With regard to increased errors on the formboard test, Teuber and Weinstein (1954) showed that veterans who had penetrating head injury took more time, made more errors, and recalled fewer forms than the controls. A later study by Weinstein and Teuber (1957b) examined the change in AGCT score from before injury to after injury and found that subjects who had penetrating head injury had a greater decline in score than the group who had peripheral nerve injury independently of preinjury education and preinjury AGCT scores. Grafman et al. (1988) found cognitive decline after brain injury as measured the AFQT. However, preinjury intelligence score was the most predictive factor in postinjury intelligence score, followed by the size of the lesion; the location of the injury was the least important. In contrast, preinjury education level did not correlate with cognitive decline.
The study of World War II veterans by Corkin et al. (1989) demonstrated poorer performance on cognitive tests in veterans who had penetrating head injury than in controls and continued decline over 30 years in the brain-injured veterans on every cognitive measure except vocabulary, which remained constant. It was noted that the site of the injury exerted a strong effect on the type of deficits. Finally, the study of Vietnam veterans by Raymont et al. (2008) demonstrated that exacerbated decline in intelligence over 30–40 years is a significant risk for veterans with penetrating head injury.
The five secondary studies also showed long-term deficits in neurocognition including intelligence (Weinstein and Teuber, 1957a); spatial orientation (Weinstein et al., 1956); memory, reasoning, and arithmetic (Salazar et al., 1986); facial discrimination (Grafman et al., 1986); and neurocognitive decline as measured with the Wisconsin Card Sorting Test (Grafman et al., 1990).
Those studies, particularly the secondary studies, suffer from various limitations, including small samples, a focus on injury sites and localization of functional outcomes (which were outside the committee’s charge), incomplete description of how subjects and controls were selected, and apparent high rates of loss of the original sample at followup times. However, the studies had advantages not seen in studies of civilian injury, including the availability of baseline cognitive test scores and the long-term nature of followup (in some cases, 40 years or more). The overall body of evidence demonstrates poor neurocognitive outcomes in people who suffer penetrating head injury.
The committee concludes, on the basis of its evaluation, that there is sufficient evidence of a relationship between sustaining a penetrating TBI and decline in neurocognitive function associated with the affected region of the brain and the volume of brain tissue lost.