EEG and evoked potential recording from the subthalamic nucleus for deep brain stimulation of intractable epilepsy Dudley S. Dinner a, * , Silvia Neme a , Dileep Nair a , Erwin B. Montgomery Jr a , Kenneth B. Baker a , Ali Rezai b , Hans O. Lu ¨ders a a Department of Neurology, The Cleveland Clinic Foundation, Desk S51, 9500 Euclid Avenue, Cleveland, OH 44195, USA b Department of Neurosurgery, The Cleveland Clinic Foundation, Desk S31, 9500 Euclid Avenue, Cleveland, OH 44195, USA Accepted 28 March 2002 Abstract Objectives: The substantia nigra in the animal model has been implicated in the control of epilepsy. The substantia nigra pars reticulata (SNpr) receives afferents from the subthalamic nucleus (STN), which thus may have an effect on the control of epilepsy. There is evidence in the animal model of a direct connection from the cortex to the STN. High-frequency STN stimulation is being used in experimental trial for the management of intractable epilepsy. Our primary objective in this study was to determine if there was epileptiform activity recorded from the STN in association with scalp recorded epileptiform activity to support the presence of a pathway from the cortex to the STN in humans as described in animals that may be important for the management of epilepsy. This article describes the interictal and ictal electroencephalo- graphic (EEG) findings as well as evoked potential recordings from the STN in these patients with intractable epilepsy. Methods: Four patients (3 males) ranging from 19 to 45 years with intractable focal epilepsy refractory to anti-epileptic drugs were studied. Two patients failed vagal nerve stimulation and one patient had previous epilepsy surgery. Depth electrodes were implanted stereotactically in the STN bilaterally. A comparative analysis of the interictal and ictal activities recorded from the scalp and STN electrodes was performed. Median nerve somatosensory evoked potentials (SEPs) and auditory evoked potentials (AEPs) were also recorded. Results: Interictal sharp waves recorded in the scalp EEG were always negative in polarity. These sharp waves were always associated with sharp waves recorded at the ipsilateral STN electrode contacts that were always positive in polarity. In addition repetitive spikes were recorded independently at the left or right STN electrode contacts, with no reflection at the scalp. These spikes were extremely stereotyped, of high amplitude and short duration, and were positive or negative in polarity. Focal scalp EEG seizures were also recorded at the ipsilateral STN electrodes. In 3 patients SEPs were recorded from the contralateral STN electrodes corresponding to the P14/N18 far-field complex. In two patients AEPs were recorded, and wave V (near-field) and wave VII (far-field) from the contralateral STN electrodes. Conclusions: This study demonstrates that scalp recorded epileptiform activity is reflected at the ipsilateral STN either following or preceding the scalp sharp waves. The STN sharp waves are most probably an expression of the direct cortico-STN glutamatergic pathways that have been demonstrated previously in animals. This pathway in man may be important with regard to a possible mechanism for the treatment of epilepsy with STN stimulation. q 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Epilepsy; Seizures; Subthalamic nucleus; Deep brain stimulation 1. Introduction Of patients with newly diagnosed epilepsy approximately 70% will become seizure free with anti-epileptic drugs (AEDs) (Annegers et al., 1979; Brorson and Wranne, 1987; Camfield et al., 1993; Shafer et al., 1988). About half of the patients who are refractory to AEDs may be candidates for surgical resection. The remaining patients may be considered for alternative management such as vagal nerve stimulation (VNS) or other treatment modalities such as deep brain stimulation (DBS). Direct stimulation of the brain was first used in the 1970s when Cooper et al. (1973, 1976) attempted to achieve control of seizures by cerebellar stimulation. This was followed by stimulation of deep brain nuclei including the centromedian thalamic nuclei (Fisher et al., 1992; Velasco et al., 1987, 1989, 1993a,b, 1995), the anterior thalamus (Cooper et al., 1980; Sussman et al., 1988), and the caudate nucleus (Sramka and Chkhenkeli, 1990). There are several epilepsy centers that are currently involved in trials of DBS of the thalamus or the subthalamic nucleus (STN) in the management of intractable epilepsy. At the Cleveland Clinical Neurophysiology 113 (2002) 1391–1402 1388-2457/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S1388-2457(02)00185-2 www.elsevier.com/locate/clinph * Corresponding author. Tel.: 11-216-444-5540; fax: 11-216-445-4378. E-mail address: dinnerd@dccf.org (D.S. Dinner). CLINPH 2001093