14 DAY TRIAL // Memory is still one of the most mysterious processes of the brain. Now, another piece in the complicated puzzle has been located: while sleeping, the reactivated memories of real-time experiences are reviewed in high "thought speed", 6-7 times more than in wake time, by the brain.
Memory is kept in modules in the brain's cortex, various modules in the cortex being linked to various types of information - sounds, sights, tastes, smells, etc., being connected to the brain nucleus of hippocampus.
The hippocampus sends a tag signal (a temporary bar code) specific to each memory back to the cortex. Each cortex module in the cortex is activated by the tag on its own activity role.
Having dinner would require memory modules for the location of the diner, the food, the surrounding sound or the bill. Still, replaying the memory of it will be just 8-10 minutes long, while dining took up about one hour in real time.
"The reason is that the speed of the consolidation process isn't constrained by the real world physical laws that regulate activity in time and space." said lead researcher Bruce McNaughton, a professor of psychology and physiology at the University of Arizona.
This time restriction occurs because a neuron cannot connect/interact with too many neurons. And the retrieval tags generated by the hippocampus are just temporary, till the cortex forms a memory on its own.
"It's a slow process. The initial creation of the tag is made through existing connections. In order to do the rewiring necessary to have the intermodular connections carry the burden takes time. What you have to do is reinstate those memories multiple times. Every time you reinstate the memory, the modules make a little shift in the connection . . . something grows this way, grows that way, a connection gets made here, gets broken there. And eventually, after you do this multiple times, then an optimal set of connections gets constructed," said Mc Naughton.
This could take place during slow-wave sleep, when the cortex does not process real-time inputs. The team employed a technology to record from various probes, each recording the activity of at least 12 neurons.
While sleeping, the hippocampus sends minute, 100-millisecond signals to the cortex up to 3 times per second.
"The more practical point, I think, is that this methodology, the ability to measure how fast the brain is processing at the level of changing the state of the brain from one 10- millisecond epoch to the next, how fast the internal state is sweeping through its memories or its allowable patterns is, I think, a model for thought speed," said McNaughton.
"Knowing the determinants for the speed of thought might allow studies of the effects of drugs, developmental anomalies and the behavioral therapies that might improve them."