Originally identified by Reil (1809) and subsequently named by Burdach (1819), the arcuate fasciculus is a white-matter, neural pathway that intersects with both the lateral temporal cortex and frontal cortex via a “dorsal projection that arches around the Sylvain fissure.” (Rilling et al., 2008, pg. 426). Classical hypotheses saw this pathway as a critical component in connecting two centres of language: Broca’s area (speech production) and Wernicke’s area (speech comprehension) (Catani and Mesulam, 2008).

Much of these assumptions were based on a tentative relationship between language-impairment and damaged portions of the brain. Notably, damage to the arcuate fasciculus is implicated in a syndrome known as conduction aphasia, where an individual has difficulty in speech repetition. Often characterised by errors in spontaneous speech, an individual with conduction aphasia will be fully aware of their mistake, retaining well-preserved auditory comprehension and speech production while also being syntactically and grammatically correct (ibid).

In addition, these lesions were in the left-hemisphere (LH), leading to further speculations on a left-lateralisation for language processing. Though as we now know: language is far more distributed, and not just confined to the left-hemisphere (LH). In fact, the right-hemisphere (RH) has been shown to process prosody, discourse comprehension, connotative meaning and many other language phenomena (cf. Bookheimer, 2002). Furthermore, recent studies (cf. Hickok and Poeppel, 2004; Dronkers et al., 2007) demonstrate the arcuate fasciculus may not implicitly involved in conduction aphasia.

Despite its diminished role in language, the arcuate fasciculus is part of a renaissance in neuroscientific investigation, largely due to recent advances in brain imaging techniques. With these new methods of analysis come new hypotheses for functional aspects of brain regions and their neural networks. In particular, the dual stream model for speech and language processing (Hickok and Poeppel, 2004) has become a key in discerning the arcuate fasciculus’ role (Glasser and Rilling, 2008; Saur et al., 2008). With this in mind, the essay will now discuss and review these accounts of the arcuate fasciculus, and attempt to place it within current accounts of speech processing.

2. The anatomy, function and evolution of the arcuate fasiculus

2.1 The flaws in classical accounts of anatomy and function of the arcuate fasciculus

Prior efforts in discerning the anatomical aspects of arcuate fasciculus[1] were largely based on observations by Constantin Von Monakow, Joseph Jules Dejerine and, later on, Norman Geschwin (cf. Catani and Mesulam, 2008). Much of these earlier studies relied on post-mortems in humans, employing relatively crude methods, such as blunt dissections and myelin stain techniques (ibid).

These methods did not reveal much in-depth information concerning the arcuate’s specific anatomical terminations, just a basic outline of its pathway – stretching from the temporal lobe to the frontal lobe. This putative anatomy was used as the basis for hypothesising the arcuate’s function: a language substrate that connected speech comprehension (Wernicke’s area) with speech production (Broca’s area). More importantly, confirmation of this hypothesis relied on accounts that disconnecting the arcuate would result in conduction aphasia (ibid).

Specifically, original accounts of conduction aphasia distinguished between two groups:“[…] the Broca-like syndrome in which the deficit in repetition is accompanied by a relative impairment in fluency and the Wernicke-like syndrome in which the deficit in repetition is accompanied by a relative impairment in comprehension. One explanation for this dichotomy is that more anterior lesions encroach on Broca’s area, whereas more posterior lesions encroach on Wernicke’s area” (Catani et al., 2004, pg. 13).

These disconnectionist approaches would later be challenged by a range of studies (including: Damasio and Damasio, 1980; Naeser et al., 1982), showing the classical arcuate cannot explain cases where Broca-like and Wernicke-like conduction aphasias emerge from subcortical lesions. Subsequent studies (Hickok et al., 2000; Dronkers et al., 2007) also argue conduction aphasia is not even associated with the arcuate. This is demonstrated in several ways, including: arcuate lesions not inducing conduction aphasia (Selnes et al., 2002); left auditory cortical lesions causing conduction aphasia (Graves et al., 2008); and, cortical stimulation eliciting conduction aphasia-like symptoms (ibid).

2.2 Arcuate Fasciculus as a direct phonetic pathway

More recently, diffusion tensor imaging (DTI) tractography, a method of reconstructing white matter pathways by tracing the diffusion of water, reveals a more complex picture of the arcuate fasciculus (Catani and Mesulam, 2008).

