**4.2 Epileptogenic focal neocortical and allocortical/limbocortical networks (pathogenesis and pathophysiology of focal-onset, aware or unaware, seizures with secondary propagation, bilateral spreading or generalization**

Focal seizures manifesting with a variable combination of auras, sensory, motor, limbic or autonomic, aware or unaware seizures with secondary unilateral or bilateral propagation and generalization represent the collective phenotype of focal-onset, propagated or secondarily generalized epilepsy. They can occur at any age, but would be more common among the adult-onset epilepsies or in patients with an apparently normal brain development, who have never had previously any seizures in young life. Although there are no obvious neurological deficits or abnormal brain development, thorough investigations may reveal a range of subtle focal brain abnormalities or insults (structural, ischaemic/vascular, inflammatory, infectious, metabolic, autoimmune, neoplastic, degenerative, epigenetic, etc) which could be part of localised or more widespread epileptogenic networks [1–6]. On the other hand, focal/multi-focal or generalized symptomatic epilepsies are usually associated with some kind of focal or generalized brain dysfunction, injury or developmental abnormality. People with symptomatic epilepsies have neurological or cognitive deficits and a higher chance of intellectual disability, cerebral palsy, Lennox-Gastaut syndrome and other neurodevelopmental conditions/ problems. Nowadays, as a result of widespread applications of epilepsy surgery with direct intracranial EEG recordings, focal neocortical and allocortical/limbocortical epileptogenic networks have been more thoroughly studied and better understood [1–6].

Please see the example below of a focal-onset musicogenic seizure with progressive ipsilateral propagation, bilateral spreading and secondary generalization in a patient who turned out to have an autoimmune (GAD65 + ve antibody-mediated) limbic encephalitis (**Figures 23**–**25**).

#### **Figure 23.**

*Against a normal background upon the patient listening to one of her favourite songs from her childhood (previously she had been exposed to all sort of different music styles, including the most dysharmonic/atonality scales of Schoenberg's dodecaphony) a single high-amplitude sharp wave appeared over the left frontotemporal (maximum at anterior temporal F7 electrode) region, followed by a widespread desynchronization/attenuation of the EEG for 1–2 s.*
