Artificial Olfactory Enhancement
The human olfactory system is responsible for perceiving the chemical world around us. By sampling the environment, we can determine the presence of other individuals, possible danger, or distinguish acceptable food. Consisting of our sense of taste and smell, the olfactory
system is a highly interrelated coordination of chemical and nerve responses. Yet as we have all experienced, human olfaction has limits. The popular image of a bloodhound leading hunters through the woods is one example of these limits. The scent trail that is all too easily picked up by the hound is completely elusive to his human companions. This is partially due to the dogís possession of nearly twenty times more olfactory neurons than humans. Another example is evident in airports across the country. Long lines of passengers wait in line while a security guard swabs a bag and passes the sample under a mysterious black box. The machine squawks an alarm and the owner of the bag is promptly arrested for concealing explosive material. These are two simple situations in which the human olfactory system is not sufficient to meet our needs. We are dependent upon these machines and animals in order to achieve our goals. They are examples where we have identified a shortcoming of human abilities and have attempted to augment them through the aid of external devices. Nearly every aspect of human ability has seen the same attempt at embellishment. Even those that have lost functioning are able to regain some ability through the aid of external devices. Yet while wheelchairs and hearing aids are effective to an extent, it is doubtless that those individuals would benefit more if they were free from mechanical restraints. To integrate the advancement into the body itself creates an autonomous individual, whether brought back to normal functioning or elevated beyond.
In the case of an individual elevated beyond normal biology, we would have expanded our own potential. An olfaction enhanced security guard could detect explosives or drugs instantaneously, without the cumbersome dependency upon a stationary device. An enhanced doctor could evaluate a patient using the subtle scent cues often present in disease. The potential for olfactory enhancement
is clear. This paper will examine the potential for an augmented human olfactory system using electronic devices implanted in the body. The operation focus will be on targeted industries in which enhanced airborne chemical detection would be an asset. The problem of artificial
olfactory enhancement will be divided into three discussions. The first is a basic explanation of the human olfactory system as it relates to this project. The second is an analysis of current electronic airborne chemical detection devices. Lastly will be an investigation into possible methods for integrating these two systems into an effective olfactory enhancement system. This will include design requirements and predicted operational parameters. Ethical and engineering issues will be discussed as they arise.
The effort of this proposal in no way means to detract from the incredible functioning of the human olfactory system. Any organ capable of detecting a chemical presence in the range of parts per billion is not to be dismissed as ineffective. With that being said, our olfactory sense begins with the passage of air through the nasal cavity. This brings the chemical samples, now to be referred to as odorants, within contact with the mucus membrane, the olfactory epithelium, that line the structure. (Rosenzweig, 241-247) Embedded in this membrane are specialized proteins. Each protein can be thought of as a lock. Only a very specific odorant, or key, can bind to the specific protein. When the correct odorant binds with a protein, a chemical cascade is begun that ends with the generation of an electron potential in nerve endings that innervate the epithelium. It is at this stage where our enhancement will interact. This electric signal is then transferred along the olfactory nerves to the olfactory bulb on the dorsal side of the brain. From there it is passed into the brain where it is processed and becomes the sense that we are able to interpret. The typical human nose contains forty to fifty million olfactory nerves. These are paired with over a hundred known olfactory proteins to respond to the incredible number of chemicals we are able to detect. (Sekuler, 542-574)
A successful electronic version of our olfactory system begins with a concept quite similar to its biological counterpart. Cyrano Sciences of Pasadena, California has developed a circuit that functions similarly to the proteins in the epithelium. In their system, an array of compound-absorbing polymers is placed on a silicon chip along conductive pathways. Each polymer is sensitive to a specific compound and will respond to its presence by swelling like a sponge. This swelling in turn alters the electrical conductivity of the pathway along which the polymer rests. A measure of changes in resistance with exposure to a vapor in several dozen of such polymers results in a pattern of responses. This pattern can then be matched to a specific compound and identified. An increased number of polymers enhances the discrimination available in the system and can be tailored to the specific requirements of the task. The advantage of this system is the relatively small size of the detection circuit. Also at an advantage is Cyranoís ability to distinguish compounds far in advance of the human olfactory system. This is what makes the technology acceptable for the application. The current array of thirty-two polymers can effectively identify hundreds of compounds. An increase in polymer count and type opens the potential for many more. (Cyrano Sciences)
