How can you protect a brain by destroying it? [Pharyngula]

Last week, Simon Davis wrote to me with questions about this cryonic brain preservation technique, which has now been published as How to Freeze Your Brain and Live Forever (Maybe). Unfortunately, my comments did not make it into the story, because, Simon politely explained, there are length restrictions and perhaps, I assume, also because my extended dismissive scorn does not translate well to polite journalism. And that’s OK! Because I have a blog, and I can rant here!

The Brain Preservation Society has a goal: to preserve dead brains today, so they can be reanimated at some distant time in the future. At least, that’s what they say — I’m more inclined to believe their goal is to pocket lots of money exploiting people’s fear of death. Their immediate plan, though, is to develop more thorough mechanisms of locking down the fine structure of brains.

Extending today’s existing small-volume neural preservation techniques to whole brains is essential to the scientific goal of mapping neuronal connectivity across an entire human brain – a goal that has been identified by the NIH and others as crucial to furthering of our knowledge of brain function – see for example the NIH’s Human Connectome Project. Furthermore, advances in neuroscience today strongly suggest that appropriately preserved brains will contain our memories, identity, and a substrate for future consciousness, so that an appropriately verified preservation technology may allow future reanimation of the memories and identity of the preserved individual, if desired.

Lovely. I’m all in favor of mapping neuronal connectivity — I did some small-scale stuff in that field decades ago. But they make extravagant claims.

The technology they are using is straightforward and useful.

We describe here a new cryobiological and neurobiological technique, aldehyde-stabilized cryopreservation (ASC), which demonstrates the relevance and utility of advanced cryopreservation science for the neurobiological research community. ASC is a new brain-banking technique designed to facilitate neuroanatomic research such as connectomics research, and has the unique ability to combine stable long term ice-free sample storage with excellent anatomical resolution. To demonstrate the feasibility of ASC, we perfuse-fixed rabbit and pig brains with a glutaraldehyde-based fixative, then slowly perfused increasing concentrations of ethylene glycol over several hours in a manner similar to techniques used for whole organ cryopreservation. Once 65% w/v ethylene glycol was reached, we vitrified brains at -135 °C for indefinite long-term storage. Vitrified brains were rewarmed and the cryoprotectant removed either by perfusion or gradual diffusion from brain slices. We evaluated ASC-processed brains by electron microscopy of multiple regions across the whole brain and by Focused Ion Beam Milling and Scanning Electron Microscopy (FIB-SEM) imaging of selected brain volumes. Preservation was uniformly excellent: processes were easily traceable and synapses were crisp in both species. Aldehyde-stabilized cryopreservation has many advantages over other brain-banking techniques: chemicals are delivered via perfusion, which enables easy scaling to brains of any size; vitrification ensures that the ultrastructure of the brain will not degrade even over very long storage times; and the cryoprotectant can be removed, yielding a perfusable aldehyde-preserved brain which is suitable for a wide variety of brain assays.

But first of all, you need to understand that their current methods don’t involve simply freezing brains. They are freezing brains and perfusing them with glutaraldehyde to fix them, better preserving the ultrastructure of the tissue. Every microscopists does this; I was fixing zebrafish brains with a cocktail of acrolein, glutaraldehyde, and paraformaldehyde in the 1980s, trying to capture detailed images of synapses in the spinal cord. It worked pretty well, too. They know what they are getting out of this: an aldehyde-preserved brain.

What I didn’t do with my experiments in aldehyde-preserved brains was claim that I was preserving all the information necessary for nervous system function. I was quite aware that I was chemically nuking all the proteins in the tissue; I was washing out most of the chemistry; I was destroying most of the physiological information to preserve a structural skeleton of what was there, so I could see the physical arrangement of the pieces. Nothing more.

Neuroscience does not suggest that fixing a brain in aldehydes will preserve “memories, identity, and a substrate for future consciousness”. There’s no reason to think their methods create “appropriately preserved brains”.

There is a respectable question to be answered with their techniques about the structure of the brain, but it is only one tiny step forward in understanding how the brain functions and generates a mind. Ultrastructure is something we can study, so it’s an issue of chasing the question that can be answered while telling everyone you’re trying to address a completely different question that can’t.

The pattern of synaptic connections is an essential part of the story, but it is not sufficient. A simple counterexample: consider the effect of MAO inhibitors and various antidepressants. They modulate the activity of the brain by affecting the intercellular concentration of neurotransmitters. Consider hormonal effects: your brain is profoundly altered by the chemical signals in your blood (and recursively, secretes hormones of its own). There’s this whole phenomenon called non-synaptic plasticity, in which the behavior of ion channels and pumps is modified by, for instance, phosphorylation, or binding of cofactors.

These things are all destroyed by fixation. The information is no longer there.

If this organization is so confident that they have preserved all the necessary information, I’d like to know why they’re playing around with just the first step of the problem, doing so in impractically complex organisms, and not working on the necessary step of recovering that information. That’s the real test.

Take a simpler organism, like a fruit fly or a nematode. Kill it, fix it, freeze it, vitrify it. That should be trivial at their tiny scale. Then rebuild a fly brain from the extracted information and show me that it still knows how to walk, fly, eat, court, and mate.

Nobody’s even close to accomplishing any of that.

Until then, any talk of an adequate preservation method is simply wishful thinking, especially when it relies on the kind of obliteration of the molecular information in the brain that the Brain “Preservation” Society is doing.

Of course, I actually know why they don’t do any of that. Fruit flies and nematodes won’t pay them a substantial annuity to have their brains vitrified and stored, and their gratitude upon being resurrected wouldn’t be at all remunerative.

But for now, they’ve got really good EM technique and can show off pretty pictures of well-fixed cells. Bravo! Who knew that I was so cutting-edge 30 years ago?