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NCT07099092
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.
NCT02629107
Background: An electroencephalogram (EEG) measures the brain s electrical activity. EEG shows that the louder the sound needed to wake a person, the deeper the person s sleep. Researchers are using functional magnetic resonance imaging (fMRI) to study people during sleep so they can view brain activity in 3D. But they still need to correlate fMRI with sound thresholds, like the EEG. Objective: To measure brain activity during sleep using fMRI and EEG. Eligibility: Healthy people ages 18 34 who can sleep on their back for several hours. Design: Participants will be screened online about their sleep and general health. At a screening visit, participants will have: Physical exam Hearing exam MRI scan. A strong magnetic field and radio waves take pictures of the brain. Participants will lie down on a bed that slides into the scanner, which is shaped like a cylinder. Participants will wear an actigraph on their wrist that records their motor activity. Participants will follow a 2-week routine. This includes regular in-to-bed and out-of-bed times and limits on alcohol, caffeine, and nicotine. During the overnight visits, participants will have: Female subjects will have a urine pregnancy test. fMRI. A coil will be placed over the head. Participants will do tasks shown on a computer screen inside the scanner. EEG. Small electrodes on the scalp will record brain waves while sleeping or doing a task in the scanner. Participants will be asked to try to sleep while researchers collect fMRI and EEG data. Participants eyes will be monitored with a video camera. Headphones will deliver sounds to wake them up throughout the night. ...
NCT02583646
Background: Studies suggest that overweight girls may be developing breast tissue, and therefore starting puberty, earlier than normal weight girls. However, it is hard to distinguish breast tissue from fatty tissue. Researchers think that by using breast ultrasound, among other tests, they can do a better job of telling whether an overweight girl has breast tissue. This will help them understand if overweight girls are truly entering puberty before normal weight girls. Objective: To find out if overweight girls go through puberty earlier than normal weight girls. Eligibility: Healthy girls 8-14 years old who: * Are normal weight or overweight * Have some breast development * Have not started their first period Design: Parents of participants will be screened over the phone. Most participants will have 1 visit. However, they can choose to have multiple visits within 4 weeks. The visit will include: * Physical exam that includes examination of the breasts and genital area * Breast ultrasound: A small hand-held device will be passed back and forth over the chest. It uses sound waves to create a picture of the breast tissue. * Pelvic ultrasound: A small, handheld device will be passed back and forth over the lower belly. It uses sound waves to create a picture of the ovaries. * Urine and blood test * A special x-ray called a DXA to measure the amount of fat in the body: The participant will lie still on a table while the x-ray takes pictures of the body. X-ray of the hand: The picture will tell researchers how mature the participant s bones are. Participants may be asked to come back 6 months later to repeat these tests.
NCT03407066
Background: When people see and hear, the brain changes signals from the eyes and ears into perceptions and thoughts. No one fully understands how this happens. Researchers want to explore how healthy brains process sights and sounds. Objectives: To explore how people understand what they see and hear when the brain processes sights and sounds. Eligibility: Participants aged 13-65 who have at least 20/40 vision in at least one eye and do not use a hearing aid. Design: Some participants will take tests online anonymously. They will do computer tasks related to colors and behavior. In-person participants will be screened with medical history and physical exam. They will complete questionnaires and vision and hearing tests. Participants will plan how many testing sessions they will have and when. Sessions last 2-5 hours. They may include: * Magnetic Resonance Imaging: Magnets and radio waves to take pictures of the brain. Participants will lie on a table that slides in and out of a tube. They will do a task during the scan. * Magnetoencephalography: Records magnetic field changes from brain activity. Participants will sit or lie down. A cone will be lowered onto their head. They may do a task during the test. * Electromyography: Electrodes attached to the skin will measure the electrical activity of muscles. * Electroencephalogram: Electrodes on the scalp will record brain waves. * Electrocardiography: Electrodes on the chest will record heart electrical activity. * Tests of memory, attention, thinking, vision, and hearing. * Eye Tracking: Cameras will follow participants eye movements. They may wear a cap with infrared cameras in front of their eyes. During the sessions, participants vital signs may be monitored.