Here, one group of studies (Catani et al., 2004; Parker et al., 2005; Powell et al., 2006) not only confirm some findings from the classical accounts, which connects the temporal lobe with the frontal lobe, they also demonstrate additional indirect pathways outside of the typical perisylvian connectivity (see figure 1). Also, there appears to be a far more extensive branching of the arcuate’s cortical terminations “[…] beyond the classical limits of Broca’s and Wernicke’s areas to include part of the middle and precentral gyrus and the posterior middle temporal gyrus, respectively.” (Catani and Mesulam, 2008, pg. 957).

Tractography reconstruction of the arcuate fasciculus showing Broca’s and Wernicke’s areas being connected through three segments: a long, direct pathway (classical arcuate); an anterior, indirect pathway; and, a posterior, indirect pathway. Taken from Catani et al. (2004).

Another reaffirmation is the apparent hemispheric asymmetry in the arcuate fasciculus. Again using DTI, Catani et al. (2007) find differences in connection patterns between the right and left hemispheres, showing a leftward lateralisation in ~80% of tested subjects. Despite language functions showing a greater degree of hemispheric distribution than originally thought (Bookheimer, 2002), left-lateralised asymmetry is still considered to be a key aspect of language processing (Catani and Mesulam, 2008).

Makris et al. (2005) observe that the left-lateralised arcuate runs alongside neuronal pathways in the superior longitudinal fasciculus (SLF). They claim the SLF can be split in four distinct components, one of which being the arcuate, and claim (on the basis of previous work by Petrides and Pandya, 2002) these fibre pathways are bidirectional. They also present a detailed anatomical description of the arcuate, showing that neurons branching out from the caudal superior temporal gyrus (which includes wernicke’s area) and the superior temporal sulcus, curving around the Sylvian fissure (caudal portion), which then: “[…] runs along with the fibers of SLF II […] AF [arcuate fasciculus] fibers continue into the frontal lobe and terminate predominantly in the dorsal part of area 8 and in area 46. AF becomes distinct mainly at the parietal opercular level.” (ibid, pg. 863).

These accounts place the classical, left-lateralised arcuate as a direct phonetic pathway, where phonologically-rooted functions are sent directly to the frontal cortex. As Catani and Mesulam (2008) explain, in discovering two additional pathways (indirect) that connect to Geschwind’s territory (corresponding to areas BA 39 and 40), the expanded arcuate also assumes a role in processing semantic information. Although, attributing semantic processing to BA 40 may not necessarily hold true, and might just be limited to BA 39 (Price, 2000). Glasser and Rilling (2008) raise issue with this, also adding that BA 40 is “[…] more likely to be involved in phonetic working memory than semantic processing, and semantic processing is found far more often in the temporal lobe.” (pg. 9). Lastly, Johnson-Frey (2008) found that grasping actions and tool use planning are represented in the left inferior parietal lobe (BA 39), leading to speculations that Geschwind’s territory might primarily be involved in complex tool use (Glasser and Rilling, 2008).

However, these anatomical and functional accounts are far from unequivocal. Another group of papers (Schmahmann et al., 2007; Saur et al., 2008; Frey et al., 2008) also place the arcuate as a direct phonetic pathway; however, they find no evidence of arcuate pathway terminations in BA 45. The basis of this assertion rests on comparative studies between humans and macaques, arguing that anatomical analysis suggests it is the extreme capsule (EmC) and the MdLF are involved in language, not the arcuate (Schmahmann et al., 2007). Instead, the arcuate, SLF, MLF and ILF (inferior longitudinal fasciculus) form a composite fibre bundle that “[…] is mainly restricted to sensory-motor mapping of sound to articulation.” (Saur et al., 2008, pg. 18035).

2.3 Arcuate fasciculus as a phonological, lexical-semantic and prosodic processor

Running contrary to the notion of the arcuate as a direct phonetic pathway are Glasser and Rilling (2008), who hypothesise it is comprised of different routes and different functions. Specifically, they posit two pathways: one terminating in the posterior superior temporal gyrus (STG) and the other in the middle temporal gyrus (MTG), with these neural pathways involving phonetic and lexical-semantic processing, respectively. Interestingly, they also implicate the right-hemispheric arcuate in phonological processing (bilateral activation) and during prosodic processing (right-lateralised activation). Both of these findings being confirmatory of a wider distributed processing of language, particularly in the right-lateralisation of prosodic processing (Ethofer et al., 2006).

