worked on this issue, due to which the course of the loop layer now seems to have been largely studied; therefore, I will try to present it in the most brief outline, dwelling mainly on controversial or poorly developed aspects of the issue.

Current Practice Diagnosing Brain Death Is Not Consistent With Legal Statutes Requiring the Absence of All Brain Function

The legal standard for the determination of death by neurologic criteria in the United States is laid out in the Uniform Determination of Death Act (UDDA), which requires the irreversible cessation of all functions of the entire brain. Most other nations endorse a “whole-brain” standard as well. However, current practice in the determination of death by neurologic criteria is not consistent with this legal standard, because some patients who are diagnosed as brain-dead, in fact retain some brain function, or retain the capacity for the return of some brain function. In response, the American Academy of Neurology published updated guidelines, which assert that hypothalamic function is consistent with the neurological standard enshrined in the UDDA. Others have suggested that it is an open question whether the hypothalamus and pituitary are part of “the entire brain,” as delineated in the UDDA. While we agree that determination of death practices are worthy of continued dialogue and refinement in practice that dialogue must adhere to reasonable standards of logic and scientific accuracy.

Are Brain Organoids Equivalent to Philosophical Zombies?

Along just over a century of research we moved from learning how to cultivate tissues in a dish to grasping the concepts for creating an entire brain in a vat. As we approach the divisive moment in which we can first detect signs of awareness in such artificially developed organoids, we need to lay foundation for what lays ahead. It is crucial that ethical, legal and moral implications of organoid research are clear and that boundaries are set to separate scientific progress from human life preservation. The largest obstacle may be the definition of consciousness itself, which has arguably been historically neglected by philosophy, psychology and neurosciences at large. One reason may be the difficulties posed by the underlying qualities of awareness, such as its subjective and heterogeneous nature. Another reason may lie on the possibly that consciousness is an overarching emergent property of our brain. For the time being, one can see brain organoids as philosophical zombies, physical analogues of the human brain which mimic sentient human reactions but lack experiential properties of sensation (a.k.a. qualia).

Epilogue

In the epilogue, a couple of kids befriend a shy stegosaurus; a different stegosaurus worries about the rise of mammals; and a tyrannosaurus presents a situation report. But mainly we consider reptilian brains, the relationship of brain size to intelligence, and the evolutionary success of mammals. Contrary to an internet meme, no one has a “reptilian” or “lizard” brain lurking within. Our entire brain is human. Regarding intelligence, brain organization matters as much as brain size and maybe more. Once dinosaurs became extinct, the mammals that supplanted them had much smaller brains than large dinosaurs had. Instead, the success of mammals depended on the emergence of the neocortex, a new part of the brain. Eventually, this evolutionary innovation came to dominate both the brain and the memories that it contains.