NCT05707806
Background: Substance use disorders (SUD) can be considered disorders in the way people process incentives, learn, and make decisions. To understand why some people develop SUD, researchers need to develop reliable tests that show how people think and learn. This natural history study seeks to develop a set of tasks that could then be used to test how people learn and make decisions. Objective: To develop and validate behavioral tasks that could be used in future studies. Eligibility: Healthy people aged 18-45 years from the Baltimore area. They must also be enrolled in the NIDA screening protocol. Design: Participants will perform different tasks. Most tasks require 1-4 study visits; some may require up to 12. Visits are 1-14 days apart. All visits will last about 1-7 hours. Participants will perform tasks on a computer. As they work they may be given different stimuli: Smells. Participants will sniff odors through a plastic tube or mask on their nose. Flavors. Participants will wear a mouthpiece and small amounts of different flavored liquids will be placed in their mouth. Pictures. Participants will look at different images. Sounds. Participants will wear headphones and various sounds will be played for them. Food. Participants may be asked to eat a meal before, during, or after a task. The researchers will provide the meal. During each task, participants will wear sensors to monitor their heart rate, blood pressure, breathing, and other physical changes in their bodies. Some participants will have a functional magnetic resonance imaging (fMRI) scan. They will lie on a table that slides into a cylinder. They will perform tasks on a computer screen during the fMRI.
NCT05545306
Background: Diet-induced thermogenesis (DIT) is the amount of energy one s body uses to eat food, absorb the nutrients from the food, and process those nutrients. Researchers would like to understand more about how changing the balances of protein, fat, carbohydrates, and total calories in the diet can affect DIT. Objective: To learn how different diets can change a person s DIT. Eligibility: Healthy people aged 18 to 60 years who have not intentionally lost weight in the past 6 months. Design: Participants will stay in a clinic for about 35 days. They will eat only the food provided. They will receive 8 different diets during the study, including 7 test diets. Participants will undergo multiple tests. They will be screened with blood and urine tests and a test of their heart function. During the first few days: Their waist, thigh, and neck circumference will be measured. They will have a DXA scan: They will lie on a padded table for about 20 minutes while an instrument measures the amount of fat in their body. They will be tested for diabetes. They will answer questionnaires about topics including eating behavior, hunger, and stress. Throughout the study: Their weight will be measured daily. Blood tests will be repeated. They will stay in a metabolic chamber a total of 9 times. They will remain in a closed room for 24 hours while researchers monitor the room temperature and levels of oxygen and carbon dioxide. Participants will collect all their urine for each 24-hour period. ...
NCT02193425
Background: \- Magnetic resonance imaging (MRI) is used to investigate brain function. Researchers want to use MRI to better understand the function patterns and connections between brain regions in healthy people. This might help people with brain diseases in the future. Objectives: * To evaluate MRI methods performed twice on the same day. * To evaluate brain function using positron emission tomography (PET). Eligibility: \- Healthy volunteers at least 18 years old. Design: * Visit 1: * Participants will be screened with medical history, physical exam, and interview about drug and alcohol use and psychiatric history. * They will give blood and urine samples. Their breath will be tested for alcohol and smoking. * Visit 2: * Participants will have urine collected. They will have MRI scans, some while resting, some while doing tasks on a computer. * The MRI scanner is a metal cylinder in a strong magnetic field. Participants will lie on a table that slides in and out of the cylinder, with a coil over their head. Participants will get earplugs for loud noises. * Visit 3: * Participants will have urine collected. * A needle will guide a thin plastic tube (catheter) into each arm. The needle will be removed, leaving the catheter in the vein. * Participants will then have a PET scan. They will get the chemical 18FDG in the catheter. They will lie on a bed that slides in and out of the PET scanner, with a cap on their head. * Participants may have tests of memory, attention, concentration, and thinking. They may complete interviews, questionnaires, tests on paper or computer, and simple actions. * Participants will wear a device for 1 week between visits to measure activity and sleep.
