"The sensation and perception of smell are largely dependent on sniffing" (Desmond et al., 1998). Research has shown that sniffing, with or without an odorant present, can cause activation in the olfactory bulb (Desmond et al. 1998). Further, they discovered that sniffing (whether or not an odor is present) stimulates activity in the piriform cortex of the temporal lobe and that actually smelling an odor stimulates the temporal lobe as well as the frontal lobe. In USA Today, John Gabrielli stated that there are two different aspects to the olfactory process. One aspect is called the exploratory phase-the sniffing, and the other is called the evaluative phase-the smelling (1998, December). These pieces of information can be applied to examine whether there is more olfactory activation in an individual with anosmia versus an individual with Alzheimer's disease. Ongoing research has been conducted on these two diseases for years but there is not a lot of research comparing the two together. It has been discovered that many patients with Alzheimer's disease also have a decreased sense of smell (Andrew et al., 2001). In contrast, anosmia is characterized by a total loss of the ability to smell. In both cases, there is damage in the olfactory area of the brain affecting the individual's sense of smell. In a magazine article from USA Today, researchers at Stanford University states that "processing of either sniff or smell signals-air rushing up the nose or odorant molecules latching onto nerve cells-could be defective in the many people who lose their ability to smell" (1998, December).

The experimental hypothesis examines whether an individual with Alzheimer's disease will have more olfactory brain activity than an individual with anosmia. The Sniffin' Sticks test battery will be used in combination with fMRI to test the olfactory activation levels of fifteen individuals with Alzheimer's disease and at least five individuals with anosmia. The Sniffin' Sticks test contains three different tests, odor threshold, odor discrimination, and odor identification (Schnieper, Welge-Luessen, & Wolfensberger, 2001). However, for the purpose of this study it will only be used in order to discriminate between the two levels of the independent variable. The experiment contains one independent variable- odor, which consists of two levels, presence and absence. The dependent variable consists of the fMRI results which determine the amount of oxygen in the blood in the olfactory bulb and can be rated on a scale from one to five (with five being the most activation and one being the least activation). Another approach to this type of experiment would be to compare the habituation rates and activation levels between the two types of participants. Allin et al. (1997) found that after repeated olfactory stimulation, habituation occurred. A different approach to comparing anosmia and Alzheimer's disease would be to have the subjects participate in the Güüttich test. Dresden et al.(1999) exposed their subjects to this type of smell test where "liquids are placed on the participants' tongue and they are then asked to describe the aroma of the liquid". The Güüttich test in this experiment would not only provide a brain activation comparison of smell but also one of taste between anosmics and Alzheimer's participants.

Is there more olfactory activation in the brain when an odor is present? In one magazine article from USA Today, it was discovered that when sniffing in the absence of an odor, brain images showed that an area called the piriform cortex was most active. But "when they actually detected a smell, other areas in the frontal lobe were most active" (1998, December). This information allows one to see that an individual with Alzheimer's disease would have more activation in the olfactory bulb than an anosmic individual, because although a person with Alzheimer's disease has olfactory damage, they still have a small ability to detect smell and thus receive stimulation from both sniffing and smelling. However, anosmic brains are only receiving stimulation from the sensation of sniffing due to their total loss of ability to smell, and because of this loss will have less activation. Even though an odor may not be present, olfactory activation is still present when an individual sniffs. The problem at hand is determining whether olfactory activation is actually higher in individuals with Alzheimer's disease versus individuals with anosmia. Based on the above research it is hypothesized that individuals with Alzheimer's disease will have more olfactory activation than an individual with general anosmia.

Participants

Previous researchers studying anosmia and Alzheimer's disease have often used a larger amount of people with Alzheimer's compared to just one person with anosmia (Desmond et al., 1998). However, the results may be more significant if there were more than one anosmic participant. For this experiment it would be beneficial to use at least five anosmic individuals and at least fifteen individuals with Alzheimer's disease. Participants should be selected by either volunteering themselves or by random sampling. Andrew et al. (2001) found that when using fMRI and testing young and elderly Alzheimer's participants, the older participants had less brain activity. Thus, in order to receive more significant results that apply to the entire population, this experiment should not be age, gender, or race specific. Solicitation of the experiment can include posting research opportunities in a newspaper, magazine, or even suggesting doctors to pass on the opportunity to Alzheimer's or anosmic patients. If necessary, compensation for participating can be provided; however, previous researchers have not compensated their participants and have not had difficulty finding subjects. The only qualifications required for participation include a DSM-IV diagnosis of Alzheimer's disease or being anosmic.

