Fernando Silva

Epilepsies as Dynamical Diseases of Brain Systems: Basic Models of the Transition Between Normal and Epileptic Activity

Summary:u2002 Purpose: The occurrence of abnormal dynamics in a physiological system can become manifest as a sudden qualitative change in the behavior of characteristic physiologic variables. We assume that this is what happens in the brain with regard to epilepsy. We consider that neuronal networks involved in epilepsy possess multistable dynamics (i.e., they may display several dynamic states). To illustrate this concept, we may assume, for simplicity, that at least two states are possible: an interictal one characterized by a normal, apparently random, steady ‐state of ongoing activity, and another one that is characterized by the paroxysmal occurrence of a synchronous oscillations (seizure).

Intracranial EEG Seizure-Offset Termination Patterns: Relation to Outcome of Epilepsy Surgery in Temporal Lobe Epilepsy

Summary: Purpose: Studies using stereo‐EEG (SEEG) and electrocorticography (ECoG) should not only identify a patients epileptogenic zone, but also should provide prognostic information for surgical outcome. In this respect, seizure‐offset patterns have so far been the subject of only one study, in which they were shown to be associated with poor outcome when recorded over cortical areas outside the temporal lobe of seizure onset. To clarify whether seizure‐offset patterns are reliable in predicting seizure outcome, we studied SEEG/ECoG in a similar group of patients with temporal lobe epilepsy (TLE).

Signal Processing of EEG: Evidence for Chaos or Noise. An Application to Seizure Activity in Epilepsy

The EEG is an important signal for the diagnosis of functional disturbances of the brain, and in particular, of epilepsy. The non-linear dynamical analysis of EEG signals recorded during seizure activity in comparison with on-going signals allowed us to formulate a hypothesis about the generation of epileptic activity. According to this model, epilepsy should be envisaged as a dynamical disease of neuronal networks, that may exhibit different types of attractors, i.e., may present bifurcations. One of these attractors is characterized by the generation of irregular oscillations, typical of epileptic seizures.

Regional Specific Changes in Glutamate and GABA A Receptors, PKC Isozymes, and Ionic Channels in Kindling Epileptogenesis of the Hippocampus of the Rat

The stimulation of certain pathways of the brain with short series of electrical pulses, repeated at regular intervals, causes progressive changes in the underlying neuronal networks. These changes become manifest as afterdischarges of progressively longer duration. At a given stage, these afterdischarges propagate to related brain areas and eventually lead to the occurrence of seizures of focal onset that can become generalized. Goddard who discovered this phenomenon,9 named it kindling, a designation that describes in a striking manner the progressive character of the development of this type of epileptogenic focus. We chose to investigate the basic mechanisms responsible for kindling epileptogenesis in the CA1 area of the hippocampus of the rat inducing kindling by stimulating the Schaffer collaterals of the axons of the CA3 pyramidal cells.