NCT05398783
Background: Scientists have long used simple measures (such as height and weight) to estimate how much a person s body uses food (calories) as energy, as commonly called the metabolic rate. But metabolism varies among people with similar body sizes. Scientists now believe the old formulas for estimating metabolic rates may not work well for all people. Researchers want to find more accurate ways to measure a person s metabolism. Objective: This natural history study will examine the relationships between metabolism, body composition, and body surface area in a wide range of people. Eligibility: Healthy children and adults aged 2 years or older. Also, people aged 2 years or older with conditions that may alter metabolism. These may include diabetes, obesity, renal disease, or cancer. Design: Participants will spend 2 days and 1 night in the hospital. They will provide a medical history and answer questions about their activity levels, the foods they eat, and their lifestyle. They will also eat a special diet. Participants will undergo many tests: They will lie in a bed with a clear hood covering their head for 30 to 45 minutes to measure the gases in their breath. They will lie on a padded table for about 15 minutes while their body is scanned. They will stand on a platform while a 3D scanner measures their body. They will have a test to measure how fast an electric signal moves through their body. They will grip an instrument to measure the strength of their hands. They will drink salty water and provide blood and urine samples. Participants may be invited to return for these 2-day visits up to 8 times per year. Return visits must be at least 2 weeks apart.
NCT06561828
Background: People with substance use disorder (SUD) often have changes in brain function that can make it difficult to control drug-seeking behavior. These changes may heighten the urge to use drugs or lessen the desire to seek nondrug-related rewards. Researchers want to know how a technique called transcranial magnetic stimulation (TMS) may cause changes in brain activity that may help people with SUD. Objective: To test TMS in healthy volunteers. Eligibility: Healthy people aged 18 to 45 years who are right-handed. Design: Participants can volunteer for up to 5 different experiments. Each experiment requires 2 to 8 clinic visits. Each visit will last 3 to 7 hours. Some visits will include TMS. A coil will be placed on the participant s head. A brief electrical current will pass through the coil to create a magnetic field. Participants may feel a tapping or pulling sensation on the skin under the coil. They may feel a twitch in their face, neck, arm, or leg muscles. Participants may be asked to tense certain muscles during TMS. Some visits will include functional magnetic resonance imaging (fMRI) scans. Participants will lie on a bed that slides into a large tube. They will perform tasks on a computer inside the tube. The fMRI will show which parts of the brain are used during each task. Participants will perform tasks on a computer. Some tasks may be done at a desk as well as during TMS and fMRI. Participants may look at images, listen to sounds, smell odors, or taste flavored liquids. Their vital signs may be monitored and their eye movements may be tracked during tasks.
NCT02669225
Background: Brain activity creates waste products. The body s glymphatic system removes this waste, especially during sleep. One brain waste product is amyloid-beta (Ab). It plays a role in Alzheimer s disease. Researchers want to study the effect of sleep on Ab in the brain. Objective: To see if sleep affects the amount of waste product removed from the brain. Eligibility: Healthy people at least 18 years of age. Design: Participants will be screened with a medical history, physical exam, and blood and urine tests. They will answer questions about drug use, psychiatric history, and family history of alcoholism or drug use. Participants will complete an MRI screening questionnaire. Participants will stay in the clinic overnight two times. On one night they will sleep through the night. On the other night they will be kept awake all night. These overnight visits can happen in any order. Participants will wear 2 activity monitors, on the wrist and the ankle. Participants will have positron emission tomography (PET) scans. A small amount of a radioactive chemical will be injected through an intravenous (IV) catheter. Participants will lie on a bed that slides into the scanner. A cap or a special mask may be placed on the participant s head. Participants will have magnetic resonance imaging (MRI) scans. The MRI scanner is a metal cylinder in a strong magnetic field. Participants will lie on a table that slides into the cylinder. A device called a coil will be placed over the head. Participants will do a task on a computer screen in the scanner. Participants will have tests of thinking, memory, and attention. They may be interviewed, complete questionnaires, take pen-and-paper or computer tests, and perform simple actions.