Materials

The materials used in previous research included a fMRI or PET scan, a television screen viewed via a mirror located in the fMRI machine, and a type of odor identification test battery. In this experiment, the Sniffin' Sticks test battery will be used to manipulate the independent variable in order to determine the difference in the levels of olfactory activation between Alzheimer's disease and anosmia . Unlike other smell identification tests, the Sniffin' Sticks test is based on pen-like devices which contain different odors (Hummel, Kobal, Konnert, & Rossenheim, 2001). The importance of this test and how it will be used is described in the procedures section. Previous researchers like Desmond et al. (1998) have used fMRI's to obtain their data. The fMRI is useful because it measures the amount of oxygen in the blood in the area of the brain one is studying. In this experiment, the results from the fMRI will be obtained from the frontal and temporal areas of the brain since these are the primary olfactory areas. An image on a television screen will be reflected onto a mirror located above the participants head in the fMRI machine, therefore, allowing the researchers to communicate with the subjects during the experiment. For example, the researchers will flash the word "sniff" on the screen instructing the subject to sniff at that moment. Previous researchers using fMRI's have also used these mirrors and television screens to communicate with their participants (Desmond et al., 1998).

Procedures

After selection of the participants and upon visitation, subjects will be instructed to sign a consent form and also provide adequate documentation of their diagnosis of either Alzheimer's disease or anosmia. Each subject will then be informed of both the importance and purpose of the research project. The order of choosing an Alzheimer's subject or anosmic subject is not important; however, it is necessary that this information be recorded so that later, the researchers know what brain image corresponds to which type of participant. The participant will then be taken to the room containing the fMRI machine where the experiment will begin. Next, they will be placed into the fMRI machine and instructed to keep their eyes focused on the mirror located above their head as to know when to sniff. The two levels of the independent variable will then be manipulated by the researchers. Whether the researcher starts with the presence or absence of the odor first is not important; however, it is necessary that this information be recorded in order to know which fMRI image is due to which level (presence versus absence). Next, the researcher will either present/not present an odor using the Sniffin' Sticks test and retrieve the image of the activated areas of the brain. At this time researchers should be paying close attention to the different areas activated by each participant (Desmond et al. ,1998). Each participant should be subjected to at least five trials of each level of the independent variable. For example, each subject should participate in at least five trials of an odor being present and at least five trials of an odor being absent. Once the participant has been exposed to ten trials, the researchers should then move onto the next subject and repeat the process stated above. If the researchers have decided to compensate their subjects for participating in the experiment, it should be offered at this time.

Design

In this experiment there is one true independent variable, odor, and each participant is exposed to both treatments (odor present and odor absent). The quasi-independent variable is participant type: Alzheimers or a general anosmic. The dependent variable consists of the fMRI results which determine the amount of oxygen in the blood that is present in the olfactory bulb. For these reasons, a two-factor mixed ANOVA may be used to analyze the data. These results will then be applied to state whether the researcher will reject or fail to reject the hypothesis. As previously stated, the experimental hypothesis examines whether an individual with Alzheimer's disease will have more olfactory activation than an individual with anosmia.

In this section, researchers will start off by stating whether or not examination of the results supported the hypothesis. An example for this experiment may state that examination of the results will support the hypothesis that individuals with Alzheimer's disease will have a higher level of olfactory activation than an individual with anosmia. It is predicted that the results of the ANOVA will reveal that there was a significant difference between the ratings for odor presence and odor absence in individuals with anosmia and Alzheimer's disease. More specifically, the individuals with Alzheimer's disease will have higher olfactory activation levels compared to the individuals with anosmia. Looking again at the original hypothesis, it is evident that the proposed findings support the hypothesis.

The current experiment assessed the difference between olfactory activation levels in anosmics and Alzheimer's disease participants based on whether an odor was present or absent. According to the possible data, the level of activation was affected by the presence/absence of an odor in each type of participant.

There are many ways to replicate this type of experiment for future research. For example, instead of testing the activation levels for the presence/absence of an odor, researchers may try comparing anosmics and Alzheimer's subjects by manipulating all three characteristics of the Sniffin' Sticks test (odor threshold, odor identification, and odor discrimination). For instance, when testing for odor discrimination participants could be asked to sniff three pens-two containing the same odor and one containing a different odor-and tell which one smelled different. Other groups of researchers have used a different type of smell test called the University of Pennsylvania Smell Identification Test (UPSIT). This quantitative test consists of forty odors where "each odor is micro encapsulated on a pad so that the participant can scratch and sniff the odor" (Kondo et al., 1998).

Although the Sniffin' Sticks test was used for this proposed experiment, as seen above there are many different types of smell identification and discrimination tests available in order to replicate this experiment. Other ways to replicate this experiment would be to test the olfactory activation levels using a PET scan. In the various experiments used in this proposal, almost all of the researchers used fMRI results. However, it is possible to achieve similar olfactory information using a PET scan. Changing the independent variable, the dependent variable and even the type and amount of participants also allows for different experiments. Alzheimer's disease is not the only degenerative disease that is characterized by a decrease in the ability to smell. Other diseases such as Parkinson's and schizophrenia affect the individual's ability to smell. Future researchers may also want to replicate this experiment comparing schizophrenics and people with Parkinson's disease. Wuensch (1993) states that more than two million Americans suffer from a significant loss of their ability to smell. With the information presented in this proposal and information yet to be discovered, researchers can apply their knowledge to future experiments in order to obtain a better understanding of these diseases and help these people suffering from Alzheimer's, Parkinson's, schizophrenia and anosmia.

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