Participants in this group have normal olfactory function, as determined by the Sniffin' Sticks test. They will undergo EEG analysis while being exposed to various olfactory stimuli to establish baseline brain wave patterns for normal olfactory responses.

(n=550)

Participants in this group have impaired olfactory function (hyposmia), confirmed through the Sniffin' Sticks test. They will undergo EEG analysis during olfactory stimulation to identify differences in brain wave patterns compared to normosmic individuals. (n=150)

This group includes participants who have both tinnitus and hyposmia. They will be subjected to EEG analysis during olfactory testing to investigate the interaction between olfactory and auditory disorders and how these conditions may influence brain wave responses. (n=150)

Participants in this group have tinnitus but normal olfactory function. They will undergo the same EEG and olfactory tests to explore the impact of tinnitus on brain wave patterns in the absence of olfactory disorders and to compare their responses with those of other groups. (n=150)

The Sniffin' Sticks test, a validated method to evaluate olfactory functions, utilizes pen-like devices to dispense scents for testing identification, discrimination, and detection of odors. In this study, participants' responses to various scents are recorded. EEG (Electroencephalography) captures electrical activity in the brain during exposure to these odors by using an EEG cap fitted with electrodes on the scalp. This allows for the monitoring of brain wave patterns in response to olfactory stimuli. Both the Sniffin' Sticks test and EEG recordings are conducted simultaneously, providing a dual assessment of behavioral reactions and brain activity to odors. The goal of the study is to compare brain wave patterns and olfactory function in normosmic (normal smell), hyposmic (reduced smell), and tinnitus patients with and without olfactory impairments, delivering comprehensive insights into the neural basis of olfactory perception.

During this period, 1000 participants > 18 y/o will be recruited and divided into four distinct groups: normosmics (550), hyposmics (150), tinnitus patients with hyposmia (150), and tinnitus patients without hyposmia (150). The primary outcome of the Neuroscent project is to assess the ability of EEG analysis to distinguish between normosmic and hyposmic participants during olfactory stimulation using the Sniffin' Sticks test.

Alpha Power: Measured in microvolts squared (µV²), representing the magnitude of Alpha wave activity during olfactory stimulation. Theta Power: Measured in microvolts squared (µV²), representing the magnitude of Theta wave activity during olfactory stimulation. We will make use of the Fourier transform as well, which is inherently dimensionless. The data acquisition setup involves placing blindfolded participants in an isolated room and administering three randomized olfactory stimuli (pure olfactory, trigeminal, and olfactory-gustatory) while collecting EEG data. Sessions start and end with a 30-second resting state.

Olfactory Threshold Scores (as per routinary diagnosis of olfactory performances): Derived from the Sniffin' Sticks test, these scores quantify participants' ability to detect odors, classifying them as normosmic or hyposmic. All the participants will undergo a complete olfactory assessment through the Sniffin' Sticks test. These are represented as numerical scores. The maximum score obtainable in the full Sniffin' Sticks test, which includes the three sub-tests (Threshold, Discrimination, Identification - TDI), is 48. This maximum score is achieved by summing the highest possible score from each of the three components: 16 for olfactory threshold (Threshold), 16 for olfactory discrimination (Discrimination), and 16 for olfactory identification (Identification).

Random Forest Model Classification Accuracy: The accuracy of the classification model used to distinguish between normosmic and hyposmic participants based on EEG data, usually expressed as a percentage or a value between 0 and 1.

Pure Tone Audiometry (PTA), as per routinary diagnosis of Tinnitus: Measures hearing thresholds across frequencies, reported in decibels Hearing Level (dB HL) to determine the degree of hearing loss. The results are plotted on an audiogram, which shows the person's hearing threshold at different frequencies; a normal audiogram threshold is 0-20 dB HL between 250 and 8k Hz.

The final outcome will involve comparing olfactory perception across four participant groups (normosmic, normosmic with tinnitus, hyposmic, and hyposmic with tinnitus) using EEG features derived from Fourier analysis, reduced via t-SNE, and classified with a Random Forest algorithm. The model's accuracy in predicting odor categories (based on EEG data) will be evaluated using metrics such as accuracy, precision, recall, specificity, and F1 score. Fleiss' kappa statistic will assess agreement across groups, comparing the algorithm's predictions with the Sniffin' Sticks test results. Statistical power analysis ensures adequate sample sizes for reliable comparisons, with post-hoc analyses conducted if significant differences are detected.