# Real-Time Localization of Epileptogenic Foci EEG Signals: An FPGA-Based Implementation
## 1 Introduction  
Epilepsy is a common neurological disorder usually described by seizures which are recurrent in nature. This disorder can be produced by different brain disorders, such as brain tumors, intracranial hemorrhages and brain malformations [1], and depending on the affected area, a disorder may generate, apart from epileptic seizures, malfunctions in motion and patient perception [2]. An epileptic seizure is a period of time where the patient experiences a set of symptoms with different levels of severity: uncontrolled shaking movements of the body with loss of consciousness(generalized tonic-clonic seizure), shaking movements of a specific part of the body with different levels of consciousness (focal seizure), or short moments of focal seizures with impairment of awareness (absence seizure). Epileptic seizures can be originated by abnormal, synchronous, or even excessive brain neural activity, causing a temporary disruption to the way that the brain normally works. Anyway, what happens to someone during a seizure depends on the affected part of the brain and how far the seizure activity disseminates in the brain. Epilepsy can be classified primarily into two types: generalized and partial (or focal) epilepsy [3]. Generalized onset seizures affect, at the same time, both sides of the brain or groups of cells on both sides of the brain. On the other hand, focal onset seizures (the term focal is used instead of partial to be more accurate when talking about where seizures begin) usually start in one area or group of cells on one side of the brain. The activity of the brain is usually registered using either electroencephalography (EEG) or functional magnetic resonance imaging (fMRI). Although fMRI has better spatial resolution, the use of the multidimensional time series generated from electroencephalogram EEG is more popular, as it allows high precision time measurements, is functionally fast and is relatively cheap. The EEG epileptogenic source's localization has been studied for decades [4; 5]; however, the methods were not implemented in clinical practices until recently. Nowadays, the EEG is considered a noninvasive and useful test to assess whether a pharmacoresistant patient can benefit from the resective epilepsy surgery [6]. As the resective surgery aims to remove surgically the brain sections involved in the focal onset epilepsy, it is important to distinguish precisely between \"focal signals,\" those recorded in brain areas where first ictal signals are detected, and \"non-focal signals,\" those registered from brain areas not related to the seizure onset [7]. Many patients with epilepsy may require EEG signals to be recorded from deep structures of the brain using intracranial electrodes. Usually, the focus localization is essentially made using registers acquired monitoring the patient 24 h a day, during a stay of several days in an epilepsy monitoring unit (EMU). In these kind of units, apart from scalp EEG (and intracranial electrodes to record signals from deep structures of the brain, in many patients), the epilepsy patients are recorded on video, along with their speech and movements. Thus, all data are collected targeting the evaluation of its seizure disorder, seeking to gather data before a seizure starts, during one and during recovery. The evaluation of this information can be used to locate candidate areas for the epileptogenic focus, although in some cases it is not enough to locate the epileptogenic focus precisely prior to the surgery. The visual analysis of the EEG recordings of seizures with intracranial electrodes can help in locating the seizure. However, visual inspection is a hard and time consuming process that can be affected by the clinician subjectivity. In addition, it is not easy to determine the seizure source by a direct visual inspection of the EEG signal recordings. To select candidate areas from EEG signals could be helpful a computerized analysis of the EEG [8; 9].