The demonstration of olfactory deficits in Alzheimer's disease and other disorders of the limbic system suggest that olfactory tests may be useful in the evaluation of these disorders. However, there are currently no objective tests of olfaction available clinically that distinguish between deficits due to central nervous disease and peripheral dysfunction e.g., nasopharyngeal disease. This five year project will develop electrophysiological measures of olfactory function in animals that can be applied clinically in the evaluation of neurologic disease. Specifically, olfactory evoked potentials elicited by odors will be recorded from intracerebral and skull electrodes in rats, rabbits, and monkeys, initially while under anesthesia. Stimuli will be generated with a constant flow olfactometer that is currently in operation. The preliminary evoked potential data discussed demonstrate that this system yields reliable potentials specific to odors. The preliminary parametric studies will be confirmed to define the effects of flow rate, stimulus duration, interstimulus interval, concentration, and nasal cannula position on the olfactory evoked potential. At first, only amyl-acetate will be examined but experiments will follow on other odorants. The olfactory evoked potential will be mapped over the skull and intracerebrally in the piriform and entorhinal cortices. Once a chronic preparation is established, evoked potentials will be recorded from animals with lesions of the limbic system such as lateral olfactory tract transection. The experience gained from this research will be applied to the development of olfactory evoked potential testing in humans for clinical use.
