Transcript NEUROANATOMY OF LANGUAGE 1 SEPT 13, 2013 – DAY 8 Brain & Language LING 4110-4890-5110-7960 NSCI 4110-4891-6110 Harry Howard Tulane University.

NEUROANATOMY OF
LANGUAGE 1
SEPT 13, 2013 – DAY 8
Brain & Language
LING 4110-4890-5110-7960
NSCI 4110-4891-6110
Harry Howard
Tulane University
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Brain & Language - Harry Howard - Tulane University
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Course organization
• The syllabus, these slides and my recordings are
available at http://www.tulane.edu/~howard/LING4110/.
• If you want to learn more about EEG and neurolinguistics,
you are welcome to participate in my lab. This is also a
good way to get started on an honor's thesis.
• The grades are posted to Blackboard.
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Review
• Syntax
1. Kiss Mary, I would never do.
2. [VP kiss Mary] I would never do
3. *Kiss, I would never do Mary.
4. *[VP kiss] I would never do [VP Mary]
• By the way, how do you know which ones are bad?
• Because you are an expert in the grammar of your native language.
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NEUROANATOMY OF
LANGUAGE
Ingram §3
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Short history of research
Date
Event
1836
Abercrombie?
1836
Marc Dax claimed that the LH of right-handers has “memory for words”
1861
Paul Broca claimed that the LH of right-handers has “faculty of articulate speech”
1874
Karl Wernicke discovered that damage to a certain area could cause receptive aphasia.
John Hughlings Jackson claimed that the LH is responsible for language, while the RH
is responsible for visual cognition (recognition, discrimination, recall).
WWIII
Many observations of the cognitive results of head injuries
end
WWII
Juhn A. Wada developed test for cerebral dominance for speech by injecting an
anesthetic into the right or left internal carotid artery
1950s
Penfield & Wilder use cortical stimulation to map the cortex > treat epilepsy, discover
the motor-sensory homunculus
1960s
Corpus callosotomy (commissurotomy) > split-brain patients
1970s
Hemifield tachistoscopy, dichotic listening > laterality research
1980s
Noninvasive imaging techniques
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Overview of methodologies
• Lesions
• Wada test
• Craniotomy & cortical stimulation
• Corpus callosotomy & split-brain patients
• Hemifield tachistoscopy
• Dichotic listening
• Imaging: C(A)T, PET, (f)MRI
• Electromagnetic: EEG, MEG - not today
• Transcranial magnetic stimulation (TMS)
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Lesions
• A lesion is a non-
specific term referring
to abnormal tissue in
the body. It can be
caused by any disease
process including
trauma (physical,
chemical, electrical),
infection, neoplasm,
metabolic and
autoimmune.
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Wada test
• The Wada test (named for a neurologist, Juhn A.
Wada) consists of behavioral testing after the
injection of an anesthetic (such as sodium
amobarbital or sodium methohexital) into the right
or left internal carotid artery.
• Depending on how the injection is made (and the
quantity), there is a certain amount of time during
which the activities of one of the cerebral
hemispheres are suspended, so the abilities
subserved by the other hemisphere can be tested
in isolation.
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Craniotomy & cortical stimulation
• A craniotomy is a surgical operation
in which part of the skull, called a
skull flap, is removed in order to
access the brain.
• Craniotomies are necessary for
many types of surgery; they are
also widely used in neuroscience in
techniques such as extracellular
recording, brain imaging, and
manipulations such as electrical
stimulation and chemical titration.
• Human craniotomy is usually
performed under general
anesthesia but can be also done
with the patient awake using a local
anaesthetic and generally does not
involve significant discomfort for the
patient.
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Corpus callosotomy (split-brain patients)
• “Split-brain” is a lay term to describe the result of
severing the corpus callosum to some degree.
• The surgical operation to produce this condition is called
corpus callosotomy.
• It is rarely performed, usually only in the case of epilepsy,
in order to mitigate the risk of accidental physical injury by
reducing the severity and violence of epileptic seizures.
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Corpus callosotomy (split-brain patients),
cont.
• A patient with a split brain, when shown an image in his or
her left visual field (the left half of what each eye sees),
will be unable to name what he or she has seen.
• This is because the speech control center is in the left
side of the brain in most people and the image from the
left visual field is sent only to the right side of the brain.
• Since the two sides of the brain cannot communicate, the
patient can't name what he or she is seeing.
• The person can, however, pick up a corresponding object
with their left hand, since that hand is controlled by the
right side of their brain.
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Divided visual-field (hemifield)
tachistoscopy
• A tachistoscope is a
device that displays an
image for a specific
amount of time.
• It can be used to
increase recognition
speed, to show
something too fast to
be consciously
recognized, or to test
which elements of an
image are memorable.
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Dichotic listening
• Dichotic listening is a procedure
commonly used for investigating
selective attention in the
auditory domain.
• Two messages are presented to
both the left and right ears (one
message to each ear), normally
using a set of headphones.
Normally, participants are asked
to pay attention to either one, or
both (divided attention condition)
of the messages and may later
be asked about the content of
both.
