19. Lugaresi E, Cirignotta F, Montagna P. Nocturnal paroxysmal dystonia. Epilepsy Res Suppl 1991;2:137-140. 20. Tinuper P, Cerullo A, Cirignotta F, Cortelli P, Lugaresi E, Montagna P. Nocturnal paroxysmal dystonia with short- lasting attacks: three cases with evidence for an epileptic fron- tal lobe origin of seizures. Epilepsia 1990;31:549-556. 21. Swartz BE, Halgren E, Delgado-Escueta AV, et al. Neuroim- aging in patients with seizures of probable frontal lobe origin. Epilepsia 1989;30:547-558. 22. Henry TR, Sutherling WW, Engel J Jr, et al. Interictal cere- bral metabolism in partial epilepsies of neocortical origin. Ep- ilepsy Res 1991;lO: 174-182. 23. Henry TR, Chugani HT, Abou-Khalil BW, Theodore WH, Swartz BE. Positron emission tomography. In: Engel J Jr, ed. Surgical treatment of the epilepsies. 2nd ed. New York: Raven Press, 1993;211-232. 24. Berkovic SF, Newton MR, Rowe CC. Localization of epileptic foci using SPECT. In: Luders H, ed. Epilepsy surgery. New York: Raven Press, 1991:251-256. 25. Berkovic SF, Newton MR, Chiron C, Dulac 0. Single photon emission tomography. In: Engel J Jr, ed. Surgical treatment of the epilepsies. 2nd ed. New York: Raven Press, 1993:233-243. 26. Stefan H, Bauer J, Feistel H, et al. Regional cerebral blood flow during focal seizures of temporal and frontocentral onset. Ann Neurol 1990;27:162-166. 27. Marks DA, Katz A, Hoffer P, Spencer SS. Localization of ex- tratemporal epileptic foci during ictal single photon emission computed tomography. Ann Neurol 1992;31:250-255. Mesial temporal spikes interfere with working memory Gregory L. Krauss, MD; Michael Summerfield; Jason Brandt, PhD; Steven Breiter, MD; and Daniel Ruchkin, DEng Article abstract-The hippocampus and other mesial temporal structures support long-term memory and also are common foci for epilepsy. Recently it was shown that these brain structures may subserve the short-term storage and rehearsal processes called working memory in humans. We determined the accuracy of verbal and visuospatial working memory in the presence and in the absence of mesial temporal spikes in eight patients who had bilateral depth electrodes implanted to evaluate intractable epilepsy. Six of eight patients had declines in working memory performance during mesial temporal spiking, with the greatest disruption in spatial and verbal recall coincident with left hippocampal spikes (p = 0.019). Overall accuracy of working memory for all patients declined an average of 6% on spike trials. The two patients who did not have decreased accuracy during spike trials also had the best overall working memory performance. Mesial temporal spikes were not detected on extracranial recordings and yet may be associated with declines in working memory in some patients with epilepsy. NEUROLOGY 1997;49:975-980 The hippocampus, long known to be involved in stor- ing episodic information and retrieving it from long- term memory, is also the most frequent seizure focus in patients with complex partial seizures. Recently it has been shown in humans that the hippocampus may be involved in the rehearsal mechanisms and short-term storage that make up working memory.2 Spikes recorded extracranially interfere with work- ing memory in some patients with temporal lobe ep- ilepsy, causing brief hesitations or errors in discrim- ination task^.^-^ It is unclear, however, whether the hippocampus is involved in these spike-related inter- ruptions, since spikes from the mesial temporal lobe are usually not detected from outside the skull.8 This study examined whether hippocampal and mesial temporal interictal spiking in patients with partial seizures interferes with working memory. We evalu- ated verbal and spatial working memoryg (figure 1) in epilepsy patients who had depth electrodes placed stereotactically in hippocampus and other mesial temporal structures (parahippocampus, amygdala) as well as orbital frontal cortex. Methods. Subjects and electrode placement. We studied eight consecutive patients who had intracranial depth elec- trodes placed symmetrically in right and left frontal and temporal cortex for the purpose of localizing seizure foci. Depth electrode wires (each with eight electrodes) were placed using CT/stereotaxy. Depth electrode targets were right and left orbital frontal cortex, entorhinal cortex and amygdala, and hippocampus and parahippocampal gyrus (figure 2). Electrodes were placed via superior frontal burr holes with a trajectory through basal ganglia to inferior frontal and mesial temporal targets. Each depth electrode wire consisted of eight platinum cylindrical electrodes spaced along an 8-cm tress. Frontal tress electrodes were spaced 6.5 mm apart. Hippocampal and amygdalar tresses consisted of five inferior temporal electrodes spaced 5 mm From the Departments of Neurology (Dr. Krauss and M. Summerfield), Psychiatry (Dr. Brandt) and Neuroradiology (Dr. Breiter), Johns Hopkins University; and the Department of Physiology (Dr. Ruchkin), University of Maryland Medical School, Baltimore, MD. Received January 17, 1997. Accepted in final form May 13, 1997. Address correspondence and reprint requests to Dr. Gregory L. Krauss, Johns Hopkins Epilepsy Center, 600 N. Wolfe Street, Meyer 2-147, Baltimore, MD 21287-7247. Copyright 0 1997 by the American Academy of Neurology 976