In a related study, Rilling et al. (2008) further delineate the arcuate, showing specific termination points, with the superior, middle and inferior temporal gyri making up the temporal projection, whilst the frontal projection consists of the ventral premotor cortex (BA 6), pars opercularis (BA 44), pars triangularis (BA 45) and the middle frontal gyrus (BA 9). Furthermore, they offer a comparative account between the arcuate connectivity in humans, chimpanzees and macaques.

In investigating the respective pathways of all three primates, Rilling et al. show how significant differences in these lineages are suggestive of gradual modifications to cortical terminations during human evolution (see figure two). As such, chimpanzees display more structural similarity to humans in their pathway trajectories, with extensive terminations in the frontal region; however, terminations in the middle and frontal gyri are less pronounced. Being of a phylogenetically older lineage, macaques lack any temporal lobe terminations.

A Schematic summary of tractography results for humans, chimpanzees and macaques (Rilling et al., 2008). Notice the more extensive projections in the human brain.

When combined with data from two additional fibre tracts (SLF and the extreme capsule), each predicted not to show any significant differences across all three of the primates, the study reveals a very strong case for the arcuate having being subjected to selective pressure on the human lineage (ibid) – somewhat countering the claims of Schmahmann et al. (2007). Even if we accept the possibility of selection, the arcuate might not have been selected because of its apparent role in language. As the authors note, there is the possibility for aspects of the arcuate being involved in other cognitively demanding behaviours, such as tool use (cf. Johnson-Frey, 2008). However, “[…] the correspondence between the structures modified in human evolution identified in this study and structures known to be involved in language function is notable.” (Rilling et al., 2008, pg. 428).

Main References

CATANI, M., & MESULAM, M. (2008). The arcuate fasciculus and the disconnection theme in language and aphasia: History and current state Cortex, 44 (8), 953-961 DOI: 10.1016/j.cortex.2008.04.002

Glasser, M., & Rilling, J. (2008). DTI Tractography of the Human Brain’s Language Pathways Cerebral Cortex, 18 (11), 2471-2482 DOI: 10.1093/cercor/bhn011

Richard Lovelace(1618-1657),English Poet and Soldier

SET YOUR MIND FREE  :

Richard Lovelace, a romantic poet was confined within the walls of Gate House, a prison in Westminister, London. From the prison, in 1642 he wrote the poem, “To Althea, from Prison.” The poem has the following famous lines :

Stone walls do not a prison make,

Nor iron bars a cage;

Minds innocent and quiet take

That for an hermitage;

If I have freedom in my love

And in my soul am free,

Angels alone, that soar above,

Enjoy such liberty.

Those who had confined him could not stop him from exercising his ability to think and dream. No one can imprison or enslave the human mind. A human being essentially seeks to exist in a free state and when imprisoned, the man can still set his mind free to think and dream. A mind that is free, expresses its freedom in speech, in writing, and in songs and music. Speech in all of its forms conveys the ability of a man to communicate his thoughts. Fluent and cohorent speech requires the formulations of propositions, which are translated into conventional symbols, earlier acquired and readily accessible, which then reach external expression by means of an efficient vocalizing apparatus. The sequences involved in efficient speech production could be interrupted at various levels to produce different types of speech defects.

DISTURBANCES OF SPEECH  :

Intellectual impairment due to drugs, disease, and old age cause Speech Disorders.

Broca's Area - Brain's Speech Center

Co-ordination of sensory and motor functions is vital for normal Speech.

Since speech is an attribute of a free mind, it is important to understand the problems of disturbances of speech:

1. Intellectual impairment : Speech is deranged as a result of a deficit of intellectual function which prevents the organization of meaningful propositions. A person who is intoxicated cannot speak well. There are several medical conditions associated with cognitive impairment, and the level of consciousness. Apart from these problems, a person, who is uneducated as he is unwilling to learn, cannot deliver good speech. In Sanskrit language such ignorant persons are identified as ‘MOORKHA’.

