Which of the following describes a simple partial seizure?

A simple partial seizure, now commonly referred to as a focal seizure without impairment of consciousness, is characterized by the activity being limited to one hemisphere of the brain while the individual maintains awareness and can recall the event afterwards. This type of seizure originates in a localized region of the brain, allowing the person to experience unusual sensations, movements, or autonomic phenomena without the confusion or altered consciousness seen in other types of seizures.

In this context, it's essential to understand the other options. Seizures that involve both hemispheres of the brain typically lead to impaired consciousness or are categorized as generalized seizures, which would not apply here. Loss of consciousness and automatism are hallmarks of complex partial seizures, not simple partial ones. Lastly, the presence of tonic-clonic activity is indicative of generalized tonic-clonic seizures, which involve both hemispheres from the onset and result in loss of awareness and motor activity.

Thus, the defining features of a simple partial seizure center on its focal nature and the preservation of consciousness, affirming that the correct description is the one that specifies the limitation to one hemisphere without any loss of consciousness.