Posts Tagged ‘ EEG ’

Catchin’ Some Waves

Our capacity for short-term memory depends on the synchronization of two types of brainwaves – rapid cycles of electrical activation – says a new study.

Theta and gamma waves try get their dance steps synced up.

When the patterns of theta waves (4-7 Hz) and gamma waves (25-50 Hz) are closely synchronized, pieces of verbal information seem to be “written” into our short-term memory. But it also turns out that longer theta cycles help us remember more bits of information, while longer gamma cycles are correlated with lower recall.

These patterns are measured using electroencephalography (EEG), a lab technique with a long and successful history. Back in the 1950s, it helped scientists unravel the distinct brainwave patterns associated with REM (rapid-eye movement) and deep sleep. More recently, it’s been used to help people with disabilities control computers, and it’s even helped home users get an up-close look at their own brain activity.

Though more modern techniques like fMRI and DTI are much better at mapping tiny activity patterns deep within the brain, EEG remains a useful tool for measuring the overall patterns of synchronized electrical activity that sweep across the entire brain in various wave-like patterns – hence the term “brainwaves.”

Several types of brainwaves have been well studied since the 1950s: alpha waves, which are correlated with active attention; beta and delta waves, which are associated with logical processing; theta waves, which are associated with meditation and acceptance; and gamma waves, which burst rapidly across the brain when we come to a realization or an understanding.

And now, as the International Journal of Psychophysiology reports, a team led by Jan Kamiński at the Polish Academy of Sciences has discovered a new way of mapping relationships between these patterns of wave activity, to arrive at a new understanding of how theta and gamma waves work together: they studied the lengths of these two cycles relative to one another – and what they found was pretty amazing:

We have observed that the longer the theta cycles, the more information ‘bites’ the subject was able to remember; the longer the gamma cycle, the less the subject remembered.

The researchers discovered this in a very straightforward way – they simply kept tabs on volunteers’ EEG activity as they sat with eyes closed and let their minds wander; then they compared these recordings against ones taken as the volunteers memorized longer and longer strings of numbers – from three digits up to nine.

The correlation between long theta cycles and greater memory for digits turned out to be quite strong – and for gamma waves, the reverse turned out to be true. This means that gamma waves are probably much more crucial for forming ideas than they are for rote memorization.

Though this finding might not seem all that revolutionary, it provides an elegant demonstration of how even older technologies like EEG can still be used to help us make brand-new discoveries. Which means that in the brains of those of us who keep pluggin’ away at home EEG experiments, there’s probably still a place of honor for those wonderful little gamma waves.

Brain Scans & Lucid Dreams

The brain activity of lucid dreamers – people who become aware that they’re in a dream state – shows some interesting similarities with that of people who are awake, says a new study.

"Ahh - nothing puts me to sleep like a roomful of bright lights!"

By studying the brain activity of lucid dreamers under electroencephalograms (EEGs) and fMRI scans, researchers have found that activity in the somatosensory and motor cortices – regions crucial for touch and movement, respectively – show very similar activation patterns during lucid dreams to those they display when people make or imagine those same movements while awake.

Though dreams have fascinated philosophers and scientists since the dawn of history – some of the earliest written texts are dream-interpretation handbooks from ancient Egypt and Babylon – it’s only in recent years that neuroscience has begun to advance the study of dreams beyond Freudian theorizing and into the realm of hard data.

In the early 1950s, scientists identified several stages of sleep, including rapid eye movement (REM) sleep – the stage in which dreaming takes place; and in 1959, a team discovered a certain class of brain waves – ponto-geniculo-occipital (PGO) waves – which only appear during REM sleep.

Then, in 2009, an EEG study found that lucid dreams exhibit slightly different wave patterns from those associated with ordinary REM sleep – and later that year, another study proposed an astonishing theory: that REM sleep might be a form of proto-consciousness, which performs maintenance and support duty for the “full” consciousness that took over for it at some point in our evolution.

Now, as the journal Current Biology reports, a team led by Michael Czisch at Germany’s Max Planck Institute has made a new leap forward in dream research. By concentrating their research on lucid dreams, the team were able to map the neural correlates of controlled and remembered dream content:

Lucid dreamers were asked to become aware of their dream while sleeping in a magnetic resonance scanner and to report this “lucid” state to the researchers by means of eye movements. They were then asked to voluntarily “dream” that they were repeatedly clenching first their right fist and then their left one for ten seconds.

This approach has provided some surprising new insights into the ways our brains function in a dream state. By having the subjects retell their lucid dreams, the researchers were able to correlate recorded activation patterns with specific actions the subjects had “performed” while asleep:

A region in the sensorimotor cortex of the brain, which is responsible for the execution of movements, was actually activated during the dream. This is directly comparable with the brain activity that arises when the hand is moved while the person is awake. Even if the lucid dreamer just imagines the hand movement while awake, the sensorimotor cortex reacts in a similar way.

This confirms that the brain’s sensorimotor areas are actively involved in planning and executing movements in dreams, rather than just passively observing events.

What’s even more exciting is that, in light of other new technologies like the thought-video recorder, it looks like we may be able to record and play back our thoughts and dreams within the next few decades.

I think this research reflects an even more fundamental shift in thinking about neuroscience, though: as we unravel more and more of the neural correlates of phenomena like sleep and consciousness, we’re coming to realize just how vast a chasm yawns between scientific data and subjective experience.

Before long, it’s going to become essential for scanners and volunteers to be involved in the same continuous feedback loop – one in which the subjects can watch, in real time, the neural correlates of their thoughts and feelings from moment to moment, and adjust them accordingly to produce useful results.

Ambitious? I guess so. But a guy’s gotta have a dream.

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