With an effective electronic detection method, what remains is to develop this technology into a form that can be integrated into the human olfactory system. Since the goal is to allow the individual to ìsmellî what is detected by the artificial circuit, the most pressing concern is the interface between man and machine. In order to mimic biological function, attempting to maintain normalcy, I propose integrating the detection circuit output with the olfactory nerve endings in the nasal cavity. This will require knowledge of the olfactory nerve function beyond current abilities. This is perhaps the most daunting challenge to the project. In order to create identifiable responses within the olfactory system, the nerves must be precisely stimulated. (Carlson, 150) For this reason it is not feasible to attempt overly complex stimulation patterns. Using electro stimulation of nerve bodies, what could be possible is the creation a relatively large signal in the olfactory system. Microstimulation of selected nerve bodies, similar to what can be accomplished currently, is effective at causing a relatively crude sensory experience. While not nearly as elegant as the response generated naturally, the artificial stimulation of a group of olfactory nerves could potentially produce a recognizable response. The task would then be to train oneís self to recognize this crude sensory experience as a specific odorant.
Having dealt with this issue, let us examine the entire chain of processing in the system. The artificial device would ideally be placed within the nasal cavity. Included in this package would be the sensing polymer chip, a processing unit, a power cell, and the nerve integration circuit. This is a great leap from current size constraints but could potentially be achieved. Cyranoís current device is the size of a large calculator. The benefit of placing the system within the nasal cavity, however, is that the normal act of sniffing would introduce the odorants to the circuit, eliminating the need for electronic air intake measures. Even with significant circuit size reduction, the package would be a significant implant in the sinus cavity. This might create the need to partially remove some sinus structures such as nasal turbinates. The result of this could be serious dehydration of the individual, which may not be acceptable. Ignoring this possibility, let us continue with the system. Odorants pass across the polymer chip through the normal act of sniffing. As described in the Cyrano information, this creates a unique chemical signature of the present odorants. This signature is processed by the unit, which then sends electronic pulses directly into the selected olfactory nerve endings in the sinus cavity. The result is a specific sensory event that can, with training, be identified by the individual.
Some engineering issues have already been discussed, such as the size of the implantation package and the interface between circuit and neurons. While daunting challenges, they could very well be overcome through the advancement of current microcircuitry and neuronal manipulation. Other difficulties include creating an effective power supply for the system and training the individual for the new sensory input. Beyond technical concerns is the ethical issue of augmenting a human with electrical circuitry directly wired to neurons. While initially shocking, similar work is being conducted with limb replacement. Interacting directly with the nerves allows for a level of integration one step closer to normal functioning, which is the ultimate goal for many of the individuals. As we better understand the neural controls of our body, we will become more comfortable with manipulating them.
Artificial olfactory enhancement extends the current capabilities of humans to an area that was once reserved for other animals and machines. With it comes the ability to experience our environment more effectively. With direct applications in security, medicine, food production, chemical safety, and many other fields, it has an easily definable market. It is an integration of advanced abilities directly into the human sensory experience. Like connecting an artificial limb with the somatosensory system, or directly stimulating ocular nerves to repair sight, olfactory enhancement has the potential to profoundly effect functioning.
Carlson, Neil R. Physiology of Behavior. Massachusetts: Allyn and Bacon, 2001.
Cyrano Sciences. http://cyranosciences.com/. April, 2002.
Rosenzweig, Leiman & Breedlove. Biological Psychology: An Introduction to Behavioral, Cognitive, and Clinical Neuroscience. Massachusetts: Sinauer Associates, Inc, 1999.
Sekuler, Robert & Blake, Randolph. Perception. New York: McGraw-Hill, 2002.