Lecture 21: Intracarotid anesthetic procedures (IAP) for speech and memory pre-surgical planning Flashcards
What are the two main reasons to carry out IAP?
1) To determine how speech and language are organized/distributed acrosss the hemispheres
- (help the surgeon really be sure about where language areas might be in a hemisphere and how language is distributed to make sure that the surgeon’s surgical approach takes these factors into account)
2) If mesial temporal resection is planned, is there risk of global amnesia aftersurgery? To assess the integrity of memory function in each hemisphere independently -
Note: The “Wada-Milner” procedure
- A lot of people refer to it as the WADA Test because he came up with half of what the test does today: he was the one that said if we put one hemisphere to sleep, we can test and see if the person can do the tasks with the other side of the brain (ex:language lateralization).
- Theodore Rasmussen worked closely with Milner. First key neuropsychology
- Milner came up more with the memory portion.
IAP Basics
- Introduced at MNI in 1950 by John Wada
- Anesthesia of one hemisphere by injection of Etomidate via internal carotid artery. Use a tube and catheter to insert anesthetic.
- also referred to as “eSAM”: etomidate speech and memory test
- Functions of the awake hemisphere are tested during inactivation of the injected one
- Simple language and memory tasks given.
General Parameters
• Drug-free practice condition before the actual test
• Angiogram (imaging technique) done beforehand to understand the vasculature of the brain, how blood vessels are distributed so know what areas will be hit by the drug. Can safely abort if there is something abnormal about vasculature in that hemisphere. Certain areas of brain you don’t want to hit (e.g., respiration, heart rate). Some patients have an anomalous blood vessel going into one of those regions.
• Anesthetic: Use micropump to get into internal carotid artery (catheter to base of brain)
• Patient wiggles hands and counts, and you look for sign of paralysis (about 40-60s)
• Anesthetic lasts for 5-7 mins for testing
• Takes some time to wear off afterward - usually over a period of 4 min after infusion is discontinued
General parameters: timeline
Before injection: establish a baseline capacity for their memory and speech and show the patients the pre injection memory objects.
- a bunch of language tests
- make sure that the patient can do these things without difficulty in fully awake condition.
- show a bunch of objects that are verbally and visually encodable (memory objects) so that after they wake up we can see if they remember the objects or not (should be able to remember them all)
During drug effect:
- speech tests are the same as during baseline (cyclically test for 7 ish minutes)
- new memory items are shown (these objects can only be processed by the hemisphere that is awake)
Stop infusion and let all of it come out of system
Test that drug is exiting by 1) simultaneous EEG recording happening and techs that are telling us about the return of electrical activity and 2) we have contralateral hemiparesis during the time that we have anesthesia so patient can only move one side of body. Keep asking patient to smile or raise hand.
Memory testing: another sort of proof/indication that the drug is washed out of system.
- Show the patient a whole bunch of objects that we showed before we made the injection, show them all the objects that we shows to only one awake hemisphere and then a bunch of objects that they have never seen (make sure they can distinguish).
ESAM speech/language tests
•Speech tasks are rotated throughout duration of hemianesthesia. We want to capture all the different abilities that hemisphere may have:
• Comprehension
• Reading single words
• Object naming
• Serial speech (e.g., name the days of the week, count)
• Spelling
• Repetition
• Note: Dr. Sziklas did not mention this this semester but you should know that these tests are administered in practice beforehand (as a control). Anything that the patient could not do is not tested during infusion.
eSAM memory tests
• 8 objects presented before injection
- to test baseline memory
• During injection show 8 more objects to awake hemisphere. Note – Dr. Sziklas did not mention this this semester but you have to make sure patient attends to these objects. “What colour is it?” “How do you use it?”
• After drug has warn off: 24 objects for a yes-no recognition test (i.e. include 8 distractor items as well)
The memory tests are simple
We do not care how the patient encodes the objects, not testing for that.
- The objects we want the patient to remember can be coded/processed visually or verbally.
- Not testing for modality-specific effects with the eSAM.
- We are testing basic memory reserve: the capacity of the hemisphere to sustain adequate function as measured by basic familiarity.
e.g. Remove right limbic MTL, patient will probably have to use verbal mnemonics to remember how to get from place to place.
Which patients undergo IAP?
- Varies across institution
- ALL surgical candidates
- selects patients
- Atypical speech dominance (to know how speech is organized)
- Further characterize memory when the routine neuropsychological exam points to bitemporal dysfunction.
Make sure that if the surgeon is going to remove some parts, that the remaining structure will be enough to support the patients memory.
Testing speech/language lateralization
One of the most important functions for humans
- Preserve during neurosurgery (needs to)
- Not all patients have language function in the left cerebral hemisphere
- Understanding how language is distributed allows us to remove safely epileptogenic (or other abnormal) areas without compromising speech/language.
Speech representation in the brain is related to?
- speech representation in the brain is related to handedness
- handedness for writing important but not guaranteed marker of speech/language representation across the brain.
- Need a more extensive “profile”of manual lateralization
REVIEW TABLE OF HANDEDNESS
How do we test speech organization?
• Not all patients have language in left hemisphere
• Speech representation in the brain is related to handedness
• See Rasmussen and Milner, 1975 table of %
• Questionnaire that taps into fine motor abilities.
• Handedness questionnaire “show me how you would put a key in a lock”, “how do you peel a potato?”, etc.
• Dichotic listening test – info to right headphone goes to left hemisphere, so right ear attending for right-handers
IAP selection criteria for language
- patient is left-handed
- not naturally right-handed
- evidence of early damage in or near left-sided speech zones
- other suggestions of right hemispheric speech representation.
Eg: seizure focus in presumed left language areas without disruption of speech (tumor, lesion)
How do we test memory function?
- The medial temporal regions in the two cerebral hemispheres play specific roles in learning and memory.
- We can use this knowledge in the clinic to lateralization medial temporal dysfunction in the brain. Give an idea of which hippocampal system may or may not be working well.
Which side of brain is more involved in learning verbal vs non-verbal in Right handed individuals.
In right handed people: Left or right side of brain is more involved, depending on what is to be learned or remembered. IN RIGHT-HANDED PEOPLE – LEFT HEM. MORE LANGUAGE, RIGHT HEM. MORE NON-VERBAL FOR MATERIAL TO BE REMEMBERED
• Verbal (L): names, numbers, word lists, stories
• Non-verbal (R: faces, abstract art, locations, melodies
• Therefore, depending on the patient deficits during testing, can try to understand where damage is
• Also carry out MRI and EEG
What about patients that show both verbal and non-verbal learning/memory problems during the psychological exam?
• Remember: Unilateral temporal damage does NOT result in global amnesia but rather in material-specific deficits in learning and memory
What about patients that show both verbal and non-verbal learning/memory problems during the psychological exam?
• Bilateral medial temporal interference.
• Is the patient at risk for severe memory deficits following unilateral medial temporal resection??
- we do not want to end up with a patient that is severely or catastrophically impaired from a memory point of view.
• IAP memory testing predicts the effect of surgery because it shows how memory can function when the targeted hemisphere is disabled.
