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.