"The question is," said Alice, "whether you can make words mean so many different
"The question is," said Humpty Dumpty, "which
is to be the master--that's all." --Lewis Carroll
(Through the Looking-Glass)
Neurologists have found a tiny area of tissue--about 1
centimetre square--near to Wernicke's area that lights up only when consonants
are heard. --Rita Carter (1998:150)
Neuro term. A component of the brain, such as
Broca's or Wernicke's area, which governs the use of manually
articulated (i.e., signed) or vocally articulated (i.e., spoken) language. Also, an association (arcuate) fiber
link, such as the arcuate fasciculus, connecting verbal components.
Usage: Verbal centers are used to control the production and/or
comprehension of linguistic communication and words.
Hypothesis. Speech seems to
have evolved its own specialized sensorimotor production-and-decoding system
(see below, Embryology and Neuro-notes)--above and beyond that
which is used for nonverbal expression (see below, Nonverbal speech
areas). However, speech has not evolved its own semantic information
content. The latter is housed in brain modules (e.g., of the parietal
association areas and the frontal lobes) which are shared by verbal and
nonverbal media alike. Thus, speech is special but not that special.
KNOWN VERBAL CENTERS
Angular gyrus. A visible bulge
on the cerebral cortex marking regions of the occipital, parietal, and temporal
lobes (behind Wernicke's area) which link visual word recognition with other
Arcuate fasciculus. A tract of association
fibers connecting Broca's and Wernicke's areas. In a less robust form, the
arcuate fasciculus may predate--and thus may be a preadaptation for--speech.
Similar tracts of association fibers (the superior longitudinal fasciculus,
inferior longitudinal fasciculus, and uncinate fasciculus) found in the
right-brain hemisphere connect nonverbal centers of the cerebral cortex.
Basal ganglia. "It is likely that the enlargement of the
prefrontal cortex reflects, in part, its role in speech production. The rewiring
appears to involve the basal ganglia; data from recent comparative studies
suggest that basal ganglia circuits may be the key to the unique brain bases of
human speech and syntax" (Lieberman 1991:106-07).
area. A premotor module of the neocortex (in the lower lateral frontal
lobe; specifically, Brodmann's areas 44 and 45) identified in 1861 by Paul Broca
as essentially involved in the production and control of human speech. Damage to
this area (called Broca's aphasia) produces problems in speaking (while
comprehension of another's speech is left unimpaired). According to Philip
Lieberman, Broca's area ". . . has no functional equivalent in nonhumans"
(Lieberman 1991:24; but see below, Evolution I and II). Recently,
a language module immediately anterior to Broca's area has been identified,
which suggests that the Broca module may be involved in sequencing complex
articulations which are not just limited to speech. Broca's area does not seem
to control syntax (i.e., the combinatorial or grammatical arrangement of speech
elements; see below, Neuro-notes II).
Insula. Some regard
the insula as a verbal center (see, e.g., Ardila 1999). Damage to the left
insula may result in language disturbances, including Broca's aphasia,
conduction aphasia, speech apraxia, mutism, and the word-deafness of Wernicke's
aphasia (Ardila 1999). ("Then on the other hand, recent studies of anatomical
connections of the insula point to an important viscero-limbic role and it has
been suggested that the insula may influence verbal motivation and verbal
affect" [Ardila 1999].)
Planum temporale. "The planum temporale
(PT) is a key site within Wernicke's posterior receptive language area in the
left hemisphere of the human brain and is thought to be an epicenter within a
dispersed mosaic of language-related regions in the cerebral cortex. The left
hemisphere predominance of the PT is more pronounced than any other human brain
asymmetry" (Gannon 1998:220). (See below, Neuro-notes.)
Wernicke's area. A supplementary-auditory module of the neocortex
(in the left temporal lobe; specifically, Brodmann's areas 39, 40, posterior 21
and 22, and part of 37) identified as involved in the understanding of auditory
words. Damage to this area (called Wernicke's aphasia) produces problems in
deciphering the meanings of the speech sounds one hears (even of one's own
speech sounds). According to a recent study, Wernicke's area is not unique to
Homo (see below, Neuro-notes).
Apes. Magnetic resonance imaging (MRI) scans of chimpanzees, bonobos,
and gorillas suggest that, like humans, these great apes also have an enlarged
Brodmann's area 44 (part of Broca's area in the human brain). Writing in the
journal Nature (2001), Claudio Cantalupo and William Hopkins (Emory
University and Georgia State University) suggest the brain homologue may be due
to a link between primate vocalization and gesture. Captive apes, the
researchers note, usually gesture with the right hand as they
Embryology. 1. "It is important to recognize
that the speech areas of the human brain are already formed before birth . . ."
(Eccles 1989:87). 2. The temporale plane is larger in the left fetal
brain hemisphere than in the right (Stromswold 1995). 3. "Development of
the cortical regions that subserve language in the left hemisphere consistently
lags behind the development of the homologous regions in the right hemisphere
[to await speech development]" (Stromswold 1995:860).
Evolution I. 1. "The evolutionary origin of human language
may have been founded on this basal anatomic substrate, which was already
lateralized to the left hemisphere in the common ancestor of chimpanzees and
humans 8 million years ago" (Gannon 1998:220). 2. Regarding endocasts of
Homo habilis skulls: "There was a further development of the inferior
frontal lobule in the Broca area, but most remarkable was the rounded fullness
of the inferior parietal lobule [corresponding to part of Wernicke's area]"
Evolution II. In non-human primates, Broca's
area controls muscles of the face and vocal tract. 1. "The homologue of
Broca's area in nonhuman primates is the part of the lower precentral cortex
that is the primary motor area for facial musculature" (Lieberman 1991:106).
