No abstract

The human brain has the capacity to rapidly change state, and in epilepsy these state changes can be catastrophic, resulting in loss of consciousness, injury and even death. Theoretical interpretations considering the brain as a dynamical system suggest that prior to a seizure, recorded brain signals may exhibit critical slowing down, a warning signal preceding many critical transitions in dynamical systems. Using long-term intracranial electroencephalography (iEEG) recordings from fourteen patients with focal epilepsy, we monitored key signatures of critical slowing down prior to seizures. The metrics used to detect critical slowing down fluctuated over temporally long scales (hours to days), longer than would be detectable in standard clinical evaluation settings. Seizure risk was associated with a combination of these signals together with epileptiform discharges. These results provide strong validation of theoretical models and demonstrate that critical slowing down is a reliable indicator that could be used in seizure forecasting algorithms.

SUMMARYPurpose: To systematically study the semiology of psychogenic nonepileptic seizures (PNES) captured by videoelectroencephalography (EEG) monitoring (VEM) and categorize the typical patterns observed. Methods: VEM records of patients who underwent evaluation from January 2002 to June 2007 were reviewed to identify those who had PNES with or without a background of epilepsy. The semiology of each event was visually analyzed and entered into a statistical database. Type of movement, anatomic distribution, synchrony, symmetry, onset, offset, course, duration, vocalization, hyperventilation, eye movements, and responsiveness were evaluated. PNES were classified into distinct groups according to the predominant motor manifestation. Results: A total of 330 PNES from 61 patients were studied. Based on semiology, six different types of PNES were observed as follows: (1) rhythmic motor PNES characterized by rhythmic tremor or rigor-like movements (46.7%); (2) hypermotor PNES characterized by violent movements (3.3%); (3) complex motor PNES characterized by complex movements such as flexion, extension, abduction, adduction, rotation, with or without clonic-like and myoclonic-like components of varying combinations and anatomic distribution (10%); (4) dialeptic PNES characterized by unresponsiveness without motor manifestations (11.2%); (5) nonepileptic auras characterized by subjective sensations without any external manifestations, marked in the VEM records as ''seizure button presses'' (23.6%); and (6) mixed PNES where combinations of above seizure types were seen (5.2%). In a given patient, all the seizures belonged to a single type of PNES in 82% of cases. Discussion: PNES can be classified into six stereotypic categories. Contrary to common belief, PNES demonstrates stereotypy both within and across patients.