Obesity has taken over one third of the world. From diabetes, to joint problems, to some types of cancers, this debilitating condition is a major health threat to those experiencing it. Obesity, however, not only concerns the physical body. Some studies have shown that the brains of obese individuals can differ from the brains of those of a normal-weight. Those with obesity have been shown to have an imbalance in their brains, in which they struggle with inhibitory control and favor attention towards food. Imagine walking into a party and eyeing the snack bar. Now imagine not being able to take your eyes off of the food, longing to control yourself, but wondering how many cookies you can sneak in without anybody noticing.
Brain scans have shown that obese individuals show decreased activity in a part of the brain called the dorsolateral prefrontal cortex (DlPFC), important for the cognitive control necessary to put a stop to an incoming binge. This section of the brain lies just beneath the forehead and plays an important role in controlling food choices and influencing the feeling of being “full”. It is unknown, however, if the under-activity in this part of the brain shows its effects at a subliminal level of processing. Osimo et al. (2019) investigated the effects of the DlPRC on subliminal processing of food in obese individuals by applying weak currents of electricity to this part of the brain, stimulating it and giving them the control to “turn on” its activity while they tested the participant’s attention to food and their cognitive control.
Firstly, to measure subliminal processing, researchers had participants look into a special device in which they were presented with a series of flashing, high contrast (nonfood-related) images. These images acted as distractors while the target stimulus (an image of food), slowly increased in contrast in one quadrant of their field of view. According to previous research, the length of time it takes for participants to notice the target image depends on how subjectively familiar and important the image is. There had been contradicting findings with this method, where some studies have found that shorter suppression times (where participants noticed the target image quickly) were predictive of important images, while other studies have found that longer suppression times were predictive of important images, where the image has some negative connotation and participants subliminally ignore the image (admitting to a guilty pleasure is hard, perhaps even at a subconscious level). Because of this, Osimo et al. (2019) expected that obese participants, compared to normal-weight participants, would show either significantly shorter or longer suppression times for food images.
It was found that participants with higher BMIs showed longer suppression times during this task, however, no bias for food images were found. These findings suggest that obese individuals experience an intentional deficit, but unexpectedly, do not favor their attention towards food at the subliminal level. This may be because an intentional bias for food in obese individuals is not found at the subliminal level of processing, but rather, at a later processing stage (good news, we may have more control than we think). Stimulating, and thus, “turning on” the DlPFC of obese individuals in this study shortened reaction times in obese participants, suggesting that this part of the brain is in fact under-active in these individuals, and when stimulated, can help with cognitive control and inhibition in those struggling with obesity.
This potential bias for food at later processing stages is further supported by the study’s “Go/No Go” task, in which participants were asked to look at a computer screen and respond as quickly as possible to different types of stimuli. They were instructed to press a button when the “Go” stimuli appeared on the screen (food images), and to refrain from pressing the button when the “No-Go” stimuli appeared (non-food images). It was found that, as expected, a higher BMI predicted longer reaction times on food “Go” trials, suggesting that those with a higher BMI struggle with food-related inhibitory control at a conscious level. The brain is a complex organ, with many mysteries yet to be solved. Understanding the dorsolateral prefrontal cortex’s role in inhibition and attention during subconscious and conscious processing of obese individuals is one step in understanding the neurological differences between BMIs.
Source: Osimo, S. A., Korb, S., & Aiello, M. (2019). Obesity, subliminal perception and inhibition: Neuromodulation of the prefrontal cortex. Behaviour Research and Therapy, 119. https://doi.org/10.1016/j.brat.2019.05.005