NCT04946851
Background: Alcohol use disorder (AUD) is a major public health problem. In the U.S., 16 to 18 million adults have an AUD. Researchers want to test an assessment tool called the ANA. It uses self-report and behavioral measures to assess 3 neuroscience domains of addiction. They hope to better understand, manage, prevent, and treat AUD. Objective: To learn how people s brains function related to their drinking. Eligibility: People ages 18 years and older who have enrolled in NIAAA natural history study 14-AA-0181. Design: Participants will complete surveys and tasks on a computer. The surveys and tasks assess a range of aspects of thinking and making decisions. The surveys and tasks also assess behaviors and feelings about alcohol and other rewards, and negative emotions. Participants will spend 90 minutes on the computer. Then they will take a break. In total, they will spend 4 blocks of time on the computer. Each block will last 90 minutes. They will take a break in between each block of time. They can take more breaks if needed. Outpatient participants and healthy volunteers will complete this study in 1 visit. It will last about 6 hours. A second visit may be scheduled if needed. Outpatient participants will take a breath alcohol test. If their test is positive, their visit may be rescheduled or they may be withdrawn from the study. Inpatient participants will complete this study over several days. Data collected from participants in this study may be combined and analyzed with their data from NIAAA study 14-AA-0181 and/or NIAAA imaging study 14-AA-0080.
NCT03258580
Objective The current proposal investigates behavioral, psychophysiological, and social processes that may help explain biases and disparate outcomes in pain. Health disparities, or health outcomes that adversely affect disadvantaged populations, are pervasive and apparent in many diseases and symptoms, including pain. Pain is the number one reason individuals seek medical treatment. Health disparities in pain encompass both differences in pain experience and treatment for pain. For instance, research indicates that Black individuals report increased pain and have reduced pain tolerance relative to White individuals, yet doctors are less likely to treat minority patients pain and underestimate their pain experience. This project aims to address this systemic discrepancy by focusing on interpersonal processes that may contribute to these disparities, including socially-relevant responses to pain (i.e. pain expression) and pain assessment (e.g. visual attention). The proposed research aims to determine whether the study of pain expressions and their assessment can yield insights on how social factors shape pain and its treatment. Further, we test the efficacy of potential interventions designed to improve accuracy and reduce biases in pain assessment. If successful, this work will form the foundation of a new research program that will link the field of pain research with the field of social neuroscience, and forge new insights on the critical problem of health disparities in pain. Study population We will accrue up to 700 total healthy volunteers to target 240 completers Design Our overall aim is to understand how social factors influence the assessment and management of pain, and to gain insight into psychosocial processes that may underlie health disparities in pain. We propose a series of studies designed to test these links. First, we will measure pain perception and physiological responses to painful stimuli in a diverse group of individuals to test for sociocultural and biological influences on pain and pain-related responses. In subsequent studies, new participants ("perceivers") will view images of these initial participants ("targets") and will provide estimates of 'targets' pain experience. We will measure a) whether perceivers can accurately estimate 'targets' pain experience; b) whether accuracy differs as a function of similarity between target and perceiver (ingroup vs outgroup); and c) whether individuals can improve accuracy through feedback. Outcome measures Primary outcome measures for all experiments will be decisions about pain (experienced by self or other) measured with visual analogue scales, reaction time, and/or categorical judgments (pain/no pain). We will also measure physiological responses (e.g., facial muscle response, skin conductance, pupil dilation) and brain responses using functional magnetic resonance imaging (fMRI) as secondary outcome measures. We will test whether pain and pain-related responses varies as a function of sociocultural/demographic factors (e.g. race, ethnicity, sex) and whether accuracy in assessing others' pain is influenced by group similarity (i.e. ingroup vs. outgroup) and training (e.g. performance-related feedback)....
NCT03324646
Background: A radioligand is a radioactive substance that is used to diagnose diseases. A new ligand is called \[11C\]PS13. This has a small amount of radioactivity that can be detected by a positron emission tomography (PET) scan. If this ligand works well in this study, researchers may be able to use it to better understand and diagnose brain disorders. Objectives: To evaluate if \[11C\]PS13 can measure its receptor, which is involved in inflammation. To see if researchers get the same results when scanning a person twice. Eligibility: Healthy people ages 18 and older who are in Protocol 01-M-0254. Design: This study requires three visits of 2-5 hours each. Participants will have 2 PET scans with \[11C\]PS13. A needle will guide a small plastic tube (catheter) into an arm vein. The needle will be removed, leaving only the catheter in the vein. The ligand will be injected through the catheter. The PET scanner is shaped like a doughnut. Participants will lie on a bed that slides in and out of the scanner. Participants will wear a molded a plastic mask that fits the head. Another catheter will be put into an artery at the wrist or elbow area. Vital signs will be monitored during the PET scan. Participants will have a test during the PET scan to monitor heart function. Participants will have blood and urine tests. Participants will have 1 magnetic resonance imaging (MRI) scan. The MRI scanner is a metal cylinder surrounded by a strong magnetic field. Participants will lie on a table that slides in and out of the cylinder.
