1. Intracarotid Amobarbital Procedure (IAP) (a.k.a. Wada Test)
Goals and Rationale
Procedure
Angiogram
Cognitive Testing
Episodic Memory - Encoding
Language
Episodic Memory – Retrieval
Case Example
Limitations and Alternatives

2. IAP – Goals & Rationale Lateralize Speech
more posterior resection >> better seizure outcome
variable speech localization within dominant temporal lobe
caution when operating in dominant hemisphere
higher rates of right or bilateral speech lateralization in epilepsy
Sites where electrical stimulation disrupted naming
of objects described (auditory) and/or shown (visual)
to 40 patients

3. IAP – Goals & Rationale Assess Functional Adequacy & Reserve
Adequacy – ability of MTL on side of resection (ipsilateral) to support memory function
Reserve – ability of MTL on other side of resection (contralateral) to support memory function
Adequacy/Reserve can be independent of structural damage
Post-op memory decline less likely with low adequacy/high reserve
Post-op memory decline more likely with high adequacy/low reserve
Side of
Resection
Contralateral
Ipsilateral
Functional
Adequacy
Functional
Reserve

4. Screening for Patients at Risk for Amnesia
10 reported cases of amnesia after ATL in 50 years (9 of 10 left ATL)
Some anatomic or neurophysiologic evidence/suggestion of low reserve in all cases
Led to idea that dentifying patients with low reserve may prevent surgery and resultant amnesia

5. IAP – Procedure
Test Speech and Memory Capacity of Each Hemisphere in Isolation
unilateral administration of short acting barbiturate (sodium amobarbital (Amytal ®))
produces 2-8 minutes of hemianesthesia (‘brain numbing”)
patient remains awake, variably alert
behavioral tasks test capacity of non-anesthetized (contralateral) hemisphere to support speech and memory
If speech is intact, other side is sufficient for speech. If not, injected side is necessary for speech.
If memory is intact, other side is sufficient for memory. If not, injected side is necessary for memory.

6. IAP – Procedure Angiogram
numb groin area (lidocaine), puncture right femoral artery
thin catheter (tube) threaded into internal carotid artery (ICA) under continuous x-ray guidance
inject radio-opaque dye to determine distribution of flow from ICA to different brain areas
Angiogram provides ‘preview’ of where amobarbital is going and structures it is expected to affect
Angio needed to identify potential problems
Cross-flow – numbs both sides, patient may go to sleep
Reflux down basilar to brain stem – patient may stop breathing

7. Vascular Supply to the Brain
ACA
MCA
PCA
IAP
Catheter tip
placed here
(ICA)
ACom
ACA
ACA
ICAs
MCA
MCA
PComs
PCA
PCA
ICA = Internal carotid artery
ACA = Anterior cerebral artery
MCA = Middle cerebral artery Acom=Anterior Communicator
PCA = Posterior cerebral artery Pcom=Posterior Communicator

8. Cerebral Angiogram Lateral View (from Side)
MCA
ACA
PCA

9. Cerebral Angiogram AP View (Anterior-to-Posterior)
ACA
MCA

10. IAP – Cognitive Testing
Patient places hands up in air, starts counting
Sufficient amobarbital injected to obtain hemiparesis (evidence of anesthetic effect)
Episodic Encoding
Show 8 objects 4-8 secs each, place in hand, ask to name, assess visual tracking if cannot name
Test arm/grip strength to monitor hemianesthesia
Stop presenting objects when arm/grip strength begins to return

11. IAP – Language Testing Critical Aspects of Language to Assess
observe frequency of paraphasic errors over time
expect gradual resolution after speech-dominant injection
poor comprehension, speech arrest or dysarthria (slurred speech) may reflect attentional or motor deficits, not primary language deficits
Language Tasks
follow simple commands (‘touch the large circle’
name pictured objects (‘harmonica’, ‘helicopter’, ‘rhinoceros’)
repeat phonemically complex phrases (‘Limes are sour.’, ’The spy fled to Greece.’, ‘Rolled Wire and Bar Mill’)

12. IAP – Episodic Retrieval
Wait until arm strength and behavior have recovered
Assess different levels of episodic retrieval
Spontaneous recall – “Tell me the objects I showed you”
Recognition
Present target objects intermixed with similar objects patient has never seen (foils)
“Did I show you the …..?
Forced Choice – if no recognition or recognize target and foil
Show target and 2 foils – “I showed you one of these. Which one did I show you?”
Memory Score = % of items correct
Also interpret qualitatively

13. Case Example 51 y.o. seizures since age 37
Video-EEG – left anterior temporal, complex partial seizures
MRI – Left MTS with benign appearing tumor
Baseline neuropsych exam – normal, except for moderate deficits in delayed verbal recall

14. Impressions from IAP Left speech dominance
Left injection – speech arrest>>> global aphasia >> frequent paraphasic errors that resolved as hemiparesis resolved
Right injection – somnolence and dysarthria – named memory items - a few questionable paraphasias, but language elements mostly intact
Left injection - Right hemisphere memory (functional reserve)
Intact - 100% correct recognition with high confidence
Right injection - Left hemisphere memory (functional adequacy)
Intact quantitatively (7/8 (87%) on forced choice)
Impaired qualitatively – no recognition, all forced choices were guesses

15. Double Dissociation of Speech and Memory in this Patient
LH Injection (‘Lesion’)
(RH functioning alone)
RH Injection (‘Lesion’)
(LH functioning alone)
Speech
Observation
Unable to name objects
Able to name objects
Interpretation
RH is insufficient
LH is necessary
RH is unnecessary
LH is sufficient
Memory
Able to recognize objects
Unable to recognize objects
RH is sufficient
(High Functional Reserve)
LH is unnecessary
RH is necessary
LH is insufficient
(Low Functional Adequacy)
High Functional Reserve + Low Functional Adequacy
= Low Risk of Post-op Memory Decline

16. Limitations General Predicting amnesia
invasive – 1% risk of stroke
over-sedation can produce ambiguous results
young children do not tolerate femoral puncture
Predicting amnesia
can’t assess reliability
always hard to predict rare outcomes
‘false’ failures (fail but don’t become amnestic after surgery) occur regularly
‘true’ failure rate is unknown (failures often don’t have surgery)
Predicting less-than-amnestic decline
Only 1 of 6 studies shows IAP adds information to other predictors

17. Is fMRI a viable Alternative?
Advantages
non-invasive
repeatable
multiple tasks
may also localize
high agreement with IAP for language
Disadvantages
requires pt. be still for ~ min.
some tasks too difficult for low IQ patients
limited validity for memory assessment so far
does not identify critical areas
may over-call mixed dominance

18. Individual fMRI Results IAP Left Dominant Patient

19. How Well Does fMRI predict IAP Language Lateralization
How Well Does fMRI predict IAP Language Lateralization? 530 subjects in 22 different studies
fMRI
Atypical
Left
Total 86 14
100
Sensitivity = 86/100= 86%
IAP 34
396
430
Specificity = 396/430= 92%
120
410
530
Accuracy = 482/530 = 91%

20. fMRI Speech Localization
Speech Dominance
Right (IAP)
Left (IAP)
Left (Hand)
Tivarus, 2012