As you read this, some 100 billion neurons are transmitting information through electrical and chemical signals via synapses in your brain.
Given the central role these cells play in neurological functioning, it’s perhaps not surprising they typically hog the limelight — after all, the signals they transmit lie at the heart of human behavior, from the simplest of movements to the most complex of thoughts.
It’s worth noting, however, that complementary cells called astrocytes actually outnumber neurons in the brain. Unfortunately, these star-shaped cells have largely been ignored in neurological research because they don’t fire electrical impulses in the same way that neurons do. Yukiko Goda of the Riken Brain Science Institute in Saitama is helping to correct this.
Goda, who was born in Osaka, went to high school in Toronto after her father was transferred to Canada for work. She stayed on to attend the University of Toronto, and then studied at Stanford University in California. She ran a neuroscience lab at University College London for 10 years before taking up her current position at the Brain Science Institute.
Goda’s most recent work suggests that astrocytes help to regulate synaptic strength.
“We have found an active mechanism that helps to increase variation in synaptic strength,” Goda says. “Surprisingly, it comes from astrocytes, which have previously been thought to play mostly passive roles in the brain.”
We often fall into the trap of thinking that the brain is like a computer and we imagine neurons as millions of tiny wires connecting the various parts. However, the brain is more dynamic than that. Every time we perform a certain action, such as ride a bicycle, or remember something, such as the date of someone’s birthday, the connections between our neurons change.
This seemingly simple statement has profound implications. For one thing, it suggests that memories change slightly each time we recall them.
Experiments have shown that if we have vivid memories that we rate as highly reliable and highly likely to be true, it does not mean they are necessarily real.
In one famous study, a cognitive psychologist named Ulric Neisser had students fill out a questionnaire the morning after the space shuttle Challenger broke apart in 1986 on their recollections. In 1988, he had the students complete the same questionnaire. When Neisser compared the answers, he found them to be completely different. Similar comparisons have been done following the Sept. 11 attacks in 2001, finding complete mismatches between what we are sure we remember and what really happened. Our mind, quite literally, plays tricks on us.
It will take a while for the implications of this to change the way our courtrooms work. It may take longer for it to change the way we think about ourselves. Let that sink in for a moment. Who do you think you are? Since the act of remembering, in and of itself, changes our memories, our perception of ourselves, in some sense, changes throughout our lives.
This is not like lying to yourself, when you know, deep down, that you are shying away from the truth. It means that, in many cases, our memories may at best be inaccurate and, at worst, completely false.
But back, for a moment, to Goda’s latest work (which incidentally has just been published in the journal Proceedings of the National Academy of Sciences).
When neurons fire, the strength of the connections between them change. Sometimes the impulse is enough to create a whole new connection and, other times, the strength of the connection between neurons is weakened or reinforced. Goda’s team looked at brain cells growing in culture and in slices of the hippocampus, the seahorse-shaped structure in the brain that is heavily involved in memory-formation. The team found that astrocytes in the hippocampus regulate changes in the brain brought on by neural activity.
“A deeper understanding of how synaptic communication is regulated will aid in discovering disease mechanisms and developing treatments,” Goda says. “Our work shows that astrocytes could be a potential target of novel therapeutics.”
Astrocytes, we are now appreciating, are important in providing maintenance and nutritional support for neurons. However, they are also vital for our experience of consciousness because of the role they play in strengthening the connections between neurons.
A couple of years ago, scientists performed a fascinating experiment that vividly demonstrates the power of astrocytes. Immature human brain cells were injected into the brains of baby mice. The cells developed into astrocytes and ousted the native mouse cells. By the time a mouse was 1 year old, its brain was a hybrid of human-derived astrocytes and regular mouse neurons.
Now, here’s the crazy thing. Human astrocytes are much larger than mouse astrocytes, which means when they were fitted into the brains of mice, they had the effect of turbo-charging the mice. When the scientists tested mice with standard tests for memory and understanding, the rodents with human astrocytes turned out to be much smarter.
In one test designed to measure memory associated with fear, for example, mice with human astrocytes performed far better than mice with regular astrocytes, suggesting their memory was much better.
We’ve learned that astrocytes are far more important in the brain than has been appreciated. However, if you remember one thing from reading this column today, remember this — your memory of it is, in all probability, completely unreliable.
Rowan Hooper is the news editor of New Scientist magazine. The second volume of Natural Selections columns translated into Japanese is published by Shinchosha. The title is “Hito wa Ima mo Shinka Shiteru” (“The Evolving Human”). Follow Rowan on Twitter @rowhoop.