NCT04694131
Background: Transcranial magnetic stimulation (TMS) of the brain has been used to change the activity and connections in the brain to improve memory. Researchers are interested in how these brain changes cause memory improvements and how activity at the time of stimulation may change the effects of TMS. Objective: To learn how brain stimulation can be used to improve memory. Eligibility: Healthy adults ages 18-40 Design: Participants will be screened with a medical record review. Participants will have 3 study visits. At visit 1, participants will have a physical exam and will talk about their health. They will have magnetic resonance imaging (MRI). The MRI scanner is a metal cylinder surrounded by a strong magnetic field. During the MRI, participants will lie on a table that can slide in and out of the scanner. A coil will be placed over the head. Participants will be asked to keep their eyes focused on a small cross on a computer screen inside the scanner. The scanner makes loud noises. Participants will get earplugs. At visits 2 and 3, participants will have TMS and perform tasks. For TMS, a wire coil encased in plastic is held on the scalp. When the coil is triggered, a brief electrical current passes through the coil and creates a magnetic pulse that stimulates the brain. During TMS, an electroencephalogram (EEG) will record brain activity. For the EEG, a cloth cap with electrodes is fitted on the participant s head. Participants will complete a memory task and a spatial processing task. They will also complete surveys about their mental state. Participation will last 2-3 weeks.
NCT05666739
Background: Laboratory tests that use blood and urine can provide a great deal of information about human health and disease. To develop even better tests and to improve the ways samples are handled for testing researchers need to experiment with samples from healthy people. Objective: This natural history study will collect blood and urine from healthy people. The samples will build a repository that will be used for all kinds of research. Eligibility: Healthy people aged 18 years or older. Design: Participants will have 1 study visit. The visit will last up to 2 hours. Participants will be screened. They will answer questions about their health history. They will list any medications they take. They will consent to donate samples for research and future use: Blood: Up to 4.5 tablespoons of blood may be collected from a needle inserted into a vein. Urine: Participants will be given a sterile container to provide a sample. Some participants may be asked to provide other types of samples. Some participants may be asked to provide new samples if their first ones are depleted.
NCT02911129
Background: After a stroke, the balance between the two halves of the brain can be lost. This may cause people to lose the ability to perceive a side of space. This is called neglect. Having people wear prism glasses (called PA) can reduce neglect symptoms. Researchers want to find out more about how PA, and whether it restores the balance in the brain. Objective: To learn how prism adaption temporarily changes vision and connections in the brain. Eligibility: People ages 18 75 with brain damage of the right side of the brain from a stroke or other cause, leading to neglect. Healthy volunteers ages 18 75. Design: Participants will have 1 3 visits. Participants will be screened with a neurological exam. They may also have: Tests of thinking and vision Tests to see which eye and hand they prefer A pregnancy test All participants will: Answer questions about their personality, style of thinking, and beliefs. Do simple tasks on paper or computer Have magnetic resonance imaging. They will lie on a table that can slide in and out of a cylinder in a strong magnetic field. Participants will lie still or do computer tasks in the scanner. Participants may also have: Transcranial magnetic stimulation. A brief electrical current passes through a wire coil on the scalp. This creates a magnetic pulse that affects brain activity. Participants may be asked to tense certain muscles or perform simple actions or tasks. PA. They will sit in front of a board and point to a dot on it while they wear prism glasses that shift vision to the left or right....