2. Dysarthria and Dysphonia : Precise enunciation of words with good volume requires normal function and co-ordination of lips, tongue, palate, and the vocal apparatus called larynx. Several medical conditions could cause a defect in motor output involved in speaking and contribute to slurring  and distortion of speech.

3. Aphasias : These are speech difficulties or absence of speech where the person has no motor disorder and the articulatory system is intact. Three major varieties of aphasias are described. a. Broca’s, motor/expressive/Non-fluent aphasia : Broca’s area of brain produces verbs, builds sentences and predicts what people are going to say. Problems in this area  makes the person’s speech non-fluent as the person has profound word finding difficulties. The person speaks slowly and with great effort. The speech is described as ‘telegraphic’ because it has no grammatic structure and small connecting words (e.g., and, or, but), are missing. The person comprehends well. The person can formulate thoughts in appropriate words i.e. internal speech is preserved, but is unable to translate them into corresponding sounds. b. Wernicke’s/Sensory/Receptive/fluent aphasia : Wernicke’s area of brain is involved in learning patterns corresponding to different types of auditory stimulation. It attaches meanings, images, and feelings to sounds and to individual words. Problems in this area would result in severe impairment in comprehension of language( both spoken and written). The person speaks fluently with ease and often in large amounts. However, the speech often goes in circles( circumlocutory) and contains incorrect word usages( paraphasias). The person fails to understand or carry out spoken instructions. Internal speech is disturbed and hence there is impairment of external speech. The person cannot understand what he hears. c. Conductive aphasia :  The nerve fibers between Broca’s and Wernicke’s areas are involved in this type of problem. The person has trouble converting auditory input to verbal output. It is characterized by a marked inability to repeat words or phrases spoken to the person. d. Dyslexia and alexia :  Impairment of reading ability in individuals with normal intelligence either due to a developmental disorder or due to acquired brain lesions.

Eloquent Speech is comparable to free flowing water, the words come out continuously without any apparent effort.

SPEECH AND MENTAL LETHARGY :

A normal healthy person with normal intelligence and abilities to speak, write, read, and sing may not automatically become a fluent speaker. Human mind needs to exist in a ‘fluid’ state to maintain and sustain a high state of alertness and activity. Mental lethargy is described in Sanskrit language as “JYAADYAA”. The mental lethargy could be due to disease (‘ROGA’), ignorance ( ‘MOORKHA’) ,or could be due to a depressed condition or state of mental activity which is described in Sanskrit language as “JADATHA”. This condition of mental weakness or diminished energy is characterized by intellectual sluggishness. The mind is dull, lazy or indifferent. Whatever term is used, mental inertia, lack of interest or energy or lassitude is an important issue , and the man’s speech lacks the fluency and the mind lacks the ‘fluidity’ that is needed for co-ordinating activities. Very often, man creates ‘mental barriers’, and erects ‘mental fences’ and impedes his own intellect from generating creative thoughts and in expressing such thoughts through creative forms of speech and music. There should be no obstacles to the flow of thoughts and to its physical expression. In its natural state, a river flows without any impediments and that ‘fluid’ flowing state is important for effective human communications.

The Concept of 'Mental Fluidity' is very important to appreciate Eloquent Speech. Eloquence has a charming quality of its own, it is pleasing to the ears of the listeners and captivates the minds of the menbers of the audience. Speech should make the same impact in terms of its appeal like a scenic picture.

Kunda's whiteness symbolizes Purity.White Lotus symbolizes PurityThe white and radiant personality symbolizes Purity.

Indian Traditions about Letters, Speech, Arts and Music :

Mind if it is responding slowly, a condition described as ‘Buddhi Mandhyam’, the man cannot realize his creative potential in the field of letters, speech, arts, and music. The Vedic River of Sarasvati is personified as the patron Goddess of Speech (‘VAC or VAK’). Sarasvati enjoys an unique autonomous position and apart from man, the entire Hindu pantheon of Gods pay obeisance to Her and seek Her protection to destroy and dissolve the problem of mental lethargy which impairs mental activity. The mind of man cannot be set free unless the mental barriers and mental fences are totally eradicated and Sarasvati is allowed to flow in its natural state without impediments.

