Neuroscientists cultivate mini-versions of human brains in the lab. Could they become conscious?
An American brain researcher warns that we may already be "perilously close" to crossing ethical boundaries. At the same time, research on so-called mini-brains can provide great opportunities to unlock some disease mysteries.
It still sounds like science fiction.
Neuroscientists at more than a hundred laboratories around the world are now cultivating small brains from human cells in glass dishes. There, they bob around in a pinkish liquid.
The lumpy blobs are more than a collection of random brain cells.
They form structures in a fashion similar to what happens during fetal development. The structures have different brain parts and organize themselves in networks. Cells fire - send off electrical signals - and thus communicate inside the pea-sized blobs.
American neuroscientist Madeline Lancaster was the first person to create a mini-brain – quite serendipitously. She was trying to grow brain cells from mice in a 2-dimensional form. But she wasn’t getting them to adhere to the glass properly.
She added a protein mixture to solve the problem. Then the cells began to clump together, divide and form what are called cerebral organoids, or mini-brains, according to a recent Financial Times interview with Lancaster.
When Lancaster and her colleagues published their first article about mini-brains made with human cells in 2013, it naturally attracted attention. The research field is now moving ahead at full speed.
Can they feel anything?
Some scientists are worried things might go wrong. At a major brain research conference in October, one of the topics on brain organoids was whether they could feel pain or "become conscious."
Could a situation arise where brains lie there and suffer in a bodyless, nightmarish state?
Elan Ohayon has developed computer models that he believes can tell us when mini-brain consciousness might arise. According to his models, research on organoids may already be "perilously close to crossing this ethical Rubicon,” the lecture introduction states.
"If there's even a chance of the organoid being sentient, we could be crossing that line," Ohayon told The Guardian ahead of the lecture.
He is the director of the Green Neuroscience lab in California, which has a particular focus on ethics.
However, most people believe that today's research on organoids is still well within what is ethically sound. The mini-brains differ greatly from real brains. The small lumps consist of one to a few million brain cells, whereas an adult human brain has 86 billion cells. Unlike human brains, the organoids are not connected to the external environment.
"Right now, I see no reason to be worried about consciousness in a six million neuron, half-a-centimetre-wide, hollow ball of cells, but we do need to be thinking about this," Professor Hank Greely, director of the Center for Law and the Biosciences at Stanford University, previously told The Guardian.
Brain organoid cultivation at NTNU
At NTNU, the Norwegian University of Science and Technology, Magnar Bjørås and his research groups are using brain organoids to research rare brain diseases. Bjørås is a professor in the Department of Clinical and Molecular Medicine at the university.
“We recreate the disease development in a mini-brain and compare it with an organoid we make from a healthy individual,” says Bjørås.
At Bjørås’ lab, researchers have been working on brain cell cultures for many years. When the first mini-brain research article came out in 2013, they decided they wanted to embark on this research.
“Previously, we had worked extensively with 2D cultures, and a bit with 3D cultures, but not of the mini-brain variety,” Bjørås said.
The earlier method of creating 3D cultures involved growing brain stem cells that "turn into clusters that float around in your medium.”
“They don’t create recognizable structures that resemble what you have in a normal brain. But the mini-brain organoids do,” he says.
Why are they so small?
At NTNU, researchers start with human skin cells. These are reprogrammed to become stem cells. The researchers do this by injecting genes that overproduce proteins typical of a stem cell.
The skin cells become what are called induced pluripotent stem cells. This is a universal cell, which can turn into many types of cells, including brain cells. Bjørås and his colleagues then place the stem cells into a suitable environment.
“We add growth factors needed for developing brain cells plus sarcoma extract, which is very rich in the factors needed for brain development. Then the cells have something to attach to and they start to resemble brain structure."
So most of the process happens almost by itself. The cells begin to divide and form mature brain cells with various functions just like in normal brain development.
“In a way we’re recreating early foetal development,” says Bjørås.
But why don't the brains get any bigger than large lentil size?
“What limits the size is that there’s no vascularization,” the researcher says.
In a human brain, lots of small blood vessels supply the cells with the nutrition they need. Brain organoids need to absorb whatever nutrients they can from the medium they are in.
“The bigger the mini-brain, the less nutrition makes it to the core of the cells. Eventually, the innermost cells begin to die. That’s why the organoids usually don’t grow more than 3- 4 millimetres using our current methods, says Bjørås.
Trying to supply blood vessels
But several researchers are trying to overcome this limitation.
Bjørås says a lot of researchers are working to get vascularization into brain organoids, including the NTNU team.
If scientists succeed at this, they’ll be able to grow brains that look more like the ones in our heads.
Mini-brain development can already be controlled, based on which parts of the brain scientists are particularly interested in.
“Most researchers have been working with so-called self-organizing mini-brains. They consist of all types of brain cells. What the structures look like is a bit random. That creates a certain variability in our experiments that makes it difficult to detect what’s random and what is disease,” says Bjørås.
“What we’re doing to a greater extent now is to create specific regions of the brain. We can direct the development towards the hippocampus, hypothalamus, forebrain or midbrain,” says Bjørås.
Measured brain waves
New studies on mini-brains are constantly emerging, and some are astonishing.
Earlier this year, researchers detected brain waves in an organoid for the first time. Researchers knew that the small blobs have a lot of electrical activity, but this time the researchers started to notice synchronized electrical impulses. That indicated that a plethora of brain cells were communicating with each other.
