Language mapping

Language mapping is often used to protect language functions during surgery for temporal lobe epilepsy or brain tumors.

Language mapping is done during surgery while the patient is awake and interactive. This is possible because the brain itself does not have pain receptors.

The patient is shown sequential pictures of common objects, while a region of the brain is electrically stimulated in one centimeter increments.

When the patient cannot successfully name objects during stimulation of a particular part of the brain, that brain area is concluded to be important for visual object naming.

The widely held belief is that visual object naming is primarily a function of the lateral [outermost] temporal lobe.

There are numerous methodologies. One protocol for cortical mapping:

1. requires awake craniotomy

2. once the temporal lobe is exposed, a recording electrode strip is placed on the brain surface

3. using a bipolar stimulator, start with a low current (e.g. 2 mA) and begin stimulating an area of the cortex for 3–5 seconds, and observe for afterdischarges (akin to a focal seizure) on the recording strip. If no afterdischarges, increase the current in 2 mA increments up to a maximum of ≈ 10 mA. If afterdischarges occur, back off by 1–2 mA and then test that area for speech changes as follows

4. stimulate cortex while patient names objects shown on picture cards (automatic verbalization, such as counting, is robust and may persist). Observe for effects including 1):

a) total speech arrest 2): on the dominant hemisphere typically in the pars opercularis or precentral gyrus, but also in frontal operculum and temporoparietal region. On the non dominant hemisphere, this ocurred only in the pars opercularis.

b) able to speak but unable to name 3) 4) (dysnomia): in dominant hemisphere, typically in posterior inferior frontal gyrus, and posterior temporal and inferior parietal regions

c) semantic errors: posterior middle temporal gyrus, anterior supramarginal gyrus and inferior frontal gyrus

d) phonological paraphrasias, neologisms and circumlocution: superior temporal sulcus

e) NB: subcortical fiber mapping may identify white matter tracts that participate in language processing (see reference 5))

5. repeat the above steps at the next area (first finding threshold for afterdischarges and then stimulating while testing).

Navigated transcranial magnetic stimulation for language mapping.

A novel analytic approach for task-related high-gamma modulation (HGM) in stereoelectroencephalography (SEEG) was developed and evaluated for language mapping.

SEEG signals, acquired from drug-resistant epilepsy patients during a visual naming task, were analyzed to find clusters of 50-150 Hz power modulations in time-frequency domain. Classifier models to identify electrode contacts within the reference neuroanatomy and electrical stimulation mapping (ESM) speech/language sites were developed and validated.

In 21 patients (9 females), aged 4.8-21.2 years, SEEG HGM model predicted electrode locations within Neurosynth language parcels with high diagnostic odds ratio (DOR 10.9, p < 0.0001), high specificity (0.85), and fair sensitivity (0.66). Another SEEG HGM model classified ESM speech/language sites with significant DOR (5.0, p < 0.0001), high specificity (0.74), but insufficient sensitivity. Time to largest power change reliably localized electrodes within Neurosynth language parcels, while, time to center-of-mass power change identified ESM sites.

SEEG HGM mapping can accurately localize neuroanatomic and ESM language sites.

Significance: Predictive modelling incorporating time, frequency, and magnitude of power change is a useful methodology for task-related HGM, which offers insights into discrepancies between HGM language maps and neuroanatomy or ESM 6).

1) , 2) , 3)
Penfield W, Roberts L. Speech and Brain Mechanisms. Princeton, NJ: Princeton University Press; 1959:103–137
4) , 5)
Chang EF, Raygor KP, Berger MS. Contemporary model of language organization: an overview for neurosurgeons. J Neurosurg. 2015; 122:250–261
Ervin B, Buroker J, Rozhkov L, Holloway T, Horn PS, Scholle C, Byars AW, Mangano FT, Leach JL, Greiner HM, Holland KD, Arya R. High-gamma modulation language mapping with stereo-EEG: A novel analytic approach and diagnostic validation. Clin Neurophysiol. 2020 Oct 16;131(12):2851-2860. doi: 10.1016/j.clinph.2020.09.023. Epub ahead of print. PMID: 33137575.
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  • Last modified: 2020/11/03 10:50
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