Enhancing Interoception Through Exercise
What the Insular Cortex Does
The insular cortex is located in the brain’s temporal lobe, deep within the lateral sulcus. This brain area is still not fully understood but is hypothesized to be the central hub for interoceptive signaling (aka how we perceive our internal bodily function) (Mohr & Fotopoulou, 2019). Researchers have shown that this region is responsible for sensory processing, anatomical and motor control, bodily awareness, and social and emotional processing (Gogolla, 2017). Most of the research on the insular cortex's function comes from injuries to this region. For example, a quasi-experimental study focusing on acute insular strokes found that the following changes occurred: (1) pseudothalamic sensory syndrome, (2) GI disorders, (3) vestibular syndrome, (4) cardiovascular deficits, and (5) neuropsychological disorder(s). This study explicitly shows what the insular cortex is responsible for through the outcomes of it being damaged by acute stroke (Cereda et al., 2002).
Another example is patients with temporal epilepsy surgery (which involves removing part of the insular cortex) (Hébert-Seropian et al., 2021). This study conducted a self-report questionnaire to 17 participants who had this surgery for their epilepsy and found that 59% reported a significant reduction in appetite. Moreover, these participants also reported gastrointestinal issues, dysfunction, and a decreased appetite.
There have also been meta-analyses exploring anatomical studies to find evidence of how the specific areas of the insular cortex are involved in particular tasks, as done by Wager and Barrett (2017). This analysis found that specific tasks engage distinct regions of the insular cortex. For example, the dorsal anterior insula is predicted to be involved in planning and updating motivational states related to physical activity, while the posterior insula is connected with pain processing. From this research, we can see how the insular cortex is involved in a wide range of tasks, including physical activity, and how poor interoceptive signaling may lead to poor health outcomes such as gastrointestinal problems (Cereda et al., 2002; Hébert-Seropian et al., 2021) or a plethora of other physiological deficits including poor balance (Cereda et al., 2002).
How Exercise Influences the Insula
We have seen that the insular cortex is involved in physical activity, but does exercise increase interoceptive signaling? Research has attempted to answer this question, such as the work of Fontes and colleagues (2020). This study used 22 male participants (who had active lifestyles) who all completed a circuit of stationary cycling while attached to an fMRI. These participants completed high and low-intensity activities during the study. The fMRI data revealed that the insular cortex was significantly more active during high and low-intensity training than at rest. Similarly, Schmitt and colleagues (2019, 2020) had 25 male participants with active lifestyles complete different exercise sessions of varying intensities (all on a treadmill). This research found that the functional connectivity of the amygdala-insular cortex modulates the perceived effort (RPE) (Schmitt et al., 2020) and the right anterior insula was most active during maximal intensities (Schmitt et al., 2019).
Balance has also been used to explore insular activity and exercise (Rogge et al., 2018). This study tested 18 adults and used 19 adults in a control group. The test group experienced a 12-week balance intervention. This training increased cortical thickness, and these changes may benefit physical outcomes and cognition. This neuroplasticity was seen in the superior temporal gyrus (including the insular sulcus), suggesting that whole-body exercises with minor intensity can create significant neural changes.
Finally, below is a figure from Lutz (2018), who reviewed how exercise influences the brain (including the insular cortex). This work concentrated on brain imaging studies. The focus on the insular cortex is how it seems to be involved in motivation and the ability of the person to reach greater RPEs. This table provides an idea of the advanced connectivity between the insular cortex and surrounding regions and how involved this brain area is in external and internal stimuli processing.
How Exercise Can Improve Insular Function
One source of empirical evidence is a review by Zarza-Rebello and colleagues (2019). This review poses the hypothesis that because exercise requires activation of the insular cortex (and the overlap of neural structures used for training and interoception), exercise can help practice better interoceptive signaling. In this way, exercise could improve interoceptive signaling by strengthening these neural outlets and causing the participant to be more aware of their body. This hypothesis is the precise idea of the current paper, being that exercise may address interoceptive signaling deficits.
Finally, research has demonstrated that physical activity can improve interoceptive ability (Weineck et al., 2019). This study used 41 females randomly assigned to daily power posing practice (test group) or no practice (control group). Measurements were taken via heartbeat tracking task, interoceptive sensibility (Body Perception Questionnaire), and confidence ratings. It was found that power posing daily increased interoceptive signaling; another example of how physical activity can positively affect interoception.
Currently, the literature on how exercise directly affects the insular function and interoceptive signaling is sparse. Most studies utilize populations with deficits in interoception (i.e., Autism, anxiety disorders, eating disorders, spinal-cord injuries). What's more, the typical variables used to explore interoception can be challenging to use if the research participant is unfamiliar with how to detect their interoceptive signals. As seen in the figure below, there are three key variables: interoceptive accuracy and interoceptive sensibility. And interoceptive attention. The most common variable is interoceptive accuracy, which is the easiest to measure. You can calculate your interoceptive accuracy without any fancy lab equipment or questionnaires.
You'll need a friend and a stopwatch to measure your interoceptive accuracy. Have your friend find your pulse and count your heartbeats for 30-seconds. As they do this, quietly try to count your heartbeats for the 30-seconds. However close you get to the actual number of heartbeats is how accurate your interoceptive signaling is (typically, being within 3-4 beats is considered excellent). You can imagine that someone who exercises will do better at this task. An athlete experiences a range of heart rates throughout their training and is exposed to varied interoceptive heart signals far more than someone primarily sedentary (and only experiences a low heart rate with little to no variation).
Research should focus on athletes across training ages and expertise domains (e.g., archery, weightlifting, swimming). I would argue that how you experience your body in your training environment heavily dictates how you unconsciously engage with your interoceptive signals. Utilizing neurophysiological markers of interception alongside subjective measures can help to ensure accuracy in our interpretations of data. If athletes have the potential to be the best at interoceptive signaling, shouldn't we be emphasizing them as our research population?