Initially, the brain waves were infrequent and of the same frequency. Eventually they became more complex. The researchers compared the activity in the mini-brain with measurements from premature babies.
One of the researchers told Gizmodo that after the mini-brains were between 24 and 40 weeks old, artificial intelligence was no longer able to distinguish their brainwaves from those of preterm babies.
Was it a step on the road to some form of consciousness?
In another experiment, described on the Science Alert website, researchers tested placing pieces of mouse muscle tissue and spinal cord near the mini-brain. Lo and behold, the organoid sent out long nerve tendrils and connected itself to the muscles and the spinal cord.
The researchers were even able to observe tiny muscle contractions triggered by these connections.
Scientists have also shown this activity in rats, where part of a brain organoid was inserted into the brain of a living rat.
“The cells that come from humans begin to integrate into the rat brain circuitry,” says Bjørås.
How far can this type of research go before ethical boundaries are crossed? When can an artificially grown brain begin to have experiences like suffering and well-being? Is this even possible without a body?
Here the research moves into unknown terrain. Despite everything that has been figured out to date, we do not have a good answer for what creates consciousness.
“The farther we take this, the further we’ll get. It’s important to emphasize that the mini-brains we’re working on today are not whole brains in any way. They recreate parts and networks that you find in normal brains,” says Bjørås.
“But clearly, when you’re able to control their development more, then it’s possible to imagine that this research could create brains that are conscious. It's something we have to take a position on the day we have the technology for it. It’s not just up to scientists to decide. We have to have clear guidelines,” he says.
The issue was addressed in a commentary in the journal Nature last year. The authors wrote that as brain organoids become larger and more sophisticated, the possibility of them having human-like characteristics becomes less remote.
“Such capacities could include being able to feel (to some degree) pleasure, pain or distress; being able to store and retrieve memories; or perhaps even having some perception of agency or awareness of self,” the authors wrote.
No solid theory
Johan Frederik Storm is a professor and brain researcher at the University of Oslo. He studies brain cell signals and has for many years been interested in theories of consciousness.
He thinks an isolated brain can have a kind of consciousness.
“We know it’s possible to have experiences without sensory impressions, such as thoughts and dreams,” he says.
When it comes to mini-brains, Storm says they are extremely small and simple compared to an intact brain.
“We have little evidence that mini-brains can have any inner life at all. At a common sense level, I don’t think there’s any experience to speak of in such a small cell cluster. But we can't actually completely exclude it in theory, since we don't know what's required for that to happen,” says Storm.
“If we had a solid and well-proven theory of consciousness, we’d also be able to say more about cases that are beyond what can be directly tested. That's how it is in physics. If you’ve tested a theory on lots of instances, and the expected outcome was confirmed each time, then you can use the same theory to predict what outcomes lie outside testable cases.
Are the senses necessary?
Storm says experiments have been conducted on isolated brains taken from rodents, including guinea pigs. The brain is kept alive by replacing the bloodstream with oxygen-rich saline.
“The concern has been raised that these brains might be experiencing something unpleasant. So there’s been a rule not to heat them to normal body temperature. They’re kept at a low enough temperature that a normal brain would be unconscious."
The brain’s inner life does not necessarily depend on the senses. But when we think, fantasize and dream, the content is largely based on past sensory experiences.
We see pictures, think in language, and feel emotions that are related to what we have experienced in the past.
“Our dreams contain elements from our sensory experiences. What would have happened if we’d never had sensory experiences? Would we have had any dreams or thoughts at all? Nobody knows, I think. So far, it’s mostly just speculation,” says Storm.
The mini-brains can hardly take in impressions of the outside world. However, it has been shown that they do have cells with photoreceptors that respond to light. The organoids at NTNU previously started to grow pupils, which can be observed as two small black dots.
Pain without body parts
When it comes to pain, Storm says it may be possible for an isolated brain to experience something like pain without having any body parts.
Phantom pain following arm or leg amputations is an example of how pain can be experienced by the brain, even though the brain is no longer connected to the body part or sensitive nerve fibres where the pain impulses would normally occur.
“Eventually we’ll be able to measure this in an isolated brain. We can look for activity in those parts of the brain that are active during pain sensations. If there is none, we can rest assured that no pain is occurring.
Furthermore, the activity that takes place in such a brain may not generate consciousness. Our own brain does a lot without any experience associated with it. For example, breathing, and sitting or standing upright, is controlled by the brain, and they happen even if we don’t consciously think about them. Many of the brain's functions are completely "automatic."
Finding treatments for brain disorders
Bjørås is studying what happens in the mini-brains with Batten disease, a serious disorder involving brain degeneration that often starts at a young age. He and his colleagues are also researching other forms of lysosomal diseases that have to do with defects in how the cells break down waste.
“What characterizes many of these diseases is that no treatment exists for them,” says Bjørås.
Mini-brains provide the possibility of finding out what causes diseases in a way that has been difficult in the past. The kind of research you can do on the brain of a living person is severely limited, and not everything that goes on in a mouse brain is the same as in a human brain.
Researchers have recreated Alzheimer's in mini-brains and can thus study what is happening and test out medications. Mini-brains are also used to investigate stroke, schizophrenia, epilepsy and other brain disorders.
“Mini-brains can be used to understand the mechanisms underlying disease development, but also to understand how the brain functions with normal physiology. It gives us new ways to look for and develop new treatments,” says Bjørås.
Mini-brain research raises many questions. It can also provide new answers about how the human brain works. We will expect to hear more about this research field.