A HYMN TO WORSHIP SARASVATI  :

Jasminum multiflorum,'KUNDA', Star Jasmine, Native of India.

Moon, 'INDU' and the radiant personality of Sarasvati.

'TUSHAAR', Snow clad peaks of Himalayas, the abode of Snow/Ice.

'VEENA', stringed musical instrument, native to South India.

Nelumbo nucifera, White Lotus flower,'Shwetha Padmaa',Native of India.

The Divine Trinity-Brahma, Vishnu, and Shankara join the worship.

The Rig Vedic River Sarasvati, the source of pure, nourishing waters. The Sanskrit language and the Devnagari script originated here.

Sarasvati, the destroyer of Mental Inertia and Lethargy.

Bhagavatee,Facilitator of man's journey from Reality to Ultimate Reality.

'AUM', the Sound Invocation for Sarasvati Vandana.

Yaa Kundendu tushaara haara dhavalaa,

Yaa Shubhra vastraavritha,

Yaa Veena vara danda manditakara,

Yaa Shwetha Padmaasanaa,

Yaa Brahma Achyutha Shankara prabhrithi bhih

Devai sadaa poojitha( Vanditha)

Saa Maam paatu Sarasvatee, Bhagavatee

Nihshyesha jyaadyaapaha.

Sarasvati is defined as “Saaram vaati iti Sarasvati”, She who flows towards the Absolute is Sarasvati. For river-like streaming and fluent speech the blessings of Sarasvati would help and the mind is set free as long as the waters flow.

http://www.youtube.com/Watch?v=BWeAwNLd23o

Shevata PadmaDHAVALA - Symbolizes the Purity, Creativity, and Nourishing Qualities

• Many discussions on various forums which, though interesting, are too changeable to reference.
• If any readers would like to recommend sites or blogs please do! Feel free to recommend your own blog or poem if you like but please don’t post your poem in the comment field (provide a link and the first lines).
• Search terms used to find these posts: Rhyme, Meter, Formal, Formalist, Poetry

Life, an epic Poem

Analysis: William Blake

William Blake’s poems are methodical in construction of the meter and rhyme, every word seemingly painstakingly chosen. He uses standard formal poetry constructions like trochaic and iambic tetrameter, rhyming couplets, and quatrains in almost every one of his poems, which helped me to fully grasp these concepts in ways I never did in high school English class.

Mike Snyder’s Formal Blog

Stephen Edgar’s Stanzas

…today I just want to point out his use of regularly varying line-lengths in rhymed, metrical poetry. I’ve seen such verse called “heterometrical,” or “het-met,” for short, but Lew Turco don’t like that, not one bit, so I won’t use the terms. Not today, anyway…. A fairly simple example is the stanza Edgar uses in “Transit of Venus,” from the sequence “Consume My Heart Away.”

Poetry Foundation

Wernicke’s Area

By Martin Earl

Since poetry is now written largely without rules (or written with self-invented rules), since the common craft of metrics, rhyming, quantifying are no longer taught, largely dispensed with by the community, the result is a less universal and a more personal poem, a poem that can no longer be “read”, except by the writer and the writer’s closest cohorts – those who know the language. There is nothing intrinsically wrong with this. There is simply no need in today’s world to write or to read epics composed in ottava rima which tell the life-stories of unlikely heroes…

The Poetry Archive

Stephen Edgar

What is most immediately distinctive about Edgar’s work, certainly among poets of his generation, is his commitment to formal verse “and for showing considerable panache in handling [it]” (Kevin Hart, Oxford Companion to Twentieth-Century Poetry). This has drawn comparisons, in Australia, with poets such as A D Hope and Gwen Harwood, but also to the likes of Anthony Hecht and Richard Wilbur. Poetry Chicago says of him that “he achieves, overall, a supple classicism that earns him a place next to the best twentieth-century American formalists.”

[Looks like this book (the paperback version?) was just posted at Amazon. The publication date is June 1, 2009.]

