We studied the incidence and clinical significance of early post-traumatic seizures after severe closed head injury.

This prospective study is based on clinical observation of 3340 adult patients with severe closed head injuries, each of them having a Glasgow Coma Scale (GCS) 3 to 8 after trauma. Anticonvulsant agents were not given to these patients unless there was evidence of seizure.

One hundred and twenty-one patients (3.6%) experienced seizures within 1 week after head injury; 42 of these (1.26% of the series) had seizures within 24 hours after trauma. The incidence of intracerebral parenchymal damage was found to be higher among those patients who developed seizures in the first week (66.1%) than in those who did not (62.7%). However this result did not reach statistical significance. The patients with early seizures had a lower mortality rate (p < 0.01). In patients who survived from the initial injury, the occurrence of early post-traumatic seizures did not appear to influence the neurological recovery at 6 months after injury.

Presence of intracerebral parenchymal damage on CT scan after severe closed head injury does not increase the risk of early post-traumatic seizures. With proper treatment, patients presenting with early seizures may have a lower mortality rate. However, the occurrence of early seizures does not influence the neurological recovery in patients who survive the initial severe closed head injury.

To determine the impact of check size and interstimulus interval (ISI) on neuromagnetic visual cortical responses.

We recorded visual evoked fields to pattern-reversal stimulation with central occlusion in ten subjects. The ~100 ms magnetic activation (P100m) was analyzed by single dipole modeling.

With 1 s ISI, P100m strengths increased as check size increased from 15' up to 120' of visual arc, and larger checks elicited less P100m activation. With 120' checks, we found no P100m attenuation as ISI decreased from 4 s to 0.16 s. P100m sources around the calcarine sulcus did not vary with check size or ISI.

The magnitude of cortical activation during visual contrast processing is check size-dependent and the 120' checks are optimum for future studies on neuromagnetic visual cortical functions using central-occluded stimulation. The corresponding neuronal activation demonstrated a short refractory period less than 0.16 s. We also found significantly overlapping cortical representation areas for different check sizes or ISIs.