Abstracts

RATIONALE: The memory application of the Intracarotid Amobarbital Procedure (IAP) gives information about medial temporal lobe (MTL) function but it is invasive and has a high financial cost. There have been some recent attempts to develop a reliable functional magnetic resonance imaging (fMRI) paradigm that may eventually replace the IAP. Using an fMRI paradigm modeled upon our IAP memory task, we investigated memory function in healthy volunteers and patients with temporal lobe epilepsy.
METHODS: Eighteen healthy volunteers and nine patients with temporal lobe epilepsy were scanned using a 1.5T clinical imaging system. The volunteers were of similar age and education as the patients. Structural MRI, EEG and neuropsychological data were available on the patients. One hundred twenty coloured pictures of objects were shown, interleaved with meaningless coloured patterns (control condition). These stimuli were chosen for similarity with our IAP, which uses a series of real objects for memory testing. Memorizing objects is expected to engage both the left and the right temporal lobes because objects are both verbal (they have names) and nonverbal (can be pictured). The fMRI task was to memorize the pictures for a later recognition test. Activity of brain regions during picture presentation was compared with that obtained in the control condition.
RESULTS: Healthy individuals recognized on average 85% of the pictures compared to 72% for the patient group. All healthy subjects showed bilateral activity in the MTL. This finding is consistent with the expected participation of either or both hemispheres during the IAP object memory task. In contrast, among the 9 patients studied, only two showed bilateral activity. Six showed unilateral activity in the left MTL, and there was no MTL activity in one. These findings will be discussed in light of the patients[ssquote] presumed damage according to EEG, anatomical MRI, basic neuropsychological data and IAP results.
CONCLUSIONS: Our fMRI memory paradigm provides analogous information to that of our IAP and is proving useful as a complementary tool in the preoperative investigation of patients with intractable temporal lobe epilepsy. Furthermore, it opens a window on details of brain structures that underlie IAP performance and memory function. Thus this fMRI task not only supplements the current IAP with additional clinical information, but it will also allow exploration of brain plasticity in learning and memory.
[Supported by: This work was supported by Grant MT144991 from the Canadian Institutes of Health Research to M. Jones-Gotman. L. Forster is supported by CNPq, Brazil.]