Magnetic Resonance Imaging (MRI)
Magnetic Resonance Imaging (MRI)
MRI uses a powerful magnetic field and radio waves and magnetic fields to detect energy emitted by hydrogen atoms in the brain, which vary depending on the type of tissue. This creates a detailed, static three-dimensional image of brain structure.
Procedure
Participants lie on a table that slides into a cylindrical scanner. The machine generates images based on the varying hydrogen concentrations across different brain regions.
Strengths
- Non-invasive and safe, with no radiation exposure.
- Provides high spatial resolution, allowing for detailed imaging of brain structure.
Limitations
- Does not provide information on brain activity.
- The procedure can cause anxiety in claustrophobic participants.
- Expensive and unsuitable for individuals with metal implants.
Maguire et al. (2000) investigated the brain structure of London taxi drivers and found increased grey matter in the hippocampus, which is associated with their advanced navigational skills. This study used MRI to identify structural differences in the brain.
Functional Magnetic Resonance Imaging (fMRI)
Functional Magnetic Resonance Imaging (fMRI)
fMRI detects changes in blood oxygenation levels (BOLD signal) to identify active brain regions during specific tasks. Active areas receive more oxygenated blood, thus it is responsive to the brain's metabolism. The result is a time map, showing when certain parts of the brain were activated.
Procedure
Participants perform cognitive tasks (e.g., viewing images or solving problems) while lying in the scanner. The machine captures changes in brain activity related to the task.
Strengths
- Combines structural and functional imaging, showing active brain regions.
- Excellent spatial resolution compared to other functional techniques.
Limitations
- Temporal resolution of about 1 second limits the detection of fast processes.
- Noise from random thoughts or movements can affect data accuracy.
- Expensive and time-intensive.
Passamonti et al. (2012) explored the impact of serotonin on the amygdala and prefrontal cortex (PFC) during the perception of social threats. The researchers utilized fMRI to examine brain activity under different serotonin conditions.
Radke et al. (2015) examined the role of testosterone in amygdala activation when participants approached threatening faces. fMRI was employed to measure how testosterone influenced brain activity during this task.
Positron Emission Tomography (PET)
Positron Emission Tomography (PET)
PET uses a radioactive tracer binds to specific molecules (e.g., glucose) in the bloodstream. Active brain areas emit higher levels of energy, indicating increased activity.
Procedure
Participants receive a mild radioactive glucose injection and perform tasks inside a scanner. The energy emissions highlight active brain areas.
Strengths
- Shows both brain structure and function.
- Useful for studying slow processes and neurotransmitter activity.
- Useful for monitoring blood flow while participants perform cognitive tasks.
Limitations
- Exposure to low levels of radiation.
- Poor temporal resolution compared to fMRI.
- If someone is diabetic and/or ate before the scan, results may be misleading.
Freed et al. (2001) investigated the role of dopamine in alleviating symptoms of Parkinson’s disease. The study used PET scans to observe the effects of dopamine on brain function and symptom improvement in participants.
Electroencephalography (EEG)
Electroencephalography (EEG)
EEG measures electrical activity generated by large groups of neurons. Electrodes on the scalp detect these signals, providing real-time data on brain wave patterns.
Procedure
Participants wear a cap with electrodes while remaining still. Changes in brain wave activity are recorded during tasks or resting states.
Strengths
- Exceptional temporal resolution, detecting millisecond-level changes.
- Non-invasive, mobile, and relatively inexpensive.
Limitations
- Poor spatial resolution; cannot pinpoint exact brain areas.
- Signals from deep brain regions are undetectable.
Comparative Overview of Techniques
| Technique | Focus | Spatial Resolution | Temporal Resolution | Key Strength | Key Limitation |
|---|---|---|---|---|---|
| MRI | Structure | Up to 1–2 mm | Not applicable | Detailed imaging of brain structure | Cannot measure brain activity |
| fMRI | Structure + Process | Up to 1–2 mm | ~1 second | Shows patterns of brain activation | Noise and cost |
| PET | Process | ~4 mm | ~30–40 seconds | Tracks specific neurotransmitter activity | Radiation exposure |
| EEG | Process | Poor | Milliseconds | Exceptional for real-time monitoring | Limited to cortical activity |
Applications in Behavioural Studies
Localization of Function
Techniques Used: fMRI
Studies using fMRI, such as Urry et al. (2012), demonstrate how specific brain regions, like the ventromedial prefrontal cortex (vmPFC), regulate emotional responses by downregulating amygdala activity.
These techniques allow researchers to pinpoint brain regions involved in specific behaviours, enhancing our understanding of how structure relates to function.
Neurochemical Effects
Techniques Used: PET
- PET scans are particularly effective for examining neurotransmitter systems, as seen in Freed et al. (2001), which used dopamine tracers to study the alleviation of Parkinson’s symptoms.
- These studies offer insights into the biochemical basis of behaviours, including aggression, anxiety, and mood regulation.
Critical Thinking Considerations
Ecological Validity
- Challenge: Many tasks in imaging studies are artificial, such as viewing static images of emotional faces while lying still. Real-life behaviours often involve dynamic and interactive environments that these studies cannot replicate.
- Implication: Findings may not translate well to real-world scenarios, limiting the generalizability of results.
- Future Direction: Virtual reality combined with fMRI may help create more immersive and realistic tasks while measuring brain activity.
Temporal and Spatial Limitations
- Challenge: fMRI has excellent spatial resolution but poor temporal resolution, limiting its ability to capture fast neural processes. Conversely, EEG excels in temporal resolution but lacks spatial accuracy.
- Implication: These limitations mean that neither technique provides a complete picture, often necessitating the use of multiple methods for more robust conclusions.
- Future Direction: Hybrid techniques, like magnetoencephalography (MEG), could bridge the gap between spatial and temporal resolution.
Interpretation of Data
- Challenge: Brain imaging data, particularly from fMRI, is complex and prone to misinterpretation. Correlation between activity and behaviour does not imply causation, yet this distinction is often overlooked.
- Implication: Overreliance on imaging data can lead to oversimplified conclusions about complex behaviours.
- Future Direction: Multimodal approaches combining imaging with behavioural and physiological data could provide a more nuanced understanding of brain-behaviour relationships.
