Electrical Stimulation of Olfactory Receptors for DigitizingSmell

Surina Hariri, Nur Ain Mustafa, Kasun Karunanayaka, Adrian David CheokImagineering Institute

Iskandar Puteri, Malaysia{surina, ain, kasun, adrian}@imagineeringinstitute.org

ABSTRACTThe digital stimulation of smell is considered as a useful stepin expanding the technology related to multisensory communi-cation. Previous methods for activating the sensation of smellchemically, has obvious disadvantages such as being complex,expensive and lower controllability. In this paper, we proposea digital interface for actuating smell sensations. This is doneby stimulating the olfactory receptors of the nasal conchae us-ing weak electrical pulses. The sensitivity and effectiveness ofelectrical stimulation on human smell receptors will be studiedby using different current and frequency parameters with realusers.

ACM Classification KeywordsH.5.m. Information Interfaces and Presentation (e.g. HCI):Miscellaneous; See http://acm.org/about/class/1998/ for thefull list of ACM classifiers. This section is required.

Author Keywordsolfactory; electrical pulses; electrical stimulation;multisensory communication

INTRODUCTIONThe early digital smell interfaces developed in the field ofHuman-Computer Interaction primarily used chemicals to gen-erate odour sensations [1, 2, 8, 9, 11, 10]. These systemsare complex, expensive to use frequently, and need routinemaintenance for smooth operation. Also there are other limi-tations such as difficulty to do fast switching between smells,difficulty control the area of stimulation over the time, anddifficulty to keep uniformly distributed concentration in thestimulation space. The floating odour molecules are the rootcause for most of these disadvantages since they are difficultto control. Therefore, generating smell sensations withoutchemicals is becoming a need for our increasingly digitizedworld. By achieving that we believe that this research willenable people to experience smell sensations digitally acrossthe internet as we experience visuals and audio in our everydaylife.

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DOI: 10.1145/1235

Figure 1. The electrode will be placed inside the nasal conchae.

We have developed a computer controllable user interfacewhich produce weak DC electrical pulses in varying the fre-quency and current. By placing the two silver electrodes ofthe device, into the nasal conchae (as shown in Figure 1) andstimulating the smell receptors, we expect that this interfacewould produce some type of smell sensations. Area near thenasal conchae is ideal to use for the stimulation because ofthe two factors. The first reason is nasal conchae has a highdensity of olfactory receptors and the second reason is wecan easily fix the two electrodes in between the superior andmiddle or middle and inferior concha. Our latest prototype isshown in the Figure 2. This is a computer controllable devicethat produces controlled stimulation parameters over the time.As the next steps of the research we are planing to conductseries of user experiments to study the sensitivity of the smellreceptors for the electrical stimulation.

RELATED RESEARCHElectrical stimulation of the olfactory system has been studiedin early research by Schonbein who suggested that peoplecan smell the effects of electric discharge (through ozone)and questioned about a truly electric smell in his paper in1851 [10]. Yamamoto has first studied the electrical stimula-tion of the olfactory mucosa and deep structures of the brain

in a rabbit [12]. The rabbits were stimulated using 0.2msec to0.5msec duration of pulse, using the voltage in the range of 1Vto 20V. Recording electrodes was placed on the scalp of fore-head, record a slow negative wave of evoked potential. Similarresearch has been performed again with rabbits that used thestimulation parameters of 2mA of current as 0.5ms durationof pulse [4]. With the 2Hz rate of stimulation, the evokedpotential showed two successive waveforms with peaks.

Then a similar research has been carried out on humans byIshimaru et al. with using the electrical stimulation of 2mAwith 0.5ms and the olfactory bulbar potentials recorded fromthe frontal sector of the human head [5]. This experimenthas suggested that olfactory nerves are producing the similarwaveforms as on rabbits. In a study, Kumar et. al [6] haspresented that electrical stimulation of the olfactory bulb andtract produces the pleasant and unpleasant smells in epilepsypatients. In one of the experiment, authors reported that, ninesubjects perceived unpleasant smells (like bitterness, smoke,or garbage, while two subject perceived a pleasant smell (likestrawberry or good food) and lastly, five subjects did not smellanything. The stimulation was based on varying the currentwith three steps; trials starting from 3mA and increased to 6mAand 9mA. The total stimulation period for a single trial was 5seconds with 50Hz frequency. The pulse duration of a singlecycle was 300 µsec. The olfactory hallucinations occurred forstimulation of 3mA and 6mA. This is the only experiment thatclearly reports electrical stimulation on olfactory receptorsgenerates smell sensations. However, this method can’t beused for the general population since it is highly invasive(this method requires electrodes to be implanted inside brain’sfrontal lobe.).

By referring to the previous research, electrical stimulationshows the possibility to stimulate the smell sensations. Pre-vious works have been conducted in the medical domain, oronly in the experimental stage, while this research will achievebreakthrough in controllability, accuracy and robustness.

METHODOLOGYThe design and development of digital smell Interface is de-scribing in this section. As shaown in Figure 2, Digital SmellInterface consists of two silver electrodes which are usedfor stimulation (these electrodes produce weak DC electricalpulses on the wall of nasal concha), a controller circuit andthe controller software.

Figure 3, shows the dimensions of the silver electrodes(100mm in length, 2.5mm in width, and 0.5mm sphere shapetip) and those were made by referring to one of the previousresearch [3]. One electrode act as the DC positive electrodeand the other electrode is configured as the ground while tipseparation between the two electrodes will be kept within0.5mm to 2mm distance.

The stimulation parameters and safety margins for the olfac-tory receptors was defined by referring the prior works. Ourdevice was purposely limited to controlling the current be-tween 1mA to 5mA to avoid uncomfortable feelings or dam-age to the subjects. Current of 2mA will be the starting currentfor our first experiment since 1mA of current is considered as

Figure 2. The electrode will be placed inside the nasal conchae.

Tip diameter of 0.5mm

100m length

Figure 3. Tip of stimulating electrode was made of silver sphere in0.5mm diameter.

too weak for stimulation, while more than 4mA could inducesome pain and 5mA of current is considered as the maximumharmless current for the human subjects [7].

There are series of experiments will be conducted. Each exper-iment will include 15 participants minimum. During the firstexperiment; we will study the effects of the electrical stimu-lation of olfactory receptors by collecting the feedback of theparticipants to find out whether they perceive any smell sen-sations. In parallel, we will do a characterization of the innerwall of the nose for electrical stimulation. Then if we receivepositive results from the first study for producing the smellsensations we will compare whether the electrical stimulationactivates the same areas of the brain as chemical stimulationsdo by using a suitable brain imaging technique.

CONCLUSIONElectrical stimulation of olfactory receptors using a non-invasive method would be useful for triggering the sense ofsmell. Previous studies had been done by applying electricalcurrent towards animals or human. In a previous research,Kumar et al. has shown by stimulating olfactory bulb inva-sively using electrical stimulation, some smell experiencescould be produced. Based on this finding, in this paper, wehave proposed an initial concept prototype which can be usedto do a electric stimulation of smell receptors non-invasively.We believe, by improving this prototype further, based on theresults of the user experiments and we will be able to intro-duce a proper technology that can generate smell sensationsdigitally in repeatable and controllable manner. Our vision isthat in the future, multisensory communication will transforminto a new era of Internet with augmentation of the five basichuman senses.

ACKNOWLEDGEMENTThe authors would like to thank greatly and acknowledge mem-bers in Imagineering Institute, Malaysia for their significantcontributions for this research.

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