Biology subjects

Krebs, R. M.

Publications and source records attributed to Krebs, R. M..

5 recordsLinked to original sources

bioRxiv2026

The Role of Locus Coeruleus and Substantia Nigra/Ventral Tegmental Area activity in Reward and Salience Processing: A High-Resolution fMRI Study

Dopaminergic neurons in the substantia nigra/ventral tegmental area (SN/VTA) are classically associated with reward processing, whereas noradrenergic neurons in the locus coeruleus (LC) have been shown to support salience processing more broadly. However, rewarding stimuli are also inherently salient, and in most paradigms reward and salience are conflated, for example when rewarded targets are also rare and/or visually distinct. As a result, it remains unclear in how far these systems are sensitive to reward-specific properties or more basic salient properties of the stimulus. Using a visual oddball paradigm with high-resolution fMRI (n = 45), we compared oddballs that were rewarded, visually salient, or neutral, while keeping stimulus probability and motor requirements constant across conditions. Participants responded more accurately to rewarded than to neutral oddballs, and faster to rewarded than to both neutral and visually salient oddballs. At the neural level, SN/VTA activity was increased for rewarded oddballs compared with both neutral and visually salient oddballs, whereas LC activity was increased for rewarded compared with visually salient oddballs. Visual salience alone did not increase activity in either region relative to neutral oddballs. Together, these findings suggest that both the noradrenergic and dopaminergic systems are preferentially engaged by motivationally relevant stimuli, beyond more basic forms of salience.

neuroscience↗

bioRxiv2024

Exploring distinct and joint contributions of the Locus Coeruleus and the Substantia Nigra/Ventral Tegmental Area complex to reward and valence processing using high-resolution fMRI

Dopaminergic neurons in the substantia nigra and the ventral tegmental area (SN/VTA) are classically viewed as key mediators in reward processing, while noradrenergic cells in the locus coeruleus (LC) are thought to modulate (negative) saliency processing. However, this conventional distinction is being revised by more recent research in animals. To explore the respective contributions of both the LC and SN/VTA in reward and valence processing in humans, we assessed fMRI data during stimulus encoding and response phase of a rewarded emotion-discrimination task (n=38). Participants responded significantly faster to reward-predicting and negative valence stimuli compared to their non-salient counterparts. LC activity was overall higher during trials involving reward prospect, and in particular for reward trials featuring positive valence, demonstrating an additive effect of reward and positive valence in LC. Moreover, LC activity was differentially increased for negative compared to positive valence in the response phase, indexing its role in invigorating responses to negative events. The SN/VTA showed increased activity in the response phase of reward trials (neutral valence) and negative valence trials (no-reward), which aligns with coding relative saliency of these events in their respective contexts. LC modulations were accompanied by covariations in occipital cortex, suggesting noradrenergic contributions to visual prioritization of salient events. The findings underscore the sensitivity of both LC and SN/VTA to reward prospects and negative valence, challenging the dominant view of SN/VTAs involvement in merely positive events and emphasizing their essential role in action invigoration above and beyond mere stimulus encoding. The intricate roles of the DA and NA system in reward and emotional valence processing in humans warrant further exploration and validation, given the limitations inherent to neuroimaging of deep brain structures.

neuroscience↗

bioRxiv2024

Mind the instructions: reward cues are liked first, wanted later

Current theories propose that mental effort is invested only when the anticipated benefits, such as rewards, outweigh the associated costs, like task difficulty. Yet, it remains unclear whether this motivational and mitigating aspect of reward processing is reflected in the evaluation of reward/difficulty cues as such, and to what extent it depends on task experience. In a pre-registered experiment (N=84), we used the affect misattribution procedure (AMP) to gauge affective evaluations of nonword cues predicting reward and task difficulty levels. Contrary to previous studies, the AMP was administered at the outset, after cue instructions, and after the cues were used in a random dot motion (RDM) task. Compared to baseline, cues predicting a larger reward were evaluated more positively after RDM task experience, and most importantly, already after cue instructions, with no difference between the two phases. This evaluative effect manifested in increased performance after larger reward cues in the RDM task. Our results suggest that AMP effects may generally capture performance expectations which are independent of task experience. Importantly, these instructed expectations of reward and difficulty play a crucial role in the evaluation and subsequent investment of mental effort.

animal behavior and cognition↗

bioRxiv2020

Neural representations of task context and temporal order during action sequence execution

Since routine action sequences can share a great deal of similarity in terms of their stimulus response mappings, their correct execution relies crucially on the ability to preserve contextual and temporal information (Lashley, 1951). However, there are few empirical studies on the neural mechanism and the brain areas maintaining such information. To address this gap in the literature, we recently recorded the blood-oxygen level dependent (BOLD) response in a newly developed coffee-tea making task (Holroyd et al., 2018). The task involves the execution of 4 action sequences that each feature 6 decision states. Here we report a reanalysis of this dataset using a data-driven approach, namely multivariate pattern analysis (MVPA), that examines context-dependent neural activity across several predefined regions of interest. Results highlight involvement of the inferior-temporal gyrus and lateral prefrontal cortex in maintaining temporal and contextual information for the execution of hierarchically-organized action sequences. Furthermore, temporal information seems to be more strongly encoded in areas over the left hemisphere.

neuroscience↗

bioRxiv2018

Motivation and Cognitive Control in Depression

Depression is linked to deficits in cognitive control and a host of other cognitive impairments arise as a consequence of these deficits. Despite of their important role in depression, there are no mechanistic models of cognitive control deficits in depression. In this paper we propose how these deficits can emerge from the interaction between motivational and cognitive processes. We review depression-related impairments in key components of motivation along with new cognitive neuroscience models that focus on the role of motivation in the decision-making about cognitive control allocation. Based on this review we propose a unifying framework which connects motivational and cognitive impairments in depression. This framework is rooted in computational models of cognitive control and offers a mechanistic understanding of cognitive control deficits in depression.

neuroscience↗