While executive function deficits are often pronounced following traumatic brain injury (TBI), memory complaints are also common and tied to medial temporal lobe vulnerability following insult. However, the extent of these memory deficits—the severity, ubiquity across domains (e.g. temporal versus spatial memory), and individual differences across patients—are still being investigated. Relational memory, or the ability to bind arbitrary information into long-lasting associations, operates across domains and delays and depends critically on the hippocampus. In the present study, two relational memory tasks, one spatial and one temporal, were employed to assess whether 1) patients with TBI demonstrate domain general relational memory deficits and 2) whether these deficits are evident even for small set sizes typically considered in the realm of working memory (3-9 items). In the spatial relational-memory task, moderate-severe TBI patients and healthy matched controls studied the locations of 2-10 abstract items on a screen for a short period of time (6-30 seconds depending on set size). The items then disappeared. After a short delay (5 seconds), the items reappeared in a line at the top of the screen and participants used the mouse to drag the items back to their original locations (reconstruction). In the temporal relational-memory task, 3-9 objects were present centrally, one at a time, during study. At test, each object was presented again in a randomized order, and participants indicated the temporal position in which that object was studied. Results demonstrated that, across both tasks patients with TBI demonstrated relational memory deficits compared to their matched controls and that these deficits emerged even at set size 4, and persisted at larger set sizes as well. While there was considerable variability in performance across patients, overall performance on the spatial task correlated with performance on the temporal task, suggesting deficits on both tasks are likely related to the same hippocampally mediated impairments, though future work incorporating both structural and functional imaging will be necessary to directly evaluate this. Overall, results suggest that TBI results in domain-general deficits on relational memory tasks, and that these deficits are evident even at set sizes as small as four items.

Traumatic Brain Injury Impairs Both Spatial and Temporal Relational Memory