In an interesting paper (open-access) by Casey and colleagues in the Proceedings of the National Academy of Sciences, the researchers looked at self-control using neuroimaging. Self-control was defined as the ability to delay immediate gratification. The researchers looked at people who had initially been assessed at the age of 4. During these initial tests the children had been presented with a marshmallow. They were instructed not to eat the marshmallow. The test was a variation on the go-no-go task. The researchers found that the children could be divided into groups of low and high-delayers. A high delayer would be able to delay eating the marshmallow when instructed not to while the opposite was true of low delayers. This was interpreted as a manifestation of self-control. There were some further subtleties in the test. If the subjects focused on non-pleasant qualities of the marshmallows like the shape they were better able to delay their response. The researchers followed up these children and assessed them decades later. They were still able to reliably divide subjects in the study into low and high-delayers. These initial findings suggested that these characteristics at age 4 would predict self-control in adulthood.
In the present study the researchers again approached the subjects who had taken part in these studies which by now were four decades earlier. In place of marshmallows they used faces. The faces were either happy or neutral/fearful. The researchers assumed that it would be more difficult for subjects to restrain their actions when presented with happy faces. Again the researchers found that there were high and low-delayers, reliably after all this time mirroring their childhood behaviour. They were distinguished by their response to the happy faces (‘hot cues’) and not the neutral/fearful faces (‘cold cues’).
The next question was where would the differences in brain activity show? To answer this question, the researchers used functional Magnetic Resonance Imaging. They imaged the subjects when they were performing the Go/No-Go task.
The researchers’ central hypothesis was that a part of the brain known as the Ventral Striatum would show increased activity (Figures 1-3 show the Striatum). The Ventral Striatum is thought to act as a reward centre in the brain. The researchers thought that this reward system would be more active in people with less self-control.
Figure 1 – The Basal Ganglia and Related Brain Structures, John Henkel, Public Domain
Figure 2 – The Striatum, 20th Edition of Gray’s Anatomy, 1918, Public Domain
Figure 3 – Lindsay Hanford/Geoff B Hall, Striatum, Structural MRI, Public Domain
Indeed in their main analysis this is exactly what the researchers found. The subjects who were low delayers i.e less able to delay gratification showed a higher activation of the Ventral Striatum. It was as if the reward system in their brain was over-firing. Perhaps this even made it more difficult for them to resist the rewards.
However this was just one part of the picture. Now that they had an idea of what might be reducing self-control in the low delayers they turned to the question of whether there was anything else that was increasing self-control for the high delayers. Unfortunately the study wasn’t designed to test this question primarily but the researchers had enough data to produce a useful answer in what they referred to as a post-hoc analysis. The researchers looked for any brain regions that would distinguish the high and low-delayers when they were presented with happy faces. This was the trickier part of the task because the subjects found it more difficult to delay their responses when presented with happy faces. The researchers found that the high-delayers, those with more self-control showed a sharp contrast in the activity of the Inferior Frontal Gyrus (which includes Brodmann Areas 44, 45 and 47) between the Go/No-Go tasks. In other words the activity in this brain region changed dramatically between the task where subjects had to inhibit their response and the task where they could respond.
The researchers had now found that the ‘happy face’ No-Go task distinguished the low and high delayers. They had also found that for the high delayers it was distinguished from the Go task by activity in the Inferior Frontal Gyrus. This brain region was therefore a likely candidate for the ability of the high-delayers to inhibit their responses. In other words the researchers’ results seemed to suggest that self-control had two components. One component was a reward signal. Perhaps the larger the reward signal (if this correlates with fMRI Ventral Striatal activity), the more difficult it was to resist. The second component was an inhibitory response in the Frontal Cortex, a part of the brain associated with thinking abilities. Furthermore they found that a test at the age of 4 seemed to predict how people would perform not only in early adulthood but also into the later adulthood.
The researchers have drawn some important conclusions using convincing longitudinal data as well as cross-sectional neuroimaging data.
Casey BJ, Somerville LH, Gotlib IH, Ayduk O, Franklin NT, Askren MK, Jonides J, Berman MG, Wilson NL, Teslovich T, Glover G, Zayas V, Mischel W, Shoda Y. Proc Natl Acad Sci U S A. 2011 Sep 6;108(36):14998-5003. Epub 2011 Aug 29. Behavioral and neural correlates of delay of gratification 40 years later.
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