Browsing by Author "Sommer, Susanne"

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Open Access
Dopamine D1/D2 receptor activity in the nucleus accumbens core but not in the nucleus accumbens shell and orbitofrontal cortex modulates risk-based decision making
(2015) Mai, Bettina; Sommer, Susanne; Hauber, Wolfgang
Background: It is well known that brain dopamine (DA) signals support risk-based decision making; however, the specific terminal regions of midbrain DA neurons through which DA signals mediate risk-based decision making are unknown. Methods: Using microinfusions of the D1/D2 receptor antagonist flupenthixol, we sought to explore the role of D1/D2 receptor activity in the rat orbitofrontal cortex (OFC) and core and shell regions of the nucleus accumbens (AcbC and AcbS, respectively) in the regulation of risky choices. A risk-discounting task was used that involves choices between a certain small-reward lever that always delivered 1 pellet or a risky large-reward lever which delivered 4 pellets but had a decreasing probability of receiving the reward across 4 subsequent within-session trial blocks (100%, 50%, 25%, 12.5%). To validate task sensitivity to experimental manipulations of DA activity, we also examined the effects of systemic amphetamine and flupenthixol. Results: Systemic amphetamine increased while systemic flupenthixol reduced risky choices. Results further demonstrate that rats that received intra-AcbC flupenthixol were able to track increasing risk associated with the risky lever but displayed a generally reduced preference for the risky lever across all trial blocks, including in the initial trial block (large reward at 100%). Microinfusions of flupenthixol into the AcbS or OFC did not alter risk-based decision making. Conclusions: Our data suggest that intra-AcbC D1/D2 receptor signaling does not support the ability to track shifts in reward probabilities but does bias risk-based decision making. That is, it increased the rats’ preference for the response option known to be associated with higher risk-related costs.
Open Access
Effects of motivational downshifts on specific Pavlovian-instrumental transfer in rats
(2022) Sommer, Susanne; Münster, Alexandra; Fehrentz, Jean-Alain; Hauber, Wolfgang
Konditionierte Umweltreize, die mit attraktiven Nahrungsmitteln assoziiert sind, können die Nahrungsaufnahme offenbar auch dann anregen, wenn dafür keine physiologische Notwendigkeit besteht, etwa bei Sättigung. Man vermutet, dass ein solcher Mechanismus Überwicht und Adipositas fördert. Unsere aktuelle Arbeit hat diese Annahme an Labornagetieren eingehend überprüft. Aus den Messungen geht übereinstimmend hervor, dass der stimulierende Einfluss von konditionierten Umweltreizen auf nahrungsbezogene Handlungen bei Sättigung massiv annahm. Unsere Ergebnisse stehen also nicht in Einklang mit der Annahme, dass das Belohnungssystem bei Darbietung von konditionierten, nahrungsprädiktiven Umweltreizen eine bestehende Sättigung überspielt und nahrungsbezogene Handlungen automatisch in Gang setzt.
Open Access
Role of the medial orbitofrontal cortex and ventral tegmental area in effort-related responding
(2020) Münster, Alexandra; Votteler, Angeline; Sommer, Susanne; Hauber, Wolfgang
Die Arbeit untersucht die Interaktion von zwei Gehirnarealen, dem medialen Orbitofrontalcortex und dem Ventralen Tegmentalen Areal, bei der Handlungssteuerung.