Causal Mechanisms of Odor-Guided Behavior in Humans

What this study involves

The registry does not currently label this study as recruiting. Ask about its status before planning a screening visit.

Study type

Interventional

Phase

Early Phase 1

Age range

18 years - 45 years

Sex eligible

All sexes

Healthy volunteers

Not accepted

Participants

80 Estimated

These are starting points, not an eligibility decision. The research team must review the full requirements.

About the research

Background:

Little is known about how different regions of the brain responsible for the human sense of smell guide behaviors. In this study, researchers use a technique called transcranial ultrasound stimulation (TUS) to learn how odors affect the brain and behavior.

Objective:

To learn more about how the human sense of smell works.

Eligibility:

Healthy people aged 18 to 45 years who are right-handed.

Design:

Participants can volunteer for up to 2 different experiments. Each experiment requires 5 visits, each about 1 week apart. Food, alcohol, and caffeine may be limited before visits.

At the start of each visit, participants will answer questions about their health and how well they slept. Their sense of smell will be assessed.

Some visits may include tasks on a computer: While doing these tasks, participants may be asked to smell different odors, look at pictures, and listen to sounds. They will wear devices to track breathing, blood pressure, pulse, and other body responses to the tasks.

Some visits may include TUS: TUS uses ultrasound waves to briefly change brain activity. A gel will be applied to the scalp and hair, and a device will be placed against the participant s head. Participants may feel a tapping, pulling, and/or warm sensation on the skin underneath the device. They may also feel a twitch in their face, neck, arm, or leg muscles. Participants will do tasks before and after TUS.

Some visits will include functional magnetic resonance imaging (fMRI) scans. fMRI uses magnet and radio waves to capture images of the activity inside the brain. Participants will lie on a table that slides into a tube. They will perform tasks inside the scanner.

Who may be able to participate?

The list below is the sponsor’s full registry wording. It can include conditions, prior treatment, test results and other requirements. A match in search does not mean you qualify.

• INCLUSION CRITERIA:

In order to be eligible to participate in this study, an individual must meet the following criteria:

1. Aged 18-45 years old. Justification: Many neural processes change with age, and these changes could introduce unwanted variability in the measured signals.
2. In good general health based on the assessment of the Medical Advisory Investigator (MAI) or delegate.
3. Right-handed.

EXCLUSION CRITERIA:

Individuals who meet any of the following criteria will be excluded from participation:

1. Any neurological disorder that would increase seizure risk from TUS such as stroke, brain lesions, previous neurosurgery, epilepsy, any history of seizure or fainting episode of unknown cause, frequent severe headache, or head trauma resulting in loss of consciousness, lasting over 30 minutes or with sequela lasting longer than one month. The MAI will also retain discretion to exclude based on a history of a neurological illness or trauma that may compromise safety or data integrity.
2. Predisposition to seizures (e.g., first-degree family history of potentially hereditary epilepsy, etc.).
3. Current use (any use in the past week, daily use for more than one week within past 3 months) of any investigational drug or of any medications with psychotropic (e.g., benzodiazepines, etc.), or anti or pro-convulsive action. This will be determined at the discretion of the MAI.
4. Unable to undergo MRI, or TUS due to certain metallic or magnetic devices or implants in the body, claustrophobia, or other reasons including numbness or paresthesia of the head.
5. History of noise-induced hearing loss or tinnitus.
6. Recent history (within past 12 months) of learning disability, major DSM-5 psychiatric disorder including major affective disorder, ADHD, obsessivecompulsive disorder, schizophrenia, or PTSD. This will be determined at the discretion of the MAI.
7. Pattern of alcohol and drug use in the past 12 months that is indicative of harmful use, loss of control over use, or physical dependence.
8. Daily nicotine, alcohol, or drug use (excluding caffeine) for at least 4 continuous weeks within the past 12 months.
9. Participation in any neuromodulation (e.g., TMS, TUS, tDCS, tACS, etc.) session (excluding the current protocol) in the past two weeks.
10. History of anaphylaxis and/or severe food and non-food allergies (e.g., latex, detergents, soap, etc.).
11. History of significant chronic obstructive pulmonary disease (COPD) or severe, uncontrolled asthma, as increased levels of carbon dioxide may increase the susceptibility to cavitation and related tissue damage.
12. Uncorrected impairments in visual acuity severe enough to affect task participation.
13. Non-English speaking. Justification: Data integrity of some of the behavioral tasks used in this study would be compromised as they have only been validated in English. Most importantly, ongoing communication regarding safety procedures is necessary when participants are undergoing TUS and MRI procedures. The inability to effectively communicate TUS and MRI safety procedures in a language other than English could compromise the safety of non-English speaking participants.
14. Serious skin disease involving the hands or head, or history of serious systemic allergy involving the skin or mucous membranes such as Stevens-Johnson syndrome, or known history of contact dermatitis to ultrasound gel. Justification: Gel will be applied to the skin on both head and hands, for transducer coupling and electrode placement, respectively. Allergic or adverse reactions to such treatment need to be ruled out.
15. Hyposmia, i.e., decreased sense of smell, or anosmia, i.e., loss of smell (Sniffin' Sticks Olfactory Identification Score \< 10). Justification: The ability to smell is paramount to task performance.
16. Pregnancy. Justification: It is unknown whether MRI and/or TUS pose risks to fetuses.
17. Any other condition that in the judgment of the investigators is incompatible with participation.

Treatment, groups and participation

The registry may describe treatments and study duration without a complete visit calendar. Ask the study team for the exact schedule, procedures, risks, costs and alternatives. Keep your usual care plan unless your treating clinician tells you otherwise.

Assignment

Not randomized

Masking

Single masked

What researchers are measuring

Outcome measures describe what is being studied. They are not proof that a treatment works.

Primary measures

Secondary measures

Research locations (1)

The overall study status and a local site’s status can differ. Confirm that location’s availability before traveling.

1 locations

Study team and timeline

Lead sponsor

National Institute on Drug Abuse (NIDA)

Study start

Nov 15, 2026 Estimated

Primary completion

Jul 14, 2035 Estimated

Study completion

Jul 14, 2035 Estimated

First posted

Aug 1, 2025 Actual

Last updated

Nov 10, 2026 Actual

Official study contacts