Functional Magnetic Resonance Imaging (fMRI)

A Brief History

Functional Magnetic Resonance Imaging (fMRI) is a non-invasive brain imaging technique that measures changes in blood flow in response to neural activity. The history of fMRI can be traced back to the 1980s when researchers first began to explore the use of MRI to investigate brain function. In 1990, a team led by Seiji Ogawa discovered that the signal from MRI scans could be affected by changes in blood flow, and that this signal change could be used to infer neural activity. This discovery led to the development of fMRI, which quickly became a popular tool for studying brain function. The first fMRI experiments were performed in the early 1990s, and by the mid-1990s, fMRI had become widely used in cognitive neuroscience. Since then, fMRI technology has continued to improve, with advances in hardware and software allowing for higher resolution and more detailed images of the brain. Today, fMRI is a standard tool used in neuroscience research, and has also found clinical applications in the diagnosis and treatment of neurological and psychiatric disorders.

Blood Oxygen Level Dependent (BOLD) Signals

BOLD (Blood Oxygenation Level Dependent) signals are changes in the magnetic properties of hemoglobin in the blood that occur when blood oxygen levels change in response to neural activity. When neurons become active, they require more oxygen, which leads to an increase in blood flow to the activated brain region. The increased blood flow brings more oxygenated hemoglobin to the area, causing a local increase in magnetic susceptibility that can be detected by fMRI scanners. This signal change is what fMRI researchers refer to as the BOLD signal. By measuring the BOLD signal, fMRI can provide information about which areas of the brain are active during a particular task or state, and how these areas are connected to one another.

There are several factors that can affect the BOLD signal in fMRI studies.

• Neural activity: The BOLD signal is closely linked to neural activity, so changes in neural activity will result in corresponding changes in the BOLD signal.

• Blood flow: The BOLD signal is also affected by changes in blood flow, as changes in blood flow will affect the amount of oxygenated hemoglobin in the brain.

• Oxygen metabolism: The rate at which neurons consume oxygen can also affect the BOLD signal, as changes in oxygen metabolism will affect the concentration of deoxygenated hemoglobin in the brain.

• Magnetic field strength: The strength of the magnetic field used in fMRI studies can affect the BOLD signal, with stronger magnetic fields typically resulting in larger signal changes.

• Field of view: The portion of the brain being imaged, or the field of view (FOV), can also affect the BOLD signal, as different brain regions have different baseline levels of oxygenation and blood flow.

• Motion artifacts: Any motion or movement by the subject during the fMRI scan can also affect the BOLD signal, as it can introduce noise and artifacts into the data.

Analysis of fMRI