NCT06050603
The goal of this interventional study is to develop an individualized approach using transcranial magnetic stimulation (TMS) in a high-precision manner. This approach will use TMS to modulate brain activity at multiple locations simultaneously. Functional magnetic resonance imaging (fMRI) and electroencephalograph (EEG) will record the responses and guide the stimulation. Specifically, the placement and orientation of TMS coils will be tailored to stimulate the targeted functional brain areas informed by fMRI. To maximize the interventional effect, stimulation pulses will be delivered based on EEG oscillations.
NCT03018262
Background: Movement disorders have many different causes and symptoms. Researchers still do not fully understand which parts of the brain are involved in fine movement. They want to learn about which brain regions could be abnormal in people with movement disorders. Objective: To better understand how the brain controls movement. Eligibility: Healthy, right-handed adults age 18-70 years old. Design: Participants will be screened with a physical exam and questions about their handedness. They may have a urine test. Participants will have 1 or 2 clinic visits. The first visit will last about 1.5 hours. The second will last about 3 hours. Participants will have structural magnetic resonance imaging (MRI). A strong magnetic field and radio waves take pictures of the brain. Participants will lie on a table that slides in and out of a metal cylinder. Participants may have transcranial magnetic stimulation. A wire coil is held on the scalp. A brief electrical current is passed through the coil and creates a magnetic pulse that stimulates the brain. Participants will wear a pair of glasses or a headband with small sensors so researchers can track head position. Participants will perform a simple index finger movement task. Participants may have surface electromyography from at least two hand muscles. Small metal disk or adhesive pad electrodes will be taped to the skin. Participants will be seated in a comfortable chair with their hands placed on a pillow. Participants may have an electroencephalography. A cap with small disc electrodes will be placed on the scalp.
NCT02798523
Background: The immune system defends the body against bacteria and other harmful invaders. But it can overact and attack healthy cells by mistake. The group of drugs called glucocorticoids (GCs) can calm down an overactive immune system. But they often cause negative side effects. Researchers want to learn how human genes respond to GCs. Genes live inside each cell of the body. They tell our cells how to function. Researchers hope the results of this study will show them how to develop better drugs that will have the benefits of GCs without the side effects. Objectives: To study how human genes respond to glucocorticoid drugs. Eligibility: Healthy adult volunteers ages 18-64. Design: Participants will be screened with a medical history and physical exam. They will have a heart test and blood tests. The study visit will last about 6 hours. Participants will have medical history, physical exam, and 3 blood draws. Participants will have a skin biopsy. An injection will numb the skin on one arm. Then a tool will remove a piece of skin about as big as a pencil eraser. A GC cream will be applied to the other arm. Participants will get the GC study drug for 30 minutes. It will be a liquid that will drip through a needle placed in an arm vein. Participants will have a skin biopsy of the arm that had the cream applied. Participants will have follow-up calls 1 and 4 days later. They will be asked about reactions or other health problems.
NCT01123499
Background: * Many treatments for immune system disorders involve the use of stem cells that have been collected from blood marrow. To obtain these stem cells without surgery, individuals receive granulocyte colony-stimulating factor (G-CSF) to encourage the production of stem cells that can be collected through blood donations. However, not all patients or normal donors respond to G-CSF alone. * Plerixafor, recently approved by the Food and Drug Administration, is different from G-CSF but also allows stem cells to be collected from donated blood. However, more research is needed on the quality and viability of the stem cells collected after using both G-CSF and plerixafor. Objectives: \- To collect and study the blood cells produced after treatment with G-CSF and plerixafor in healthy volunteers. Eligibility: \- Healthy volunteers between 18 and 65 years of age who are eligible to donate blood. Design: * Participants will be screened with a medical history, physical examination, and initial blood tests. * At the start of the study cycle, participants will receive daily morning injections of G-CSF for 5 days. These may be given at the clinical center or by the participant after teaching, depending on the participant s preference. * On the morning of Day 4, participants will visit the clinical center to provide a blood sample after the injection. On the evening of Day 4, participants will receive an injection of plerixafor. * Participants will have the final injection of G-CSF on the morning of Day 5, and will provide another blood sample. * On Day 5, participants will have apheresis to separate the stem cells from the rest of the blood. The apheresis may take up to 5 hours to complete. * The study will end after a follow-up phone call 7 to 14 days after the apheresis procedure.