Emotions are an inherent part of our everyday experiences – which is a cliché thing to say, but it’s true! Just today, I got out of bed irritated, but I felt much better after my morning coffee, only to get scared by a driver running a red light right in front of me on my way to university – and all of that before 9AM. It’s no wonder that the spectrum of emotions experienced by each one of us fascinates scientists and philosophers alike. Neuroscientists employ a wide range of methods and perspectives in trying to pinpoint the underlying neural correlates of precisely that: how, and why, we experience emotion.
Together we will be exploring different topics pertaining to affective neuroscience; however neuroscience, while fascinating, is bound and limited by the methods it employs. Today I would like to briefly talk about four methods you will read about throughout our adventure here: functional magnetic resonance imaging (fMRI), encephalography (EEG), eye tracking, and psychophysiology. And let’s do that in the context of this question: how can we change the way we feel?
In their 2002 study, Ochsner and his colleagues looked at how we can consciously control how we feel. Participants were presented with a set of neutral or negative photographs, and asked to view the photo, understand its content, and allow themselves to experience or feel any emotional response elicited by the said photograph. The tricky part was that sometimes they would be asked to reinterpret the negative photo so that it no longer made them feel bad – a process called reappraisal. Through effortful reinterpretation of the photograph, the participants managed to actually feel a bit less negatively when presented with the picture.
Evidence suggests that there are two structures in our brains that are responsible for this: the amygdala is hypothesized to evaluate a stimulus as affectively relevant, while the medial orbital frontal cortex is involved in keeping track of the contextual meaning of the said stimulus. In exploring whether they are important for reappraisal, Ochsner used functional magnetic resonance imaging. And here’s how it works: increased activity in particular regions of your brain requires oxygen and energy, and that is delivered through your blood flow. Oxygen-rich and oxygen-poor blood have different magnetic properties, and therefore it is possible to trace which areas of your brain are more active than the others at a particular time. fMRI has a great spatial resolution: it is possible to focus in great detail on very small areas and reliably trace their involvement. However what fMRI lacks is good temporal resolution: because blood flows rather slowly in comparison to some neural processes, the signal lags behind the actual neuronal event. We can therefore use fMRI to answer the question of where the process is occurring, but not really how.
Carretié and colleagues (2001) explored the interaction between attention and emotion. They wanted to see whether emotional visual stimuli (in this case also pictures) received more attention than neutral stimuli. In order to do so, they presented their participants with four types of pictures: positively arousing, negatively arousing, relaxing, and neutral, and focused on analyzing the activation of two areas: the anterior cingulate cortex and the visual association cortex (as they are related to visual attention). Carretié wanted to study not whether participants visually attended to their stimuli, but how attention differed across types of emotional pictures. They employed another method: electroencephalography. EEG records electrical activity over the scalp – long story short, when neurons become active, they fire minute electrical charges. By placing electrodes on the scalp, we can analyze those charges and therefore observe the activity of the brain with excellent temporal resolution; neurons fire immediately as a stimulus is being processed, and since there is no delay between the onset of processing and the delivery of oxygen and energy by blood, Carretié and colleagues were able to observe different stages of neuronal processing down to milliseconds. They concluded that we respond much faster to pictures of negative stimulation, but process pictures of positive stimulation longer.
Similar findings were presented by Nummenmaa and colleagues (2006): in comparison to neutral pictures, we tend to focus more on negative and positive photographs, even when instructed otherwise. This study looked at how emotions affect our attention using eye tracking methodology. While we like to think that our eye movements are largely voluntary and easy to control, they actually tend to go off on their own quite a lot; by following these instances of involuntary movement, we can infer about underlying cognitive processes. However eye tracking has a serious limitation: we can measure where one is looking, but we can’t be quite certain how that information is processed.
And lastly, let us circle back to the question of emotion regulation, this time by emotional suppression. Because here’s the thing: I might not be able to control what I pay attention to, and I might be able to convince myself to feel differently about it. But between noticing an emotional stimulus and reappraising it, can I pretend to not be affected by it – and how will this pretending actually affect me? Gross and Levenson (1993) explored this question using the last set of methods I want to talk about today, namely analyzing physiology, self-reports, and expressive behaviors. They asked their participants to watch a short, disgust-eliciting film and behave “in such a way that a person watching you would not know you were feeling anything.” The session was recorded with a video camera and later analyzed for presence of particular behaviors that indicate particular feelings; the participants were also asked to complete questionnaires on how they felt after viewing each film, and had their pulse, temperature, and skin conductance monitored. While brains are awesome and very important for neuroscientists, we all know the feeling of sweaty palms or racing heart in a stressful situation. Psychophysiological measures focus precisely on that: our bodily responses to emotions. Gross and Levenson found greater sweating or blinking (indicating effort) when people suppressed their emotional expression, but lowered heart rate, and no changes in self-reports of the emotion their participants felt.
To summarize – we cannot control the initial emotion we feel, but we can pretend to not be affected, which then should buy us time to persuade ourselves to actually feel differently. And there’s another conclusion coming from all this: there isn’t a single method best suited for studying human emotion. The most coherent overview would perhaps be provided if we put a person in an MRI, with an EEG cap and an eye tracker on, connected to a number of different physiological sensors and providing an ongoing self-report. But how real would their emotions be then?
Carretié, L., Martín-Loeches, M., Hinojosa, J.A., & Mercado, F. (2001). Emotion and attention interaction studied through event-related potentials. Journal of Cognitive Neuroscience, 13(8), 1109-1128.
Gross, J.J., & Levenson, R.W. (1993). Emotional suppression: physiology, self-report, and expressive behavior. Journal of Personality and Social Psychology, 64(6), 970-986.
Nummenmaa, L., Hyona, J., & Calvo, M.G. (2006). Eye movement assessment of selective attentional capture by emotional pictures. Emotion, 6(2), 257-268.
Ochsner, K.N., Bunge, S.A., Gross, J.J., & Gabrieli, J.D.E. (2002). Rethinking feelings: An fMRI study of cognitive regulation of emotion. Journal of Cognitive Neuroscience, 14(8), 1215-1229.
A lot can happen before 9AM. That’s why I wish I could sleep in more often!
Good point about hooking people up to all of those methods at once… the generalizability of that scenario may indeed be a bit questionable. That being said, lots of researchers do try to measure lots of these at the same time. Pretty interesting stuff.