Amazon.Com

Fourteen on Form: Conversations with Poets (Paperback)

Fourteen on Form: Conversations with Poets by William Baer. Interviews with Willis Barnstone, Robert Conquest, Wendy Cope, Douglas Dunn, Anthony Hecht, John Hollander, Donald Justice, X. J. Kennedy, Maxine Kumin, Frederick Morgan, John Frederick Nims, W. D. Snodgrass, Derek Walcott, and Richard Wilbur. When free verse and its many movements seemed to dominate poetry, other writers worked steadfastly, insistently, and majestically in traditional forms of rhyme and meter. Such poets as Anthony Hecht, Donald Justice, Derek Walcott, and Richard Wilbur utilized sonnets, villanelles, blank verse, and many other forms to create dazzling, lasting work. Their writing posed a counterpoint to free verse, sustained a tradition in English language verse, and eventually inspired the movement called New Formalism. Fourteen on Form: Conversations with Poets collects interviews with some of the most influential poets of the last fifty years.

Poetry Foundation

By Annie Finch

Listening to Poetry: On The Free Verse Brain and the Metrical Brain

Poetry’s connection with music and the right brain may be its basic identifying use and distinction as an art form, the reason it has survived through the millennia. And perhaps this essential connection is the reason that, after a century dominated so hugely by free verse, the caricature of poetry in the popular mind still remains, against all apparent reason and the weight of a century’s lived experience, inherently associated with meter…

Metrical poetry, traditionally, offers up its riches to the receptive, listening mind. The meter itself guides, and the inner or outer ear has only to hear. Reading a metrical poem aloud is rather like performing a piece of music using the instrument of your voice (and just as in music, the degree of skill in composition will significantly affect the result). When John Donne opens a sonnet with “Death be not proud, though some have called thee / Mighty and dreadful, for, thou are not so,” the weight and length of the stressed first syllable of each of these lines, in contrast to the unstressed syllable of the iambic openings of the rest of the lines in the poem, are very specifically determined. Because a metrical poem modulates individual phrases against the scaffolding of a rhythm and line-length that is mutually expected by both poet and reader, the poet can indicate, even on the page, the exact timber, tempo, and other physical characteristics the reading-aloud process should take at each point in the poem…..

PoemShape

The Art & Writing of Iambic Pentameter

The art to writing Iambic Pentameter is partly in knowing when not to write it.

Chaucer was the first poet to write full length “poems” in Iambic Pentameter. But his language was middle English, not modern. The first drama (that we know about) written in Modern English and in Iambic Pentameter (Blank Verse) was Gorboduc not by one author, but two – Sackville and Norton. Since this was probably their first crack at Iambic Pentameter, and since they wanted to make a good impression, they didn’t vary the pattern one iota. In other words, they didn’t quite know when not to write it.

Despite the fact that I’ve seen some really impactful primate related research lately, I’ve completely neglected updating Primatology.net with it. I can’t believe it has been almost three months since I’ve posted there! I should really resume posting there. Actually, I was considering putting up this following blog post over there, since it has to do with differences in neuroanatomy of the primate brain… but because these comparative studies are in the context of identifying specific architectural differences in the human brain related to language, I think posting it here is more fitting.

If you’re a reader of Neurophilosophy, you may have an idea of what research I’m referring too, the new Nature Neuroscience paper from James Rilling and team. Before I jump into this paper, “The evolution of the arcuate fasciculus revealed with comparative DTI,” please let me share another recent paper that gives some introduction about what I’m gonna talk about.

See earlier this month, Current Biology published a paper, “Communicative Signaling Activates ‘Broca’s’ Homolog in Chimpanzees,” where researchers not only confirmed that the Broca’s area as an important area of the human brain for language comprehension, but also chimpanzees have similar activity in the homologous area of their brains when communicative signals are produced or heard. The Broca’s area has long been thought to be one of the specialized functional areas of the brain for language comprehension. In fact was discovered almost 150 years ago by a physician named Pierre Paul Broca, who conducted an autopsy of patient with a speech deficit. Broca was able to determine the patient had a syphilitic lesion in the left cerebral hemisphere and identified this area as his namesake.

If you’ve heard anything about Broca’s area, it larger in the left hemisphere of the brain. Comparing activity levels between the two hemisphere, during language-related tasks, have shown the left hemisphere Broca’s area is more active. That’s due to the lateralization of the brain, which I’m sure you’ve heard of.

