Canli et al. (brain scans and emotions)

Study author(s): Turhan Canli, Zuo Zhao, James Brewer, John D. E. Gabrieli,, and Larry Cahill
Year: 2000
Title: Event-Related Activation in the Human Amygdala Associates with Later Memory for Individual Emotional Experience
Key terms: Brain scans and emotion

Background of study

Brain scanning techniques allows psychologists to study the brains of living people and draw conclusions about the relationship between behaviour and brain structure/activity.

Two basic types of medical scan: functional and structural.

  • Structural scans take detailed (static) pictures of the structure of the brain.
  • Functional scans are able to show activity (dynamic) levels in different areas of the brain.

Functional magnetic resonance imaging (fMRI) is a neuroimaging procedure using MRI technology that measures brain activity by detecting changes associated with blood flow. During an fMRI scan, patients are placed in a scanner that sends a strong magnetic field through their head. The magnetic field causes the nuclei in hydrogen molecules in the brain to spin in a particular way, and the scanner picks this up. Because hydrogen concentrations vary in different parts of the brain, the scanner is able to create a very detailed picture of the brain.

How does fMRI work?

FMRI is a method of measuring the flow of oxygenated blood in the brain. It is based on the BOLD effect that stands for blood oxygen-level dependent. BOLD MRI is accomplished by first exposing a patient or volunteer to a stimulus or having them engage in a cognitive activity while acquiring single-shot images of their brain. The region of the brain that is responding to the stimulus or is engaged in the activity will experience an increase in metabolism. This metabolic increase will require additional oxygen. Therefore, there will be an increase in oxygenated blood flow (oxyhemoglobin) to the local brain area that is active. Oxyhemoglobin differs in it’s magnetic properties from deoxyhemoglobin. Oxyhemoglobin is diamagnetic (materials that are freely magnetized when placed in the magnetic field) like water and cellular tissue. Deoxyhemoglobin is more paramagnetic than tissue so it produces a stronger MR interaction. We take advantage of these differences between oxy and deoxyhemoglobin in BOLD imaging by acquiring images during an “active” state (more oxyhemoglobin) and in a “resting” state (more deoxyhemoglobin). We see a signal increase in the “active” state and a signal decrease in the resting state. (Source)

In the simplest fMRI study a participant would alternate between periods of completing a specific task and a control or rest state to measure baseline activity. The fMRI data is then analysed to identify brain areas in which the signal changed between the activity and the rest state and it is inferred that these areas were activated by the task. The data from an fMRI scan is used to generate images that can illustrate how the brain is working during different tasks. Such a scan allows a living brain to be seen without resorting to surgery.

Over the last few decades, researchers have used fMRI scans to identify areas of the brain that have specific functions. Areas that have been shown to have a significant association with emotion and memory are the subcortical areas of the brain, including the amygdala. The amygdala is an almond-shaped set of neurons located deep in the brain’s medial temporal lobe and has been shown to play a key role in the processing of emotions such as pleasure, fear and anger. Importantly, the amygdala is also responsible for determining where memories are stored in the brain and which ones are kept.

Reflections: If you had the use of a brain scanner what behaviour would you want to locate and why? Is it an advantage for the human brain to have specialised locations for some tasks or is there a benefit to having tasks distributed across the brain?

LaBar and Phelps (1998) suggested that emotional experiences are often better recalled than non-emotional ones and emotional arousal appears to increase the likelihood of memory consolidation during the storage stage of memory (the process of creating a permanent record of the encoded information). Brain imaging studies have shown that amygdala activation correlates with emotional memory in the brain. 

Previous research by Canli et al. (1999) showed that participants who had a strong amygdala activation in response to a set of emotional stimuli also showed superior memory for those stimuli. However, Canli et al. (2000) suggested that, because an independent measures design was used for these experiments, there could be other explanations for the findings. 

The present study used fMRI in a repeated measures, subsequent-memory design to test the predictions that those emotionally intense stimuli that produce greater amygdala activation would be recalled more easily than stimuli that generate less amygdala activation. Participants saw neutral and negative scenes and indicated how they experienced the emotional intensity in each case. A separate fMRI response was recorded in the amygdala for each such emotional experience. Three weeks later, participants’ memories for the experiences were assessed to see if those images that generated greater activation of the amygdala were remembered better.