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%0 Thesis
%A Nabbefeld, Gerion
%T Signatures of cortical multisensory integration in mice performing a novel visuotactile evidence accumulation task
%I RWTH Aachen University
%V Dissertation
%C Aachen
%M RWTH-2023-08096
%P 1 Online-Ressource : Illustrationen, Diagramme
%D 2022
%Z Veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2023
%Z Dissertation, RWTH Aachen University, 2022
%X Much effort has been focused on studying how the brain processes information from our individual senses. However, the neural mechanisms, that allow the effortless integration of unisensory inputs into multisensory percepts, are largely unknown. To study how neural circuits integrate visual and tactile information, we developed a multisensory discrimination task for head-fixed mice. Here, two sequences of visual, tactile or combined visuotactile stimuli are presented on both sides of the mouse, which has to indicate the higher-rate target-side to obtain a water reward. To ensure integration of sensory information over the entire stimulus period, a short delay was added before the response. Mice achieved high accuracy in all conditions, with improved performance in the multisensory condition. This behavioral task gave us the opportunity to investigate the neural circuits that allow mice to synergistically use both the visual and tactile sensory information to solve the behavioral task. We then used widefield imaging to measure cortex-wide activity in transgenic mice expressing the Ca2+-indicator GCaMP6s in all cortical excitatory neurons. Here, we found that multisensory stimuli evoked higher neuronal activity compared to unisensory stimulation. This was most evident in the rostrolateral association area RL and parts of medial frontal cortex (mFC), which reliably responded to both visual and tactile stimuli. To better isolate sensory responses from co-occurring task- or behavior-related activity, we used a linear encoding model. Including a multisensory interaction-term significantly improved the predictions of cortical activity. With this approach we identified two key features of sensory evoked responses, depending on the stimulus condition. First, in unisensory trials mice display cross-modal inhibition. Here, in addition to the main sensory responses in the corresponding sensory cortex, robust inhibition of activity in the non-matching sensory cortex was found. Second, we found additional superadditive responses in multisensory trials, likely representing the absence of cross-modal inhibition as well as increased activity in areas RL and mFC. To understand how sensory information is used to guide behavioral decisions, we first investigated which brain areas displayed activity that reliably reflected the target stimulus side. Here, the medial motor cortex more faithfully reflected the target-side in tactile trials, while secondary visual areas were more reliable in visual trials. In multisensory trials, both regions accurately reflected the target-side, likely resulting in higher certainty and improved performance in multisensory trials. Finally, using a choice-decoder we identified choice-related neural activity in the anterolateral motor cortex (ALM), as well as in licking-related regions of the primary motor and somatosensory cortex. With this approach, we found no clear modality-specific differences, suggesting that the same neural circuits form decisions in all stimulus conditions. Our results demonstrate that multisensory stimulation cause widespread cortical activation in mice, which leads to improved task performance. Here, cross-modal inhibition in unisensory trials and superadditive multisensory integration especially in RL and mFC were found in multisensory trials, likely aiding mice in performing the individual task condition. Sensory information is then accumulated over the stimulus period in secondary visual areas and medial motor cortex and this information converges in the secondary motor cortex to form modality-unspecific decisions. These findings give us a much deeper understanding of how the brain processes and generalizes sensory information in order to guide behavioral decisions.
%F PUB:(DE-HGF)11
%9 Dissertation / PhD Thesis
%R 10.18154/RWTH-2023-08096
%U https://publications.rwth-aachen.de/record/964006