Anyways, the results of this study have important implications in figuring out the functional and structural differences of the human and chimpanzee brain. Why? Well, for starters, the linguistic abilities of humans have been thought to be unique to us for a while. This is a really big misconception because research on signing apes and other communicating animals, have begun to show us that we’re not alone in our abilities to symbolize information and exchange it by way of complex sound and gesture.

In order to investigate the differences of the activity between Broca’s areas in humans and related structure in chimpanzees, Taglialatela et al., put three chimpanzee subjects in PET and fMRI machines and stimulated to vocalize by putting treats just out of their reach. They then recorded the activity of the subjects would vocalize in frustration. They were able to see the very same the neuroanatomical structures associated with the production of communicative behaviors in humans, fire in chimpanzees.

Now, of course that doesn’t mean chimpanzees are gonna be reciting Shakespeare anytime soon. This leads me to the first paper I mentioned today, the one from Rilling and crew. Rilling et al., did a comparative anatomical study on the structure of arcuate fasciculus, a large white matter tract, in humans, chimpanzees and macaques. The arcuate fasciculus functions as a linker between Broca’s area and another language associated area of the brain, Wernicke’s area. The researchers used diffusion tensor imaging (DTI), a type of noninvasive medical imaging that’s a lot like MRI but it compares and contrasts the local characteristics of water diffusion within tissues.

While the arcuate fasiculus of the rhesus macaque, the chimpanzee, and the human linked up to the frontal cortex — including with Broca’s area, it was observed that the human arcuate fasiculus is much larger. It more spreads deep into the middle temporal lobe, leaving the classical Wernicke’s area. In chimps, the arcuate fasciculus made very superficial connections to the temporal cortex regions homologous to Wernicke’s area. Macaques showed a much lower extend of this integration. Rilling commented,

“We know from previous functional imaging studies that the middle temporal lobe is involved with analyzing the meanings of words. In humans, it seems the brain not only evolved larger language regions but also a network of fibers to connect those regions, which supports humans’ superior language capabilities.”

This following diagram was published in Rilling et al.’s paper and illustrates their results:

So from these two papers, the evolution of specialized language areas maybe active in both chimpanzee and human brains but as the human brain diverged from other primate counterparts, major re-wiring at the arcuate fasciculus accompanied the massive expansion of brain size. Ultimately the area that is associated with understanding word meaning, Wernicke’s area, has been strongly connected with Broca’s area.

Rilling, J.K., Glasser, M.F., Preuss, T.M., Ma, X., Zhao, T., Hu, X., Behrens, T.E. (2008). The evolution of the arcuate fasciculus revealed with comparative DTI. Nature Neuroscience DOI: 10.1038/nn2072

TAGLIALATELA, J., RUSSELL, J., SCHAEFFER, J., HOPKINS, W. (2008). Communicative Signaling Activates ‘Broca’s’ Homolog in Chimpanzees. Current Biology, 18(5), 343-348. DOI: 10.1016/j.cub.2008.01.049

from Cerebral Cortex

Functional magnetic resonance imaging and repetitive transcranial magnetic stimulation (rTMS) were used to explore the pathophysiology of auditory/verbal hallucinations (AVHs). Sixteen patients with schizophrenia-spectrum disorder were studied with continuous or near continuous AVHs. For patients with intermittent hallucinations (N = 8), blood oxygenation level–dependent (BOLD) activation maps comparing hallucination and nonhallucination periods were generated. For patients with continuous hallucinations (N = correlations between BOLD signal time course in Wernicke’s area, and other regions were used to map functional coupling to the former. These maps were used to identify 3–6 cortical sites per patient that were probed with 1-Hz rTMS and sham stimulation. Delivering rTMS to left temporoparietal sites in Wernicke’s area and the adjacent supramarginal gyrus was accompanied by a greater rate of AVH improvement compared with sham stimulation and rTMS delivered to anterior temporal sites. For intermittent hallucinators, lower levels of hallucination-related activation in Broca’s area strongly predicted greater rate of response to left temporoparietal rTMS. For continuous hallucinators, reduced coupling between Wernicke’s and a right homologue of Broca’s area strongly predicted greater left temporoparietal rTMS rate of response. These findings suggest that dominant hemisphere temporoparietal areas are involved in expressing AVHs, with higher levels of coactivation and/or coupling involving inferior frontal regions reinforcing underlying pathophysiology.