Prefrontal Cortex Origin for Rhythmic Ictal Nonclonic Hand Motions

Semiological Challenges in Frontotemporal Seizure Localization

The localization of focal seizures depends heavily on ictal semiology, the clinical signs that reflect the activation of specific brain networks during an event [1]. For patients with drug-resistant epilepsy, interpreting these signs is a cornerstone of presurgical evaluation, offering vital clues to the seizure onset zone [2]. However, the diagnostic process is often complicated by an overlap of symptoms between different epileptogenic networks, particularly within frontotemporal regions [3]. While advanced neuroimaging and video analysis are improving the objective quantification of seizure-related movements, the clinician's interpretation of specific motor signs remains paramount for guiding invasive monitoring [4, 5]. A recent case study provides detailed intracerebral evidence that refines the localizing value of a specific hand motion previously associated primarily with temporal lobe networks.

Clinical Presentation of Prefrontal Seizure Activity

The investigation centered on a 37-year-old right-handed man with non-lesional focal drug-resistant epilepsy, a challenging clinical scenario where seizures persist despite appropriate medication and standard structural imaging reveals no clear abnormality. To precisely identify the seizure origin, the patient underwent stereoelectroencephalography (SEEG), an invasive monitoring technique where depth electrodes are surgically placed to record electrical activity directly from deep brain structures. His seizures presented with a complex motor sequence, often beginning with right upper limb elevation and left hemiballistic movements, which are large-amplitude, involuntary flinging motions suggesting involvement of high-level motor control pathways.

Characterizing Rhythmic Ictal Nonclonic Hand Motions

A key semiological feature in this case was the presence of rhythmic ictal nonclonic hand (RINCH) motions of the right hand. These movements are clinically distinct from the more common manual automatisms, such as fumbling or picking, as they possess a sustained, rhythmic quality without the jerking of a clonic seizure. While often seen contralateral to the seizure focus in temporal lobe epilepsy, their manifestation in this patient offered a crucial diagnostic clue. The timing of these movements was consistent, occurring 3 to 13 seconds after seizure onset, suggesting a close link to the initial ictal discharge rather than later propagation. Furthermore, RINCH motions were present in half of the recorded seizures, establishing them as a reliable marker in this patient's semiology. Critically for localization, the study found that these rhythmic hand motions could be the only motor sign of a seizure. This observation suggests that when RINCH occurs in isolation, it may serve as a primary indicator of seizure origin, pointing toward the prefrontal cortex.

Intracerebral Evidence for Frontal Localization

The stereoelectroencephalography (SEEG) recordings provided definitive, high-resolution intracranial evidence of the seizure's origin. The data revealed that seizure onset occurred in the left caudal prefrontal cortex, directly linking the patient's complex motor semiology to the frontal lobe. This finding is significant because it demonstrates that signs often attributed to temporal lobe networks can, in fact, arise from primary discharges in prefrontal regions. The seizure onset zone was further localized to the left middle frontal gyrus and sulcus, an area involved in motor planning and executive function. This anatomical precision establishes a direct electrographic correlation between ictal discharges in the middle frontal gyrus and the observed RINCH motions of the contralateral (right) hand. By identifying this specific gyrus as the source, the study provides strong evidence that early-onset RINCH can reliably indicate a prefrontal seizure organization.

Reevaluating the Localizing Value of RINCH

Rhythmic ictal nonclonic hand (RINCH) motions have traditionally been considered a useful lateralizing sign in temporal lobe epilepsy (TLE), where they are usually observed contralateral to the seizure focus. The findings from this case, however, reinforce that the localizing value of this sign requires a more nuanced interpretation. RINCH motions have been previously associated with frontal or fronto-temporal epilepsy, and their correlation with prefrontal ictal discharges has been described in a small series of patients with TLE, suggesting prefrontal network involvement even when the seizure originates elsewhere. This case provides direct evidence that the middle frontal gyrus can serve as the primary generator of these movements. For the practicing clinician, this has direct implications for presurgical evaluation. The authors conclude that early onset RINCH movements, whether isolated or part of broader motor semiology, can indicate a prefrontal organization of the seizures. Their appearance within seconds of an event should prompt consideration of a frontal lobe focus, a critical distinction that can guide electrode placement and surgical planning by challenging the conventional association with temporal lobe dysfunction.

References

1. Chowdhury FA, Silva R, Whatley B, Walker MC. Localisation in focal epilepsy: a practical guide. Practical Neurology. 2021. doi:10.1136/practneurol-2019-002341

2. Beniczky S, Tatum WO, Blumenfeld H, et al. Seizure semiology: ILAE glossary of terms and their significance. Epileptic Disorders. 2022. doi:10.1684/epd.2022.1430

3. Oane I, Barborică A, Mı̂ndruță I. Ictal semiology in temporo‐frontal epilepsy: A systematic review and meta‐analysis. Epileptic Disorders. 2024. doi:10.1002/epd2.20328

4. Ahmedt‐Aristizabal D, Armin MA, Hayder Z, et al. Deep learning approaches for seizure video analysis: A review. Epilepsy & Behavior. 2024. doi:10.1016/j.yebeh.2024.109735

5. Caroppo A, Manni A, Rescio G, Carluccio AM, Siciliano P, Leone A. Movement Disorders and Smart Wrist Devices: A Comprehensive Study. Sensors. 2025. doi:10.3390/s25010266