Olfactory Memory Dysfunction in Patients with Traumatic Brain Injury

Traumatic brain injury (TBI) severity is typically classified using clinical indices that may have limited prognostic value. Objective measures of olfactory function depend on sensory, limbic, and memory networks and may provide a more specific marker of injury-related neural dysfunction. Seventy-nine individuals with TBI (48 mild, 31 moderate-to-severe) and 59 healthy controls completed an olfactory battery, including tests of odor percept identification (OPID9, OPID18), odor discrimination (OD10), and odor memory (POEM) ~4.04 (4.45) years after their most recent TBI. General linear models examined associations between olfactory outcomes and TBI severity, adjusting for age, age, sex, and education. Additional models examined the relationship between loss of consciousness (LOC) and olfactory functioning. The severity of the most recent TBI was significantly associated with all olfactory outcomes, after adjusting for age, sex, and education. Compared with controls, participants with moderate-to-severe TBI showed lower OPID9, OPID18, POEM, and OD10 performance, while participants with mild TBI showed lower OPID18 and POEM performance. LOC was associated specifically with odor memory in these models, as participants with prolonged (> 30min) LOC or LOC of unknown duration had lower POEM scores than those with no LOC. In TBI-only models, LOC remained associated with POEM after adjustment for TBI severity, whereas TBI severity was not associated with POEM after LOC was included. Long term olfactory functioning is sensitive to TBI severity, with generalized impairments across odor identification, discrimination, and odor memory. LOC characteristics appear especially relevant to odor memory, suggesting that olfactory memory may capture injury-related features beyond TBI severity classification alone.