A lot happened in the past week: Winter storm Jonas rued the weekend with record-breaking snowfall. Megyn Kelly single handedly rendered the seventh republican debate Trump-less, inevitably furthering her “I bust balls on the left and right” reputation. Still, neither Kelly nor Jonas had the best week ever. That distinction goes to a little neurobiological process called synaptic pruning. During the process, the brain sheds old, weak connections to make room for new ones. And in a landmark study, researchers presented the first concrete neurobiological explanation for schizophrenia: an over-pruned brain. This breakthrough will reverberate through everything connected to neuroscience, including sleep.
How it Works
Synapses are the connections between neurons that transmit chemical messages. When we learn new information and skills, synapses get stronger. We even generate new ones, a process called neurogenesis. During vital periods of cognitive development, we shed old synapses to make room for higher quality connections that can support more complex mental function. This neural spring cleaning is called synaptic pruning.
A neuroscience professor offered this pruning analogy in a Quora post:
“Imagine a new city. It needs roads connecting all the houses and buildings. If roads were built like the nervous system builds connections between cells, then every new city would start by crazily building roads connecting everything. There would be too many roads, and the arrangement might not be very useful. There might be 15 roads to one house, and 2 roads to another, and maybe no roads to another. There might be a bunch of roads between places that will never need them. How to fix this mess? Over time, the roads that are not used are removed, leaving just the roads that carry traffic, and more roads between places that carry the most traffic. In the end, it looks like everything was elegantly planned. Everything is very efficient. But actually, it was a result of crazy ambitious road building followed by 'roadway pruning'.”
The first period of synaptic pruning occurs during early childhood. In fact, researchers once thought our brains only pruned during our earliest years. But, thanks to advancements in Science(™), they discovered a second pruning period during adolescence. They now know that teenage pruning actually continues into early adulthood, petering out sometime in our late 20s.
The brain loses about half of its synapses during the process, leaving it "plastic," meaning extraordinarily vulnerable to change. The plasticity enables growth in and between brain regions crucial to thinking like an adult. Mostly, we’re talking about the Prefrontal Cortex (PFC), which is heavily involved in the decision-making processes and risk assessment at which old folks excel and teens are notoriously awful.
For a few years now, researchers have had a hunch that glitchy pruning plays a role in the development of psychiatric disorders, many of which show up during late adolescence or early adulthood. They got their hunch from neuroimaging studies that showed fewer neural connections in the prefrontal brain regions of people diagnosed with mental disorders, compared to those with “neuro-typical” brains.
But, they lacked both evidence to support the connection and a way to explain the basis of “pruning gone awry,” as the New York Times put it, in the two million Americans diagnosed with schizophrenia. Now they have both, thanks to researchers from Harvard and Boston Children’s Hospital.
For the mammoth project, these researchers studied immune system proteins in mice and analyzed both post-mortem brain tissue and DNA from more than 100,000 people. Their findings, per the Times, showed that “people with schizophrenia have a gene variant that apparently facilitates aggressive “tagging” of connections for pruning, in effect accelerating the process.”
Using this knowledge to develop treatment for schizophrenia or de-pruning meds, is a long way off, study authors said.
What’s interesting to consider — besides everything about the discovery — is how sleep might factor into this equation.
According to the latest research, sleep (particularly the slow-wave variety) is a period of brain restoration crucial to learning and memory consolidation. What happens during said restoration? Among other things, scientists believe, reorganizing and pruning of synapses.
By day, as the brain learns new info and soaks up the world, its neural connections get stronger. At night, the brain cleans shop and focuses its resources on the mightiest synapses.
Neuroscientists have hypothesized that the adolescent brain goes particularly hard on pruning. Makes sense. And now we have evidence that schizophrenic brains are over-pruned. What's more, we also know that disturbed sleep is a hallmark feature of schizophrenia. So, sleep, synaptic pruning and schizophrenia are three points in an unfinished triangle.
It’s not so clear where and how shoddy sleep enters the picture. Cause? Symptom? Exacerbating factor? All three? We’re excited to find out.