Language Testing

What paradigms do you use to test language function prior to surgery?  

"Classic" and "Dual Stream" models of language processing. Classic model is centered on Wernicke's (receptive) and Broca's (expressive) areas. "Dual stream" model incorporates these areas into a ventral stream (red) serving comprehension and a dorsal stream (blue) for articulation.

The "classic" model for language processing focuses on two specialized brain regions in the left hemisphere: 1) Wernicke's area (green) along the posterior superior temporal gyrus, involved in the reception and comprehension of language, and 2) Broca's area (blue) along the posterior inferior frontal gyrus, involved in expression/articulation of speech. Conduction of information from Wernicke's to Broca's areas takes place along subcortical white matter pathways, primarily the arcuate fasciculus.

Over the last decade a more complex "dual stream" model has been embraced by much of the neuroscience community, recognizing the role of additional involvement of the temporal, parietal, and frontal lobes in language processing. In this model a bilaterally organized ventral stream processes speech signals for comprehension and a strongly left-dominant dorsal stream maps acoustic speech to articulatory networks in the frontal lobe.

---

Language-related fMRI for pre-surgical planning has two primary goals: localization of eloquent cortex (Wernicke's and Broca's areas) and determination of hemispheric language dominance. No standard paradigms exist across all practices, but the most commonly used are available at the ASFNR web site referenced below. A minimum of one semantic and one phonological paradigm should be employed, and the best centers typically employ 2-3 of each. Regardless of the protocol selected, an important principle is to occupy the patient with non-language activities during control periods (e.g., showing them scrambled letters or meaningless symbols). This is required because many patients will default to language functions during rest, introducing confounding variables.

Phonologic Paradigms

Phonological paradigms are used to elicit activation of Broca's area and other parts of the dorsal stream involved in the production of sounds and articulation of language. One of the most commonly used of these is silent word generation. The subject is shown a letter (e.g., "B") and over the next 5-10 seconds is asked to silently think of as many words as possible starting with that letter ("baby", "bed", etc.) During the control/rest periods the subject is shown nonsense symbols (e.g., "✜​", "⌘").

(A)

(B)

(C)

Silent word generation task producing activation of left prefrontal cortex (A);
bilateral Broca's areas, left greater than right (B); and right cerebellum (C)

Other (mostly) phonological paradigms include rhyming ("Think of as many words that rhyme with the displayed word" or "Push the button if the pair of displayed words rhyme"), naming ("What is the object in this picture?", and antonyms ("What is the opposite of hot?"). It should be noted that no paradigm is "pure" in that both dorsal and ventral streams are commonly activated to some degree in most patients.

Semantic Paradigms

Semantic paradigms are primarily designed to elicit activation of Wernicke's area as well as other portions of the ventral stream involved in decoding language and establishing meaning. As with phonologic paradigms, some activation of Broca's area invariably occurs. The input may be auditory or visual.

Typical semantic tasks used in fMRI studies include sentence completion ("I drive to work in my ____"), true/false statements ("Is the displayed statement true or false?"), reading comprehension (whole paragraphs with questions), and listening comprehension (spoken language with questions vs garbled speech). Many other interesting variations are possible and fill the annals of neuropsychology journals.

(A)

(B)

(C)

Sentence completion paradigm. Note strong activation of Wernicke's area (A), but also other portions of the superior and anterior left temporal lobe (B,C).

Advanced Discussion (show/hide)»

Bilingual Patients

Bilingual subjects demonstrate few fMRI differences in their temporal lobe language association (Wernicke's) areas from single language patients. Broca's areas are different, however. Here the distinction is whether the second language was acquired early (in childhood) or late (as teenagers or adults).  Late bilingual subject typically have separate expressive language areas while these areas are shared in early bilingual subjects.

Kim K et al. Distinct cortical areas associated with native and second languages. Nature 1997; 388, 171-174.

Hemispheric Dominance

The degree of hemispheric dominance in an fMRI activation experiment can be quantified by a Laterality Index (LI) defined as

LI = (L− R) / (L + R)

Using this metric, a highly left hemisphere dominant person would receive a score of +1, a highly right dominant person would receive −1, and a perfectly balanced person would receive a score of zero (0). However, the LI is somewhat arbitrary in that it may change depending on the statistical thresholds used to define activation.

---

References
     Agarwal S, Sair HI, Guiar S, Pillai JJ. Language mapping with fMRI. Current standards and reproducibility. Top Magn Reson Imaging 2019; 28:225-233.  [DOI Link] (excellent recent review).
     Black DF, Vachha B, Mian A, et al. American Society of Functional Neuroradiology-recommended fMRI paradigm algorithms for presurgical language assessment. AJNR Am J Neuroradiol 2017; 38:E65-73. [DOI Link]
​    Drobyshevsky A, Baumann SB, Schneider W. A rapid fMRI task battery for mapping of visual, motor, cognitive and emotional function. NeuroImage 2006; 31:732-744. [DOI Link] (A practical and fairly comprehensive protocol for eloquent cortex mapping that can be performed in 30 min)
    Hickok G. The functional neuroanatomy of language. Phys Life Rev 2009; 6:121-143. [DOI Link] (good review by the originator of the modern "dual stream" model of speech processing)
     Hill VB, Cankurtaran CZ, Liu BP, et al. A practical review of functional MRI anatomy of the language and motor systems. Am J Neuroradiol AJNR 2019; 40:1083-1090. [DOI Link]
     Klein AP, Sabsevits DS, Ulmer JL, Mark LP. Imaging of cortical and white matter language processing. Semin Ultrasound CT MRI 2015; 36:249-259. [DOI Link]
     Price CJ. A review and synthesis of the first 20 years of PET and fMRI studies of heard speech, spoken language and reading. Neuroimage 2012; 62:816-847. [DOI Link]
    Smits M, Visch-Brink E, Schraa-Tam CK, et al. Functional MR imaging of language processing: an overview of easy-to-implement paradigms for patient care and clinical research. Radiographics 2006; 26:S145-158. [DOI Link]
     Zaca D, Jarsol S, Pillai JJ. Role of semantic paradigms for optimization of language mapping in clinical fMRI studies. AJNR Am J Neuroradiol 2013 34: 1966-1971. [DOI Link]

---

Related Questions
     Why do you have to do an "on-off" comparison? Why not just measure the absolute BOLD signal instead?
​     How are those activation "blobs" on an fMRI image created, and what exactly do they represent?

---

←  Previous Question

Next Question  →

↑ Complete List of Questions ↑