Traumatic brain injury assessed with olfactory event-related brain potentials

Olfactory event-related potentials (OERPs) were evaluated to develop an obj ective, quantitative assessment of sensory and cognitive olfactory loss fol lowing traumatic brain injury (TBI). Subjects included 25 TBI patients and 25 age/gender-matched healthy controls. Following standard clinical evaluat ion of smell function, TBI patients were divided into three groups: 12 anos mics (loss of smell), 6 hyposmics (reduced smell), and 7 normosmics (normal smell). Cognitive ability was assessed using the Trail Making Test (A and B). OERPs were recorded monopolarly from midline electrode sites using an a myl acetate stimulus with a 60-second interstimulus interval; subjects esti mated the magnitude of each odor stimulus. Anosmic TBI patients were also t ested with OERPs using ammonia to ensure trigeminal nerve function. Amyl ac etate OERPs demonstrated that the sensory N1 and P2 amplitudes and the cogn itive P3 amplitudes were absent in the anosmic TBI patients and greatly red uced in the hyposmic and normosmic TBI patients compared to healthy control s. The trigeminal OERPs from the anosmic TBI patients were within normal li mits, indicating that the primary olfactory deficits were objectively measu red with OERPs. The relationship between the OERPs and neuropsychologic tes t performance supports the cognitive loss associated with TBI. The present study lends support to the utility of OERPs as an objective tool for measur ing sensory and cognitive loss after traumatic brain injury.