What characterizes a "generalized seizure"?

A generalized seizure is characterized by the involvement of both hemispheres of the brain simultaneously. This means that the electrical activity that leads to the seizure spreads across both sides, causing widespread effects. These seizures can manifest in various forms, including tonic-clonic seizures, absence seizures, and myoclonic seizures, among others. The bilateral nature signifies that the seizure does not originate from a specific focal point but instead engages the entire brain, which can lead to a loss of consciousness or altered awareness depending on the type of generalized seizure.

In contrast, the other options describe different seizure characteristics. A seizure affecting one hemisphere of the brain refers to focal or partial seizures, which can remain localized and may or may not spread to other areas. A seizure that occurs without any warning signs might suggest an absence seizure, but it does not encapsulate the concept of generalized seizure, which is defined by its bilateral involvement. Thus, the defining feature of a generalized seizure is indeed its simultaneous effect on both hemispheres.