Summary fMRI data & statistics 2025
WEEK 1: Introduction
Book chapters: 1, 13, 14
Chapter 1
Localization of function: The idea that arose in the 19th century that aspects of the mind are
represented in different brain regions.
Phrenology: Maps made from anecdotes on functioning bumps in the skull. Not
enough scientific grounding- abandoned theory.
Cases of brain damage: Provided critical info about the organization of the brain.
However, there is insufficient ground to study complex functions or direct
manipulations.
fMRI: This technique localizes function by isolating particular brain functions. It is
used to understand connectivity.
fMRI: It uses a magnetic field to create images of biological tissue. It is non-invasive and
provides information about brain metabolism
Pulse sequence = A series of changing magnetic field gradients and electromagnetic
pulses that create images sensitive to a physical property. This depends on the
frequency of the electromagnetic fields of the atomic nuclei. These alterations do not
affect macroscopic functioning or influence neuronal firing or blood flow.
o Scanners are tuned to the frequency of hydrogen nuclei (most common in the
human body due to water molecules)
o After absorption, electromagnetic energy is released by the nuclei. The
amount of released energy depends on the number and types of nuclei
present depending on the pulse sequence used; the scanner can detect
different tissue properties
Static magnetic field = The strong magnetic field at the centre of the MRI scanner
whose strength does not change over time. The strengths are expressed in tesla (T). A
typical scanner is 3T, but scanners can range between 1.5 and 7+ T.
Two imaging techniques:
1. Structural neuroimaging: This involves the brain’s physical structure and the
localization and distribution of tissue types. Limitation: No short-term physiological
changes are associated with the brain's active functioning.
2. Functional neuroimaging: Brain’s functional properties. Patterns of brain activation
associated with processes. Common techniques, including fMRI, PET, and optical
imaging
Other imaging techniques:
, Electroencephalography (EEG): Measures electrical potential of the brain. High
temporal resolution, lower spatial resolution.
Magnetoencephalography (MEG) measures small changes in magnetic fields caused
by the electrical activity of neurons. It has a high spatial and temporal resolution and
is expensive.
Transcranial magnetic stimulation (TMS): Temporary stimulation of a brain region to
disrupt its function. It can establish causal relations between brain regions and
functions, and it is non-invasive. However, is limited to cortical regions.
Contrast-to-noise ratio (CNR): The measure of how well two different tissue types can be
distinguished in an MRI image.
= The magnitude of the intensity difference between different quantities is divided by the
variability in their measurements. The contrast-to-noise ratio depends on the signal change
and the variability of the signal.
Higher CNR: Structures are easily distinguishable
Lower CNR: Differentiation is difficult
T1-weighted images show fluid as dark and white matter as lighter than gray matter.
T2-weighted images show fluid as bright and gray matter as lighter than white matter.
Note: T1 contrast is based on recovery time (T1 relaxation = recovery), while T2 contrast is
based on decay time (T2 relaxation = decay).
Functional contrast: The ability to map physiological variation to underlying mental
processes or behaviors: A physiological correlate of brain function. In fMRI: Total amount of
deoxygenated hemoglobin in the blood.
Spatial resolution:
- Pixel: 2D picture element
- Voxel: 3D volume element. In MRI: each voxel around 1mm, fMRI: 3mm
Temporal resolution: Sampling rate: Frequency in time with which a measurement is made
In fMRI, one brain volume is often found every 1-2 seconds
However, fMRI measures hemodynamic changes (the BOLD response), reflecting
changes in blood flow and oxygenation rather than direct neural activity.
The BOLD response is inherently slow: After neural activation, blood flow increases
gradually, peaking 4–6 seconds later and returning to baseline after 10–12 seconds.
So: Even with a high sampling rate (e.g., scanning every second), fMRI cannot precisely track
rapid neural events within milliseconds.
WEEK 1: Introduction
Book chapters: 1, 13, 14
Chapter 1
Localization of function: The idea that arose in the 19th century that aspects of the mind are
represented in different brain regions.
Phrenology: Maps made from anecdotes on functioning bumps in the skull. Not
enough scientific grounding- abandoned theory.
Cases of brain damage: Provided critical info about the organization of the brain.
However, there is insufficient ground to study complex functions or direct
manipulations.
fMRI: This technique localizes function by isolating particular brain functions. It is
used to understand connectivity.
fMRI: It uses a magnetic field to create images of biological tissue. It is non-invasive and
provides information about brain metabolism
Pulse sequence = A series of changing magnetic field gradients and electromagnetic
pulses that create images sensitive to a physical property. This depends on the
frequency of the electromagnetic fields of the atomic nuclei. These alterations do not
affect macroscopic functioning or influence neuronal firing or blood flow.
o Scanners are tuned to the frequency of hydrogen nuclei (most common in the
human body due to water molecules)
o After absorption, electromagnetic energy is released by the nuclei. The
amount of released energy depends on the number and types of nuclei
present depending on the pulse sequence used; the scanner can detect
different tissue properties
Static magnetic field = The strong magnetic field at the centre of the MRI scanner
whose strength does not change over time. The strengths are expressed in tesla (T). A
typical scanner is 3T, but scanners can range between 1.5 and 7+ T.
Two imaging techniques:
1. Structural neuroimaging: This involves the brain’s physical structure and the
localization and distribution of tissue types. Limitation: No short-term physiological
changes are associated with the brain's active functioning.
2. Functional neuroimaging: Brain’s functional properties. Patterns of brain activation
associated with processes. Common techniques, including fMRI, PET, and optical
imaging
Other imaging techniques:
, Electroencephalography (EEG): Measures electrical potential of the brain. High
temporal resolution, lower spatial resolution.
Magnetoencephalography (MEG) measures small changes in magnetic fields caused
by the electrical activity of neurons. It has a high spatial and temporal resolution and
is expensive.
Transcranial magnetic stimulation (TMS): Temporary stimulation of a brain region to
disrupt its function. It can establish causal relations between brain regions and
functions, and it is non-invasive. However, is limited to cortical regions.
Contrast-to-noise ratio (CNR): The measure of how well two different tissue types can be
distinguished in an MRI image.
= The magnitude of the intensity difference between different quantities is divided by the
variability in their measurements. The contrast-to-noise ratio depends on the signal change
and the variability of the signal.
Higher CNR: Structures are easily distinguishable
Lower CNR: Differentiation is difficult
T1-weighted images show fluid as dark and white matter as lighter than gray matter.
T2-weighted images show fluid as bright and gray matter as lighter than white matter.
Note: T1 contrast is based on recovery time (T1 relaxation = recovery), while T2 contrast is
based on decay time (T2 relaxation = decay).
Functional contrast: The ability to map physiological variation to underlying mental
processes or behaviors: A physiological correlate of brain function. In fMRI: Total amount of
deoxygenated hemoglobin in the blood.
Spatial resolution:
- Pixel: 2D picture element
- Voxel: 3D volume element. In MRI: each voxel around 1mm, fMRI: 3mm
Temporal resolution: Sampling rate: Frequency in time with which a measurement is made
In fMRI, one brain volume is often found every 1-2 seconds
However, fMRI measures hemodynamic changes (the BOLD response), reflecting
changes in blood flow and oxygenation rather than direct neural activity.
The BOLD response is inherently slow: After neural activation, blood flow increases
gradually, peaking 4–6 seconds later and returning to baseline after 10–12 seconds.
So: Even with a high sampling rate (e.g., scanning every second), fMRI cannot precisely track
rapid neural events within milliseconds.
