The incidence, causes, and secular trends of head trauma in Olmsted County, Minnesota, 1935-1974.

Records in the Mayo Clinic linkage system were reviewed to determine the incidence of head trauma in Olmsted County, Minnesota, from 1935-1974. Minimum criteria for inclusion--loss of consciousness, posttraumatic amnesia, or skull fracture--were met by 3587 cases. During the decade from 1965-1974, the age-adjusted incidence rates per 100,000 population were 270 in males and 116 in females. The rate was highest--658--in males aged 15 to 24, but it was at least 50 in all age and sex groups. Major causes of head injury were automobile accidents (37%) and falls (29%). The incidence of head injuries related to automobiles and recreation has been increasing, whereas most other categories have remained stable or have declined. Of all cases, 446 were fatal, the average annual incidence being 32 per 100,000 in males and 9 per 100,000 in females. Among the groups at high risk of head trauma are those who have had head trauma previously.

Short-term outcomes of skull fracture: a population-based study of survival and neurologic complications.

All Olmsted County, Minnesota, residents who experienced brain injury from 1935 through 1979 were identified and their medical records reviewed for survival and neurologic outcome. Minimum inclusion criteria included loss of consciousness or post-traumatic amnesia or neurologic evidence of brain injury or skull fracture. Of 4,660 cases identified, skull fractures were observed in 28%. Over half of brain-injured patients who died did so within 24 hours of trauma; among 1-day survivors, subsequent survival was moderately impaired, especially in older individuals. Mortality was lowest in subjects without a skull fracture and increased with fracture severity. Associated neurologic injuries, complications, and deficits were generally more common in patients with skull fracture than those without and were much more frequent with more severe skull fractures. The types of neurologic deficits differed little between those with and without fractures, except that subjects with complicated skull fractures had higher proportions of special sensory deficits and multiple deficits.

Seizures after head trauma: a population study.

A cohort of 2747 patients with head injuries was followed for 28,176 person-years to determine the magnitude and duration of the risk of posttraumatic seizures. Injuries were classified as severe (brain contusion, intracerebral or intracranial hematoma, or 24 hours of eight unconsciousness of amnesia), moderate (skull fracture or 30 minutes to 24 hours of unconsciousness or amnesia), and mild (briefer unconsciousness or amnesia). The risk of posttraumatic seizures after severe injury was 7.1% within 1 year and 11.5% in 5 years, after moderate injury the risk was 0.7 and 1.6%, and after mild injury the risk was 0.1 and 0.6%. The incidence of seizures after mild head injuries was not significantly greater than in the general population.

Summated auditory evoked potentials in the cerebellum and inferior colliculus in the young rat.

The summated auditory evoked responses recorded at the superior surface and depth of the cerebellum of the young rat had a similar latency and configuration as did summated auditory evoked potentials in the inferior colliculus. Electric stimulation of the inferior colliculus did not evoke a response (other than the shock-artifact response) at the cerebellum. Stimulation of the cerebellum did not modify the evoked responses to click in the inferior colliculus (unless current levels were large enough to cause current spread to the brain stem). There is insufficient evidence to conclude that the cerebellum has an auditory receiving area in the young rat.

Head trauma and subsequent brain tumors.

A long term study of 2,953 persons with 29,859 person-years of follow-up after head injury provided an opportunity to investigate the long-debated association between head trauma and subsequent intracranial tumor. In this series the observed number of cases of subsequent brain tumor did not differ from the number we expected. Because brain tumors are relatively rare, the results of this large series cannot absolutely refute the possibility that head trauma predisposes to brain tumor, but the individual risk is very small, and the weight of evidence does not support an etiological association. The occurrence of subsequent brain tumors in this series was not associated with the severity or location of the head injury. Head trauma does not seem to be a significant etiological factor in meningioma; that tumor has a higher incidence in females, whereas males have 2- to 3-fold greater incidence of head trauma. If any association between head trauma and subsequent brain tumor does exist, it is extremely small or occurs only in the presence of other factors, which themselves must be rare.

The cost of head trauma in Olmsted County, Minnesota, 1970-74.

A study of the total cost of head injury in Olmsted County, Minnesota, with the costs projected to the United States population, revealed that the annual cost for head trauma in the US can be estimated at approximately +12.5 billion using a 6 per cent discount rate. The nonmedical costs accounted for more than 92 per cent (+11.5 billion) of the total cost, while direct medical costs amounted to +1.0 billion.

A comparison of EEG activity in the left and right cerebral hemispheres by power-spectrum analysis during language and non-language tasks.

In 10 female subjects, power-spectrum analysis was performed on the alpha activity elicted during the resting state, 4 right hemispheric tasks, and 3 left hemispheric tasks. The data were treated in 3 ways: approach 1, comparing the right and left hemispheric alpha activity; approach 2, comparing the right and left hemispheric alpha activity adjusted for the resting state; and approach 3, comparing the right and left hemispheric alpha activity adjusted for the previous task. Approaches 1 and 2 revealed few significant differences in the alpha activity of the hemispheres, but approach 3 provided data that better fit the theory of decreased power spectrum of attenuation of activity in the activated hemisphere. Thus, approach 3 may be useful in developing an electroencephalographic test for determining cerebral dominance for language.

Summated potentials evoked by speech sounds for determining cerebral dominance for language.

Ten normal adult right-handed subjects receive phonemic combinations (/epik/, /epak/, /a/, /pi/, /pa/) and pure tones (2500 and 8000 Hz) binaurally through matched earphones. Fifty responses from electrodes at P5, P6, C5, C6, F7 and F8 (referenced to linked mastoids) were summated, and evoked potentials from homologous areas were measured separately and superimposed in order to observe differences. Visual inspection of superimposed responses showed no consistent gross asymmetries that lateralized to either hemisphere. Comparison between amplitude of evoked potentials (N1, P2) at P5 and P6 were not significant (P < 0.05; paired t test). We suggest that our technique may not be a useful clinical test for cerebral dominance.