Stimulus timing effects on Wada memory testing

D. W. Loring, K. J. Meador, G. P. Lee, D. W. King, B. B. Gallagher, A. M. Murro and J. R. Smith
Department of Neurology, Medical College of Georgia, Augusta.

OBJECTIVE: To determine the effects of presenting Wada memory stimuli at different times after intracarotid amobarbital injection on Wada memory asymmetries. DESIGN: Wada memory asymmetries from three timing series were related to the laterality of eventual temporal lobectomy. SETTING: Academic institution epilepsy surgery program. PATIENTS: Forty-three patients with complex partial seizures who later underwent anterior temporal lobectomy (left temporal lobectomy, 24 patients; right temporal lobectomy, 19 patients). No patient included had abnormalities on magnetic resonance imaging scans to suggest a lesion other than gliosis. RESULTS: Memory performance for objects whose presentation began approximately 45 seconds after amobarbital administration differentiated laterality of seizure onset. Memory for items presented later and after partial return of language (on average 3 minutes 40 seconds postinjection) also differed as a function of ipsilateral vs contralateral injection, but at a lower level of statistical significance. Memory for items presented last during the procedure (on average 6 minutes postinjection) discriminated seizure groups at a still lower level of statistical significance. When used to predict lateralized temporal lobe impairment in individual patients, early object memory performance was significantly better than memory performance employing either middle (56%) or late (43%) stimulus presentation timings. CONCLUSION: The results of early object memory testing are superior to those obtained from stimulus presentation later in the procedure in documenting temporal lobe dysfunction associated with a lateralized seizure onset.