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Broca's Area Identified
French neurologist Paul Broca identified lesions in the anterior region of the left hemisphere of the brain as affecting speech production. -
Wernicke's Area Identified
(date is approximate-definitely 1874) German neurologist and psychiatrist Carl Wernicke observed brain lesions in the left posterior section of the superior temporal gyrus that caused aphasia (major impairment of language comprehension but little change in speech patterns). -
Mr. C. Cannot Read
For a few days in the fall of 1887, Mr. C experienced some minor, sporadic symptoms that today we recognize as strokes. Suddenly, on October 16, he could no longer read although he could still speak, recognize objects and people, and write brief notes. Thinking he might have a vision problem, he consulted his ophthalmologist, who referred him to a neurologist (Dehaene 54). -
Diagnosis: "Pure Verbal Blindness"
Mr. C was examined by French neurologist Joseph-Jules Dejerine on November 15, 1887. Dr. Dejerine's diagnosis was the first recorded scientific conclusion about the cerebral bases of reading. He called Mr. C's problem "pure verbal blindness" or loss of the visual recognition of letter strings. The implication was that the brain contains a cortical "visual center for letters" designated just for reading (Dehaene 55). -
Autopsy Reveals a Lesion of Left Posterior Hemisphere
A second stroke 4 years later killed Mr. C, who had never recovered his ability to read. Autopsy revealed lesions in "the occipital lobe, and particularly the circumvolutions of the occipital pole, starting at the base of the cuneus, as well as those of the lingual and fusiform lobules." Dejerine proposed that the lesions caused a disconnect with other areas of the brain that normally add knowledge of letters to visual stimulus. (Dehaene 60). -
Electroencephalography Applied to Human Brain
Hans Berger measures differences in neural currents on the scalp's surface. It becomes the first human EEG. EEG uses a voltmeter to measure the differences in voltage generated on the scalp's surface by neural currents (Dehaene 77). -
Magnetoencephalography is Invented.
David Cohen and his colleagues at MIT design the Magnetoencephalography (MEG) which measures real-time brain activity. Later, Tarkiainen and colleagues conduct MEG studies to reveal that the brain processes words on the left side of the brain and faces on the right side of the brain. -
Use of Positron Emission Topography (PET)
Steve Petersen, Michael Posner, Marcus Raichle, and colleagues are first to use PET to visualize which brain areas consume energy when a person reads. For details on how this is done, see pages 66-67. PET has validated earlier work by Broca and extended knowledge of brain activity related to speech and reading. -
Talairich's Atlas of the Brain Published
A system of mapping cortical locations was developed by French surgeon Jean Talairach and refined by researchers at the Montreal Neurological Institute. Similar to geometrical positioning systems like the earth's GPS, Talairach's system uses three perpendicular axes that fit the brain's size. Talairach's mapping shows that the letterbox area is similar across individuals and experimental laboratories. (Dehaene 70). -
Ogawa's Team at Bell Laboratories Invent Functional Magnetic Resonance Imaging (fMRI)
Modern MRI creates computer images of lesions from patients and pastes them together in a unified space, correcting for individual differences in brain shape and size. This allows scientists to pinpoint the area that plays a crucial role in the fast identification of a letter string and its transmission to other areas that compute pronunciation and meaning. The anatomical location is the left occipito-temporal area, which the author calls "visual word form area" or "the brain's letterbox." -
Allison, McCarthy, & Colleagues Conduct Intracranial Research at Yale
In the 1990's Allison, McCarthy, & Colleagues from Yale University conducted intracranial research on over 100 patients. By placing electrodes in direct contact with the brain's cortical surface, the studies confirmed what was discovered earlier: signals appeared in the left hemisphere for words and the right hemisphere for faces. Furthermore, single electrodes would react massively to words while its neighboring electrodes exhibited no response. These were later termed microterritories. -
Puce Maps Visual Stimuli Differences
Neuroradiologist Aina Puce was the first to use fMRI to investigate visual preferences in the brain. Scientists can tell that neurons in the visual cortex are specialized for certain categories of shapes, but knowledge is limited because they cannot see the actual neurons--just the peak responses to faces or words, etc. This and other evidence indicates the letterbox area is dedicated to visual analysis and ignores the spoken word. -
Allison et al Discover Left-hemisphere Preference for Words vs. Faces
Neurologists Truett Allison, Gregory McCarthy, and colleagues at Yale University surgically placed electrodes in direct contact with the cortical surface, confirming the incredible speed of our visual system and verifying data from all other sources. "The ventral surface of ...brain contains a systematic arrangement of visual recognition devices, all tuned to different categories of images... the letterbox area is..sandwiched between areas responsive to faces and objects" (Dehaene 82). -
Culture Fashions the Brain
Tarkiainen's (1999) study uses MRI results to show how the brain responds better to real words than to strings of letters that violate spelling patterns of the participants' language. -
Cohen, 2000, & Molko, 2002 Observe Hemi-Lexia
Words entering the visual system from the right and left side are both filtered to the left hemisphere language, or letterbox, areas. If the corpus callosum (large bundle of nerves connecting both hemispheres) is damaged, images from the opposite visual side cannot enter the left hemisphere resulting in a reading impairment. -
Logothetis and Group at Max Planck Institute Prove fMRI Shows Functioning vs. Non-functioning Neurons
Functional magnetic resonance imaging (fMRI) has largely supplanted the PET scan because it is widely available and is totally harmless, requiring no injection of radioactive substances. It allows scientists to measure the variances in the cerebral network for reading from person to person. Functional MRI has verified that everyone has a letterbox in approximately the same location, even though the details of individual cortical folds are unique. -
Dehaene Further Studies Subliminal Word Recognition
In 2001 Dehaene's experiments reveal that written words can be recognized subliminally. When words were flashed and repeated in a sequence, the response time for the repeated word recognition increased, and activity in the left hemisphere diminished with the recognition. This was true even if the word's graphic form was changed from upper to lowercase. -
Tarkiainen, Cornelissen and Salmelin Use MEG to Track Time To the Letterbox
Antti Tarkiainen and colleagues at the University of Helsinki used magnetoencephalography (MEG) to measure magnetic activity in the brains of volunteers viewing words and faces. Visual processing includes 2 stages: first-pass analysis within 100 milliseconds after the image first appeared on the retina; sorting of the input images 50 milliseconds later. During sorting, words evoked a response in the left hemisphere and faces evoked a response predominantly in the right side (Dehaene 78). -
Polk & Farah Experiment with Mixed-Case Words
Polk and Farah measure brain activity using an MRI while participants read words in mixed case, such as HoTeL. Words in mixed case, as well as words in homogenous case, triggered the same amount of brain activity.