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The cocktail party effect
• Dichotic listening was developed to mimic processing demands
in the natural world, where sensory overload is common.
• Consider the cocktail party or, more appropriate for today, the
wine-tasting party.
• We may attempt to speak with one individual, but the speaker's
voice is intermixed with a multitude of incoming auditory
signals: conversations going on about us, music from the
compact disc player, the clatter of plates being filled at the
buffet table, the children watching a video in the next room.
• Despite this cacophony of sound, we are quite proficient at
focusing on the relevant signal—the words being spoken by
our conversational partner.
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The right-ear advantage
• In the seminal study of Kimura (1961), the stimuli were digits,
presented so that one digit was heard in the left ear at the same time
as a second digit was heard in the right ear.
• Kimura found that people were much more likely to report having
heard the stimuli presented to the right ear, an effect dubbed the rightear advantage.
• Kimura’s usage of dichotic listening to confirm the lateralization of
language to the left hemisphere in normal subjects was soon
substantiated by studies with lesioned subjects.
• Kimura (1961b) showed that patients with left temporal lobe lesions performed
worse at the task than did patients with right temporal lobe lesions.
• In addition, split-brain patients showed a considerable right ear advantage in a study
using words as stimuli.
• They succeeded in recognizing words presented to the right ear, but performed no
better than chance for words presented to the left ear.
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Computerized (Axial) Tomography
(CT/CAT)
• Computed
tomography
(CT), originally known as
computed
axial
tomography (CAT or CT
scan),
employs
tomography
(digital
geometry processing) to
generate a 3D image of
the internals of an object
from a large series of twodimensional X-ray images
taken around a single axis
of rotation.
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Positron Emission Tomography (PET)
To produce a PET scan, a patient
is administered a solution of a
metabolically-active substance,
such as glucose, tagged with a
positron-emitting isotope. The
substance eventually makes its
way to the brain and concentrates
in areas of high metabolism and
blood flow, which are presumably
triggered by increased neural
activity. The positrons emitted by
the isotopes are collected by
detectors arrayed around the
patients’ body and converted into
signals which are amplified and
sent to a computer for
construction of an image.
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PET vs CT
• PET differs from CT in that it uses the body’s basic
biochemistry to produce images.
• The positron-emitting isotope is chosen from elements
that the body already uses, such as carbon, nitrogen,
oxygen, and fluorine.
• By relying on normal metabolism, PET is able to show a
biochemical change even in diseases such as
Alzheimer’s in which there is no gross structural
abnormality.
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Magnetic Resonance Imaging (MRI)
•
•
•
•
In 1977, a team lead by Raymond
Damadian produced the first
image of the interior of the human
body with a prototype device
using nuclear magnetic
resonance.
Damadian’s device uses liquid
helium to supercool magnets in
the walls of a cylindrical chamber.
A subject is introduced into the
chamber and so exposed to a
powerful magnetic field.
This magnetic field has a
particular effect on the nuclei of
hydrogen atoms in the water
which all cells contain that forms
the basis of the imaging
technique.
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Magnetic Resonance Imaging (MRI)
All atoms spin on their axes. Nuclei have a positive electronic charge,
and any spinning charged particle will act as a magnet with north and
south poles located on the axis of spin. The spin-axes of the nuclei in
the subject line up with the chamber’s field, with the north poles of the
nuclei pointing in the ‘southward’ direction of the field. Then a radio
pulse is broadcast toward the subject. The pulse causes the axes of the
nuclei to tilt with respect to the chamber’s magnetic field, and as it
wears off, the axes gradually return to their resting position (within the
magnetic field). As they do so, each nucleus becomes a miniature radio
transmitter, giving out a characteristic pulse that changes over time,
depending on the microenvironment surrounding it. For example,
hydrogen nuclei in fats have a different microenvironment than do
those in water, and thus transmit different pulses. Due to such
contrasts, different tissues transmit different radio signals. These radio
transmissions can be coordinated by a computer into an image. This
method is known as magnetic resonance imaging (MRI), and it can be
used to scan the human body safely and accurately
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functional Magnetic Resonance Imaging
(fMRI)
An elaboration of MRI called functional MRI (fMRI) has become the
dominant technique for the study of the functional organization of the
human brain during cognitive, perceptual, sensory, and motor tasks. As
Gregg (2002) explains it, the principle of fMRI imaging is to take a
series of images in quick succession and then to analyze them
statistically for differences. For example, in the blood-oxygen-level
dependent (BOLD) method introduced by Ogawa et al. (1990), the fact
that hemoglobin and deoxyhemoglobin are magnetically different is
exploited. Hemoglobin shows up better on MRI images than
deoxyhemoglobin, which is to say that oxygenated blood shows up
better then blood whose oxygen has been depleted by neural
metabolism. This has been exploited in the following type of procedure:
a series of baseline images are taken of the brain region of interest
when the subject is at rest. The subject then performs a task, and a
second series is taken. The first set of images is subtracted from the
second, and the areas that are most visible in the resulting image are
presumed to have been activated by the task.
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NEXT TIME
Ingram §3: Neuroanatomy of language, any leftovers
☞ Go over questions at end of chapter.