Recent quotes:

Synapses shrink 20% every night?!

The team deliberately did not know whether they were analyzing the brain cells of a well-rested mouse or one that had been awake. When they finally "broke the code" and correlated the measurements with the amount of sleep the mice had during the six to eight hours before the image was taken, they found that a few hours of sleep led on average to an 18 percent decrease in the size of the synapses. These changes occurred in both areas of the cerebral cortex and were proportional to the size of the synapses. The scaling occurred in about 80 percent of the synapses but spared the largest ones, which may be associated with the most stable memory traces.

Brain has internal ‘odometer’ and ‘stopwatch’

To prove the contrary, researchers put rats on treadmills and recorded the activity of grid cells, keeping either distance or duration of running unchanged, and only varying the speed. As a result, 92% of grid cells in rats emitted signals at specific moments: for instance, one cell would fire 8 seconds into the run, not taking into account speed or distance covered, and another cell would emit a signal every 400 cm, not depending on speed or duration of the run. 50 percent of the cells were affected by distance, another half by time, and around 40 percent by both factors. "Space and time are ever-present dimensions by which events can be organized in memory," senior study author Howard Eichenbaum, a psychologist and neuroscientist at Boston University, said in the official press release.

EyeWire game to map mouse eye neurons

In 2012, Seung started EyeWire, an online game that challenges the public to trace neuronal wiring — now using computers, not pens — in the retina of a mouse’s eye. Seung’s artificial-­intelligence algorithms process the raw images, then players earn points as they mark, paint-by-numbers style, the branches of a neuron through a three-dimensional cube. The game has attracted 165,000 players in 164 countries. In effect, Seung is employing artificial intelligence as a force multiplier for a global, all-volunteer army that has included Lorinda, a Missouri grandmother who also paints watercolors, and Iliyan (a.k.a. @crazyman4865), a high-school student in Bulgaria who once played for nearly 24 hours straight. Computers do what they can and then leave the rest to what remains the most potent pattern-recognition technology ever discovered: the human brain.

Neurons as adventurous voyagers

Each neuron is imprisoned in your brain. I now think of these as cells within cells, as cells within prison cells. Realize that every neuron in your brain, every human cell in your body (leaving aside all the symbionts), is a direct descendent of eukaryotic cells that lived and fended for themselves for about a billion years as free-swimming, free-living little agents. They fended for themselves, and they survived.              They had to develop an awful lot of know-how, a lot of talent, a lot of self-protective talent to do that. When they joined forces into multi-cellular creatures, they gave up a lot of that. They became, in effect, domesticated. They became part of larger, more monolithic organizations. My hunch is that that's true in general. We don't have to worry about our muscle cells rebelling against us, or anything like that. When they do, we call it cancer, but in the brain I think that (and this is my wild idea) maybe only in one species, us, and maybe only in the obviously more volatile parts of the brain, the cortical areas, some little switch has been thrown in the genetics that, in effect, makes our neurons a little bit feral, a little bit like what happens when you let sheep or pigs go feral, and they recover their wild talents very fast. Maybe a lot of the neurons in our brains are not just capable but, if you like, motivated to be more adventurous, more exploratory or risky in the way they comport themselves, in the way they live their lives. They're struggling amongst themselves with each other for influence, just for staying alive, and there's competition going on between individual neurons. As soon as that happens, you have room for cooperation to create alliances, and I suspect that a more free-wheeling, anarchic organization is the secret of our greater capacities of creativity, imagination, thinking outside the box and all that, and the price we pay for it is our susceptibility to obsessions, mental illnesses, delusions and smaller problems.

Sleep trimming synapses

While we’re awake, your brain is forming memories. Memory formation involves a process called long-term potentiation (LTP), which is essentially the strengthening of synaptic connections between nerve cells. We also know that learning can actually cause neurons to sprout entirely new synapses. Yet this poses a problem for the brain. If LTP and synapse formation is constantly strengthening our synapses, and we are learning all our lives, might the synapses eventually reach a limit? Couldn’t they “max out,” so that they could never get any stronger? Worse, most of the synapses that strengthen during memory are based on glutamate. Glutamate is dangerous. It’s the most common neurotransmitter in the brain, and it’s also a popular flavouring: “MSG”, monosodium glutamate. But in the brain, too much of it is toxic. Glutamate works as a transmitter molecule by opening channels on the cells that receive it. The channels allow calcium into the cells on the receiving end, which activates them, allowing messages to go through. But too much glutamate can cause excess calcium to build up inside the very cells that receive the message, a harmful process called excitotoxicity. So, if our brains were constantly forming stronger glutamate synapses, we might eventually run into serious problems. One function of sleep, according to the theory, is to protect the brain against excitotoxicity or other “synaptic overload” problems by pruning the synapses. If the brain is essentially removing the “extra” synaptic strength formed during the previous day, it must do so in a way that preserves the new information. One possible mechanism for this is synaptic scaling. After some of the neural connections into a given cell, or “inputs,” become stronger, then all of the synapses on that cell could be weakened. This would preserve the relative strength of the different inputs, while keeping the total inputs constant. It’s as if each neuron were a cup, and each synapse corresponds to a different liquid. During the day, memories form and certain synapses get stronger, which means pouring more of those particular liquids into the cup. At night, synaptic scaling pours some of the mixture back out, bringing it back to the baseline level without changing the relative proportions of the mix. We know that synaptic scaling happens in the brain, but it’s not yet clear whether it has anything to do with sleep. This is an area of ongoing research. While synaptic scaling seems to treat each neuron like a cup to be kept from overfilling, the effect of sleep on for the brain overall may be more like disk defragmentation, according to this idea. After heavy use, hard disks tend to get “fragmented.” This is because when data gets stored, it is written to wherever there happens to be free space on the disk. This makes it inefficient to keep track of it all as files may be split and written in many different places. A defrag consolidates the same data into a more logical order. Defragmentation is a taxing chore for the computer, so many people schedule it to happen overnight. In the same way, sleep may serve to reorganize and reconsolidate memories. The mechanics of how this defragmentation works remain unclear; synaptic scaling might be just one of several processes at work. Defragmentation is not an exact analogy, however. The process could also be likened to archiving your emails to make room in your inbox, or compressing data into zipped files, to free up room on the disk. (This theory is specifically about slow-wave sleep (SWS). It doesn’t try to explain rapid eye movement (REM) sleep, when dreams happen. Interestingly, some animals do not have REM, but they all have SWS. In some animals, like dolphins, only one side of the brain has it at a time, which is strong evidence that SWS, but not REM, is vital for life.)