A device for controlling odorant stimulation and olfactory evoked responses in humans

Quantitative EEG analysis in post-traumatic anosmia

Many objective and quantitative methods have been developed to create a procedure or a device to prove, describe and quantify olfactory deficit and anosmia, especially after a head trauma. Electrophysiological testing throughout olfactoelectroencephalography (olfactoEEG) is based on brain activity desynchronisation, and on the subsequent disappearance of alpha activity on the posterior regions after an olfactory stimulus. Yet traditional evaluation of EEG can be difficult, because of little or hardly detectable alpha activity on the posterior regions ('alpha rare'). The aim of this study was to evaluate the Olfactory Stop Reaction (OSR) by means of frequency band power calculation and subsequent topographical mapping in patients with post-traumatic anosmia, who presented 'alpha rare' EEG. Twenty-five consecutive patients, affected by anosmia caused by head trauma, were submitted to an EEG recording with olfactory stimulation. After signal processing and analysis, an Olfactory Stop Reaction was detected in 17 out of 25 patients; moreover, in these patients we detected a significant decrease in alpha band power in the occipital regions and an increase in theta band power on midline frontal and central regions after olfactory stimulation. In the remaining eight patients, no significant variation in band power was observed. In conclusion, an objective evaluation of the olfactory function with this method of automatic EEG signal analysis allows the limits given by psychophysical methods and traditional EEG to be overcome and attempts to fulfil the requirements for standardization of olfactory function evalution.

Olfactory event-related potentials in normal subjects and patients with smell disorders

We developed a device to record olfactory event-related potentials (OERP) from the human scalp. Methyl-cyclopentenolone was used as the odorant element. A total of 50 stimuli were delivered. Each stimulus lasted 0.5 sec and was delivered once every three inspirations. Normal OERPs were obtained with this device. The positive peak latencies were approximately 350 msec (P1) and 700 msec (P2), respectively. OERPs were also recorded in 40 patients with smell disorders. A positive response at about 300-400 msec was recorded in 7 patients (all females, 15-59 years old). The other 33 patients showed no response. The high potential area of this positive peak was located in the centro-occipital region of the scalp. The latency and the high potential area of this peak were similar to P1 recorded in normal subjects. The source of this peak was considered identical to that of P1. This may be a response to the trigeminal nerve during odor administration. P2 was not recorded in the patients with smell disorders. P2 may therefore be a response to the olfactory nerve.

Early results of an objective olfactometer

Although many people comment on their ability or inability to smell an odour, the accurate measurement of olfaction remains an elusive goal. Currently, there are no instruments available to objectively measure olfaction. This article outlines the design and early test results of a low cost, computer-based olfactometer which uses the frequency content of evoked potentials to quantify a subject's response to an olfactory stimulus. Clinical trials have been undertaken to establish the validity of the olfactometer and over a thousand tests have been carried out. Early results suggest that the methodology employed is appropriate and could be developed to enable a commercial olfactometer to be produced.