Abstracts

Magnetoencephalography (MEG) and has been used to evaluate lateralization of language function. A simple word-recognition task has been demonstrated to activate receptive language areas of the dominant hemisphere. Since this task involves memory as well as language, it may be useful to evoke activity in left mesial temporal structures subserving memory function. A non-invasive assessment of mesial temporal activity during memory processes may be a useful tool in the study of patients with temporal lobe epilepsy. We present data on mesial temporal activity as detected by MEG from a small cohort of healthy subjects during a word-recognition memory task. Data was obtained from the data sets of two previous studies using an identical protocol described below. All subjects were normal controls in those previous studies and were right-handed, native English-speaking adults with no known cognitive or neurologic abnormalities.
The word recognition-memory task involves auditory presentation of 30 words immediately prior to data acquisition with instructions to remember as many words as possible. During data acquisition subjects are audibly presented a random sequence of the 30 words they have just heard and 10 foils. Subjects were instructed to raise their right index finger if they recognize a word from the initial list of words. Event-related data were recorded over six 40-word series in each run; two runs were conducted for each subject.
Averaged event-related data were analyzed using a single equivalent current dipole model. Dipole fits were performed every 3 ms from 200 ms to 800 ms. Dipoles meeting reasonable goodness of fit and confidence volume criteria were coregistered to each subject[apos]s MRI. The presence or absence of dipole clusters in the mesial temporal regions was noted for each run. 10 subjects were screened for inclusion in this study; three were excluded due to noise or artifact in the MEG data.
Of the seven subjects, six (86%) showed left mesial temporal activation in at least one of two experimental runs; three (43%) showed left mesial temporal activity in both runs and three (43%) showed activity in only one of two runs. In contrast, only one subject (14%) showed evidence of right mesial temporal activity, and that was only in one of two runs, which also showed left mesial temporal activity. Group analysis of all runs combined shows that mesial temporal activity was detected in nine of fourteen runs (64%) on the left and one of fourteen runs (7%) on the right. MEG is capable of detecting left mesial temporal activity during a verbal memory task in some patients. While sensitivity is suboptimal using this technique, these results are encouraging. Future development of methodology and task design may yield more robust and clinically useful measurements. (Supported in part by a Clinical Research Training Fellowship from the Epilepsy Foundation of America and Abbott Laboratories.)