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Functional Mapping

Functional Mapping. • Locating motor, sensory and language functions during surgery is important for minimizing post-op deficits. Knowing cortical and subcortical anatomy important for predicting where areas are on pre-op images.

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Functional Mapping

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  1. Functional Mapping

  2. • Locating motor, sensory and language functions during surgery is important for minimizing post-op deficits. • Knowing cortical and subcortical anatomy important for predicting where areas are on pre-op images.

  3. • Frontal operculum and temporal lobe are important for language and speech. • Broca’sis the posterior, inferior frontal gyrus (or frontal operculum), is for speech production (measured as speech arrest during counting). • Wernicke’sproduces anomia, where you can’t name stuff.

  4. • Neocortex is the phylogenetically newest, and has 6 layers. • Layer 4 gets lots of input, layers 2 and 3 have small/med pyramidal cells for cortico-cortical connections, and layers 5 has large pyramidal cells that go to subcortical targets, and layer 6 has multipolar neurons that go to the thalamus.

  5. Brodmann organized it by number, according to cytological characteristics. • Cells may be pyramidal neurons that project to other parts of cortex and subcortical areas, or they may be interneurons for processing within the cortex.

  6. • Neurons have columnar organization in their connections. • Sensory cortex has a big layer 4 (input), motor cortex a big layer 5 (output to CST). • • The internal capsule is full of projections to and from the cortex.

  7. o Anterior limb – contains anterior thalamic peduncle and corticopontinetract. • This was disrupted in old-school lobotomies for mental illness. • o Genu – coticobulbar and corticoreticular tracts.

  8. o Posterior limb – corticospinal tract, superior thalamic peduncle, corticotecal/rubral/reticular tracts. • Motor stuff is anterior to sensory stuff. • The anterior motor parts are organized somatotopically with the face medial and arm/leg lateral.

  9. Strokes that only affect the motor part are common, called pure motor stroke. • The posterior part has sensory fibers from the thalamus. • o Retrolenticular portion – posterior thalamic peduncle for visual info.

  10. o Sublenticular IC – inferior thalamic peduncle for auditory info. • • Blood supply to the internal capsule: The posterior limb and retrolenticular are supplied by the internal carotid, via the posterior communicating and anterior choroidal arteries.

  11. The anterior limb is partially supplied by the anterior cerebral, via the recurrent artery of Heubner. • The middle cerebral artery supplies most of the internal capsule via lenticulostriate branches to the anterior/posterior limbs and genu.

  12. • fMRI can detect changes in brain hemodynamics, allowing you to see what brain structures participate in different functions. • This may allow for language localization as part of presurgicalplanning. • But, fMRI is still insufficient compared to cortical stimulation, since fMRI also highlights a lot of noncritical language sites. • It is used to speed up the cortical stimulation procedure though.

  13. • Diffusion tensor imagine tracks the diffusion of water through the brain. • It diffuses faster parallel to axons due to membrane hydrophobicity, so can delinate specific neuronal tracts.

  14. This may help you find key landmarks in pathologically distorted images. • Subcorticalstimulation mapping is still the best. • • Intraoperative cortical stimulation is done with an Ojemann cortical stimulator.

  15. It is the gold standard for localizing motor/sensory/language areas. • Lower frequency stimulation is less likely to stimulate an area, but also less likely to cause a seizure.

  16. • A strip electrode is used for motor mapping, and may be supplemented by a handheld stimulator if borders need to be better defined. • With motor stimulation, the surgeon applies the current and the anesthesiologist looks for associated movement. • EMG activity is also observed. • Areas producing effects are labeled.

  17. • Stimulation mapping of speech is done by having the patient count during stimulation. • Awake intraoperative stimulation is done to localize language areas near Broca’s and Wernicke’s areas.

  18. Although the mechanism is poorly understood, disrupting these areas is most easily detected as changes in inhibitory speech systems.

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