Determining the foundations of verbal memory dysfunction following high-velocity closed-head injury: New lessons from the CVLT

The underlying cause for verbal memory deficits following high-velocity closed-head injury (HVCHI) has been a topic of debate. List learning studies of memory following HVCHI have yielded mixed results with some evidence suggesting disrupted encoding and other data indicating difficulties with consolidation as the cause of HVCHI verbal memory deficits. The possible discrepancy among findings from studies of verbal memory following TBI may be due to flawed measurement of memory deficits and/or heterogeneity between study samples. In the current study, California Verbal Learning Test (CVLT) data from a homogeneous sample of 63 HVCHI participants is compared to 63 age and education matched controls. The CVLT data were analyzed at the item level using an item specific deficit approach, and indices of consolidation and retrieval were controlled for level of acquisition. The HVCHI group showed significant difficulties on item specific deficit indices of encoding (items acquired at a low level), consolidation (items lost/items gained), and retrieval (items recovered/items gained). Hierarchical regression analysis showed that both encoding and consolidation difficulties accounted for unique variance in HVCHI participant long-delay free recall on the CVLT, although encoding difficulties accounted for the majority of the variance in long-delay free recall. Examination of strategy use showed that HVCHI underutilized semantic clustering during list learning and showed lower semantic clustering at the short delay-recall test. Additionally, the HVCHI group, unlike the control group, did not show increased semantic clustering at the long-delay recall free recall test (following the short-delay semantically cued recall test). HVCHI and control participants did not differ with respect to the use of serial clustering.