Measuring subjective clustering of verbal information after moderate-severe traumatic brain injury: a preliminary study.

BACKGROUND: There is no agreed upon measure of subjective clustering for clinical use in patients following moderate-severe traumatic brain injury (TBI). OBJECTIVE: This study investigated whether measures of subjective clustering, subjective organization (SO) and adjusted ratio of clustering (ARC), were appropriate for use in patients following moderate-severe TBI. METHODS: Twenty participants with moderate-severe TBI in the chronic stage of recovery and 20 control participants recalled a list of unrelated words over six trials. The authors assessed if the SO and ARC measures could discriminate the groups' ability to subjectively cluster the words. The authors also examined whether the SO and ARC measures correlated with recall and learning rate, and if combining the measures improved the predictive accuracy. RESULTS: Participants with moderate-severe TBI performed significantly worse on the SO measure, but there were no group differences regarding the ARC measure. The SO measure positively correlated with recall, but not learning rate. The ARC measure did not positively correlate with recall or learning rate, and combining the measures did not enhance the predictive accuracy. CONCLUSIONS: The SO measure is likely an appropriate candidate for clinical use. However, there are problems with the ARC measure that limit its use as a clinical tool.

Long Term Memory Outcome of Repetitive, Low-Level Dietary Exposure to Domoic Acid in Native Americans.

Domoic acid (DA) is a marine-based neurotoxin that, if ingested via tainted shellfish, is associated with Amnesic Shellfish Poisoning (ASP). These acute effects of elevated DA exposure in humans have been well described. In contrast, the long-term impacts of lower level, repetitive, presumably safe doses of DA (less than 20 ppm) are minimally known. Since Native Americans (NA) residing in coastal communities of the Pacific NW United States are particularly vulnerable to DA exposure, this study focuses on the long-term, 8-year memory outcome associated with their repeated dietary consumption of the neurotoxin. Measures of razor clam consumption, memory, clerical speed and accuracy, and depression were administered over eight years to 500 randomly selected adult NA men and women ages 18-64. Data were analyzed using GEE analyses taking into consideration the year of study, demographic factors, and instrumentation in examining the association between dietary exposure and outcomes. Findings indicated a significant but small decline in total recall memory within the context of otherwise stable clerical speed and accuracy and depression scores. There is reason to believe that a continuum of memory difficulties may be associated with DA exposure, rather than a unitary ASP syndrome.