Insulin Modulation of fMRI Connectivity in Healthy Adults

Insulin Modulation of fMRI Connectivity and Food Reward

This study evaluates the effects of changing insulin levels on brain activity. Participants will complete functional magnetic resonance imaging (fMRI) scans during fasting conditions, then during an insulin infusion.

Insulin is a hormone released by the pancreas in response to increases in glucose levels that result from food intake. In addition to stimulating glucose uptake in the periphery, insulin signals the central nervous system to induce satiety and inhibit feeding behavior.

To begin to identify the specific effects of circulating insulin on brain networks, the current study will recruit healthy participants who will undergo two functional magnetic resonance imaging scans. One scan will be performed in the fasted state, and the alternate scan will be conducted during an isoglycemic hyperinsulinemic clamp.

This project will allow us to identify the specific effects of circulating insulin on brain reactivity to palatable food.

Inclusion Criteria:

• Body mass index between 18 and 24
• HOMA-IR < 1.55 (homeostatic model assessment of insulin resistance - ((glucose x insulin) / 405)).

Exclusion Criteria:

• Current or lifetime history of any cardiovascular disease or surgery (including hypertension, stroke, myocardial infarction, congestive heart failure, atrial or ventricular arrhythmias, coronary bypass, carotid artery, or peripheral vascular surgery)
• Current or lifetime history of cancer, a chronic kidney or liver condition, type I or II diabetes, or any pulmonary or respiratory disease
• Current or lifetime diagnoses of any substance abuse
• Positive urine drug screen
• Current or lifetime use of glucocorticoid medications for >1 month
• A previous cerebrovascular accident or trauma involving loss of consciousness
• Previous neurosurgery or history of a neurological condition
• Pregnancy (females)
• Claustrophobia
• Ferrous metallic implants or any surgically placed medical device not cleared for safety at 3Tesla MRI strength
• Peripheral vascular disease
• Liver, kidney, or active blood disease
• Peripheral neuropathy
• Anemia (hematocrit <34%)
• Inability and/or willingness to comply with the protocol as written
• Fasting glucose > 126 mg/dL
• Currently taking blood thinners such as coumadin, Lovenox, etc.
• Currently taking any medications that can alter glucose homeostasis (steroids, glucocorticoids, nicotinic acid)
• Current use of any psychotropic medications (SSRI, SNRI, etc.)
• Currently taking thiazolidinediones or insulin
• Currently use of statins or anti-hypertensive medications
• Use of medications related to HIV that can affect insulin sensitivity. We will NOT specifically test for HIV serostatus.
• Females currently on hormone replacement therapy (HRT) less than 6 months
• Participants will be instructed to abstain from eating, drinking (other than water), smoking and exercise for the 12 hours prior to each study visit.
• Being left handed
• Body mass index above 24 or below 18
• Milk allergy / lactose intolerance
• Polycystic ovary syndrome