fMRI AS A TOOL IN NEUROTECHNOLOGY

Who is credited with conducting the first functional MRI (fMRI) experiment, demonstrating changes in brain activity using the BOLD signal?

• Raymond Damadian

• Paul Lauterbur

• Alan Turing

• Seiji Ogawa

Answer explanation

Seiji Ogawa is a Japanese neuroscientist known for his contributions to the development of fMRI technology.

He identified the brain's oxyhemoglobin and deoxyhemoglobin signals, which fMRI uses to map brain activity.

Ogawa's work has significantly advanced the field of neuroscience, enabling researchers to non-invasively study brain function and structure.

His discovery has led to numerous applications in understanding brain disorders, such as Alzheimer's disease and stroke, and has improved our understanding of the brain's neural mechanisms.

What is the primary physiological signal measured by fMRI?

• Neural action potentials

• Blood-oxygen-level-dependent (BOLD) signal

• Cerebral blood volume (CBV)

• Synaptic transmission

Answer explanation

• Utilises the magnetic properties of hemoglobin, the protein that carries oxygen in red blood cells.

• Active neurons need more energy, triggering an increase in blood flow that delivers oxygen-rich hemoglobin, known as oxyhemoglobin

• This leads to a temporary decrease in deoxyhemoglobin.

• This change in magnetic properties is detected by fMRI as the blood oxygen level-dependent (BOLD) signal.

Why does fMRI rely on the magnetic properties of hemoglobin?

• To measure electrical activity directly from neurons

• To visualize the anatomical structure of the brain

• To measure neurotransmitter levels in the brain

• To detect changes in the concentration of oxyhemoglobin and deoxyhemoglobin

Answer explanation

fMRI uses the magnetic properties of hemoglobin to indirectly measure blood flow in the brain.

Hemoglobin is diamagnetic when oxygenated and paramagnetic when deoxygenated. This difference in magnetic properties causes small differences in the MRI signal of blood, which can be used to detect brain activity

When fMRI detects an increase in oxyhemoglobin concentration in a brain region, what conclusions can we draw?

• The region is less active due to reduced energy demands

• The region is engaged in passive blood flow regulation

• The region is highly active, requiring more oxygen

• Deoxyhemoglobin levels are causing a decrease in the magnetic field

Answer explanation

When neurons in a specific brain region are engaged in a task, such as thinking, moving, or processing sensory information, they consume more energy. This increased energy demand is met by an increase in blood flow to that region, delivering oxygen and nutrients required for neuronal function.

Since deoxyhemoglobin is paramagnetic (weakly magnetic), a decrease in its concentration leads to less disruption of the magnetic field, resulting in a stronger BOLD (Blood-Oxygen-Level-Dependent) signal. fMRI captures these changes, allowing researchers to identify active brain regions based on the dynamic patterns of oxygen utilization and blood flow.

Select the correct answer regarding the hemodynamic response function (HRF) in fMRI

• The initial dip in the HRF is caused by a temporary increase in oxygen consumption by neurons before blood flow increases

• The peak of the Hemodynamic Response Function (HRF) typically occurs 4–6 seconds after a stimulus

• The peak of the HRF typically occurs immediately (0–2 seconds) after the stimulus

• The HRF is directly caused by neuronal electrical activity.

Answer explanation

• Initial Dip: A slight initial decrease in the BOLD signal may occur due to a transient reduction in oxygenated blood volume before vasodilation begins. This dip reflects the immediate oxygen consumption by active neurons.

• Delayed Peak: The BOLD signal does not increase immediately but takes several seconds (typically around 5–15 seconds) to reach its peak. This delay corresponds to the time required for the hemodynamic response, including increased blood flow and oxygen delivery, to fully develop.

• Gradual Decrease: After reaching its peak, the BOLD signal gradually returns to baseline. This decline is slower than the initial rise, as blood flow and oxygenation take time to normalize following the cessation of neural activity.

Which of the following MRI pulse sequence techniques is commonly used for fMRI?

• T1-weighted imaging

• Diffusion-weighted imaging (DWI)

• Echo-planar imaging (EPI)

• Gradient-recalled echo (GRE)

Answer explanation

• Gradient Echo Echo-Planar Imaging (GE-EPI):

• A fast fMRI sequence highly sensitive to BOLD signals (T2* weighting), capable of capturing whole brain volumes in seconds, but prone to artefacts and lower signal-to-noise ratio.

• Spin Echo Echo-Planar Imaging (SE-EPI) :

• A type of EPI that uses a spin-echo pulse to improve image quality and temporal resolution, but it is slower and less sensitive to BOLD signals than GE-EPI.

Select the correct answer regarding paradigm design.

• Block designs involve alternating periods of task and rest conditions

• Mixed designs combine elements of block and event-related paradigms

• Event-related designs reduce movement artifacts and are useful for analyzing trial-specific effects.

• Event-related designs have higher statistical power compared to blocked designs

Answer explanation

Blocked Design

• Stimuli are grouped into multiple blocks with rest periods in between.

• Same type of stimulus (e.g., objects, scenes, or faces) is presented repeatedly within each block.

Event-Related Design

• Stimuli from different categories are presented randomly and individually.

• Jittered inter-trial intervals (ITIs) ensure better temporal precision.

Mixed Design

• Combines blocked structure with jittered ITIs for event-specific analysis.

• Captures both sustained and transient neural activity.

What is the purpose of slice timing correction in fMRI preprocessing?

• To reduce head motion artifacts

• To align anatomical and functional images

• To acquire the BOLD signal for the whole brain at the same time point

• To normalize brain shapes to a standard space

Answer explanation

Slice Timing Correction:
In fMRI, the BOLD signal is acquired at different layers of the brain at varying time points during a scan. To ensure consistency, slice timing correction adjusts the data so that the signals from all brain slices are aligned to represent the same time point. This process enhances the statistical power of fMRI analysis by reducing temporal discrepancies in the dataset.

Which of the following preprocessing steps aligns all functional images in the same orientation and position?

• Coregistration

• Normalization

• Realignment

• Smoothing

Answer explanation

Realignment corrects for head motion artifacts by aligning all functional images in a time series to ensure they are in the same spatial orientation and position, using a rigid-body transformation with six parameters (three for translation and three for rotation)

What is the main goal of spatial smoothing in fMRI preprocessing?

• To increase temporal resolution

• To reduce random noise and improve signal-to-noise ratio

• To align functional and anatomical images

• To transform the brain to a standard template

Answer explanation

Smoothing reduces random noise and improves the signal-to-noise ratio in fMRI data by applying a blurring kernel to average voxel values with those of their neighbours, enhancing the detection of significant brain activations