Key brain region was 'recycled' as humans developed the ability to read
Part of the visual cortex dedicated to recognizing objects appears
predisposed to identifying words and letters, a study finds

Date:
August 4, 2020
Source:
Massachusetts Institute of Technology
Summary:
A new study offers evidence that the brain's inferotemporal
cortex, which is specialized to perform object recognition, has
been repurposed for a key component of reading called orthographic
processing -- the ability to recognize written letters and words.



FULL STORY ========================================================================== Humans began to develop systems of reading and writing only within the
past few thousand years. Our reading abilities set us apart from other
animal species, but a few thousand years is much too short a timeframe
for our brains to have evolved new areas specifically devoted to reading.


==========================================================================
To account for the development of this skill, some scientists have
hypothesized that parts of the brain that originally evolved for other
purposes have been "recycled" for reading. As one example, they suggest
that a part of the visual system that is specialized to perform object recognition has been repurposed for a key component of reading called orthographic processing -- the ability to recognize written letters
and words.

A new study from MIT neuroscientists offers evidence for this
hypothesis. The findings suggest that even in nonhuman primates, who do
not know how to read, a part of the brain called the inferotemporal (IT)
cortex is capable of performing tasks such as distinguishing words from nonsense words, or picking out specific letters from a word.

"This work has opened up a potential linkage between our rapidly
developing understanding of the neural mechanisms of visual processing and
an important primate behavior -- human reading," says James DiCarlo, the
head of MIT's Department of Brain and Cognitive Sciences, an investigator
in the McGovern Institute for Brain Research and the Center for Brains,
Minds, and Machines, and the senior author of the study.

Rishi Rajalingham, an MIT postdoc,, is the lead author of the study, which appears today in Nature Communications. Other MIT authors are postdoc
Kohitij Kar and technical associate Sachi Sanghavi. The research team
also includes Stanislas Dehaene, a professor of experimental cognitive psychology at the Colle`ge de France.

Word recognition Reading is a complex process that requires recognizing
words, assigning meaning to those words, and associating words with their corresponding sound. These functions are believed to be spread out over different parts of the human brain.



========================================================================== Functional magnetic resonance imaging (fMRI) studies have identified
a region called the visual word form area (VWFA) that lights up when
the brain processes a written word. This region is involved in the
orthographic stage: It discriminates words from jumbled strings of
letters or words from unknown alphabets. The VWFA is located in the
IT cortex, a part of the visual cortex that is also responsible for
identifying objects.

DiCarlo and Dehaene became interested in studying the neural mechanisms
behind word recognition after cognitive psychologists in France reported
that baboons could learn to discriminate words from nonwords, in a study
that appeared in Science in 2012.

Using fMRI, Dehaene's lab has previously found that parts of the IT
cortex that respond to objects and faces become highly specialized for recognizing written words once people learn to read.

"However, given the limitations of human imaging methods, it has been challenging to characterize these representations at the resolution
of individual neurons, and to quantitatively test if and how these representations might be reused to support orthographic processing,"
Dehaene says. "These findings inspired us to ask if nonhuman primates
could provide a unique opportunity to investigate the neuronal mechanisms underlying orthographic processing." The researchers hypothesized that
if parts of the primate brain are predisposed to process text, they
might be able to find patterns reflecting that in the neural activity
of nonhuman primates as they simply look at words.



==========================================================================
To test that idea, the researchers recorded neural activity from about
500 neural sites across the IT cortex of macaques as they looked at
about 2,000 strings of letters, some of which were English words and
some of which were nonsensical strings of letters.

"The efficiency of this methodology is that you don't need to train
animals to do anything," Rajalingham says. "What you do is just record
these patterns of neural activity as you flash an image in front of
the animal." The researchers then fed that neural data into a simple
computer model called a linear classifier. This model learns to combine
the inputs from each of the 500 neural sites to predict whether the
string of letters that provoked that activity pattern was a word or
not. While the animal itself is not performing this task, the model
acts as a "stand-in" that uses the neural data to generate a behavior, Rajalingham says.

Using that neural data, the model was able to generate accurate
predictions for many orthographic tasks, including distinguishing words
from nonwords and determining if a particular letter is present in a
string of words. The model was about 70 percent accurate at distinguishing words from nonwords, which is very similar to the rate reported in the
2012 Science study with baboons.

Furthermore, the patterns of errors made by model were similar to those
made by the animals.

Neuronal recycling The researchers also recorded neural activity from
a different brain area that also feeds into IT cortex: V4, which is
part of the visual cortex. When they fed V4 activity patterns into the
linear classifier model, the model poorly predicted (compared to IT)
the human or baboon performance on the orthographic processing tasks.

The findings suggest that the IT cortex is particularly well-suited to
be repurposed for skills that are needed for reading, and they support
the hypothesis that some of the mechanisms of reading are built upon
highly evolved mechanisms for object recognition, the researchers say.

The researchers now plan to train animals to perform orthographic tasks
and measure how their neural activity changes as they learn the tasks.

The research was funded by the Simons Foundation and the U.S. Office of
Naval Research.


========================================================================== Story Source: Materials provided by
Massachusetts_Institute_of_Technology. Original written by Anne
Trafton. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Rishi Rajalingham, Kohitij Kar, Sachi Sanghavi, Stanislas Dehaene,
James
J. DiCarlo. The inferior temporal cortex is a potential cortical
precursor of orthographic processing in untrained monkeys. Nature
Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-17714-3 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200804134734.htm

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