Loudness Dependence of Auditory-evoked Potentials, a Marker of Central Serotonergic Activity, is Affected by Fasting and Selective Uptake of Food

Abstract

Serotonin is an important neuromodulator involved in many physiological processes including mood and satiety. In the brain, serotonin is manufactured from tryptophan, as serotonin itself cannot cross the blood–brain barrier. Previous research has shown that blood-tryptophan levels increase upon ingestion of carbohydrates and decrease upon protein consumption. How this translates into serotonin availability is as yet under-researched. Therefore, we examined the effect of fasting versus consuming carbohydrates or protein on central serotonergic activity using a repeated-measures crossover design in a sample of 37 healthy men. The loudness dependence of auditory-evoked potentials (LDAEP) serves as a noninvasive method to study central serotonergic activity. Blood-glucose levels and mood changes were also monitored before and after the nutritional intervention. The intervention had a significant nutrition-specific effect on LDAEP and blood-glucose levels. A significant difference emerged between the fasting condition and satiety, with LDAEP being lower during satiety, irrespective of the type of food. Thus, this indicator of serotonergic activity increased after food consumption, which was further related to mood improvement. Moreover, the LDAEP differed between the 2 measurements only for the carbohydrate testing day, suggesting that LDAEP can be selectively modulated by the type of nutrition consumed. Our data further indicate a high intraindividual stability of LDAEP, as the electrophysiological signals were very similar in the fasting condition across the 2 testing days. Together, these findings demonstrate that the LDAEP can serve as a biological marker for central serotonergic activity, while at the same time being sensitive to nutritional changes.

Short-Term Fasting and Ingestion of Caloric Drinks Affect Heartbeat-Evoked Potentials and Autonomic Nervous System Activity in Males

“…The study was approved by the Ethics Committee of the Medical Faculty of the Ruhr-University Bochum (project number 18-6378-BR) and is in accordance with the Helsinki Declaration. Unrelated behavioral results and results of another EEG-paradigm archived by this study were published previously, but are independent of the present publication ( Bamberg et al, 2021a , b ).…”

“…Indeed, the nutritional composition has been shown to selectively affect another electrophysiological marker, the LDAEP, which has been proposed to be related to the activity of the neurotransmitter serotonin in the brain, as suggested based on additional data of the present study. More detailed, the marker for central serotonergic activity was increased after food intake compared to fasting conditions, whereas this effect was more prominent for the carbohydrate consumption than after proteins ( Bamberg et al, 2021b ). Thus, the nutritional composition impacts on various physiological processes via hormonal pathways and metabolism of the nutrients, whereas subjective feelings of hunger and probably also electrophysiological correlates of cardiac interoception might be more affected by gastric distension.…”

“…After application of the EEG-cap and placement of ECG electrodes, all subjects completed hunger and mood surveys ( Abele-Brehm and Brehm, 1986 ) and a measurement of baseline blood-glucose was conducted. Participants marked their hunger on a visual-analog scale spanning 10 cm, ranging from “I am not hungry at all” to “I am very hungry.” The measurement of blood-glucose levels has been described elsewhere ( Bamberg et al, 2021a , b ). In short, 10–50 μL of blood were drawn by pricking the fingertips and the blood-glucose level was measured (in mg/dL) with a CONTOUR ® XT device by Bayer AG.…”

“…Subsequently, a resting state EEG and parallel ECG recording followed for 8 min. Then, tones with varying loudness levels were presented to the participants for 12 min in order to analyse the so called “Loudness Dependence of Auditory Evoked Potentials” (LDAEP, results published in Bamberg et al (2021b) . For a few additional minutes, participants played the Trust Game ( Bamberg et al, 2021a ).…”