The Relationship between Insulin Resistance, Resting EEG Alpha Wave Asymmetry, and Eye Blink Startle Reflex during International Affective Picture System Presentation
Authors: Wolf Tovah , Willette Auriel 
Published: November 2023

According to the CDC, it is estimated that more than one in three U.S. adults have pre‐diabetes. Pre‐diabetes etiology is characterized by insulin resistance (IR), which is a reduced cellular response to insulin and characterized by lower glucose uptake in the brain. IR is also related to deficits in cognitive and affective processing, particularly reactivity to psychological stress. The goal of our analysis was to determine how IR or hyperglycemia predict eye blink startle reflex (EBR) magnitude and amplitude, an objective index of the startle response, in response to positive, negative and neutral pictures using the International Affective Picture System (IAPS). We similarly assessed if IR predicted resting right frontal asymmetry using electroencephalography (EEG), an established biomarker of predisposition toward negative affect. We hypothesized that individuals with higher IR or hyperglycemia would show greater EBR and EEG right frontal asymmetry.The analysis incorporated healthy adults (N=331 participants), aged 36–84 years old, from the University of Wisconsin‐Madison's MIDUS (Midlife in the United States) II longitudinal study. As described in the MIDUS protocol, fasted blood samples were collected during an overnight stay. EBR in response to IAPS visual stimuli paired with acoustic startle was measured by placing two mini electrodes below the eye. Picture duration was 4,000ms. For a given trial, the acoustic startle stimulus occurred for 50ms during one of three phases: 1) The “early” phase at 2,900ms after picture onset while the picture was on the screen to assess reactivity; 2) the “middle” phase at 400ms after picture offset and removal to assess short‐term recovery; and 3) the “late” phase at 1,900ms after picture offset and removal to assess longer‐term recovery.Resting EEG right frontal asymmetry was collected prior to the IAPS presentation.Data was analyzed using SPSS 23.0. Linear mixed models were used to analyze the main effect of log‐transformed homeostasis model assessment of insulin resistance (HOMA‐IR) on EBR, as well as its interaction with IAPS picture valence (positive, neutral, negative). Higher log10 HOMA‐IR predicted greater EBR amplitude during negative versus positive pictures when paired with the startle stimulus (n=290, p<.05, r2=0.127). Resting state EEG at frontal F3/F4 alpha 1 (8–13 Hz) showed that participants with hyperglycemia had more left than right alpha power (−0.0324 +/− 0.026 vs. 0.0126 +/− 0.028) indicating greater right EEG frontal asymmetry. This result is consistent with Jackson et al. (2003) that hyperglycemia individuals are predisposed to negative emotion/affect. In conclusion, higher IR and type 2 diabetes are related to biomarkers of psychological stress reactivity.Support or Funding InformationThis work is directly supported by the National Institute on Aging (AG047282). Data collection and sharing for this project was funded by the Alzheimer's Disease Neuroimaging Initiative (ADNI) (National Institutes of Health Grant U01 AG024904). The grantee organization is the Northern California Institute for Research and Education, and the study is coordinated by the Alzheimer's Disease Cooperative Study at the University of California, San Diego. ADNI data are disseminated by the Laboratory for Neuro Imaging at the University Southern California. This research was also supported by NIH grants P30 AG010129 and K01 AG030514.