Prefrontal oxygenation changes associated with working memory following yoga practice in type 2 diabetes mellitus patients

Abstract

BACKGROUND In recent years, cognitive impairments and dementia (including Alzheimer's disease) have been recognized as common complications and comorbidities of Type1 diabetes (T1DM) and Type2 diabetes mellitus (T2DM). It is estimated that 7% of people aged 60–64 are affected by mild cognitive impairment (MCI) and that 25% may develop cognitive impairment as they get older. It has been found that the risk of converting mild cognitive impairment to dementia is 1.53 times higher in individuals with diabetes. Diabetes-related complications, such as glucose and insulin imbalances, microvascular and macrovascular complications significantly predispose patients to the progression of MCI and dementia. Additionally, several risk factors for cognitive dysfunction in diabetes were identified, such as hypertension, dyslipidemia, depression, age, duration of diabetes, genetic factors and educational level of patients. Brain imaging studies show that T2DM is associated with both degenerative and vascular brain damage, which is likely to contribute to abnormalities in brain functional and structural connectivity leading to cognitive dysfunction. It has been found that, even at an early stage of cognitive decline, there was a clear abnormality in cerebral hemodynamics and oxygenation parameters. Working memory, a cognitive ability that enables one to actively maintain and manipulate information and forms an essential part of the human memory system, is implicated along with other cognitive functions such as attention, executive function, verbal memory and information processing speed. Besides medications, non-pharmacological approaches such as physical exercise, yoga, computer-based training, nutrition, brain stimulation, sleep, and music are gaining importance in treating cognitive deficits. Yoga has been one such non-pharmacological approach gaining popularity as a form of complementary and alternative medicine worldwide and its therapeutic benefits are being explored in various clinical conditions. AIMS AND OBJECTIVES The study investigated the effect of yoga practice on oxygenation changes in the prefrontal cortex (PFC) associated with working memory in T2DM participants. The study also examined the effects of yoga practice on heart rate variability and psychological conditions (rumination x and preservative thinking). The objectives of the study were to assess the effect of 12-week yoga practice in T2DM participants on  Oxygenation in the PFC region during resting and while performing a working memory task  Working memory performance – accuracy and reaction time  Resting-state heart rate variability  Psychological conditions, namely rumination and perseverative thinking METHODS Participants: Participants were, both male and female, with ages ranging from 35 to 65 years, diagnosed with type 2 diabetes mellitus based on established criteria including medical history, medication use, glucose levels and undergoing conventional treatment. Design: This study was a randomized controlled trial (RCT). The participants were randomized into two groups, the yoga and waitlist control groups. Assessments: The pre- (day 1), mid- (6 weeks) and post-intervention (12 weeks) assessments included measurement of PFC oxygenation while performing working memory tasks (n-back) using functional near-infrared spectroscopy. The Accuracy and Reaction time of working memory performance were assessed. Heart rate variability parameters such as mean heart rate (HR), Square Root of the Mean Squared Difference between adjacent RR intervals (RMSSD), Standard Deviation of normal-to-normal interval (SDNN), Low-frequency component (LF), High-frequency component (HF) and LF/HF ratio were assessed. The psychological conditions, namely rumination and perseverative thinking were assessed using the Rumination Response Scale (RRS) and Perseverative Thinking Questionnaire (PTQ). Intervention: Participants in the yoga group engaged in twelve weeks of yoga practice. Waitlist control group members were instructed not to engage in any form of exercise such as running, jogging, swimming, or lifting weights during the study period. The waitlist control group received yoga practice for four weeks upon completion of the trial. RESULTS Following a 12-week intervention, the yoga group showed improved performance in working memory [accuracy ( geometric mean difference of 3.15%, 95% CI [ 2.33,3.96], p = 0.001) and xi reaction time (mean difference of -100.8 milliseconds,95% CI [ -166.6, -35.1], p=0.002] in the high task load (2-back) associated with higher oxygenation in dorsolateral PFC (β coefficient mean difference of 95.6, 95% CI [0.23,191], p=0.049) and ventrolateral PFC (β coefficient mean difference of 53.4, 95% CI [7.8,98.9], p=0.018) regions. Higher oxygenation in dorsolateral PFC during the 2-back task was positively correlated with accuracy (r(23)= 0.65, p<0.001) and negatively correlated with reaction time ( r(23)= -0.47,p=0.017). The yoga group showed improved autonomic functions with a decreased mean HR, decreased LF component and increased HF component values. Decreased mean HR at post-intervention compared to pre- and mid-intervention with a mean difference of -7.0, 95% CI [-9.5, -4.4], p < 0.001 and -6.1, 95% CI [-10.1, -2.2], p = 0.002 respectively. Decreased LF value at post-intervention compared to pre- and mid-intervention with a mean difference of -10.7, 95% CI [-21.0, -0.3], p = 0.041 and -10.6, 95% CI [-20.5, -0.6], p = 0.034 respectively. Increased HF value at post intervention compared to pre- and mid-intervention with a mean difference of 10.7, 95% CI [0.23, 21.1], p = 0.043 and 11.3, 95% CI [1.1, 21.5], p = 0.03 respectively. The yoga group showed reduced rumination following the yoga intervention with a decrease in RRS score at post-intervention compared to pre-intervention, with a mean difference of -4.72, 95% CI [-8.5, -1.0], p = 0.011. The decrease in rumination scores (at post-intervention) was positively correlated with the improvement in reaction time (at post-intervention) compared to pre-intervention, r (25) = 0.65, p < 0.001. CONCLUSION The findings suggest that yoga practice may improve working memory performance associated with higher PFC oxygenation in patients with T2DM. Also, yoga may prevent the onset of a depressive condition by reducing rumination symptoms and influence positively on cognitive functions. Yoga practice may be an effective adjunct approach for enhancing cognitive functions in clinical populations.