Similar categories of situations are processed
differently in Different brains
“Neuroscience one of the Extraordinary Ease of Ordinal
Series”
Familiar categories whose members appear in orderly
sequences are processed differently than others in the brain, according to new
research published by David Eagleman in the open access journal Frontiers in
Neuroscience on December 20th, 2012. The study suggests that ordinal sequences
have a strong spatial quality and activate a region of the brain not thought to
be directly involved in language acquisition and production. Also, sequences
shown in the correct order stimulated less brain activity in comparison to
sequences that were not in the correct order, implying that the brain could
predict what was coming and needed less activity to understand it.
"When an event happens, the brain can use less energy
in its response if it has already predicted that event," says Eagleman of
the Baylor College of Medicine in Houston, Texas. "Fundamentally, its job
is to make a good model of the world so that it can avoid being surprised. The
better it predicts, the more energy it saves."
Previous research suggested that so-called ordinal
categories have unique properties that are encoded differently from non-ordinal
sequences.
In some forms of dementia, for example, memories for
ordinal stimuli such as numbers are spared, while those for non-ordinal
stimuli, such as the names of animals or fruits, are impaired. And in a
neurological condition called synesthesia, sensory experiences such as colour
are triggered by unrelated inputs, especially ordinal stimuli such as numbers,
letters and months of the year.
Until now, however, little was known about the neural
representation of ordinal sequences.
To investigate, David Eagleman and his team recruited 35
participants and used functional magnetic resonance imaging (fMRI) to measure
their brain activity while they performed an "oddball" task.
The participants were presented with lists of five words
that appeared one after the other for half a second each. In one condition,
ordinal words were shown in their correct order (e.g. Monday, Tuesday,
Wednesday, Thursday, Friday). The second condition involved ordinal words
presented in a scrambled order, and the third contained words belonging to
non-ordinal categories.
Each participant completed 20 practice trials before
being placed into the scanner to perform 120 more. During half of the trials,
the fifth word in the sequence was replaced with an oddball stimulus, such as
four days of the week followed by the word "banana," or four fruits
followed by a number.
After completing each trial, the participants were simply
required to indicate whether or not it contained an oddball stimulus, by
pressing one of two buttons.
The researchers compared the brain scans obtained during
the different trials, to determine which brain regions responded to ordinal
words, and how the predictability of the word sequences affected the patterns
of brain activity. Scrambled sequences (such as Sunday, Wednesday, Tuesday,
Friday) elicited greater activity than did sequences in their correct order.
In other words, the more predictable a sequence of
ordinal words was, the less brain activity it evoked. This, the researchers
say, is direct evidence that long-term experience dampens neural activity. The
brain pays little attention to stimuli that are familiar, but alarm bells start
to ring when those that do not meet our expectations.
Further, the study revealed that the processing of ordinal
words involves more activation of the right hemisphere than the left -- a
surprise finding given that language is typically a left hemisphere phenomenon.
"We are just beginning experiments in which we teach
people with synesthesia a new alphabet of arbitrary symbols -- what we call an
'alien' alphabet. Through the use of video games, we rigorously train them on
this novel sequence. We predict that the arbitrary symbols will take on
synesthetic colors, and that the representation of those symbols move from the
left to the right hemisphere."
Image Source: http://www.sxc.hu/photo/1148998
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