2. In monkeys, the link between Broca-like and Wernicke-like areas is not
as massively connected as it is in humans (Aboitiz and Garcia
Nonverbal speech areas. With regard to language,
relationships between the right (nonverbal) and left (verbal) hemispheres are
still poorly understood, with more deference being paid by researchers to the
left-hand (i.e., dominant) side. 1. In the right cerebral hemisphere,
modules control the production and interpretation of the nonverbal communication
that accompanies words, e.g., facial
expressions, voice tones, and gestures of the arms and hands. (Some of the latter, hand
gestures are actually more verbal than nonverbal [see, e.g., MIME
CUE].) 2. Prosody--the emotional content of
speech--is right hemispheric in human beings with left-hemisphere verbal
centers. 3. The right (or non-dominant) hemisphere is less involved in
literal meanings of a speech element than it is with interpreting the figurative
meanings conveyed by, e.g., hesitations, humor, metaphor, poetry, and voice
tone. 4. Damage to the right parietal lobe's angular gyrus and
supra-marginal gyrus results in a. problems using spatial concepts,
b. difficulties dressing one's own body, c. feeling spatially
disoriented, d. inability to draw simple 3D pictures, and e.
neglect of left-handed body parts and objects to the
Stuttering. "But the stutterers were far less left-dominant;
activation in their brains was shifted toward the right in both the motor and
auditory language areas, revealing an inherent difference in the way the two
groups [normal and stutterers] process language" (Barinaga 1995:1438).
E-Commentary: "I have two
questions about the arcuate fasciculus, the fiber bundle from Wernicke's area to
Broca's area. Can anyone help me? 1. Are there also fibers going in the opposite direction, from Broca's
area to Wernicke's (we know that many cortico-cortical connections are
bidirectional--what about this one?)? 2. How many fibers are we talking about? 3. A third question: What can anyone tell me
about connections between Wernicke's area and the angular gyrus? (Bidirectional?
How many fibers?) Thanx loads." --Syd Lamb, Linguistics and Cognitive Science,
Rice University Houston TX 77251-1892 USA; smlamb@OWLNET.RICE.EDU (Sydney M
Lamb) (Tue Jan 30 14:02:03 1996)
Neuro-notes I. In most humans, Wernicke's area is significantly
larger in the left hemisphere than it is in the right. Its asymmetry dwarfs that
of most other cerebral-cortex modules. And yet, though specialized for language,
Wernicke's area is not unique to Homo. Recently, e.g., Patrick Gannon and
his colleagues measured the corresponding area of chimpanzee brains. After
spreading apart 15 chimp brains at the temporal lobe (i.e., at the sylvian
fissure), they measured the planum temporale, and found it to be larger on the
left than on the right in 14 cases (Gannon et al. 1998).
II. "Lesions to Broca's area and its vicinity do not affect semantic
abilities, nor do they disrupt basic syntactic abilities. Most notably, Broca's
aphasics combine lexical meaning into propositions, create and analyze sentences
of considerably complex structure, and are also able to synthesize and analyze
words morphophonologically. It thus follows that most human linguistic
abilities, including most syntax, are not localized in the anterior language
areas--Broca's area and deeper white matter, operculum, and anterior insula"
Neuro-notes III. 1. "We can assert
unequivocally: no combinatorial language abilities reside in the non-dominant
cerebral hemisphere" (Grodzinsky2000). 2. "Thus the evidence is that this
side of the brain has an important an role in communication, but makes no
syntactic contribution to language use" (Grodzinsky2000).
IV. "However, it should be kept in mind that neither of the classical
language areas, Broca's area and Wernicke's area, are cortical areas in the
strict sense in which the term area is used by an [sic] neuroanatomist. For
example, they are not defined according to the same strict and multiple criteria
that are employed in defining primary visual cortex (area 17), and each includes
more than one architectonically distinct area" (Killackey 1995:1248).
Neuro-notes V. Mirror neurons: Mirror neurons may play an important role in Broca's area: A. Consider Maurizio Gentilucci's abstract for the 2012 conference on "Mirror Neurons: New Frontiers 20 Years After Their Discovery": "Studies of primate premotor cortex, and, in particular, of the so-called mirror system, including humans, suggest the existence of a double hand/mouth motor command system involved in ingestion activities. This may be the platform on which a combined manual and vocal communication system was constructed. . . . we suggest that this system evolved a system controlling words and gestures: we propose that this system is located in Broca's area." B. ". . . Broca's area activates when subjects observe another individual speaking without hearing the sound . . ." (Fogassi and Ferrari 2007:139).
Neuro-notes VI. Mirror neurons: Broca's area mediates the production of speech as well as certain hand movements: "First, area F5 [of the monkey premotor cortex (which is homologous with our Broca's area)] contains motor neurons related to the execution of both hand and mouth actions. Similarly, brain-imaging experiments in humans demonstrated that Broca's area, traditionally considered a 'speech' area, is also involved in hand-movement tasks such as complex finger movements, mental imagery of grasping actions, and hand-imitation tasks (Rizzolatti & Craighero, 2004)" (Fogassi and Ferrari 2007:139).
Copyright 1998 - 2013 (David B. Givens/Center
for Nonverbal Studies)