Authors: Canli et al. (2000)
Key terms: Brain scans and emotion
Approach: Biological approach
Background/context: people are more likely to recall emotional experiences than non-emotional ones, and the amygdala appears to play a crucial role in emotional memory. Studies using PET and MRI scans have shown correlations between amygdala activation and the presentation and recall of emotional stimuli. The correlations could be for three reasons:
some people are more responsive to emotional experiences than others
some people had an enhanced emotional state during the scanning
the amygdala is sensitive to the emotional intensity of a stimulus
Aims/hypotheses: emotionally intense stimuli will cause greater activation of the amygdala and lead to better recall than less emotionally intense stimuli.
Method: laboratory experiment. Variables:
IV — intensity ratings of each stimulus (picture) on the 4-point scale from 0 = not emotionally intense to 3 = extremely emotionally intense.
DV — the self-report percentages of forgotten, familiar and remembered with certainty; functional images of 11 frames per trial resulting in a 'pixel count'.
Design: all ten participants saw all 96 pictures, so the design is repeated measures.
Participants and sampling technique: the participants were ten right-handed healthy female volunteers, so the sampling technique is self-selecting (although how they came to volunteer is not stated by Canli et al.) Females were chosen because they are more likely to respond physiologically and are more likely to report intense emotional experiences.
Apparatus:
A functional magnetic resonance image (fMRI) scanner which, unlike a PET scan is non-invasive (no injections and no radioactivity). The scanner works by measuring the contrast in blood-oxygen levels between areas of activation and non-activation in the brain.
A positron emission tomography (PET) scan is invasive: the scanner detects a radioactive substance injected into the body. A magnetic resonance image (MRI) scan is non-invasive (no injection and no radioactivity) and uses magnets to record changes in blood flow in the brain.
Controls: all participants were female, healthy and right-handed. The order of the pictures was randomised. Each picture was presented for 2.88 seconds with 12.96 seconds in between when the participants would focus on a fixation cross (to keep them looking at the same spot).
Procedure:
Scanning: participants were settled in the scanner, told to fixate on the cross, and when they saw a picture, press one of four buttons with their right hand. The buttons ranged from 0 = not emotionally intense to 3 = extremely emotionally intense. The same procedure was repeated until all 96 pictures had been viewed.
Testing: 3 weeks later the participants completed a recognition test in the laboratory. They viewed all 96 previously seen pictures and an additional 48 new scenes (called foils) that were matched to the original 96 for valence and arousal. Responses were coded as follows: '1' for not remembered/forgotten; '2' for familiar; and '3' for remembered with certainty.
Data: the data were quantitative:
the self-report percentages of forgotten, familiar and remembered with certainty
functional images of 11 frames per trial resulting in a 'pixel count'
Findings:
Participants' self-report ratings of emotional intensity (scale 0-3) were spread across the rating scale with 29% scoring '0, 22%'1', 24% '21, and 25% '3' (see Figure).
Figure 1 Correlation of scan frame, participants' intensity ratings and percentage activation of amygdala
Amygdala activation was significantly bilaterally (both sides) correlated with ratings of emotional arousal. In Figure 1, rating '3' shows much more activation that ratings '2', '1' or '0'.
Memory recall was much better for pictures rated '3' (more emotionally intense) than pictures rated '0, '1' or '2'.
Left amygdala activation (but not right) predicted whether an individual picture would be forgotten, appear familiar or be remembered.
Left amygdala activation was also found to correlate with the emotional intensity of the memory.
Other brain locations in the frontal and temporal regions also correlated with emotional experience and subsequent memory.
Conclusions: amygdala activation is significantly correlated with higher ratings of individually experienced emotional intensity.
Evaluation
Scientific equipment - the use of scientific equipment in psychological experiments such as an MRI scanner has many advantages, such as reliability (strength).
Biological approach - this study provides evidence of specific brain function (the role of the amygdala) and this is likely to be generalisable to all people (strength).
Correlations - correlation studies can provide evidence of cause and effect (strength), however in this case, there might be some other variable that has not been considered by the researchers (weakness). Be cautious when drawing conclusions from correlations.
Sample - can the findings of this study be generalised to males and people who are left-handed? (weakness)